thymian: common/date/tz.cpp comparison

comparison common/date/tz.cpp @ 0:a4671277546c tip

created the repository for the thymian project

author	ferencd
date	Tue, 17 Aug 2021 11:19:54 +0200
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--1:000000000000
+:a4671277546c
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016, 2017 Howard Hinnant
+// Copyright (c) 2015 Ville Voutilainen
+// Copyright (c) 2016 Alexander Kormanovsky
+// Copyright (c) 2016, 2017 Jiangang Zhuang
+// Copyright (c) 2017 Nicolas Veloz Savino
+// Copyright (c) 2017 Florian Dang
+// Copyright (c) 2017 Aaron Bishop
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+//
+// Our apologies.  When the previous paragraph was written, lowercase had not yet
+// been invented (that would involve another several millennia of evolution).
+// We did not mean to shout.
+#ifdef _WIN32
+// windows.h will be included directly and indirectly (e.g. by curl).
+// We need to define these macros to prevent windows.h bringing in
+// more than we need and do it early so windows.h doesn't get included
+// without these macros having been defined.
+// min/max macros interfere with the C++ versions.
+#  ifndef NOMINMAX
+#    define NOMINMAX
+#  endif
+// We don't need all that Windows has to offer.
+#  ifndef WIN32_LEAN_AND_MEAN
+#    define WIN32_LEAN_AND_MEAN
+#  endif
+// for wcstombs
+#  ifndef _CRT_SECURE_NO_WARNINGS
+#    define _CRT_SECURE_NO_WARNINGS
+#  endif
+// None of this happens with the MS SDK (at least VS14 which I tested), but:
+// Compiling with mingw, we get "error: 'KF_FLAG_DEFAULT' was not declared in this scope."
+// and error: 'SHGetKnownFolderPath' was not declared in this scope.".
+// It seems when using mingw NTDDI_VERSION is undefined and that
+// causes KNOWN_FOLDER_FLAG and the KF_ flags to not get defined.
+// So we must define NTDDI_VERSION to get those flags on mingw.
+// The docs say though here:
+// https://msdn.microsoft.com/en-nz/library/windows/desktop/aa383745(v=vs.85).aspx
+// that "If you define NTDDI_VERSION, you must also define _WIN32_WINNT."
+// So we declare we require Vista or greater.
+#  ifdef __MINGW32__
+#    ifndef NTDDI_VERSION
+#      define NTDDI_VERSION 0x06000000
+#      define _WIN32_WINNT _WIN32_WINNT_VISTA
+#    elif NTDDI_VERSION < 0x06000000
+#      warning "If this fails to compile NTDDI_VERSION may be to low. See comments above."
+#    endif
+// But once we define the values above we then get this linker error:
+// "tz.cpp:(.rdata$.refptr.FOLDERID_Downloads[.refptr.FOLDERID_Downloads]+0x0): "
+//     "undefined reference to `FOLDERID_Downloads'"
+// which #include <initguid.h> cures see:
+// https://support.microsoft.com/en-us/kb/130869
+#    include <initguid.h>
+// But with <initguid.h> included, the error moves on to:
+// error: 'FOLDERID_Downloads' was not declared in this scope
+// Which #include <knownfolders.h> cures.
+#    include <knownfolders.h>
+#  endif  // __MINGW32__
+#  include <windows.h>
+#endif  // _WIN32
+#include "date/tz_private.h"
+#ifdef __APPLE__
+#  include "date/ios.h"
+#else
+#  define TARGET_OS_IPHONE 0
+#endif
+#if USE_OS_TZDB
+#  include <dirent.h>
+#endif
+#include <algorithm>
+#include <cctype>
+#include <cstdlib>
+#include <cstring>
+#include <cwchar>
+#include <exception>
+#include <fstream>
+#include <iostream>
+#include <iterator>
+#include <memory>
+#if USE_OS_TZDB
+#  include <queue>
+#endif
+#include <sstream>
+#include <string>
+#include <tuple>
+#include <vector>
+#include <sys/stat.h>
+// unistd.h is used on some platforms as part of the the means to get
+// the current time zone. On Win32 windows.h provides a means to do it.
+// gcc/mingw supports unistd.h on Win32 but MSVC does not.
+#ifdef _WIN32
+#  ifdef WINAPI_FAMILY
+#    include <winapifamily.h>
+#    if WINAPI_FAMILY != WINAPI_FAMILY_DESKTOP_APP
+#      define WINRT
+#      define INSTALL .
+#    endif
+#  endif
+#  include <io.h> // _unlink etc.
+#  if defined(__clang__)
+struct IUnknown;    // fix for issue with static_cast<> in objbase.h
+//   (see https://github.com/philsquared/Catch/issues/690)
+#  endif
+#  include <shlobj.h> // CoTaskFree, ShGetKnownFolderPath etc.
+#  if HAS_REMOTE_API
+#    include <direct.h> // _mkdir
+#    include <shellapi.h> // ShFileOperation etc.
+#  endif  // HAS_REMOTE_API
+#else   // !_WIN32
+#  include <unistd.h>
+#  if !USE_OS_TZDB
+#    include <wordexp.h>
+#  endif
+#  include <limits.h>
+#  include <string.h>
+#  if !USE_SHELL_API
+#    include <sys/stat.h>
+#    include <sys/fcntl.h>
+#    include <dirent.h>
+#    include <cstring>
+#    include <sys/wait.h>
+#    include <sys/types.h>
+#  endif //!USE_SHELL_API
+#endif  // !_WIN32
+#if HAS_REMOTE_API
+// Note curl includes windows.h so we must include curl AFTER definitions of things
+// that affect windows.h such as NOMINMAX.
+#if defined(_MSC_VER) && defined(SHORTENED_CURL_INCLUDE)
+// For rmt_curl nuget package
+#  include <curl.h>
+#else
+#  include <curl/curl.h>
+#endif
+#endif
+#ifdef _WIN32
+static CONSTDATA char folder_delimiter = '\\';
+#else   // !_WIN32
+static CONSTDATA char folder_delimiter = '/';
+#endif  // !_WIN32
+#if defined(__GNUC__) && __GNUC__ < 5
+// GCC 4.9 Bug 61489 Wrong warning with -Wmissing-field-initializers
+#  pragma GCC diagnostic push
+#  pragma GCC diagnostic ignored "-Wmissing-field-initializers"
+#endif  // defined(__GNUC__) && __GNUC__ < 5
+#if !USE_OS_TZDB
+#  ifdef _WIN32
+#    ifndef WINRT
+namespace
+{
+struct task_mem_deleter
+{
+void operator()(wchar_t buf[])
+{
+if (buf != nullptr)
+CoTaskMemFree(buf);
+}
+};
+using co_task_mem_ptr = std::unique_ptr<wchar_t[], task_mem_deleter>;
+}
+// We might need to know certain locations even if not using the remote API,
+// so keep these routines out of that block for now.
+static
+std::string
+get_known_folder(const GUID& folderid)
+{
+std::string folder;
+PWSTR pfolder = nullptr;
+HRESULT hr = SHGetKnownFolderPath(folderid, KF_FLAG_DEFAULT, nullptr, &pfolder);
+if (SUCCEEDED(hr))
+{
+co_task_mem_ptr folder_ptr(pfolder);
+const wchar_t* fptr = folder_ptr.get();
+auto state = std::mbstate_t();
+const auto required = std::wcsrtombs(nullptr, &fptr, 0, &state);
+if (required != 0 && required != std::size_t(-1))
+{
+folder.resize(required);
+std::wcsrtombs(&folder[0], &fptr, folder.size(), &state);
+}
+}
+return folder;
+}
+#      ifndef INSTALL
+// Usually something like "c:\Users\username\Downloads".
+static
+std::string
+get_download_folder()
+{
+return get_known_folder(FOLDERID_Downloads);
+}
+#      endif  // !INSTALL
+#    endif // WINRT
+#  else // !_WIN32
+#    if !defined(INSTALL)
+static
+std::string
+expand_path(std::string path)
+{
+#      if TARGET_OS_IPHONE
+return date::iOSUtils::get_tzdata_path();
+#      else  // !TARGET_OS_IPHONE
+::wordexp_t w{};
+std::unique_ptr<::wordexp_t, void(*)(::wordexp_t*)> hold{&w, ::wordfree};
+::wordexp(path.c_str(), &w, 0);
+if (w.we_wordc != 1)
+throw std::runtime_error("Cannot expand path: " + path);
+path = w.we_wordv[0];
+return path;
+#      endif  // !TARGET_OS_IPHONE
+}
+static
+std::string
+get_download_folder()
+{
+return expand_path("~/Downloads");
+}
+#    endif // !defined(INSTALL)
+#  endif  // !_WIN32
+#endif  // !USE_OS_TZDB
+namespace date
+{
+// +---------------------+
+// | Begin Configuration |
+// +---------------------+
+using namespace detail;
+#if !USE_OS_TZDB
+static
+std::string&
+access_install()
+{
+static std::string install
+#ifndef INSTALL
+= get_download_folder() + folder_delimiter + "tzdata";
+#else   // !INSTALL
+#  define STRINGIZEIMP(x) #x
+#  define STRINGIZE(x) STRINGIZEIMP(x)
+= STRINGIZE(INSTALL) + std::string(1, folder_delimiter) + "tzdata";
+#undef STRINGIZEIMP
+#undef STRINGIZE
+#endif  // !INSTALL
+return install;
+}
+void
+set_install(const std::string& s)
+{
+access_install() = s;
+}
+static
+const std::string&
+get_install()
+{
+static const std::string& ref = access_install();
+return ref;
+}
+#if HAS_REMOTE_API
+static
+std::string
+get_download_gz_file(const std::string& version)
+{
+auto file = get_install() + version + ".tar.gz";
+return file;
+}
+#endif  // HAS_REMOTE_API
+#endif  // !USE_OS_TZDB
+// These can be used to reduce the range of the database to save memory
+CONSTDATA auto min_year = date::year::min();
+CONSTDATA auto max_year = date::year::max();
+CONSTDATA auto min_day = date::January/1;
+CONSTDATA auto max_day = date::December/31;
+#if USE_OS_TZDB
+CONSTCD14 const sys_seconds min_seconds = sys_days(min_year/min_day);
+#endif  // USE_OS_TZDB
+#ifndef _WIN32
+static
+std::string
+discover_tz_dir()
+{
+struct stat sb;
+using namespace std;
+#  ifndef __APPLE__
+CONSTDATA auto tz_dir_default = "/usr/share/zoneinfo";
+CONSTDATA auto tz_dir_buildroot = "/usr/share/zoneinfo/uclibc";
+// Check special path which is valid for buildroot with uclibc builds
+if(stat(tz_dir_buildroot, &sb) == 0 && S_ISDIR(sb.st_mode))
+return tz_dir_buildroot;
+else if(stat(tz_dir_default, &sb) == 0 && S_ISDIR(sb.st_mode))
+return tz_dir_default;
+else
+throw runtime_error("discover_tz_dir failed to find zoneinfo\n");
+#  else  // __APPLE__
+#      if TARGET_OS_IPHONE
+return "/var/db/timezone/zoneinfo";
+#      else
+CONSTDATA auto timezone = "/etc/localtime";
+if (!(lstat(timezone, &sb) == 0 && S_ISLNK(sb.st_mode) && sb.st_size > 0))
+throw runtime_error("discover_tz_dir failed\n");
+string result;
+char rp[PATH_MAX+1] = {};
+if (readlink(timezone, rp, sizeof(rp)-1) > 0)
+result = string(rp);
+else
+throw system_error(errno, system_category(), "readlink() failed");
+auto i = result.find("zoneinfo");
+if (i == string::npos)
+throw runtime_error("discover_tz_dir failed to find zoneinfo\n");
+i = result.find('/', i);
+if (i == string::npos)
+throw runtime_error("discover_tz_dir failed to find '/'\n");
+return result.substr(0, i);
+#      endif
+#  endif  // __APPLE__
+}
+static
+const std::string&
+get_tz_dir()
+{
+static const std::string tz_dir = discover_tz_dir();
+return tz_dir;
+}
+#endif
+// +-------------------+
+// | End Configuration |
+// +-------------------+
+#ifndef _MSC_VER
+static_assert(min_year <= max_year, "Configuration error");
+#endif
+static std::unique_ptr<tzdb> init_tzdb();
+tzdb_list::~tzdb_list()
+{
+const tzdb* ptr = head_;
+head_ = nullptr;
+while (ptr != nullptr)
+{
+auto next = ptr->next;
+delete ptr;
+ptr = next;
+}
+}
+tzdb_list::tzdb_list(tzdb_list&& x) noexcept
+: head_{x.head_.exchange(nullptr)}
+{
+}
+void
+tzdb_list::push_front(tzdb* tzdb) noexcept
+{
+tzdb->next = head_;
+head_ = tzdb;
+}
+tzdb_list::const_iterator
+tzdb_list::erase_after(const_iterator p) noexcept
+{
+auto t = p.p_->next;
+p.p_->next = p.p_->next->next;
+delete t;
+return ++p;
+}
+struct tzdb_list::undocumented_helper
+{
+static void push_front(tzdb_list& db_list, tzdb* tzdb) noexcept
+{
+db_list.push_front(tzdb);
+}
+};
+static
+tzdb_list
+create_tzdb()
+{
+tzdb_list tz_db;
+tzdb_list::undocumented_helper::push_front(tz_db, init_tzdb().release());
+return tz_db;
+}
+tzdb_list&
+get_tzdb_list()
+{
+static tzdb_list tz_db = create_tzdb();
+return tz_db;
+}
+#if !USE_OS_TZDB
+#ifdef _WIN32
+static
+void
+sort_zone_mappings(std::vector<date::detail::timezone_mapping>& mappings)
+{
+std::sort(mappings.begin(), mappings.end(),
+[](const date::detail::timezone_mapping& lhs,
+const date::detail::timezone_mapping& rhs)->bool
+{
+auto other_result = lhs.other.compare(rhs.other);
+if (other_result < 0)
+return true;
+else if (other_result == 0)
+{
+auto territory_result = lhs.territory.compare(rhs.territory);
+if (territory_result < 0)
+return true;
+else if (territory_result == 0)
+{
+if (lhs.type < rhs.type)
+return true;
+}
+}
+return false;
+});
+}
+static
+bool
+native_to_standard_timezone_name(const std::string& native_tz_name,
+std::string& standard_tz_name)
+{
+// TOOD! Need be a case insensitive compare?
+if (native_tz_name == "UTC")
+{
+standard_tz_name = "Etc/UTC";
+return true;
+}
+standard_tz_name.clear();
+// TODO! we can improve on linear search.
+const auto& mappings = date::get_tzdb().mappings;
+for (const auto& tzm : mappings)
+{
+if (tzm.other == native_tz_name)
+{
+standard_tz_name = tzm.type;
+return true;
+}
+}
+return false;
+}
+// Parse this XML file:
+// https://raw.githubusercontent.com/unicode-org/cldr/master/common/supplemental/windowsZones.xml
+// The parsing method is designed to be simple and quick. It is not overly
+// forgiving of change but it should diagnose basic format issues.
+// See timezone_mapping structure for more info.
+static
+std::vector<detail::timezone_mapping>
+load_timezone_mappings_from_xml_file(const std::string& input_path)
+{
+std::size_t line_num = 0;
+std::vector<detail::timezone_mapping> mappings;
+std::string line;
+std::ifstream is(input_path);
+if (!is.is_open())
+{
+// We don't emit file exceptions because that's an implementation detail.
+std::string msg = "Error opening time zone mapping file \"";
+msg += input_path;
+msg += "\".";
+throw std::runtime_error(msg);
+}
+auto error = [&input_path, &line_num](const char* info)
+{
+std::string msg = "Error loading time zone mapping file \"";
+msg += input_path;
+msg += "\" at line ";
+msg += std::to_string(line_num);
+msg += ": ";
+msg += info;
+throw std::runtime_error(msg);
+};
+// [optional space]a="b"
+auto read_attribute = [&line, &error]
+(const char* name, std::string& value, std::size_t startPos)
+->std::size_t
+{
+value.clear();
+// Skip leading space before attribute name.
+std::size_t spos = line.find_first_not_of(' ', startPos);
+if (spos == std::string::npos)
+spos = startPos;
+// Assume everything up to next = is the attribute name
+// and that an = will always delimit that.
+std::size_t epos = line.find('=', spos);
+if (epos == std::string::npos)
+error("Expected \'=\' right after attribute name.");
+std::size_t name_len = epos - spos;
+// Expect the name we find matches the name we expect.
+if (line.compare(spos, name_len, name) != 0)
+{
+std::string msg;
+msg = "Expected attribute name \'";
+msg += name;
+msg += "\' around position ";
+msg += std::to_string(spos);
+msg += " but found something else.";
+error(msg.c_str());
+}
+++epos; // Skip the '=' that is after the attribute name.
+spos = epos;
+if (spos < line.length() && line[spos] == '\"')
+++spos; // Skip the quote that is before the attribute value.
+else
+{
+std::string msg = "Expected '\"' to begin value of attribute \'";
+msg += name;
+msg += "\'.";
+error(msg.c_str());
+}
+epos = line.find('\"', spos);
+if (epos == std::string::npos)
+{
+std::string msg = "Expected '\"' to end value of attribute \'";
+msg += name;
+msg += "\'.";
+error(msg.c_str());
+}
+// Extract everything in between the quotes. Note no escaping is done.
+std::size_t value_len = epos - spos;
+value.assign(line, spos, value_len);
+++epos; // Skip the quote that is after the attribute value;
+return epos;
+};
+// Quick but not overly forgiving XML mapping file processing.
+bool mapTimezonesOpenTagFound = false;
+bool mapTimezonesCloseTagFound = false;
+std::size_t mapZonePos = std::string::npos;
+std::size_t mapTimezonesPos = std::string::npos;
+CONSTDATA char mapTimeZonesOpeningTag[] = { "<mapTimezones " };
+CONSTDATA char mapZoneOpeningTag[] = { "<mapZone " };
+CONSTDATA std::size_t mapZoneOpeningTagLen = sizeof(mapZoneOpeningTag) /
+sizeof(mapZoneOpeningTag[0]) - 1;
+while (!mapTimezonesOpenTagFound)
+{
+std::getline(is, line);
+++line_num;
+if (is.eof())
+{
+// If there is no mapTimezones tag is it an error?
+// Perhaps if there are no mapZone mappings it might be ok for
+// its parent mapTimezones element to be missing?
+// We treat this as an error though on the assumption that if there
+// really are no mappings we should still get a mapTimezones parent
+// element but no mapZone elements inside. Assuming we must
+// find something will hopefully at least catch more drastic formatting
+// changes or errors than if we don't do this and assume nothing found.
+error("Expected a mapTimezones opening tag.");
+}
+mapTimezonesPos = line.find(mapTimeZonesOpeningTag);
+mapTimezonesOpenTagFound = (mapTimezonesPos != std::string::npos);
+}
+// NOTE: We could extract the version info that follows the opening
+// mapTimezones tag and compare that to the version of other data we have.
+// I would have expected them to be kept in synch but testing has shown
+// it typically does not match anyway. So what's the point?
+while (!mapTimezonesCloseTagFound)
+{
+std::ws(is);
+std::getline(is, line);
+++line_num;
+if (is.eof())
+error("Expected a mapTimezones closing tag.");
+if (line.empty())
+continue;
+mapZonePos = line.find(mapZoneOpeningTag);
+if (mapZonePos != std::string::npos)
+{
+mapZonePos += mapZoneOpeningTagLen;
+detail::timezone_mapping zm{};
+std::size_t pos = read_attribute("other", zm.other, mapZonePos);
+pos = read_attribute("territory", zm.territory, pos);
+read_attribute("type", zm.type, pos);
+mappings.push_back(std::move(zm));
+continue;
+}
+mapTimezonesPos = line.find("</mapTimezones>");
+mapTimezonesCloseTagFound = (mapTimezonesPos != std::string::npos);
+if (!mapTimezonesCloseTagFound)
+{
+std::size_t commentPos = line.find("<!--");
+if (commentPos == std::string::npos)
+error("Unexpected mapping record found. A xml mapZone or comment "
+"attribute or mapTimezones closing tag was expected.");
+}
+}
+is.close();
+return mappings;
+}
+#endif  // _WIN32
+// Parsing helpers
+static
+std::string
+parse3(std::istream& in)
+{
+std::string r(3, ' ');
+ws(in);
+r[0] = static_cast<char>(in.get());
+r[1] = static_cast<char>(in.get());
+r[2] = static_cast<char>(in.get());
+return r;
+}
+static
+unsigned
+parse_dow(std::istream& in)
+{
+CONSTDATA char*const dow_names[] =
+{"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};
+auto s = parse3(in);
+auto dow = std::find(std::begin(dow_names), std::end(dow_names), s) - dow_names;
+if (dow >= std::end(dow_names) - std::begin(dow_names))
+throw std::runtime_error("oops: bad dow name: " + s);
+return static_cast<unsigned>(dow);
+}
+static
+unsigned
+parse_month(std::istream& in)
+{
+CONSTDATA char*const month_names[] =
+{"Jan", "Feb", "Mar", "Apr", "May", "Jun",
+"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};
+auto s = parse3(in);
+auto m = std::find(std::begin(month_names), std::end(month_names), s) - month_names;
+if (m >= std::end(month_names) - std::begin(month_names))
+throw std::runtime_error("oops: bad month name: " + s);
+return static_cast<unsigned>(++m);
+}
+static
+std::chrono::seconds
+parse_unsigned_time(std::istream& in)
+{
+using namespace std::chrono;
+int x;
+in >> x;
+auto r = seconds{hours{x}};
+if (!in.eof() && in.peek() == ':')
+{
+in.get();
+in >> x;
+r += minutes{x};
+if (!in.eof() && in.peek() == ':')
+{
+in.get();
+in >> x;
+r += seconds{x};
+}
+}
+return r;
+}
+static
+std::chrono::seconds
+parse_signed_time(std::istream& in)
+{
+ws(in);
+auto sign = 1;
+if (in.peek() == '-')
+{
+sign = -1;
+in.get();
+}
+else if (in.peek() == '+')
+in.get();
+return sign * parse_unsigned_time(in);
+}
+// MonthDayTime
+detail::MonthDayTime::MonthDayTime(local_seconds tp, tz timezone)
+: zone_(timezone)
+{
+using namespace date;
+const auto dp = date::floor<days>(tp);
+const auto hms = make_time(tp - dp);
+const auto ymd = year_month_day(dp);
+u = ymd.month() / ymd.day();
+h_ = hms.hours();
+m_ = hms.minutes();
+s_ = hms.seconds();
+}
+detail::MonthDayTime::MonthDayTime(const date::month_day& md, tz timezone)
+: zone_(timezone)
+{
+u = md;
+}
+date::day
+detail::MonthDayTime::day() const
+{
+switch (type_)
+{
+case month_day:
+return u.month_day_.day();
+case month_last_dow:
+return date::day{31};
+case lteq:
+case gteq:
+break;
+}
+return u.month_day_weekday_.month_day_.day();
+}
+date::month
+detail::MonthDayTime::month() const
+{
+switch (type_)
+{
+case month_day:
+return u.month_day_.month();
+case month_last_dow:
+return u.month_weekday_last_.month();
+case lteq:
+case gteq:
+break;
+}
+return u.month_day_weekday_.month_day_.month();
+}
+int
+detail::MonthDayTime::compare(date::year y, const MonthDayTime& x, date::year yx,
+std::chrono::seconds offset, std::chrono::minutes prev_save) const
+{
+if (zone_ != x.zone_)
+{
+auto dp0 = to_sys_days(y);
+auto dp1 = x.to_sys_days(yx);
+if (std::abs((dp0-dp1).count()) > 1)
+return dp0 < dp1 ? -1 : 1;
+if (zone_ == tz::local)
+{
+auto tp0 = to_time_point(y) - prev_save;
+if (x.zone_ == tz::utc)
+tp0 -= offset;
+auto tp1 = x.to_time_point(yx);
+return tp0 < tp1 ? -1 : tp0 == tp1 ? 0 : 1;
+}
+else if (zone_ == tz::standard)
+{
+auto tp0 = to_time_point(y);
+auto tp1 = x.to_time_point(yx);
+if (x.zone_ == tz::local)
+tp1 -= prev_save;
+else
+tp0 -= offset;
+return tp0 < tp1 ? -1 : tp0 == tp1 ? 0 : 1;
+}
+// zone_ == tz::utc
+auto tp0 = to_time_point(y);
+auto tp1 = x.to_time_point(yx);
+if (x.zone_ == tz::local)
+tp1 -= offset + prev_save;
+else
+tp1 -= offset;
+return tp0 < tp1 ? -1 : tp0 == tp1 ? 0 : 1;
+}
+auto const t0 = to_time_point(y);
+auto const t1 = x.to_time_point(yx);
+return t0 < t1 ? -1 : t0 == t1 ? 0 : 1;
+}
+sys_seconds
+detail::MonthDayTime::to_sys(date::year y, std::chrono::seconds offset,
+std::chrono::seconds save) const
+{
+using namespace date;
+using namespace std::chrono;
+auto until_utc = to_time_point(y);
+if (zone_ == tz::standard)
+until_utc -= offset;
+else if (zone_ == tz::local)
+until_utc -= offset + save;
+return until_utc;
+}
+detail::MonthDayTime::U&
+detail::MonthDayTime::U::operator=(const date::month_day& x)
+{
+month_day_ = x;
+return *this;
+}
+detail::MonthDayTime::U&
+detail::MonthDayTime::U::operator=(const date::month_weekday_last& x)
+{
+month_weekday_last_ = x;
+return *this;
+}
+detail::MonthDayTime::U&
+detail::MonthDayTime::U::operator=(const pair& x)
+{
+month_day_weekday_ = x;
+return *this;
+}
+date::sys_days
+detail::MonthDayTime::to_sys_days(date::year y) const
+{
+using namespace std::chrono;
+using namespace date;
+switch (type_)
+{
+case month_day:
+return sys_days(y/u.month_day_);
+case month_last_dow:
+return sys_days(y/u.month_weekday_last_);
+case lteq:
+{
+auto const x = y/u.month_day_weekday_.month_day_;
+auto const wd1 = weekday(static_cast<sys_days>(x));
+auto const wd0 = u.month_day_weekday_.weekday_;
+return sys_days(x) - (wd1-wd0);
+}
+case gteq:
+break;
+}
+auto const x = y/u.month_day_weekday_.month_day_;
+auto const wd1 = u.month_day_weekday_.weekday_;
+auto const wd0 = weekday(static_cast<sys_days>(x));
+return sys_days(x) + (wd1-wd0);
+}
+sys_seconds
+detail::MonthDayTime::to_time_point(date::year y) const
+{
+// Add seconds first to promote to largest rep early to prevent overflow
+return to_sys_days(y) + s_ + h_ + m_;
+}
+void
+detail::MonthDayTime::canonicalize(date::year y)
+{
+using namespace std::chrono;
+using namespace date;
+switch (type_)
+{
+case month_day:
+return;
+case month_last_dow:
+{
+auto const ymd = year_month_day(sys_days(y/u.month_weekday_last_));
+u.month_day_ = ymd.month()/ymd.day();
+type_ = month_day;
+return;
+}
+case lteq:
+{
+auto const x = y/u.month_day_weekday_.month_day_;
+auto const wd1 = weekday(static_cast<sys_days>(x));
+auto const wd0 = u.month_day_weekday_.weekday_;
+auto const ymd = year_month_day(sys_days(x) - (wd1-wd0));
+u.month_day_ = ymd.month()/ymd.day();
+type_ = month_day;
+return;
+}
+case gteq:
+{
+auto const x = y/u.month_day_weekday_.month_day_;
+auto const wd1 = u.month_day_weekday_.weekday_;
+auto const wd0 = weekday(static_cast<sys_days>(x));
+auto const ymd = year_month_day(sys_days(x) + (wd1-wd0));
+u.month_day_ = ymd.month()/ymd.day();
+type_ = month_day;
+return;
+}
+}
+}
+std::istream&
+detail::operator>>(std::istream& is, MonthDayTime& x)
+{
+using namespace date;
+using namespace std::chrono;
+assert(((std::ios::failbit | std::ios::badbit) & is.exceptions()) ==
+(std::ios::failbit | std::ios::badbit));
+x = MonthDayTime{};
+if (!is.eof() && ws(is) && !is.eof() && is.peek() != '#')
+{
+auto m = parse_month(is);
+if (!is.eof() && ws(is) && !is.eof() && is.peek() != '#')
+{
+if (is.peek() == 'l')
+{
+for (int i = 0; i < 4; ++i)
+is.get();
+auto dow = parse_dow(is);
+x.type_ = MonthDayTime::month_last_dow;
+x.u = date::month(m)/weekday(dow)[last];
+}
+else if (std::isalpha(is.peek()))
+{
+auto dow = parse_dow(is);
+char c{};
+is >> c;
+if (c == '<' || c == '>')
+{
+char c2{};
+is >> c2;
+if (c2 != '=')
+throw std::runtime_error(std::string("bad operator: ") + c + c2);
+int d;
+is >> d;
+if (d < 1 || d > 31)
+throw std::runtime_error(std::string("bad operator: ") + c + c2
++ std::to_string(d));
+x.type_ = c == '<' ? MonthDayTime::lteq : MonthDayTime::gteq;
+x.u = MonthDayTime::pair{ date::month(m) / d, date::weekday(dow) };
+}
+else
+throw std::runtime_error(std::string("bad operator: ") + c);
+}
+else  // if (std::isdigit(is.peek())
+{
+int d;
+is >> d;
+if (d < 1 || d > 31)
+throw std::runtime_error(std::string("day of month: ")
++ std::to_string(d));
+x.type_ = MonthDayTime::month_day;
+x.u = date::month(m)/d;
+}
+if (!is.eof() && ws(is) && !is.eof() && is.peek() != '#')
+{
+int t;
+is >> t;
+x.h_ = hours{t};
+if (!is.eof() && is.peek() == ':')
+{
+is.get();
+is >> t;
+x.m_ = minutes{t};
+if (!is.eof() && is.peek() == ':')
+{
+is.get();
+is >> t;
+x.s_ = seconds{t};
+}
+}
+if (!is.eof() && std::isalpha(is.peek()))
+{
+char c;
+is >> c;
+switch (c)
+{
+case 's':
+x.zone_ = tz::standard;
+break;
+case 'u':
+x.zone_ = tz::utc;
+break;
+}
+}
+}
+}
+else
+{
+x.u = month{m}/1;
+}
+}
+return is;
+}
+std::ostream&
+detail::operator<<(std::ostream& os, const MonthDayTime& x)
+{
+switch (x.type_)
+{
+case MonthDayTime::month_day:
+os << x.u.month_day_ << "                  ";
+break;
+case MonthDayTime::month_last_dow:
+os << x.u.month_weekday_last_ << "           ";
+break;
+case MonthDayTime::lteq:
+os << x.u.month_day_weekday_.weekday_ << " on or before "
+<< x.u.month_day_weekday_.month_day_ << "  ";
+break;
+case MonthDayTime::gteq:
+if ((static_cast<unsigned>(x.day()) - 1) % 7 == 0)
+{
+os << (x.u.month_day_weekday_.month_day_.month() /
+x.u.month_day_weekday_.weekday_[
+(static_cast<unsigned>(x.day()) - 1)/7+1]) << "              ";
+}
+else
+{
+os << x.u.month_day_weekday_.weekday_ << " on or after "
+<< x.u.month_day_weekday_.month_day_ << "  ";
+}
+break;
+}
+os << date::make_time(x.s_ + x.h_ + x.m_);
+if (x.zone_ == tz::utc)
+os << "UTC   ";
+else if (x.zone_ == tz::standard)
+os << "STD   ";
+else
+os << "      ";
+return os;
+}
+// Rule
+detail::Rule::Rule(const std::string& s)
+{
+try
+{
+using namespace date;
+using namespace std::chrono;
+std::istringstream in(s);
+in.exceptions(std::ios::failbit | std::ios::badbit);
+std::string word;
+in >> word >> name_;
+int x;
+ws(in);
+if (std::isalpha(in.peek()))
+{
+in >> word;
+if (word == "min")
+{
+starting_year_ = year::min();
+}
+else
+throw std::runtime_error("Didn't find expected word: " + word);
+}
+else
+{
+in >> x;
+starting_year_ = year{x};
+}
+std::ws(in);
+if (std::isalpha(in.peek()))
+{
+in >> word;
+if (word == "only")
+{
+ending_year_ = starting_year_;
+}
+else if (word == "max")
+{
+ending_year_ = year::max();
+}
+else
+throw std::runtime_error("Didn't find expected word: " + word);
+}
+else
+{
+in >> x;
+ending_year_ = year{x};
+}
+in >> word;  // TYPE (always "-")
+assert(word == "-");
+in >> starting_at_;
+save_ = duration_cast<minutes>(parse_signed_time(in));
+in >> abbrev_;
+if (abbrev_ == "-")
+abbrev_.clear();
+assert(hours{-1} <= save_ && save_ <= hours{2});
+}
+catch (...)
+{
+std::cerr << s << '\n';
+std::cerr << *this << '\n';
+throw;
+}
+}
+detail::Rule::Rule(const Rule& r, date::year starting_year, date::year ending_year)
+: name_(r.name_)
+, starting_year_(starting_year)
+, ending_year_(ending_year)
+, starting_at_(r.starting_at_)
+, save_(r.save_)
+, abbrev_(r.abbrev_)
+{
+}
+bool
+detail::operator==(const Rule& x, const Rule& y)
+{
+if (std::tie(x.name_, x.save_, x.starting_year_, x.ending_year_) ==
+std::tie(y.name_, y.save_, y.starting_year_, y.ending_year_))
+return x.month() == y.month() && x.day() == y.day();
+return false;
+}
+bool
+detail::operator<(const Rule& x, const Rule& y)
+{
+using namespace std::chrono;
+auto const xm = x.month();
+auto const ym = y.month();
+if (std::tie(x.name_, x.starting_year_, xm, x.ending_year_) <
+std::tie(y.name_, y.starting_year_, ym, y.ending_year_))
+return true;
+if (std::tie(x.name_, x.starting_year_, xm, x.ending_year_) >
+std::tie(y.name_, y.starting_year_, ym, y.ending_year_))
+return false;
+return x.day() < y.day();
+}
+bool
+detail::operator==(const Rule& x, const date::year& y)
+{
+return x.starting_year_ <= y && y <= x.ending_year_;
+}
+bool
+detail::operator<(const Rule& x, const date::year& y)
+{
+return x.ending_year_ < y;
+}
+bool
+detail::operator==(const date::year& x, const Rule& y)
+{
+return y.starting_year_ <= x && x <= y.ending_year_;
+}
+bool
+detail::operator<(const date::year& x, const Rule& y)
+{
+return x < y.starting_year_;
+}
+bool
+detail::operator==(const Rule& x, const std::string& y)
+{
+return x.name() == y;
+}
+bool
+detail::operator<(const Rule& x, const std::string& y)
+{
+return x.name() < y;
+}
+bool
+detail::operator==(const std::string& x, const Rule& y)
+{
+return y.name() == x;
+}
+bool
+detail::operator<(const std::string& x, const Rule& y)
+{
+return x < y.name();
+}
+std::ostream&
+detail::operator<<(std::ostream& os, const Rule& r)
+{
+using namespace date;
+using namespace std::chrono;
+detail::save_ostream<char> _(os);
+os.fill(' ');
+os.flags(std::ios::dec | std::ios::left);
+os.width(15);
+os << r.name_;
+os << r.starting_year_ << "    " << r.ending_year_ << "    ";
+os << r.starting_at_;
+if (r.save_ >= minutes{0})
+os << ' ';
+os << date::make_time(r.save_) << "   ";
+os << r.abbrev_;
+return os;
+}
+date::day
+detail::Rule::day() const
+{
+return starting_at_.day();
+}
+date::month
+detail::Rule::month() const
+{
+return starting_at_.month();
+}
+struct find_rule_by_name
+{
+bool operator()(const Rule& x, const std::string& nm) const
+{
+return x.name() < nm;
+}
+bool operator()(const std::string& nm, const Rule& x) const
+{
+return nm < x.name();
+}
+};
+bool
+detail::Rule::overlaps(const Rule& x, const Rule& y)
+{
+// assume x.starting_year_ <= y.starting_year_;
+if (!(x.starting_year_ <= y.starting_year_))
+{
+std::cerr << x << '\n';
+std::cerr << y << '\n';
+assert(x.starting_year_ <= y.starting_year_);
+}
+if (y.starting_year_ > x.ending_year_)
+return false;
+return !(x.starting_year_ == y.starting_year_ && x.ending_year_ == y.ending_year_);
+}
+void
+detail::Rule::split(std::vector<Rule>& rules, std::size_t i, std::size_t k, std::size_t& e)
+{
+using namespace date;
+using difference_type = std::vector<Rule>::iterator::difference_type;
+// rules[i].starting_year_ <= rules[k].starting_year_ &&
+//     rules[i].ending_year_ >= rules[k].starting_year_ &&
+//     (rules[i].starting_year_ != rules[k].starting_year_ ||
+//      rules[i].ending_year_ != rules[k].ending_year_)
+assert(rules[i].starting_year_ <= rules[k].starting_year_ &&
+rules[i].ending_year_ >= rules[k].starting_year_ &&
+(rules[i].starting_year_ != rules[k].starting_year_ ||
+rules[i].ending_year_ != rules[k].ending_year_));
+if (rules[i].starting_year_ == rules[k].starting_year_)
+{
+if (rules[k].ending_year_ < rules[i].ending_year_)
+{
+rules.insert(rules.begin() + static_cast<difference_type>(k+1),
+Rule(rules[i], rules[k].ending_year_ + years{1},
+std::move(rules[i].ending_year_)));
+++e;
+rules[i].ending_year_ = rules[k].ending_year_;
+}
+else  // rules[k].ending_year_ > rules[i].ending_year_
+{
+rules.insert(rules.begin() + static_cast<difference_type>(k+1),
+Rule(rules[k], rules[i].ending_year_ + years{1},
+std::move(rules[k].ending_year_)));
+++e;
+rules[k].ending_year_ = rules[i].ending_year_;
+}
+}
+else  // rules[i].starting_year_ < rules[k].starting_year_
+{
+if (rules[k].ending_year_ < rules[i].ending_year_)
+{
+rules.insert(rules.begin() + static_cast<difference_type>(k),
+Rule(rules[i], rules[k].starting_year_, rules[k].ending_year_));
+++k;
+rules.insert(rules.begin() + static_cast<difference_type>(k+1),
+Rule(rules[i], rules[k].ending_year_ + years{1},
+std::move(rules[i].ending_year_)));
+rules[i].ending_year_ = rules[k].starting_year_ - years{1};
+e += 2;
+}
+else if (rules[k].ending_year_ > rules[i].ending_year_)
+{
+rules.insert(rules.begin() + static_cast<difference_type>(k),
+Rule(rules[i], rules[k].starting_year_, rules[i].ending_year_));
+++k;
+rules.insert(rules.begin() + static_cast<difference_type>(k+1),
+Rule(rules[k], rules[i].ending_year_ + years{1},
+std::move(rules[k].ending_year_)));
+e += 2;
+rules[k].ending_year_ = std::move(rules[i].ending_year_);
+rules[i].ending_year_ = rules[k].starting_year_ - years{1};
+}
+else  // rules[k].ending_year_ == rules[i].ending_year_
+{
+rules.insert(rules.begin() + static_cast<difference_type>(k),
+Rule(rules[i], rules[k].starting_year_,
+std::move(rules[i].ending_year_)));
+++k;
+++e;
+rules[i].ending_year_ = rules[k].starting_year_ - years{1};
+}
+}
+}
+void
+detail::Rule::split_overlaps(std::vector<Rule>& rules, std::size_t i, std::size_t& e)
+{
+using difference_type = std::vector<Rule>::iterator::difference_type;
+auto j = i;
+for (; i + 1 < e; ++i)
+{
+for (auto k = i + 1; k < e; ++k)
+{
+if (overlaps(rules[i], rules[k]))
+{
+split(rules, i, k, e);
+std::sort(rules.begin() + static_cast<difference_type>(i),
+rules.begin() + static_cast<difference_type>(e));
+}
+}
+}
+for (; j < e; ++j)
+{
+if (rules[j].starting_year() == rules[j].ending_year())
+rules[j].starting_at_.canonicalize(rules[j].starting_year());
+}
+}
+void
+detail::Rule::split_overlaps(std::vector<Rule>& rules)
+{
+using difference_type = std::vector<Rule>::iterator::difference_type;
+for (std::size_t i = 0; i < rules.size();)
+{
+auto e = static_cast<std::size_t>(std::upper_bound(
+rules.cbegin()+static_cast<difference_type>(i), rules.cend(), rules[i].name(),
+[](const std::string& nm, const Rule& x)
+{
+return nm < x.name();
+}) - rules.cbegin());
+split_overlaps(rules, i, e);
+auto first_rule = rules.begin() + static_cast<difference_type>(i);
+auto last_rule = rules.begin() + static_cast<difference_type>(e);
+auto t = std::lower_bound(first_rule, last_rule, min_year);
+if (t > first_rule+1)
+{
+if (t == last_rule || t->starting_year() >= min_year)
+--t;
+auto d = static_cast<std::size_t>(t - first_rule);
+rules.erase(first_rule, t);
+e -= d;
+}
+first_rule = rules.begin() + static_cast<difference_type>(i);
+last_rule = rules.begin() + static_cast<difference_type>(e);
+t = std::upper_bound(first_rule, last_rule, max_year);
+if (t != last_rule)
+{
+auto d = static_cast<std::size_t>(last_rule - t);
+rules.erase(t, last_rule);
+e -= d;
+}
+i = e;
+}
+rules.shrink_to_fit();
+}
+// Find the rule that comes chronologically before Rule r.  For multi-year rules,
+// y specifies which rules in r.  For single year rules, y is assumed to be equal
+// to the year specified by r.
+// Returns a pointer to the chronologically previous rule, and the year within
+// that rule.  If there is no previous rule, returns nullptr and year::min().
+// Preconditions:
+//     r->starting_year() <= y && y <= r->ending_year()
+static
+std::pair<const Rule*, date::year>
+find_previous_rule(const Rule* r, date::year y)
+{
+using namespace date;
+auto const& rules = get_tzdb().rules;
+if (y == r->starting_year())
+{
+if (r == &rules.front() || r->name() != r[-1].name())
+std::terminate();  // never called with first rule
+--r;
+if (y == r->starting_year())
+return {r, y};
+return {r, r->ending_year()};
+}
+if (r == &rules.front() || r->name() != r[-1].name() ||
+r[-1].starting_year() < r->starting_year())
+{
+while (r < &rules.back() && r->name() == r[1].name() &&
+r->starting_year() == r[1].starting_year())
+++r;
+return {r, --y};
+}
+--r;
+return {r, y};
+}
+// Find the rule that comes chronologically after Rule r.  For multi-year rules,
+// y specifies which rules in r.  For single year rules, y is assumed to be equal
+// to the year specified by r.
+// Returns a pointer to the chronologically next rule, and the year within
+// that rule.  If there is no next rule, return a pointer to a defaulted rule
+// and y+1.
+// Preconditions:
+//     first <= r && r < last && r->starting_year() <= y && y <= r->ending_year()
+//     [first, last) all have the same name
+static
+std::pair<const Rule*, date::year>
+find_next_rule(const Rule* first_rule, const Rule* last_rule, const Rule* r, date::year y)
+{
+using namespace date;
+if (y == r->ending_year())
+{
+if (r == last_rule-1)
+return {nullptr, year::max()};
+++r;
+if (y == r->ending_year())
+return {r, y};
+return {r, r->starting_year()};
+}
+if (r == last_rule-1 || r->ending_year() < r[1].ending_year())
+{
+while (r > first_rule && r->starting_year() == r[-1].starting_year())
+--r;
+return {r, ++y};
+}
+++r;
+return {r, y};
+}
+// Find the rule that comes chronologically after Rule r.  For multi-year rules,
+// y specifies which rules in r.  For single year rules, y is assumed to be equal
+// to the year specified by r.
+// Returns a pointer to the chronologically next rule, and the year within
+// that rule.  If there is no next rule, return nullptr and year::max().
+// Preconditions:
+//     r->starting_year() <= y && y <= r->ending_year()
+static
+std::pair<const Rule*, date::year>
+find_next_rule(const Rule* r, date::year y)
+{
+using namespace date;
+auto const& rules = get_tzdb().rules;
+if (y == r->ending_year())
+{
+if (r == &rules.back() || r->name() != r[1].name())
+return {nullptr, year::max()};
+++r;
+if (y == r->ending_year())
+return {r, y};
+return {r, r->starting_year()};
+}
+if (r == &rules.back() || r->name() != r[1].name() ||
+r->ending_year() < r[1].ending_year())
+{
+while (r > &rules.front() && r->name() == r[-1].name() &&
+r->starting_year() == r[-1].starting_year())
+--r;
+return {r, ++y};
+}
+++r;
+return {r, y};
+}
+static
+const Rule*
+find_first_std_rule(const std::pair<const Rule*, const Rule*>& eqr)
+{
+auto r = eqr.first;
+auto ry = r->starting_year();
+while (r->save() != std::chrono::minutes{0})
+{
+std::tie(r, ry) = find_next_rule(eqr.first, eqr.second, r, ry);
+if (r == nullptr)
+throw std::runtime_error("Could not find standard offset in rule "
++ eqr.first->name());
+}
+return r;
+}
+static
+std::pair<const Rule*, date::year>
+find_rule_for_zone(const std::pair<const Rule*, const Rule*>& eqr,
+const date::year& y, const std::chrono::seconds& offset,
+const MonthDayTime& mdt)
+{
+assert(eqr.first != nullptr);
+assert(eqr.second != nullptr);
+using namespace std::chrono;
+using namespace date;
+auto r = eqr.first;
+auto ry = r->starting_year();
+auto prev_save = minutes{0};
+auto prev_year = year::min();
+const Rule* prev_rule = nullptr;
+while (r != nullptr)
+{
+if (mdt.compare(y, r->mdt(), ry, offset, prev_save) <= 0)
+break;
+prev_rule = r;
+prev_year = ry;
+prev_save = prev_rule->save();
+std::tie(r, ry) = find_next_rule(eqr.first, eqr.second, r, ry);
+}
+return {prev_rule, prev_year};
+}
+static
+std::pair<const Rule*, date::year>
+find_rule_for_zone(const std::pair<const Rule*, const Rule*>& eqr,
+const sys_seconds& tp_utc,
+const local_seconds& tp_std,
+const local_seconds& tp_loc)
+{
+using namespace std::chrono;
+using namespace date;
+auto r = eqr.first;
+auto ry = r->starting_year();
+auto prev_save = minutes{0};
+auto prev_year = year::min();
+const Rule* prev_rule = nullptr;
+while (r != nullptr)
+{
+bool found = false;
+switch (r->mdt().zone())
+{
+case tz::utc:
+found = tp_utc < r->mdt().to_time_point(ry);
+break;
+case tz::standard:
+found = sys_seconds{tp_std.time_since_epoch()} < r->mdt().to_time_point(ry);
+break;
+case tz::local:
+found = sys_seconds{tp_loc.time_since_epoch()} < r->mdt().to_time_point(ry);
+break;
+}
+if (found)
+break;
+prev_rule = r;
+prev_year = ry;
+prev_save = prev_rule->save();
+std::tie(r, ry) = find_next_rule(eqr.first, eqr.second, r, ry);
+}
+return {prev_rule, prev_year};
+}
+static
+sys_info
+find_rule(const std::pair<const Rule*, date::year>& first_rule,
+const std::pair<const Rule*, date::year>& last_rule,
+const date::year& y, const std::chrono::seconds& offset,
+const MonthDayTime& mdt, const std::chrono::minutes& initial_save,
+const std::string& initial_abbrev)
+{
+using namespace std::chrono;
+using namespace date;
+auto r = first_rule.first;
+auto ry = first_rule.second;
+sys_info x{sys_days(year::min()/min_day), sys_days(year::max()/max_day),
+seconds{0}, initial_save, initial_abbrev};
+while (r != nullptr)
+{
+auto tr = r->mdt().to_sys(ry, offset, x.save);
+auto tx = mdt.to_sys(y, offset, x.save);
+// Find last rule where tx >= tr
+if (tx <= tr || (r == last_rule.first && ry == last_rule.second))
+{
+if (tx < tr && r == first_rule.first && ry == first_rule.second)
+{
+x.end = r->mdt().to_sys(ry, offset, x.save);
+break;
+}
+if (tx < tr)
+{
+std::tie(r, ry) = find_previous_rule(r, ry);  // can't return nullptr for r
+assert(r != nullptr);
+}
+// r != nullptr && tx >= tr (if tr were to be recomputed)
+auto prev_save = initial_save;
+if (!(r == first_rule.first && ry == first_rule.second))
+prev_save = find_previous_rule(r, ry).first->save();
+x.begin = r->mdt().to_sys(ry, offset, prev_save);
+x.save = r->save();
+x.abbrev = r->abbrev();
+if (!(r == last_rule.first && ry == last_rule.second))
+{
+std::tie(r, ry) = find_next_rule(r, ry);  // can't return nullptr for r
+assert(r != nullptr);
+x.end = r->mdt().to_sys(ry, offset, x.save);
+}
+else
+x.end = sys_days(year::max()/max_day);
+break;
+}
+x.save = r->save();
+std::tie(r, ry) = find_next_rule(r, ry);  // Can't return nullptr for r
+assert(r != nullptr);
+}
+return x;
+}
+// zonelet
+detail::zonelet::~zonelet()
+{
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+using minutes = std::chrono::minutes;
+using string = std::string;
+if (tag_ == has_save)
+u.save_.~minutes();
+else
+u.rule_.~string();
+#endif
+}
+detail::zonelet::zonelet()
+{
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+::new(&u.rule_) std::string();
+#endif
+}
+detail::zonelet::zonelet(const zonelet& i)
+: gmtoff_(i.gmtoff_)
+, tag_(i.tag_)
+, format_(i.format_)
+, until_year_(i.until_year_)
+, until_date_(i.until_date_)
+, until_utc_(i.until_utc_)
+, until_std_(i.until_std_)
+, until_loc_(i.until_loc_)
+, initial_save_(i.initial_save_)
+, initial_abbrev_(i.initial_abbrev_)
+, first_rule_(i.first_rule_)
+, last_rule_(i.last_rule_)
+{
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+if (tag_ == has_save)
+::new(&u.save_) std::chrono::minutes(i.u.save_);
+else
+::new(&u.rule_) std::string(i.u.rule_);
+#else
+if (tag_ == has_save)
+u.save_ = i.u.save_;
+else
+u.rule_ = i.u.rule_;
+#endif
+}
+#endif  // !USE_OS_TZDB
+// time_zone
+#if USE_OS_TZDB
+time_zone::time_zone(const std::string& s, detail::undocumented)
+: name_(s)
+, adjusted_(new std::once_flag{})
+{
+}
+enum class endian
+{
+native = __BYTE_ORDER__,
+little = __ORDER_LITTLE_ENDIAN__,
+big    = __ORDER_BIG_ENDIAN__
+};
+static
+inline
+std::uint32_t
+reverse_bytes(std::uint32_t i)
+{
+return
+(i & 0xff000000u) >> 24 |
+(i & 0x00ff0000u) >> 8 |
+(i & 0x0000ff00u) << 8 |
+(i & 0x000000ffu) << 24;
+}
+static
+inline
+std::uint64_t
+reverse_bytes(std::uint64_t i)
+{
+return
+(i & 0xff00000000000000ull) >> 56 |
+(i & 0x00ff000000000000ull) >> 40 |
+(i & 0x0000ff0000000000ull) >> 24 |
+(i & 0x000000ff00000000ull) >> 8 |
+(i & 0x00000000ff000000ull) << 8 |
+(i & 0x0000000000ff0000ull) << 24 |
+(i & 0x000000000000ff00ull) << 40 |
+(i & 0x00000000000000ffull) << 56;
+}
+template <class T>
+static
+inline
+void
+maybe_reverse_bytes(T&, std::false_type)
+{
+}
+static
+inline
+void
+maybe_reverse_bytes(std::int32_t& t, std::true_type)
+{
+t = static_cast<std::int32_t>(reverse_bytes(static_cast<std::uint32_t>(t)));
+}
+static
+inline
+void
+maybe_reverse_bytes(std::int64_t& t, std::true_type)
+{
+t = static_cast<std::int64_t>(reverse_bytes(static_cast<std::uint64_t>(t)));
+}
+template <class T>
+static
+inline
+void
+maybe_reverse_bytes(T& t)
+{
+maybe_reverse_bytes(t, std::integral_constant<bool,
+endian::native == endian::little>{});
+}
+static
+void
+load_header(std::istream& inf)
+{
+// Read TZif
+auto t = inf.get();
+auto z = inf.get();
+auto i = inf.get();
+auto f = inf.get();
+#ifndef NDEBUG
+assert(t == 'T');
+assert(z == 'Z');
+assert(i == 'i');
+assert(f == 'f');
+#else
+(void)t;
+(void)z;
+(void)i;
+(void)f;
+#endif
+}
+static
+unsigned char
+load_version(std::istream& inf)
+{
+// Read version
+auto v = inf.get();
+assert(v != EOF);
+return static_cast<unsigned char>(v);
+}
+static
+void
+skip_reserve(std::istream& inf)
+{
+inf.ignore(15);
+}
+static
+void
+load_counts(std::istream& inf,
+std::int32_t& tzh_ttisgmtcnt, std::int32_t& tzh_ttisstdcnt,
+std::int32_t& tzh_leapcnt,    std::int32_t& tzh_timecnt,
+std::int32_t& tzh_typecnt,    std::int32_t& tzh_charcnt)
+{
+// Read counts;
+inf.read(reinterpret_cast<char*>(&tzh_ttisgmtcnt), 4);
+maybe_reverse_bytes(tzh_ttisgmtcnt);
+inf.read(reinterpret_cast<char*>(&tzh_ttisstdcnt), 4);
+maybe_reverse_bytes(tzh_ttisstdcnt);
+inf.read(reinterpret_cast<char*>(&tzh_leapcnt), 4);
+maybe_reverse_bytes(tzh_leapcnt);
+inf.read(reinterpret_cast<char*>(&tzh_timecnt), 4);
+maybe_reverse_bytes(tzh_timecnt);
+inf.read(reinterpret_cast<char*>(&tzh_typecnt), 4);
+maybe_reverse_bytes(tzh_typecnt);
+inf.read(reinterpret_cast<char*>(&tzh_charcnt), 4);
+maybe_reverse_bytes(tzh_charcnt);
+}
+template <class TimeType>
+static
+std::vector<detail::transition>
+load_transitions(std::istream& inf, std::int32_t tzh_timecnt)
+{
+// Read transitions
+using namespace std::chrono;
+std::vector<detail::transition> transitions;
+transitions.reserve(static_cast<unsigned>(tzh_timecnt));
+for (std::int32_t i = 0; i < tzh_timecnt; ++i)
+{
+TimeType t;
+inf.read(reinterpret_cast<char*>(&t), sizeof(t));
+maybe_reverse_bytes(t);
+transitions.emplace_back(sys_seconds{seconds{t}});
+if (transitions.back().timepoint < min_seconds)
+transitions.back().timepoint = min_seconds;
+}
+return transitions;
+}
+static
+std::vector<std::uint8_t>
+load_indices(std::istream& inf, std::int32_t tzh_timecnt)
+{
+// Read indices
+std::vector<std::uint8_t> indices;
+indices.reserve(static_cast<unsigned>(tzh_timecnt));
+for (std::int32_t i = 0; i < tzh_timecnt; ++i)
+{
+std::uint8_t t;
+inf.read(reinterpret_cast<char*>(&t), sizeof(t));
+indices.emplace_back(t);
+}
+return indices;
+}
+static
+std::vector<ttinfo>
+load_ttinfo(std::istream& inf, std::int32_t tzh_typecnt)
+{
+// Read ttinfo
+std::vector<ttinfo> ttinfos;
+ttinfos.reserve(static_cast<unsigned>(tzh_typecnt));
+for (std::int32_t i = 0; i < tzh_typecnt; ++i)
+{
+ttinfo t;
+inf.read(reinterpret_cast<char*>(&t), 6);
+maybe_reverse_bytes(t.tt_gmtoff);
+ttinfos.emplace_back(t);
+}
+return ttinfos;
+}
+static
+std::string
+load_abbreviations(std::istream& inf, std::int32_t tzh_charcnt)
+{
+// Read abbreviations
+std::string abbrev;
+abbrev.resize(static_cast<unsigned>(tzh_charcnt), '\0');
+inf.read(&abbrev[0], tzh_charcnt);
+return abbrev;
+}
+#if !MISSING_LEAP_SECONDS
+template <class TimeType>
+static
+std::vector<leap>
+load_leaps(std::istream& inf, std::int32_t tzh_leapcnt)
+{
+// Read tzh_leapcnt pairs
+using namespace std::chrono;
+std::vector<leap> leap_seconds;
+leap_seconds.reserve(static_cast<std::size_t>(tzh_leapcnt));
+for (std::int32_t i = 0; i < tzh_leapcnt; ++i)
+{
+TimeType     t0;
+std::int32_t t1;
+inf.read(reinterpret_cast<char*>(&t0), sizeof(t0));
+inf.read(reinterpret_cast<char*>(&t1), sizeof(t1));
+maybe_reverse_bytes(t0);
+maybe_reverse_bytes(t1);
+leap_seconds.emplace_back(sys_seconds{seconds{t0 - (t1-1)}},
+detail::undocumented{});
+}
+return leap_seconds;
+}
+template <class TimeType>
+static
+std::vector<leap>
+load_leap_data(std::istream& inf,
+std::int32_t tzh_leapcnt, std::int32_t tzh_timecnt,
+std::int32_t tzh_typecnt, std::int32_t tzh_charcnt)
+{
+inf.ignore(tzh_timecnt*static_cast<std::int32_t>(sizeof(TimeType)) + tzh_timecnt +
+tzh_typecnt*6 + tzh_charcnt);
+return load_leaps<TimeType>(inf, tzh_leapcnt);
+}
+static
+std::vector<leap>
+load_just_leaps(std::istream& inf)
+{
+// Read tzh_leapcnt pairs
+using namespace std::chrono;
+load_header(inf);
+auto v = load_version(inf);
+std::int32_t tzh_ttisgmtcnt, tzh_ttisstdcnt, tzh_leapcnt,
+tzh_timecnt,    tzh_typecnt,    tzh_charcnt;
+skip_reserve(inf);
+load_counts(inf, tzh_ttisgmtcnt, tzh_ttisstdcnt, tzh_leapcnt,
+tzh_timecnt,    tzh_typecnt,    tzh_charcnt);
+if (v == 0)
+return load_leap_data<int32_t>(inf, tzh_leapcnt, tzh_timecnt, tzh_typecnt,
+tzh_charcnt);
+#if !defined(NDEBUG)
+inf.ignore((4+1)*tzh_timecnt + 6*tzh_typecnt + tzh_charcnt + 8*tzh_leapcnt +
+tzh_ttisstdcnt + tzh_ttisgmtcnt);
+load_header(inf);
+auto v2 = load_version(inf);
+assert(v == v2);
+skip_reserve(inf);
+#else  // defined(NDEBUG)
+inf.ignore((4+1)*tzh_timecnt + 6*tzh_typecnt + tzh_charcnt + 8*tzh_leapcnt +
+tzh_ttisstdcnt + tzh_ttisgmtcnt + (4+1+15));
+#endif  // defined(NDEBUG)
+load_counts(inf, tzh_ttisgmtcnt, tzh_ttisstdcnt, tzh_leapcnt,
+tzh_timecnt,    tzh_typecnt,    tzh_charcnt);
+return load_leap_data<int64_t>(inf, tzh_leapcnt, tzh_timecnt, tzh_typecnt,
+tzh_charcnt);
+}
+#endif  // !MISSING_LEAP_SECONDS
+template <class TimeType>
+void
+time_zone::load_data(std::istream& inf,
+std::int32_t tzh_leapcnt, std::int32_t tzh_timecnt,
+std::int32_t tzh_typecnt, std::int32_t tzh_charcnt)
+{
+using namespace std::chrono;
+transitions_ = load_transitions<TimeType>(inf, tzh_timecnt);
+auto indices = load_indices(inf, tzh_timecnt);
+auto infos = load_ttinfo(inf, tzh_typecnt);
+auto abbrev = load_abbreviations(inf, tzh_charcnt);
+#if !MISSING_LEAP_SECONDS
+auto& leap_seconds = get_tzdb_list().front().leaps;
+if (leap_seconds.empty() && tzh_leapcnt > 0)
+leap_seconds = load_leaps<TimeType>(inf, tzh_leapcnt);
+#endif
+ttinfos_.reserve(infos.size());
+for (auto& info : infos)
+{
+ttinfos_.push_back({seconds{info.tt_gmtoff},
+abbrev.c_str() + info.tt_abbrind,
+info.tt_isdst != 0});
+}
+auto i = 0u;
+if (transitions_.empty() || transitions_.front().timepoint != min_seconds)
+{
+transitions_.emplace(transitions_.begin(), min_seconds);
+auto tf = std::find_if(ttinfos_.begin(), ttinfos_.end(),
+[](const expanded_ttinfo& ti)
+{return ti.is_dst == 0;});
+if (tf == ttinfos_.end())
+tf = ttinfos_.begin();
+transitions_[i].info = &*tf;
+++i;
+}
+for (auto j = 0u; i < transitions_.size(); ++i, ++j)
+transitions_[i].info = ttinfos_.data() + indices[j];
+}
+void
+time_zone::init_impl()
+{
+using namespace std;
+using namespace std::chrono;
+auto name = get_tz_dir() + ('/' + name_);
+std::ifstream inf(name);
+if (!inf.is_open())
+throw std::runtime_error{"Unable to open " + name};
+inf.exceptions(std::ios::failbit | std::ios::badbit);
+load_header(inf);
+auto v = load_version(inf);
+std::int32_t tzh_ttisgmtcnt, tzh_ttisstdcnt, tzh_leapcnt,
+tzh_timecnt,    tzh_typecnt,    tzh_charcnt;
+skip_reserve(inf);
+load_counts(inf, tzh_ttisgmtcnt, tzh_ttisstdcnt, tzh_leapcnt,
+tzh_timecnt,    tzh_typecnt,    tzh_charcnt);
+if (v == 0)
+{
+load_data<int32_t>(inf, tzh_leapcnt, tzh_timecnt, tzh_typecnt, tzh_charcnt);
+}
+else
+{
+#if !defined(NDEBUG)
+inf.ignore((4+1)*tzh_timecnt + 6*tzh_typecnt + tzh_charcnt + 8*tzh_leapcnt +
+tzh_ttisstdcnt + tzh_ttisgmtcnt);
+load_header(inf);
+auto v2 = load_version(inf);
+assert(v == v2);
+skip_reserve(inf);
+#else  // defined(NDEBUG)
+inf.ignore((4+1)*tzh_timecnt + 6*tzh_typecnt + tzh_charcnt + 8*tzh_leapcnt +
+tzh_ttisstdcnt + tzh_ttisgmtcnt + (4+1+15));
+#endif  // defined(NDEBUG)
+load_counts(inf, tzh_ttisgmtcnt, tzh_ttisstdcnt, tzh_leapcnt,
+tzh_timecnt,    tzh_typecnt,    tzh_charcnt);
+load_data<int64_t>(inf, tzh_leapcnt, tzh_timecnt, tzh_typecnt, tzh_charcnt);
+}
+#if !MISSING_LEAP_SECONDS
+if (tzh_leapcnt > 0)
+{
+auto& leap_seconds = get_tzdb_list().front().leaps;
+auto itr = leap_seconds.begin();
+auto l = itr->date();
+seconds leap_count{0};
+for (auto t = std::upper_bound(transitions_.begin(), transitions_.end(), l,
+[](const sys_seconds& x, const transition& ct)
+{
+return x < ct.timepoint;
+});
+t != transitions_.end(); ++t)
+{
+while (t->timepoint >= l)
+{
+++leap_count;
+if (++itr == leap_seconds.end())
+l = sys_days(max_year/max_day);
+else
+l = itr->date() + leap_count;
+}
+t->timepoint -= leap_count;
+}
+}
+#endif  // !MISSING_LEAP_SECONDS
+auto b = transitions_.begin();
+auto i = transitions_.end();
+if (i != b)
+{
+for (--i; i != b; --i)
+{
+if (i->info->offset == i[-1].info->offset &&
+i->info->abbrev == i[-1].info->abbrev &&
+i->info->is_dst == i[-1].info->is_dst)
+i = transitions_.erase(i);
+}
+}
+}
+void
+time_zone::init() const
+{
+std::call_once(*adjusted_, [this]() {const_cast<time_zone*>(this)->init_impl();});
+}
+sys_info
+time_zone::load_sys_info(std::vector<detail::transition>::const_iterator i) const
+{
+using namespace std::chrono;
+assert(!transitions_.empty());
+assert(i != transitions_.begin());
+sys_info r;
+r.begin = i[-1].timepoint;
+r.end = i != transitions_.end() ? i->timepoint :
+sys_seconds(sys_days(year::max()/max_day));
+r.offset = i[-1].info->offset;
+r.save = i[-1].info->is_dst ? minutes{1} : minutes{0};
+r.abbrev = i[-1].info->abbrev;
+return r;
+}
+sys_info
+time_zone::get_info_impl(sys_seconds tp) const
+{
+using namespace std;
+init();
+return load_sys_info(upper_bound(transitions_.begin(), transitions_.end(), tp,
+[](const sys_seconds& x, const transition& t)
+{
+return x < t.timepoint;
+}));
+}
+local_info
+time_zone::get_info_impl(local_seconds tp) const
+{
+using namespace std::chrono;
+init();
+local_info i;
+i.result = local_info::unique;
+auto tr = upper_bound(transitions_.begin(), transitions_.end(), tp,
+[](const local_seconds& x, const transition& t)
+{
+return sys_seconds{x.time_since_epoch()} -
+t.info->offset < t.timepoint;
+});
+i.first = load_sys_info(tr);
+auto tps = sys_seconds{(tp - i.first.offset).time_since_epoch()};
+if (tps < i.first.begin + days{1} && tr != transitions_.begin())
+{
+i.second = load_sys_info(--tr);
+tps = sys_seconds{(tp - i.second.offset).time_since_epoch()};
+if (tps < i.second.end)
+{
+i.result = local_info::ambiguous;
+std::swap(i.first, i.second);
+}
+else
+{
+i.second = {};
+}
+}
+else if (tps >= i.first.end && tr != transitions_.end())
+{
+i.second = load_sys_info(++tr);
+tps = sys_seconds{(tp - i.second.offset).time_since_epoch()};
+if (tps < i.second.begin)
+i.result = local_info::nonexistent;
+else
+i.second = {};
+}
+return i;
+}
+std::ostream&
+operator<<(std::ostream& os, const time_zone& z)
+{
+using namespace std::chrono;
+z.init();
+os << z.name_ << '\n';
+os << "Initially:           ";
+auto const& t = z.transitions_.front();
+if (t.info->offset >= seconds{0})
+os << '+';
+os << make_time(t.info->offset);
+if (t.info->is_dst > 0)
+os << " daylight ";
+else
+os << " standard ";
+os << t.info->abbrev << '\n';
+for (auto i = std::next(z.transitions_.cbegin()); i < z.transitions_.cend(); ++i)
+os << *i << '\n';
+return os;
+}
+#if !MISSING_LEAP_SECONDS
+leap::leap(const sys_seconds& s, detail::undocumented)
+: date_(s)
+{
+}
+#endif  // !MISSING_LEAP_SECONDS
+#else  // !USE_OS_TZDB
+time_zone::time_zone(const std::string& s, detail::undocumented)
+: adjusted_(new std::once_flag{})
+{
+try
+{
+using namespace date;
+std::istringstream in(s);
+in.exceptions(std::ios::failbit | std::ios::badbit);
+std::string word;
+in >> word >> name_;
+parse_info(in);
+}
+catch (...)
+{
+std::cerr << s << '\n';
+std::cerr << *this << '\n';
+zonelets_.pop_back();
+throw;
+}
+}
+sys_info
+time_zone::get_info_impl(sys_seconds tp) const
+{
+return get_info_impl(tp, static_cast<int>(tz::utc));
+}
+local_info
+time_zone::get_info_impl(local_seconds tp) const
+{
+using namespace std::chrono;
+local_info i{};
+i.first = get_info_impl(sys_seconds{tp.time_since_epoch()}, static_cast<int>(tz::local));
+auto tps = sys_seconds{(tp - i.first.offset).time_since_epoch()};
+if (tps < i.first.begin)
+{
+i.second = std::move(i.first);
+i.first = get_info_impl(i.second.begin - seconds{1}, static_cast<int>(tz::utc));
+i.result = local_info::nonexistent;
+}
+else if (i.first.end - tps <= days{1})
+{
+i.second = get_info_impl(i.first.end, static_cast<int>(tz::utc));
+tps = sys_seconds{(tp - i.second.offset).time_since_epoch()};
+if (tps >= i.second.begin)
+i.result = local_info::ambiguous;
+else
+i.second = {};
+}
+return i;
+}
+void
+time_zone::add(const std::string& s)
+{
+try
+{
+std::istringstream in(s);
+in.exceptions(std::ios::failbit | std::ios::badbit);
+ws(in);
+if (!in.eof() && in.peek() != '#')
+parse_info(in);
+}
+catch (...)
+{
+std::cerr << s << '\n';
+std::cerr << *this << '\n';
+zonelets_.pop_back();
+throw;
+}
+}
+void
+time_zone::parse_info(std::istream& in)
+{
+using namespace date;
+using namespace std::chrono;
+zonelets_.emplace_back();
+auto& zonelet = zonelets_.back();
+zonelet.gmtoff_ = parse_signed_time(in);
+in >> zonelet.u.rule_;
+if (zonelet.u.rule_ == "-")
+zonelet.u.rule_.clear();
+in >> zonelet.format_;
+if (!in.eof())
+ws(in);
+if (in.eof() || in.peek() == '#')
+{
+zonelet.until_year_ = year::max();
+zonelet.until_date_ = MonthDayTime(max_day, tz::utc);
+}
+else
+{
+int y;
+in >> y;
+zonelet.until_year_ = year{y};
+in >> zonelet.until_date_;
+zonelet.until_date_.canonicalize(zonelet.until_year_);
+}
+if ((zonelet.until_year_ < min_year) ||
+(zonelets_.size() > 1 && zonelets_.end()[-2].until_year_ > max_year))
+zonelets_.pop_back();
+}
+void
+time_zone::adjust_infos(const std::vector<Rule>& rules)
+{
+using namespace std::chrono;
+using namespace date;
+const zonelet* prev_zonelet = nullptr;
+for (auto& z : zonelets_)
+{
+std::pair<const Rule*, const Rule*> eqr{};
+std::istringstream in;
+in.exceptions(std::ios::failbit | std::ios::badbit);
+// Classify info as rule-based, has save, or neither
+if (!z.u.rule_.empty())
+{
+// Find out if this zonelet has a rule or a save
+eqr = std::equal_range(rules.data(), rules.data() + rules.size(), z.u.rule_);
+if (eqr.first == eqr.second)
+{
+// The rule doesn't exist.  Assume this is a save
+try
+{
+using namespace std::chrono;
+using string = std::string;
+in.str(z.u.rule_);
+auto tmp = duration_cast<minutes>(parse_signed_time(in));
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+z.u.rule_.~string();
+z.tag_ = zonelet::has_save;
+::new(&z.u.save_) minutes(tmp);
+#else
+z.u.rule_.clear();
+z.tag_ = zonelet::has_save;
+z.u.save_ = tmp;
+#endif
+}
+catch (...)
+{
+std::cerr << name_ << " : " << z.u.rule_ << '\n';
+throw;
+}
+}
+}
+else
+{
+// This zone::zonelet has no rule and no save
+z.tag_ = zonelet::is_empty;
+}
+minutes final_save{0};
+if (z.tag_ == zonelet::has_save)
+{
+final_save = z.u.save_;
+}
+else if (z.tag_ == zonelet::has_rule)
+{
+z.last_rule_ = find_rule_for_zone(eqr, z.until_year_, z.gmtoff_,
+z.until_date_);
+if (z.last_rule_.first != nullptr)
+final_save = z.last_rule_.first->save();
+}
+z.until_utc_ = z.until_date_.to_sys(z.until_year_, z.gmtoff_, final_save);
+z.until_std_ = local_seconds{z.until_utc_.time_since_epoch()} + z.gmtoff_;
+z.until_loc_ = z.until_std_ + final_save;
+if (z.tag_ == zonelet::has_rule)
+{
+if (prev_zonelet != nullptr)
+{
+z.first_rule_ = find_rule_for_zone(eqr, prev_zonelet->until_utc_,
+prev_zonelet->until_std_,
+prev_zonelet->until_loc_);
+if (z.first_rule_.first != nullptr)
+{
+z.initial_save_ = z.first_rule_.first->save();
+z.initial_abbrev_ = z.first_rule_.first->abbrev();
+if (z.first_rule_ != z.last_rule_)
+{
+z.first_rule_ = find_next_rule(eqr.first, eqr.second,
+z.first_rule_.first,
+z.first_rule_.second);
+}
+else
+{
+z.first_rule_ = std::make_pair(nullptr, year::min());
+z.last_rule_ = std::make_pair(nullptr, year::max());
+}
+}
+}
+if (z.first_rule_.first == nullptr && z.last_rule_.first != nullptr)
+{
+z.first_rule_ = std::make_pair(eqr.first, eqr.first->starting_year());
+z.initial_abbrev_ = find_first_std_rule(eqr)->abbrev();
+}
+}
+#ifndef NDEBUG
+if (z.first_rule_.first == nullptr)
+{
+assert(z.first_rule_.second == year::min());
+assert(z.last_rule_.first == nullptr);
+assert(z.last_rule_.second == year::max());
+}
+else
+{
+assert(z.last_rule_.first != nullptr);
+}
+#endif
+prev_zonelet = &z;
+}
+}
+static
+std::string
+format_abbrev(std::string format, const std::string& variable, std::chrono::seconds off,
+std::chrono::minutes save)
+{
+using namespace std::chrono;
+auto k = format.find("%s");
+if (k != std::string::npos)
+{
+format.replace(k, 2, variable);
+}
+else
+{
+k = format.find('/');
+if (k != std::string::npos)
+{
+if (save == minutes{0})
+format.erase(k);
+else
+format.erase(0, k+1);
+}
+else
+{
+k = format.find("%z");
+if (k != std::string::npos)
+{
+std::string temp;
+if (off < seconds{0})
+{
+temp = '-';
+off = -off;
+}
+else
+temp = '+';
+auto h = date::floor<hours>(off);
+off -= h;
+if (h < hours{10})
+temp += '0';
+temp += std::to_string(h.count());
+if (off > seconds{0})
+{
+auto m = date::floor<minutes>(off);
+off -= m;
+if (m < minutes{10})
+temp += '0';
+temp += std::to_string(m.count());
+if (off > seconds{0})
+{
+if (off < seconds{10})
+temp += '0';
+temp += std::to_string(off.count());
+}
+}
+format.replace(k, 2, temp);
+}
+}
+}
+return format;
+}
+sys_info
+time_zone::get_info_impl(sys_seconds tp, int tz_int) const
+{
+using namespace std::chrono;
+using namespace date;
+tz timezone = static_cast<tz>(tz_int);
+assert(timezone != tz::standard);
+auto y = year_month_day(floor<days>(tp)).year();
+if (y < min_year || y > max_year)
+throw std::runtime_error("The year " + std::to_string(static_cast<int>(y)) +
+" is out of range:[" + std::to_string(static_cast<int>(min_year)) + ", "
++ std::to_string(static_cast<int>(max_year)) + "]");
+std::call_once(*adjusted_,
+[this]()
+{
+const_cast<time_zone*>(this)->adjust_infos(get_tzdb().rules);
+});
+auto i = std::upper_bound(zonelets_.begin(), zonelets_.end(), tp,
+[timezone](sys_seconds t, const zonelet& zl)
+{
+return timezone == tz::utc ? t < zl.until_utc_ :
+t < sys_seconds{zl.until_loc_.time_since_epoch()};
+});
+sys_info r{};
+if (i != zonelets_.end())
+{
+if (i->tag_ == zonelet::has_save)
+{
+if (i != zonelets_.begin())
+r.begin = i[-1].until_utc_;
+else
+r.begin = sys_days(year::min()/min_day);
+r.end = i->until_utc_;
+r.offset = i->gmtoff_ + i->u.save_;
+r.save = i->u.save_;
+}
+else if (i->u.rule_.empty())
+{
+if (i != zonelets_.begin())
+r.begin = i[-1].until_utc_;
+else
+r.begin = sys_days(year::min()/min_day);
+r.end = i->until_utc_;
+r.offset = i->gmtoff_;
+}
+else
+{
+r = find_rule(i->first_rule_, i->last_rule_, y, i->gmtoff_,
+MonthDayTime(local_seconds{tp.time_since_epoch()}, timezone),
+i->initial_save_, i->initial_abbrev_);
+r.offset = i->gmtoff_ + r.save;
+if (i != zonelets_.begin() && r.begin < i[-1].until_utc_)
+r.begin = i[-1].until_utc_;
+if (r.end > i->until_utc_)
+r.end = i->until_utc_;
+}
+r.abbrev = format_abbrev(i->format_, r.abbrev, r.offset, r.save);
+assert(r.begin < r.end);
+}
+return r;
+}
+std::ostream&
+operator<<(std::ostream& os, const time_zone& z)
+{
+using namespace date;
+using namespace std::chrono;
+detail::save_ostream<char> _(os);
+os.fill(' ');
+os.flags(std::ios::dec | std::ios::left);
+std::call_once(*z.adjusted_,
+[&z]()
+{
+const_cast<time_zone&>(z).adjust_infos(get_tzdb().rules);
+});
+os.width(35);
+os << z.name_;
+std::string indent;
+for (auto const& s : z.zonelets_)
+{
+os << indent;
+if (s.gmtoff_ >= seconds{0})
+os << ' ';
+os << make_time(s.gmtoff_) << "   ";
+os.width(15);
+if (s.tag_ != zonelet::has_save)
+os << s.u.rule_;
+else
+{
+std::ostringstream tmp;
+tmp << make_time(s.u.save_);
+os <<  tmp.str();
+}
+os.width(8);
+os << s.format_ << "   ";
+os << s.until_year_ << ' ' << s.until_date_;
+os << "   " << s.until_utc_ << " UTC";
+os << "   " << s.until_std_ << " STD";
+os << "   " << s.until_loc_;
+os << "   " << make_time(s.initial_save_);
+os << "   " << s.initial_abbrev_;
+if (s.first_rule_.first != nullptr)
+os << "   {" << *s.first_rule_.first << ", " << s.first_rule_.second << '}';
+else
+os << "   {" << "nullptr" << ", " << s.first_rule_.second << '}';
+if (s.last_rule_.first != nullptr)
+os << "   {" << *s.last_rule_.first << ", " << s.last_rule_.second << '}';
+else
+os << "   {" << "nullptr" << ", " << s.last_rule_.second << '}';
+os << '\n';
+if (indent.empty())
+indent = std::string(35, ' ');
+}
+return os;
+}
+#endif  // !USE_OS_TZDB
+#if !MISSING_LEAP_SECONDS
+std::ostream&
+operator<<(std::ostream& os, const leap& x)
+{
+using namespace date;
+return os << x.date_ << "  +";
+}
+#endif  // !MISSING_LEAP_SECONDS
+#if USE_OS_TZDB
+# ifdef __APPLE__
+static
+std::string
+get_version()
+{
+using namespace std;
+auto path = get_tz_dir() + string("/+VERSION");
+ifstream in{path};
+string version;
+in >> version;
+if (in.fail())
+throw std::runtime_error("Unable to get Timezone database version from " + path);
+return version;
+}
+# endif
+static
+std::unique_ptr<tzdb>
+init_tzdb()
+{
+std::unique_ptr<tzdb> db(new tzdb);
+//Iterate through folders
+std::queue<std::string> subfolders;
+subfolders.emplace(get_tz_dir());
+struct dirent* d;
+struct stat s;
+while (!subfolders.empty())
+{
+auto dirname = std::move(subfolders.front());
+subfolders.pop();
+auto dir = opendir(dirname.c_str());
+if (!dir)
+continue;
+while ((d = readdir(dir)) != nullptr)
+{
+// Ignore these files:
+if (d->d_name[0]                      == '.'    || // curdir, prevdir, hidden
+memcmp(d->d_name, "posix", 5)     == 0      || // starts with posix
+strcmp(d->d_name, "Factory")      == 0      ||
+strcmp(d->d_name, "iso3166.tab")  == 0      ||
+strcmp(d->d_name, "right")        == 0      ||
+strcmp(d->d_name, "+VERSION")     == 0      ||
+strcmp(d->d_name, "zone.tab")     == 0      ||
+strcmp(d->d_name, "zone1970.tab") == 0      ||
+strcmp(d->d_name, "tzdata.zi")    == 0      ||
+strcmp(d->d_name, "leapseconds")  == 0      ||
+strcmp(d->d_name, "leap-seconds.list") == 0   )
+continue;
+auto subname = dirname + folder_delimiter + d->d_name;
+if(stat(subname.c_str(), &s) == 0)
+{
+if(S_ISDIR(s.st_mode))
+{
+if(!S_ISLNK(s.st_mode))
+{
+subfolders.push(subname);
+}
+}
+else
+{
+db->zones.emplace_back(subname.substr(get_tz_dir().size()+1),
+detail::undocumented{});
+}
+}
+}
+closedir(dir);
+}
+db->zones.shrink_to_fit();
+std::sort(db->zones.begin(), db->zones.end());
+#  if !MISSING_LEAP_SECONDS
+std::ifstream in(get_tz_dir() + std::string(1, folder_delimiter) + "right/UTC",
+std::ios_base::binary);
+if (in)
+{
+in.exceptions(std::ios::failbit | std::ios::badbit);
+db->leaps = load_just_leaps(in);
+}
+else
+{
+in.clear();
+in.open(get_tz_dir() + std::string(1, folder_delimiter) +
+"UTC", std::ios_base::binary);
+if (!in)
+throw std::runtime_error("Unable to extract leap second information");
+in.exceptions(std::ios::failbit | std::ios::badbit);
+db->leaps = load_just_leaps(in);
+}
+#  endif  // !MISSING_LEAP_SECONDS
+#  ifdef __APPLE__
+db->version = get_version();
+#  endif
+return db;
+}
+#else  // !USE_OS_TZDB
+// link
+link::link(const std::string& s)
+{
+using namespace date;
+std::istringstream in(s);
+in.exceptions(std::ios::failbit | std::ios::badbit);
+std::string word;
+in >> word >> target_ >> name_;
+}
+std::ostream&
+operator<<(std::ostream& os, const link& x)
+{
+using namespace date;
+detail::save_ostream<char> _(os);
+os.fill(' ');
+os.flags(std::ios::dec | std::ios::left);
+os.width(35);
+return os << x.name_ << " --> " << x.target_;
+}
+// leap
+leap::leap(const std::string& s, detail::undocumented)
+{
+using namespace date;
+std::istringstream in(s);
+in.exceptions(std::ios::failbit | std::ios::badbit);
+std::string word;
+int y;
+MonthDayTime date;
+in >> word >> y >> date;
+date_ = date.to_time_point(year(y));
+}
+static
+bool
+file_exists(const std::string& filename)
+{
+#ifdef _WIN32
+return ::_access(filename.c_str(), 0) == 0;
+#else
+return ::access(filename.c_str(), F_OK) == 0;
+#endif
+}
+#if HAS_REMOTE_API
+// CURL tools
+static
+int
+curl_global()
+{
+if (::curl_global_init(CURL_GLOBAL_DEFAULT) != 0)
+throw std::runtime_error("CURL global initialization failed");
+return 0;
+}
+namespace
+{
+struct curl_deleter
+{
+void operator()(CURL* p) const
+{
+::curl_easy_cleanup(p);
+}
+};
+}  // unnamed namespace
+static
+std::unique_ptr<CURL, curl_deleter>
+curl_init()
+{
+static const auto curl_is_now_initiailized = curl_global();
+(void)curl_is_now_initiailized;
+return std::unique_ptr<CURL, curl_deleter>{::curl_easy_init()};
+}
+static
+bool
+download_to_string(const std::string& url, std::string& str)
+{
+str.clear();
+auto curl = curl_init();
+if (!curl)
+return false;
+std::string version;
+curl_easy_setopt(curl.get(), CURLOPT_USERAGENT, "curl");
+curl_easy_setopt(curl.get(), CURLOPT_URL, url.c_str());
+curl_write_callback write_cb = [](char* contents, std::size_t size, std::size_t nmemb,
+void* userp) -> std::size_t
+{
+auto& userstr = *static_cast<std::string*>(userp);
+auto realsize = size * nmemb;
+userstr.append(contents, realsize);
+return realsize;
+};
+curl_easy_setopt(curl.get(), CURLOPT_WRITEFUNCTION, write_cb);
+curl_easy_setopt(curl.get(), CURLOPT_WRITEDATA, &str);
+curl_easy_setopt(curl.get(), CURLOPT_SSL_VERIFYPEER, false);
+auto res = curl_easy_perform(curl.get());
+return (res == CURLE_OK);
+}
+namespace
+{
+enum class download_file_options { binary, text };
+}
+static
+bool
+download_to_file(const std::string& url, const std::string& local_filename,
+download_file_options opts)
+{
+auto curl = curl_init();
+if (!curl)
+return false;
+curl_easy_setopt(curl.get(), CURLOPT_URL, url.c_str());
+curl_easy_setopt(curl.get(), CURLOPT_SSL_VERIFYPEER, false);
+curl_write_callback write_cb = [](char* contents, std::size_t size, std::size_t nmemb,
+void* userp) -> std::size_t
+{
+auto& of = *static_cast<std::ofstream*>(userp);
+auto realsize = size * nmemb;
+of.write(contents, static_cast<std::streamsize>(realsize));
+return realsize;
+};
+curl_easy_setopt(curl.get(), CURLOPT_WRITEFUNCTION, write_cb);
+decltype(curl_easy_perform(curl.get())) res;
+{
+std::ofstream of(local_filename,
+opts == download_file_options::binary ?
+std::ofstream::out | std::ofstream::binary :
+std::ofstream::out);
+of.exceptions(std::ios::badbit);
+curl_easy_setopt(curl.get(), CURLOPT_WRITEDATA, &of);
+res = curl_easy_perform(curl.get());
+}
+return res == CURLE_OK;
+}
+std::string
+remote_version()
+{
+std::string version;
+std::string str;
+if (download_to_string("https://www.iana.org/time-zones", str))
+{
+CONSTDATA char db[] = "/time-zones/releases/tzdata";
+CONSTDATA auto db_size = sizeof(db) - 1;
+auto p = str.find(db, 0, db_size);
+const int ver_str_len = 5;
+if (p != std::string::npos && p + (db_size + ver_str_len) <= str.size())
+version = str.substr(p + db_size, ver_str_len);
+}
+return version;
+}
+// TODO! Using system() create a process and a console window.
+// This is useful to see what errors may occur but is slow and distracting.
+// Consider implementing this functionality more directly, such as
+// using _mkdir and CreateProcess etc.
+// But use the current means now as matches Unix implementations and while
+// in proof of concept / testing phase.
+// TODO! Use <filesystem> eventually.
+static
+bool
+remove_folder_and_subfolders(const std::string& folder)
+{
+#  ifdef _WIN32
+#    if USE_SHELL_API
+// Delete the folder contents by deleting the folder.
+std::string cmd = "rd /s /q \"";
+cmd += folder;
+cmd += '\"';
+return std::system(cmd.c_str()) == EXIT_SUCCESS;
+#    else  // !USE_SHELL_API
+// Create a buffer containing the path to delete. It must be terminated
+// by two nuls. Who designs these API's...
+std::vector<char> from;
+from.assign(folder.begin(), folder.end());
+from.push_back('\0');
+from.push_back('\0');
+SHFILEOPSTRUCT fo{}; // Zero initialize.
+fo.wFunc = FO_DELETE;
+fo.pFrom = from.data();
+fo.fFlags = FOF_NO_UI;
+int ret = SHFileOperation(&fo);
+if (ret == 0 && !fo.fAnyOperationsAborted)
+return true;
+return false;
+#    endif  // !USE_SHELL_API
+#  else   // !_WIN32
+#    if USE_SHELL_API
+return std::system(("rm -R " + folder).c_str()) == EXIT_SUCCESS;
+#    else // !USE_SHELL_API
+struct dir_deleter {
+dir_deleter() {}
+void operator()(DIR* d) const
+{
+if (d != nullptr)
+{
+int result = closedir(d);
+assert(result == 0);
+}
+}
+};
+using closedir_ptr = std::unique_ptr<DIR, dir_deleter>;
+std::string filename;
+struct stat statbuf;
+std::size_t folder_len = folder.length();
+struct dirent* p = nullptr;
+closedir_ptr d(opendir(folder.c_str()));
+bool r = d.get() != nullptr;
+while (r && (p=readdir(d.get())) != nullptr)
+{
+if (strcmp(p->d_name, ".") == 0 || strcmp(p->d_name, "..") == 0)
+continue;
+// + 2 for path delimiter and nul terminator.
+std::size_t buf_len = folder_len + strlen(p->d_name) + 2;
+filename.resize(buf_len);
+std::size_t path_len = static_cast<std::size_t>(
+snprintf(&filename[0], buf_len, "%s/%s", folder.c_str(), p->d_name));
+assert(path_len == buf_len - 1);
+filename.resize(path_len);
+if (stat(filename.c_str(), &statbuf) == 0)
+r = S_ISDIR(statbuf.st_mode)
+? remove_folder_and_subfolders(filename)
+: unlink(filename.c_str()) == 0;
+}
+d.reset();
+if (r)
+r = rmdir(folder.c_str()) == 0;
+return r;
+#    endif // !USE_SHELL_API
+#  endif  // !_WIN32
+}
+static
+bool
+make_directory(const std::string& folder)
+{
+#  ifdef _WIN32
+#    if USE_SHELL_API
+// Re-create the folder.
+std::string cmd = "mkdir \"";
+cmd += folder;
+cmd += '\"';
+return std::system(cmd.c_str()) == EXIT_SUCCESS;
+#    else  // !USE_SHELL_API
+return _mkdir(folder.c_str()) == 0;
+#    endif // !USE_SHELL_API
+#  else  // !_WIN32
+#    if USE_SHELL_API
+return std::system(("mkdir -p " + folder).c_str()) == EXIT_SUCCESS;
+#    else  // !USE_SHELL_API
+return mkdir(folder.c_str(), 0777) == 0;
+#    endif  // !USE_SHELL_API
+#  endif  // !_WIN32
+}
+static
+bool
+delete_file(const std::string& file)
+{
+#  ifdef _WIN32
+#    if USE_SHELL_API
+std::string cmd = "del \"";
+cmd += file;
+cmd += '\"';
+return std::system(cmd.c_str()) == 0;
+#    else  // !USE_SHELL_API
+return _unlink(file.c_str()) == 0;
+#    endif // !USE_SHELL_API
+#  else  // !_WIN32
+#    if USE_SHELL_API
+return std::system(("rm " + file).c_str()) == EXIT_SUCCESS;
+#    else // !USE_SHELL_API
+return unlink(file.c_str()) == 0;
+#    endif // !USE_SHELL_API
+#  endif  // !_WIN32
+}
+#  ifdef _WIN32
+static
+bool
+move_file(const std::string& from, const std::string& to)
+{
+#    if USE_SHELL_API
+std::string cmd = "move \"";
+cmd += from;
+cmd += "\" \"";
+cmd += to;
+cmd += '\"';
+return std::system(cmd.c_str()) == EXIT_SUCCESS;
+#    else  // !USE_SHELL_API
+return !!::MoveFile(from.c_str(), to.c_str());
+#    endif // !USE_SHELL_API
+}
+// Usually something like "c:\Program Files".
+static
+std::string
+get_program_folder()
+{
+return get_known_folder(FOLDERID_ProgramFiles);
+}
+// Note folder can and usually does contain spaces.
+static
+std::string
+get_unzip_program()
+{
+std::string path;
+// 7-Zip appears to note its location in the registry.
+// If that doesn't work, fall through and take a guess, but it will likely be wrong.
+HKEY hKey = nullptr;
+if (RegOpenKeyExA(HKEY_LOCAL_MACHINE, "SOFTWARE\\7-Zip", 0, KEY_READ, &hKey) == ERROR_SUCCESS)
+{
+char value_buffer[MAX_PATH + 1]; // fyi 260 at time of writing.
+// in/out parameter. Documentation say that size is a count of bytes not chars.
+DWORD size = sizeof(value_buffer) - sizeof(value_buffer[0]);
+DWORD tzi_type = REG_SZ;
+// Testing shows Path key value is "C:\Program Files\7-Zip\" i.e. always with trailing \.
+bool got_value = (RegQueryValueExA(hKey, "Path", nullptr, &tzi_type,
+reinterpret_cast<LPBYTE>(value_buffer), &size) == ERROR_SUCCESS);
+RegCloseKey(hKey); // Close now incase of throw later.
+if (got_value)
+{
+// Function does not guarantee to null terminate.
+value_buffer[size / sizeof(value_buffer[0])] = '\0';
+path = value_buffer;
+if (!path.empty())
+{
+path += "7z.exe";
+return path;
+}
+}
+}
+path += get_program_folder();
+path += folder_delimiter;
+path += "7-Zip\\7z.exe";
+return path;
+}
+#    if !USE_SHELL_API
+static
+int
+run_program(const std::string& command)
+{
+STARTUPINFO si{};
+si.cb = sizeof(si);
+PROCESS_INFORMATION pi{};
+// Allegedly CreateProcess overwrites the command line. Ugh.
+std::string mutable_command(command);
+if (CreateProcess(nullptr, &mutable_command[0],
+nullptr, nullptr, FALSE, CREATE_NO_WINDOW, nullptr, nullptr, &si, &pi))
+{
+WaitForSingleObject(pi.hProcess, INFINITE);
+DWORD exit_code;
+bool got_exit_code = !!GetExitCodeProcess(pi.hProcess, &exit_code);
+CloseHandle(pi.hProcess);
+CloseHandle(pi.hThread);
+// Not 100% sure about this still active thing is correct,
+// but I'm going with it because I *think* WaitForSingleObject might
+// return in some cases without INFINITE-ly waiting.
+// But why/wouldn't GetExitCodeProcess return false in that case?
+if (got_exit_code && exit_code != STILL_ACTIVE)
+return static_cast<int>(exit_code);
+}
+return EXIT_FAILURE;
+}
+#    endif // !USE_SHELL_API
+static
+std::string
+get_download_tar_file(const std::string& version)
+{
+auto file = get_install();
+file += folder_delimiter;
+file += "tzdata";
+file += version;
+file += ".tar";
+return file;
+}
+static
+bool
+extract_gz_file(const std::string& version, const std::string& gz_file,
+const std::string& dest_folder)
+{
+auto unzip_prog = get_unzip_program();
+bool unzip_result = false;
+// Use the unzip program to extract the tar file from the archive.
+// Aim to create a string like:
+// "C:\Program Files\7-Zip\7z.exe" x "C:\Users\SomeUser\Downloads\tzdata2016d.tar.gz"
+//     -o"C:\Users\SomeUser\Downloads\tzdata"
+std::string cmd;
+cmd = '\"';
+cmd += unzip_prog;
+cmd += "\" x \"";
+cmd += gz_file;
+cmd += "\" -o\"";
+cmd += dest_folder;
+cmd += '\"';
+#    if USE_SHELL_API
+// When using shelling out with std::system() extra quotes are required around the
+// whole command. It's weird but necessary it seems, see:
+// http://stackoverflow.com/q/27975969/576911
+cmd = "\"" + cmd + "\"";
+if (std::system(cmd.c_str()) == EXIT_SUCCESS)
+unzip_result = true;
+#    else  // !USE_SHELL_API
+if (run_program(cmd) == EXIT_SUCCESS)
+unzip_result = true;
+#    endif // !USE_SHELL_API
+if (unzip_result)
+delete_file(gz_file);
+// Use the unzip program extract the data from the tar file that was
+// just extracted from the archive.
+auto tar_file = get_download_tar_file(version);
+cmd = '\"';
+cmd += unzip_prog;
+cmd += "\" x \"";
+cmd += tar_file;
+cmd += "\" -o\"";
+cmd += get_install();
+cmd += '\"';
+#    if USE_SHELL_API
+cmd = "\"" + cmd + "\"";
+if (std::system(cmd.c_str()) == EXIT_SUCCESS)
+unzip_result = true;
+#    else  // !USE_SHELL_API
+if (run_program(cmd) == EXIT_SUCCESS)
+unzip_result = true;
+#    endif // !USE_SHELL_API
+if (unzip_result)
+delete_file(tar_file);
+return unzip_result;
+}
+static
+std::string
+get_download_mapping_file(const std::string& version)
+{
+auto file = get_install() + version + "windowsZones.xml";
+return file;
+}
+#  else  // !_WIN32
+#    if !USE_SHELL_API
+static
+int
+run_program(const char* prog, const char*const args[])
+{
+pid_t pid = fork();
+if (pid == -1) // Child failed to start.
+return EXIT_FAILURE;
+if (pid != 0)
+{
+// We are in the parent. Child started. Wait for it.
+pid_t ret;
+int status;
+while ((ret = waitpid(pid, &status, 0)) == -1)
+{
+if (errno != EINTR)
+break;
+}
+if (ret != -1)
+{
+if (WIFEXITED(status))
+return WEXITSTATUS(status);
+}
+printf("Child issues!\n");
+return EXIT_FAILURE; // Not sure what status of child is.
+}
+else // We are in the child process. Start the program the parent wants to run.
+{
+if (execv(prog, const_cast<char**>(args)) == -1) // Does not return.
+{
+perror("unreachable 0\n");
+_Exit(127);
+}
+printf("unreachable 2\n");
+}
+printf("unreachable 2\n");
+// Unreachable.
+assert(false);
+exit(EXIT_FAILURE);
+return EXIT_FAILURE;
+}
+#    endif // !USE_SHELL_API
+static
+bool
+extract_gz_file(const std::string&, const std::string& gz_file, const std::string&)
+{
+#    if USE_SHELL_API
+bool unzipped = std::system(("tar -xzf " + gz_file + " -C " + get_install()).c_str()) == EXIT_SUCCESS;
+#    else  // !USE_SHELL_API
+const char prog[] = {"/usr/bin/tar"};
+const char*const args[] =
+{
+prog, "-xzf", gz_file.c_str(), "-C", get_install().c_str(), nullptr
+};
+bool unzipped = (run_program(prog, args) == EXIT_SUCCESS);
+#    endif // !USE_SHELL_API
+if (unzipped)
+{
+delete_file(gz_file);
+return true;
+}
+return false;
+}
+#  endif // !_WIN32
+bool
+remote_download(const std::string& version)
+{
+assert(!version.empty());
+#  ifdef _WIN32
+// Download folder should be always available for Windows
+#  else  // !_WIN32
+// Create download folder if it does not exist on UNIX system
+auto download_folder = get_install();
+if (!file_exists(download_folder))
+{
+if (!make_directory(download_folder))
+return false;
+}
+#  endif  // _WIN32
+auto url = "https://data.iana.org/time-zones/releases/tzdata" + version +
+".tar.gz";
+bool result = download_to_file(url, get_download_gz_file(version),
+download_file_options::binary);
+#  ifdef _WIN32
+if (result)
+{
+auto mapping_file = get_download_mapping_file(version);
+result = download_to_file(
+			"https://raw.githubusercontent.com/unicode-org/cldr/master/"
+			"common/supplemental/windowsZones.xml",
+mapping_file, download_file_options::text);
+}
+#  endif  // _WIN32
+return result;
+}
+bool
+remote_install(const std::string& version)
+{
+auto success = false;
+assert(!version.empty());
+std::string install = get_install();
+auto gz_file = get_download_gz_file(version);
+if (file_exists(gz_file))
+{
+if (file_exists(install))
+remove_folder_and_subfolders(install);
+if (make_directory(install))
+{
+if (extract_gz_file(version, gz_file, install))
+success = true;
+#  ifdef _WIN32
+auto mapping_file_source = get_download_mapping_file(version);
+auto mapping_file_dest = get_install();
+mapping_file_dest += folder_delimiter;
+mapping_file_dest += "windowsZones.xml";
+if (!move_file(mapping_file_source, mapping_file_dest))
+success = false;
+#  endif  // _WIN32
+}
+}
+return success;
+}
+#endif  // HAS_REMOTE_API
+static
+std::string
+get_version(const std::string& path)
+{
+std::string version;
+std::ifstream infile(path + "version");
+if (infile.is_open())
+{
+infile >> version;
+if (!infile.fail())
+return version;
+}
+else
+{
+infile.open(path + "NEWS");
+while (infile)
+{
+infile >> version;
+if (version == "Release")
+{
+infile >> version;
+return version;
+}
+}
+}
+throw std::runtime_error("Unable to get Timezone database version from " + path);
+}
+static
+std::unique_ptr<tzdb>
+init_tzdb()
+{
+using namespace date;
+const std::string install = get_install();
+const std::string path = install + folder_delimiter;
+std::string line;
+bool continue_zone = false;
+std::unique_ptr<tzdb> db(new tzdb);
+#if AUTO_DOWNLOAD
+if (!file_exists(install))
+{
+auto rv = remote_version();
+if (!rv.empty() && remote_download(rv))
+{
+if (!remote_install(rv))
+{
+std::string msg = "Timezone database version \"";
+msg += rv;
+msg += "\" did not install correctly to \"";
+msg += install;
+msg += "\"";
+throw std::runtime_error(msg);
+}
+}
+if (!file_exists(install))
+{
+std::string msg = "Timezone database not found at \"";
+msg += install;
+msg += "\"";
+throw std::runtime_error(msg);
+}
+db->version = get_version(path);
+}
+else
+{
+db->version = get_version(path);
+auto rv = remote_version();
+if (!rv.empty() && db->version != rv)
+{
+if (remote_download(rv))
+{
+remote_install(rv);
+db->version = get_version(path);
+}
+}
+}
+#else  // !AUTO_DOWNLOAD
+if (!file_exists(install))
+{
+std::string msg = "Timezone database not found at \"";
+msg += install;
+msg += "\"";
+throw std::runtime_error(msg);
+}
+db->version = get_version(path);
+#endif  // !AUTO_DOWNLOAD
+CONSTDATA char*const files[] =
+{
+"africa", "antarctica", "asia", "australasia", "backward", "etcetera", "europe",
+"pacificnew", "northamerica", "southamerica", "systemv", "leapseconds"
+};
+for (const auto& filename : files)
+{
+std::ifstream infile(path + filename);
+while (infile)
+{
+std::getline(infile, line);
+if (!line.empty() && line[0] != '#')
+{
+std::istringstream in(line);
+std::string word;
+in >> word;
+if (word == "Rule")
+{
+db->rules.push_back(Rule(line));
+continue_zone = false;
+}
+else if (word == "Link")
+{
+db->links.push_back(link(line));
+continue_zone = false;
+}
+else if (word == "Leap")
+{
+db->leaps.push_back(leap(line, detail::undocumented{}));
+continue_zone = false;
+}
+else if (word == "Zone")
+{
+db->zones.push_back(time_zone(line, detail::undocumented{}));
+continue_zone = true;
+}
+else if (line[0] == '\t' && continue_zone)
+{
+db->zones.back().add(line);
+}
+else
+{
+std::cerr << line << '\n';
+}
+}
+}
+}
+std::sort(db->rules.begin(), db->rules.end());
+Rule::split_overlaps(db->rules);
+std::sort(db->zones.begin(), db->zones.end());
+db->zones.shrink_to_fit();
+std::sort(db->links.begin(), db->links.end());
+db->links.shrink_to_fit();
+std::sort(db->leaps.begin(), db->leaps.end());
+db->leaps.shrink_to_fit();
+#ifdef _WIN32
+std::string mapping_file = get_install() + folder_delimiter + "windowsZones.xml";
+db->mappings = load_timezone_mappings_from_xml_file(mapping_file);
+sort_zone_mappings(db->mappings);
+#endif // _WIN32
+return db;
+}
+const tzdb&
+reload_tzdb()
+{
+#if AUTO_DOWNLOAD
+auto const& v = get_tzdb_list().front().version;
+if (!v.empty() && v == remote_version())
+return get_tzdb_list().front();
+#endif  // AUTO_DOWNLOAD
+tzdb_list::undocumented_helper::push_front(get_tzdb_list(), init_tzdb().release());
+return get_tzdb_list().front();
+}
+#endif  // !USE_OS_TZDB
+const tzdb&
+get_tzdb()
+{
+return get_tzdb_list().front();
+}
+const time_zone*
+#if HAS_STRING_VIEW
+tzdb::locate_zone(std::string_view tz_name) const
+#else
+tzdb::locate_zone(const std::string& tz_name) const
+#endif
+{
+auto zi = std::lower_bound(zones.begin(), zones.end(), tz_name,
+#if HAS_STRING_VIEW
+[](const time_zone& z, const std::string_view& nm)
+#else
+[](const time_zone& z, const std::string& nm)
+#endif
+{
+return z.name() < nm;
+});
+if (zi == zones.end() || zi->name() != tz_name)
+{
+#if !USE_OS_TZDB
+auto li = std::lower_bound(links.begin(), links.end(), tz_name,
+#if HAS_STRING_VIEW
+[](const link& z, const std::string_view& nm)
+#else
+[](const link& z, const std::string& nm)
+#endif
+{
+return z.name() < nm;
+});
+if (li != links.end() && li->name() == tz_name)
+{
+zi = std::lower_bound(zones.begin(), zones.end(), li->target(),
+[](const time_zone& z, const std::string& nm)
+{
+return z.name() < nm;
+});
+if (zi != zones.end() && zi->name() == li->target())
+return &*zi;
+}
+#endif  // !USE_OS_TZDB
+throw std::runtime_error(std::string(tz_name) + " not found in timezone database");
+}
+return &*zi;
+}
+const time_zone*
+#if HAS_STRING_VIEW
+locate_zone(std::string_view tz_name)
+#else
+locate_zone(const std::string& tz_name)
+#endif
+{
+return get_tzdb().locate_zone(tz_name);
+}
+#if USE_OS_TZDB
+std::ostream&
+operator<<(std::ostream& os, const tzdb& db)
+{
+os << "Version: " << db.version << "\n\n";
+for (const auto& x : db.zones)
+os << x << '\n';
+#if !MISSING_LEAP_SECONDS
+os << '\n';
+for (const auto& x : db.leaps)
+os << x << '\n';
+#endif  // !MISSING_LEAP_SECONDS
+return os;
+}
+#else  // !USE_OS_TZDB
+std::ostream&
+operator<<(std::ostream& os, const tzdb& db)
+{
+os << "Version: " << db.version << '\n';
+std::string title("--------------------------------------------"
+"--------------------------------------------\n"
+"Name           ""Start Y ""End Y   "
+"Beginning                              ""Offset  "
+"Designator\n"
+"--------------------------------------------"
+"--------------------------------------------\n");
+int count = 0;
+for (const auto& x : db.rules)
+{
+if (count++ % 50 == 0)
+os << title;
+os << x << '\n';
+}
+os << '\n';
+title = std::string("---------------------------------------------------------"
+"--------------------------------------------------------\n"
+"Name                               ""Offset      "
+"Rule           ""Abrev      ""Until\n"
+"---------------------------------------------------------"
+"--------------------------------------------------------\n");
+count = 0;
+for (const auto& x : db.zones)
+{
+if (count++ % 10 == 0)
+os << title;
+os << x << '\n';
+}
+os << '\n';
+title = std::string("---------------------------------------------------------"
+"--------------------------------------------------------\n"
+"Alias                                   ""To\n"
+"---------------------------------------------------------"
+"--------------------------------------------------------\n");
+count = 0;
+for (const auto& x : db.links)
+{
+if (count++ % 45 == 0)
+os << title;
+os << x << '\n';
+}
+os << '\n';
+title = std::string("---------------------------------------------------------"
+"--------------------------------------------------------\n"
+"Leap second on\n"
+"---------------------------------------------------------"
+"--------------------------------------------------------\n");
+os << title;
+for (const auto& x : db.leaps)
+os << x << '\n';
+return os;
+}
+#endif  // !USE_OS_TZDB
+// -----------------------
+#ifdef _WIN32
+static
+std::string
+getTimeZoneKeyName()
+{
+DYNAMIC_TIME_ZONE_INFORMATION dtzi{};
+auto result = GetDynamicTimeZoneInformation(&dtzi);
+if (result == TIME_ZONE_ID_INVALID)
+throw std::runtime_error("current_zone(): GetDynamicTimeZoneInformation()"
+" reported TIME_ZONE_ID_INVALID.");
+auto wlen = wcslen(dtzi.TimeZoneKeyName);
+char buf[128] = {};
+assert(sizeof(buf) >= wlen+1);
+wcstombs(buf, dtzi.TimeZoneKeyName, wlen);
+if (strcmp(buf, "Coordinated Universal Time") == 0)
+return "UTC";
+return buf;
+}
+const time_zone*
+tzdb::current_zone() const
+{
+std::string win_tzid = getTimeZoneKeyName();
+std::string standard_tzid;
+if (!native_to_standard_timezone_name(win_tzid, standard_tzid))
+{
+std::string msg;
+msg = "current_zone() failed: A mapping from the Windows Time Zone id \"";
+msg += win_tzid;
+msg += "\" was not found in the time zone mapping database.";
+throw std::runtime_error(msg);
+}
+return locate_zone(standard_tzid);
+}
+#else  // !_WIN32
+const time_zone*
+tzdb::current_zone() const
+{
+// On some OS's a file called /etc/localtime may
+// exist and it may be either a real file
+// containing time zone details or a symlink to such a file.
+// On MacOS and BSD Unix if this file is a symlink it
+// might resolve to a path like this:
+// "/usr/share/zoneinfo/America/Los_Angeles"
+// If it does, we try to determine the current
+// timezone from the remainder of the path by removing the prefix
+// and hoping the rest resolves to a valid timezone.
+// It may not always work though. If it doesn't then an
+// exception will be thrown by local_timezone.
+// The path may also take a relative form:
+// "../usr/share/zoneinfo/America/Los_Angeles".
+{
+struct stat sb;
+CONSTDATA auto timezone = "/etc/localtime";
+if (lstat(timezone, &sb) == 0 && S_ISLNK(sb.st_mode) && sb.st_size > 0) {
+using namespace std;
+char rp[PATH_MAX+1] = {};
+if (realpath(timezone, rp) == nullptr)
+throw system_error(errno, system_category(), "realpath() failed");
+#if HAS_STRING_VIEW
+string_view result = rp;
+CONSTDATA string_view zoneinfo = "/zoneinfo/";
+const size_t pos = result.rfind(zoneinfo);
+if (pos == result.npos)
+throw runtime_error(
+"current_zone() failed to find \"/zoneinfo/\" in " + string(result));
+result.remove_prefix(pos + zoneinfo.size());
+#else
+string result = rp;
+CONSTDATA char zoneinfo[] = "/zoneinfo/";
+const size_t pos = result.rfind(zoneinfo);
+if (pos == result.npos)
+throw runtime_error(
+"current_zone() failed to find \"/zoneinfo/\" in " + result);
+result.erase(0, pos + sizeof(zoneinfo) - 1);
+#endif
+return locate_zone(result);
+}
+}
+// On embedded systems e.g. buildroot with uclibc the timezone is linked
+// into /etc/TZ which is a symlink to path like this:
+// "/usr/share/zoneinfo/uclibc/America/Los_Angeles"
+// If it does, we try to determine the current
+// timezone from the remainder of the path by removing the prefix
+// and hoping the rest resolves to valid timezone.
+// It may not always work though. If it doesn't then an
+// exception will be thrown by local_timezone.
+// The path may also take a relative form:
+// "../usr/share/zoneinfo/uclibc/America/Los_Angeles".
+{
+struct stat sb;
+CONSTDATA auto timezone = "/etc/TZ";
+if (lstat(timezone, &sb) == 0 && S_ISLNK(sb.st_mode) && sb.st_size > 0) {
+using namespace std;
+string result;
+char rp[PATH_MAX+1] = {};
+if (readlink(timezone, rp, sizeof(rp)-1) > 0)
+result = string(rp);
+else
+throw system_error(errno, system_category(), "readlink() failed");
+const size_t pos = result.find(get_tz_dir());
+if (pos != result.npos)
+result.erase(0, get_tz_dir().size() + 1 + pos);
+return locate_zone(result);
+}
+}
+{
+// On some versions of some linux distro's (e.g. Ubuntu),
+// the current timezone might be in the first line of
+// the /etc/timezone file.
+std::ifstream timezone_file("/etc/timezone");
+if (timezone_file.is_open())
+{
+std::string result;
+std::getline(timezone_file, result);
+if (!result.empty())
+return locate_zone(result);
+}
+// Fall through to try other means.
+}
+{
+// On some versions of some bsd distro's (e.g. FreeBSD),
+// the current timezone might be in the first line of
+// the /var/db/zoneinfo file.
+std::ifstream timezone_file("/var/db/zoneinfo");
+if (timezone_file.is_open())
+{
+std::string result;
+std::getline(timezone_file, result);
+if (!result.empty())
+return locate_zone(result);
+}
+// Fall through to try other means.
+}
+{
+// On some versions of some bsd distro's (e.g. iOS),
+// it is not possible to use file based approach,
+// we switch to system API, calling functions in
+// CoreFoundation framework.
+#if TARGET_OS_IPHONE
+std::string result = date::iOSUtils::get_current_timezone();
+if (!result.empty())
+return locate_zone(result);
+#endif
+// Fall through to try other means.
+}
+{
+// On some versions of some linux distro's (e.g. Red Hat),
+// the current timezone might be in the first line of
+// the /etc/sysconfig/clock file as:
+// ZONE="US/Eastern"
+std::ifstream timezone_file("/etc/sysconfig/clock");
+std::string result;
+while (timezone_file)
+{
+std::getline(timezone_file, result);
+auto p = result.find("ZONE=\"");
+if (p != std::string::npos)
+{
+result.erase(p, p+6);
+result.erase(result.rfind('"'));
+return locate_zone(result);
+}
+}
+// Fall through to try other means.
+}
+throw std::runtime_error("Could not get current timezone");
+}
+#endif  // !_WIN32
+const time_zone*
+current_zone()
+{
+return get_tzdb().current_zone();
+}
+}  // namespace date
+#if defined(__GNUC__) && __GNUC__ < 5
+# pragma GCC diagnostic pop
+#endif

Mercurial > thymian

comparison common/date/tz.cpp @ 0:a4671277546c tip