# Copyright 2022 Mattia Giambirtone & All Contributors
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import game
import util/matrix


type
    Move = ref object
        ## A specific state in a
        ## tic-tac-toe match, with
        ## all of its children states
        state: Matrix[int]
        # Since tic-tac-toe is a rather
        # simple game, we can generate all
        # possible (legal) board configurations
        # and then look up the current board when
        # playing against the user in order to find
        # the best move to win the match
        next: array[9, Move]
        parent: Move
        depth: int


proc generateMoves*(map: Matrix[int], turn: TileKind, depth: int = 0): Move =
    ## Generates the full tree of all
    ## possible tic tac toe moves starting
    ## from a given board state
    new(result)
    result.state = map.copy()
    result.depth = depth
    if result.state.asGame().get() != Playing:
        # The game is over, no need to generate
        # any more moves!
        return
    for row in 0..<map.shape.rows:
        for col in 0..<map.shape.cols:
            if TileKind(result.state[row, col]) == Empty:
                let index = row * map.shape.cols + col
                new(result.next[index])
                result.next[index].parent = result
                var copy = result.state.copy()
                copy[row, col] = turn.int()
                result.next[index] = generateMoves(copy, if turn == Self: Enemy else: Self, depth + 1)


proc exists*(map: Matrix[int], tree: Move): int =
    ## Returns the depth of a given move in
    ## the solution tree. A return value of -1
    ## indicates the move is illegal
    if all(map == tree.state):
        echo map.asGame()
        return tree.depth
    else:
        var i = 0
        var idx: tuple[row, col: int]
        while i < 9:
            idx = ind2sub(i, map.shape)
            if tree.next[i].isNil() or tree.next[i].state[idx.row, idx.col] != map[idx.row, idx.col]:
                inc(i)
                continue
            elif map.exists(tree.next[i]) != -1:
                return tree.next[i].depth
            inc(i)
        return -1


proc print(self: Move) =
    ## Traverses the move tree recursively
    ## (meant for debugging)
    if self.isNil():
        return
    var board = self.state.asGame()
    echo board
    echo board.get(), "\n"
    for i in 0..<9:
        print(self.next[i])


when isMainModule:
    var g = build(@[0, 0, 0, 0, 0, 0, 0, 0, 0])
    let m = generateMoves(g.map, Self)
    g = build(@[1, 1, 2, 2, 2, 1, 1, 2, 1])
    echo g.map.exists(m)
    g = build(@[1, 1, 2, 2, 2, 1, 1, 2, 2])
    echo g.map.exists(m)