import random

from cell import Cell


class Board:

    def __init__(self):

        self.grid = [[0 for _ in range(9)] for _ in range(9)]
        self.cells = []

    def generate(self):

        self._fill_board()

        self.create_cells()

    def create_cells(self):

        self.cells = []

        for row in range(9):

            for col in range(9):

                self.cells.append(
                    Cell(
                        row=row,
                        col=col,
                        value=self.grid[row][col]
                    )
                )

    def _find_empty(self):

        for row in range(9):

            for col in range(9):

                if self.grid[row][col] == 0:
                    return row, col

        return None

    def _valid(self, row, col, num):

        if num in self.grid[row]:
            return False

        for r in range(9):
            if self.grid[r][col] == num:
                return False

        box_row = (row // 3) * 3
        box_col = (col // 3) * 3

        for r in range(box_row, box_row + 3):
            for c in range(box_col, box_col + 3):

                if self.grid[r][c] == num:
                    return False

        return True

    def _fill_board(self):

        empty = self._find_empty()

        if empty is None:
            return True

        row, col = empty

        nums = list(range(1, 10))
        random.shuffle(nums)

        for num in nums:

            if self._valid(row, col, num):

                self.grid[row][col] = num

                if self._fill_board():
                    return True

                self.grid[row][col] = 0

        return False