buffer.todo

input =  Sudoku::Reader.read_sudoku(raw)

def fill_rows(sudoku)
  updated = true
  while updated do
    updated = false
    result = sudoku
    sudoku.each_with_index do |row, i|
      row.each_with_index do |cell, j|
        next unless cell == '_'

        possibilities = '123456789'.split('')
        possibilities = possibilities - get_square_neighbors(sudoku, i, j) - get_column_neighbors(sudoku, i, j)
        if possibilities.length == 1
          p result[i][j]
          result[i][j] = possibilities[0]
            p result[i][j]
          updated = true
          p result
        end
      end
    end
  end
  result
end

def get_column_neighbors(sudoku, x, y)
  result = []
  sudoku.each_with_index do |row, i|
    next if i == x

    result << sudoku[i][y]
  end
  result.reject { |c| c == '_' }
end

def get_square_neighbors(sudoku, x, y)
  result = []
  sudoku.each_with_index do |row, i|
    row.each_with_index do |cell, j|
      next if [i, j] == [x, y]
      result << cell if get_square_id(i, j) == get_square_id(x, y)
    end
  end
  result.reject { |c| c == '_' }
end

def get_square_id(x, y)
  [x / 3, y / 3]
end

# p fill_rows(input)