#!/usr/bin/env ruby

# Class to play the game of Tic-Tac-Toe
class TicTacToe

	# Initialize an instance of this class
	def initialize
		initialize_game
	end

	# Play tic-tac-toe as long as user wants
	def play
		while true
			play_game
			break unless play_again?
		end
		puts "Thanks for playing...come back soon :-)"
	end

  # *********************************************
  # ************  PRIVATE METHODS  **************
  # *********************************************
	private

	# Reset instance variable to begin a new game
	def initialize_game
		@moves = 0
		@player = PIECE[:x]
		@board = []
		9.times { @board << PIECE[:blank] }
	end

	# play a game of tic-tac-toe
	def play_game
		initialize_game
		puts HOW_TO_PLAY_TEXT

		while true
			display_board
			set_move get_valid_move
			@moves += 1
			break if game_over?
			switch_player
		end
	end

	# Display current state of the game board
	def display_board
		print "\t"
		@board.each_with_index do |piece, index|
			display_piece_by_location(piece, index)
		end
	end

	# Display a game piece and separators between game pieces
	# based on the location of the piece on the game board
	def display_piece_by_location(piece, location)
		if location == 2 || location == 5
			print_piece(piece, "\n\t")
			print_separator_line
		elsif location == 8
			print_piece(piece, "\n")
		else
			print_piece(piece, SEPARATOR[:vertical])
		end
	end

	# Display a single game piece and separator(s) around it
	def print_piece(piece, separator)
		print " #{ piece } #{ separator }"
	end

	# Display the line that separates two game board rows
	def print_separator_line
		line = ""
		3.times do
			3.times { line << SEPARATOR[:horizontal] }
			line << SEPARATOR[:cross]
		end
		puts line[0...line.length - 1]
		print "\t"
	end

	# Set location specified by move to the current player's piece
	def set_move move
		@board[move] = @player
	end

	# Get a move that is valid
	def get_valid_move
		while true
			move = get_move
			if valid_move?(move)
				return move
			else
				puts "Position #{ move + 1 } is occupied...Enter a free position"
			end
		end
	end

	# Get a position to place a new piece
	def get_move
		while true
			question = "Player #{ @player }, Enter play position (1 - 9)"
		  move = (get_response_for question).to_i
		  if move.between?(1, 9)
		  	return move - 1
		  else
		  	puts "Invalid input...Enter a number between 1 and 9"
		  end
	  end
	end

	# Get the response to a question from the player
	def get_response_for question
		print question + ": "
		gets.chomp
	end

	# Check if a move is valid
	def valid_move? move
		@board[move] == PIECE[:blank]
	end

	# Determine if game is over.
	# Display appropriate message if the game is over.
	def game_over?
		win_formations = [ [0, 1, 2], [3, 4, 5], [6, 7, 8], [0, 4, 8],
		                   [2, 4, 6], [0, 3, 6], [1, 4, 7], [2, 5, 7] ]
		win_formations.each do |win_formation|
			if formation_met?(win_formation)
				end_game_message "Player #{ @player } Won."
				return true
			end
		end
		draw?
	end

  # Determine if a player has pieces in a certain formation
	def formation_met? formation
		pieces = [@board[formation[0]], @board[formation[1]], @board[formation[2]]]
		pieces.uniq.length == 1 && (pieces[0] != PIECE[:blank])
	end

	# Display relevant message when the game is over
	def end_game_message(message)
		system "clear"
		puts "GAME OVER: #{ message }"
		display_board
	end

	# Determine if game ended in a draw; display message if so
	def draw?
		if @moves >= 9
			end_game_message "Game Ended in a draw."
			true
		else
			false
		end
	end

	# Switch the current player
	def switch_player
		if @player == PIECE[:x]
			@player = PIECE[:o]
		else
			@player = PIECE[:x]
		end
	end

	# Determine if user what to play another tic-tac-toe game
	def play_again?
		while true
			play_again = (get_response_for "Play again (y/n)").downcase
			case play_again
			when 'y', 'yes' then return true
			when 'n', 'no' then return false
			end
		end
	end


	PIECE = { x: 'X', o: 'O', blank: ' ' }
	SEPARATOR = { vertical: "\u2503", horizontal: "\u2501", cross: "\u254b" }
  HOW_TO_PLAY_TEXT = <<-END.gsub(/^\s+\|/, '')
   |
   | 1 | 2 | 3   The positions to play on the tic-tac-toe board are
   |---+---+---  represented by the numbers 1 - 9 as shown in the
   | 4 | 5 | 6   figure at the left.
   |---+---+---  To place an 'X' or 'O' in a certain position, simply
   | 7 | 8 | 9   enter the number corresponding to that position.
   |
   |
  END
end

if $PROGRAM_NAME == __FILE__
	tic_tac_toe = TicTacToe.new
	tic_tac_toe.play
end