#pragma once

#include <iostream>
#include <optional>
#include <string_view>
#include <type_traits>
#include <cstdint>

using namespace std;

const int N = 9;
const int BOARDMID = N * (N/2) + N/2;

const uint8_t EMPTY = 0, WHITE = 1, KING = 2, BLACK = 4;


struct Move {
	int from, to;

	Move() = default;
	Move(int from, int to);

	static optional<Move> parse(string_view str);
};

struct Board {
	uint8_t cells[N * N];

	static Board makeInitial();

	void apply(Move mv);
	int applyCW(Move mv);
	int checkWin() const;  // 1=win white, -1=win black, 0=none yet

	bool isValid(Move mv, int player) const;

	// Calls the callback for each valid move of the specified player.
	// F should have a signature compatible with bool F(Move mv).
	// If the callback returns true, iteration is stopped.
	// Callback should not modify this Board instance.
	template <typename F,
	          typename = enable_if_t<is_invocable_r<bool, F, Move>::value>>
	void forEachMove(int player, F callback) const {
		static const int deltas[4][2] = {{-1, 0}, {0, -1}, {1, 0}, {0, 1}};

		for (int y = 0; y < N; y++)
		for (int x = 0; x < N; x++) {
			uint8_t v = cells[N * y + x];
			if (player == 1 ? v != WHITE && v != KING : v != BLACK) continue;

			for (int i = 0; i < 4; i++) {
				int x2 = x + deltas[i][0], y2 = y + deltas[i][1];
				while (x2 >= 0 && x2 < N && y2 >= 0 && y2 < N) {
					if (cells[N * y2 + x2] != EMPTY) break;
					if (N * y2 + x2 != BOARDMID) {
						bool ret = callback(Move(N * y + x, N * y2 + x2));
						if (ret) goto stop_iteration;
					}

					x2 += deltas[i][0];
					y2 += deltas[i][1];
				}
			}
		}

	stop_iteration: ;
	}

private:
	Board();

	bool isValid(Move mv) const;
	bool stoneFlankedH(int pos, uint8_t by) const;
	bool stoneFlankedV(int pos, uint8_t by) const;
	bool kingEncircled(int pos) const;
};

ostream& operator<<(ostream &os, const Move &mv);
ostream& operator<<(ostream &os, const Board &bd);