--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/cell.rb	Sun Sep 15 11:46:47 2019 +0200
@@ -0,0 +1,85 @@
+#---
+# Excerpted from "Mazes for Programmers",
+# published by The Pragmatic Bookshelf.
+# Copyrights apply to this code. It may not be used to create training material, 
+# courses, books, articles, and the like. Contact us if you are in doubt.
+# We make no guarantees that this code is fit for any purpose. 
+# Visit http://www.pragmaticprogrammer.com/titles/jbmaze for more book information.
+#---
+
+# Direction constants
+NORTH, SOUTH, EAST, WEST, NOWHERE = 1, 2, 4, 8, 0
+
+DIRECTIONS = { :EAST => 'E', :WEST => 'W', :NORTH => 'N', :SOUTH => 'S', :NOWHERE => '?'}
+
+require 'distances'
+
+class Cell
+  attr_reader :row, :column
+  attr_accessor :north, :south, :east, :west
+
+  def initialize(row, column)
+    @row, @column = row, column
+    @links = {}
+  end
+
+  def link(cell, bidi=true)
+    @links[cell] = true
+    cell.link(self, false) if bidi
+    self
+  end
+
+  def unlink(cell, bidi=true)
+    @links.delete(cell)
+    cell.unlink(self, false) if bidi
+    self
+  end
+
+  def links
+    @links.keys
+  end
+
+  def linked?(cell)
+    @links.key?(cell)
+  end
+
+  def neighbors
+    list = []
+    list << north if north
+    list << south if south
+    list << east  if east
+    list << west  if west
+    list
+  end
+
+  def distances
+    distances = Distances.new(self) 
+    frontier = [ self ]
+
+    while frontier.any? 
+      new_frontier = [] 
+
+      frontier.each do |cell| 
+        cell.links.each do |linked| 
+          next if distances[linked] 
+          distances[linked] = distances[cell] + 1 
+          new_frontier << linked 
+        end
+      end
+
+      frontier = new_frontier 
+    end
+
+    distances
+  end
+
+
+  def direction(cell)
+    return NORTH if cell == north
+    return SOUTH if cell == south
+    return EAST if cell == east
+    return WEST if cell == west
+    0
+  end
+
+end