module Sudoku

  class BoardException < Exception
  end

  class Board

    alias Value = Nil | Int32

    @grid : Array(Array(Value))
    getter grid

    def initialize(@size : Int32, @block_size : Int32)
      raise BoardException.new() unless @size.divisible_by?(@block_size)
      @grid = Array(Array(Value)).new(@size) { Array(Value).new(@size, nil) }
    end

    def put(value : Value, x, y)
      @grid[y][x] = value
    end

    def get(x, y)
      @grid[y][x]
    end

    def check_valid(value : Value, x, y)

    end

    def extract_row(y)
      @grid[y]
    end

    def extract_column(x)
      (0..@size - 1).map { |i| get(x, i) }
    end

    def extract_block(x, y)
      block_start_x = x - (x % @block_size)
      block_start_y = y - (y % @block_size)

      (block_start_y..block_start_y + @block_size - 1).map { |j|
        (block_start_x..block_start_x + @block_size - 1).map { |i|
          get(i, j)
        }
      }
    end
      
  end

end