#!/usr/bin/ruby

# Dave's Cheap Ruby Sokoban
#######========--------   --- -   -
# A response to Ruby Quiz of the Week #5 [ruby-talk:118250]
#
# Author: Dave Burt <dave at burt.id.au>
# Created: 1 Nov 2004
# Last modified: 4 Nov 2004
#
# Fine print: Provided as is. Use at your own risk. Unauthorized copying is
#             not disallowed. Credit's appreciated if you use my code. I'd
#             appreciate seeing any modifications you make to it.

module Sokoban

	NORTH = [-1,0]
	SOUTH = [1,0]
	EAST = [0,1]
	WEST = [0,-1]

	class SokobanError < StandardError; end

	class Tile
		def self.create(chr = nil)
			case chr
			when '#'
				Wall.new
			when ' '
				Floor.new
			when '@'
				Floor.new(Person.new)
			when 'o'
				Floor.new(Crate.new)
			when '.'
				Storage.new
			when '+'
				Storage.new(Person.new)
			when '*'
				Storage.new(Crate.new)
			else
				CharTile.new(chr)
			end
		end
		def to_s
			'~'
		end
	end

	class CharTile < Tile
		attr_reader :chr
		def initialize(chr)
			@chr = chr
		end
		def to_s
			chr
		end
	end

	class Wall < Tile
		def to_s
			'#'
		end
	end

	class Floor < Tile
		attr_accessor :resident
		def initialize(resident = nil)
			@resident = resident
		end
		def to_s
			return resident.to_s if resident
			' '
		end
		def clear
			r = @resident
			@resident = nil
			r
		end
		def add(resident)
			throw SokobanError.new("Can't go there - this tile is full") if @resident
			@resident = resident
		end
		alias :<< :add
	end

	class Storage < Floor
		def has_crate?
			Crate === resident
		end
		def to_s
			case resident
			when Crate
				'*'
			when Person
				'+'
			else
				'.'
			end
		end
	end

	class Crate
		def to_s
			'o'
		end
	end

	class Person
		def to_s
			'@'
		end
	end

	class Level
		attr_reader :moves
		def initialize(str)
			@grid = str.split("\n").map{|ln| ln.split(//).map{|c| Tile.create(c) } }
			throw SokobanError.new('No player found on level') if !player_index
			throw SokobanError.new('No challenge!') if solved?
			@moves = 0
		end
		def [](r, c)
			@grid[r][c]
		end
		def to_s
			@grid.map{|row| row.join }.join("\n")
		end
		# returns a 2-element array with the row and column of the player's position, respectively
		def player_index
			@grid.each_index do |row|
				@grid[row].each_index do |col|
					if @grid[row][col].respond_to?(:resident) && Person === @grid[row][col].resident
						return [row, col]
					end
				end
			end
			nil
		end
		def solved?
			# a level is solved when every Storage tile has a Crate
			@grid.flatten.all? {|tile| !(Storage === tile) || tile.has_crate? }
		end
		def move(dir)
			if [NORTH,SOUTH,EAST,WEST].include?(dir)
				pos = player_index
				target = @grid[pos[0] + dir[0]][pos[1] + dir[1]]
				if Floor === target
					if Crate === target.resident
						indirect_target = @grid[pos[0] + 2*dir[0]][pos[1] + 2*dir[1]]
						if Floor === indirect_target && !indirect_target.resident
							@grid[pos[0] + 2*dir[0]][pos[1] + 2*dir[1]] << @grid[pos[0] + dir[0]][pos[1] + dir[1]].clear
							@grid[pos[0] + dir[0]][pos[1] + dir[1]] << @grid[pos[0]][pos[1]].clear
							return @moves += 1
						end
					else
						@grid[pos[0] + dir[0]][pos[1] + dir[1]] << @grid[pos[0]][pos[1]].clear
						return @moves += 1
					end
				end
			end
			nil
		end
	end
	
	# command-line interface
	def self.cli(levels_file = 'sokoban_levels.txt')
		cli_help = <<-end

			Dave's Cheap Ruby Sokoban
			© Dave Burt 2004
			
			@ is you
			+ is you standing on storage
			# is a wall
			. is empty storage
			o is a crate
			* is a crate on storage
			
			Move all the crates onto storage.
			
			to move:     n/k
			              |
			         w/h -+- e/l
			              |
			             s/j
			to restart the level: r
			to quit: x or q or !
			to show this message: ?
			
			You can queue commands like this: nwwwnnnwnwwsw...

		end
		cli_help.gsub!(/\t+/,'  :  ')
		puts cli_help
		puts 'Press [enter] to begin.'
		gets

		File.read(levels_file).split("\n\n").each_with_index do |level_string, level_index|
			level = Level.new(level_string)
			while !level.solved? do
				puts level
				print 'L:' + (level_index+1).to_s + ' M:' + level.moves.to_s + ' > '
				gets.split(//).each do |c|
					case c
					when 'w', 'h'
						level.move(WEST)
					when 's', 'j'
						level.move(SOUTH)
					when 'n', 'k'
						level.move(NORTH)
					when 'e', 'l'
						level.move(EAST)
					when 'r'
						level = Level.new(level_string)
					when 'q', 'x', '!'
						puts 'Bye!'
						exit
					when 'd' # debug - ruby prompt
						print 'ruby> '
						begin
							puts eval(gets)
						rescue
							puts $!
						end
					when '?'
						puts cli_help
					when "\n", "\r", "\t", " "
						# ignore whitespace
					else
						puts "Invalid command: '#{c}'"
						puts cli_help
					end
				end
			end
			puts "\nCongratulations - you beat level #{level_index + 1}!\n\n"
		end
	end
end

if $0 == __FILE__
	Sokoban::cli
end