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class Sudoku

  def initialize(string)
    string_of_array = string.split("")
    @board = Array.new(9) {string_of_array.shift(9)}
  end


  def solve!
    first_empty = find_empty_cell
    possible = possibilities(first_empty)
    puts "This is: #{first_empty[0]}, #{first_empty[1]}, #{possible}"
    reassign(first_empty[0], first_empty[1], possible)
  end

  def find_empty_cell(x_coordinate = 0, y_coordinate = 0) 
    x_coordinate.upto(8) do |x|
      y_coordinate.upto(8) do |y|

        if @board[x][y] == '0'
          x_coordinate = x
          y_coordinate = y
          return [x_coordinate, y_coordinate]
        end

      end
    end

  end

  def possibilities(first_empty)
    x_coordinate = first_empty[0]
    y_coordinate = first_empty[1]
    possibilities = ['1','2','3','4','5','6','7','8','9']

    row = evaluate_row(x_coordinate, y_coordinate, possibilities)
    col = evaluate_column(x_coordinate, y_coordinate, possibilities)
    grid = evaluate_grid(x_coordinate, y_coordinate, possibilities)

    possibilities = row + col + grid
    possibilities.select { |number| possibilities.count(number) > 2 }.uniq
  end

  def evaluate_row(x_coordinate, y_coordinate, possibilities) 
    possibilities = possibilities - @board[x_coordinate]
  end

  def evaluate_column(x_coordinate, y_coordinate, possibilities) 
    column = []
    @board.each do |num|
      column << @board[@board.index(num)][y_coordinate]
    end
    possibilities = possibilities - column  
  end


  def evaluate_grid(x_coordinate, y_coordinate, possibilities)

    grid_array = 
      [ [[0,0], [0,1], [0,2], [1,0], [1,1], [1,2], [2,0], [2,1], [2,2]], 
        [[0,3], [0,4], [0,5], [1,3], [1,4], [1,5], [2,3], [2,4], [2,5]], 
        [[0,6], [0,7], [0,8], [1,6], [1,7], [1,8], [2,6], [2,7], [2,8]],
        [[3,0], [3,1], [3,2], [4,0], [4,1], [4,2], [5,0], [5,1], [5,2]], 
        [[3,3], [3,4], [3,5], [4,3], [4,4], [4,5], [5,3], [5,4], [5,5]], 
        [[3,6], [3,7], [3,8], [4,6], [4,7], [4,8], [5,6], [5,7], [5,8]],
        [[6,0], [6,1], [6,2], [7,0], [7,1], [7,2], [8,0], [8,1], [8,2]], 
        [[6,3], [6,4], [6,5], [7,3], [7,4], [7,5], [8,3], [8,4], [8,5]], 
        [[6,6], [6,7], [6,8], [7,6], [7,7], [7,8], [8,6], [8,7], [8,8]]
      ]
    
    grid = []
  
    grid_array.each do |x|
      if x.include?([x_coordinate, y_coordinate])
          grid = x
      end
    end

    grid_poss = []

    grid.each do |x,y|
      grid_poss << @board[x][y]
    end

    possibilities = possibilities - grid_poss
  end

  def reassign(x_coordinate, y_coordinate, possibilities)
    if possibilities.length == 1
      p "This is from evaluate_grid, solved @  x = #{x_coordinate}, y = #{y_coordinate}: #{possibilities}"
      self.next_cell(x_coordinate, y_coordinate, possibilities[0])
    else
      if y_coordinate == 8
        y_coordinate = 0
        x_coordinate = x_coordinate + 1
         self.find_empty_cell(x_coordinate, y_coordinate)
      else
        self.find_empty_cell(x_coordinate, y_coordinate+1)
      end
    end  
  end

  def next_cell(x_coordinate, y_coordinate, answer)
     p "This is the original board:"
     p self
    
     @board[x_coordinate][y_coordinate] = answer
     
     puts "This is from reassign, new value: #{@board[x_coordinate][y_coordinate]}"
     p "This is the new board:"
     p self
     self.find_empty_cell(y_coordinate)
  end

  def to_s
    @board.map{|r| r.join(" ")}.join "\n"
  end

end

 
# board_string = File.readlines('sample.unsolved.txt').first.chomp
 
game = Sudoku.new('003021600900305001001806400008102900700000008006708200002609500800203009005010300')
 
puts game

puts game.solve!