/*
 * Slide puzzle core game logic
 * Copyright © 2022 Nick Bowler
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

#ifndef RRACE_GAME_H_
#define RRACE_GAME_H_

#include <inttypes.h>

enum {
	TILE_EMPTY,
	TILE_RED,
	TILE_ORANGE,
	TILE_YELLOW,
	TILE_GREEN,
	TILE_BLUE,
	TILE_WHITE,
	TILE_MAX
};

enum { GOAL_SHIFT = 6 };
struct board {
	/*
	 * Bit planes representing the current game area.
	 *
	 * The 5x5 game board is represented by these four 25-bit values.
	 * The bits are arranged in row-major order so, for example, bit 0
	 * corresponds to position (0,0), bit 4 is position (4,0) and bit 25
	 * is position (4, 4).
	 *
	 *   game[0] - least significant bit of the tile's colour.
	 *   game[1] - tile colour.
	 *   game[2] - most significant bit of the tile's colour.
	 *   game[3] - the board mask, all bits set except one indicating the
	 *             absense of a tile at this position.
	 */
	uint_least32_t game[4];

	/*
	 * Bit planes representing the goal area.
	 *
	 * These are encoded identically to the game area, except the values
	 * are shifted right by 6 as only bits 6 through 18 are relevant.
	 *
	 *   goal[0] - least significant bit of the tile's colour.
	 *   goal[2] - tile colour.
	 *   goal[3] - most significant bit of the tile's colour.
	 */
	uint_least16_t goal[3];

	/* (x, y) position of the current empty position. */
	uint_least8_t x, y;
};

/* Return the board bitmap with all bits in column x set */
static inline uint_fast32_t board_column(int x)
{
	return 0x108421ul << x;
}

/* Return the board bitmap with all bits in row y set */
static inline uint_fast32_t board_row(int y)
{
	return 0x1ful << 5*y;
}

/* Return the board bitmap with the bit at position (x, y) set. */
static inline uint_fast32_t board_position(int x, int y)
{
	return 1ul << x << 5*y;
}

/*
 * Return the board bitmap with set bits indicating tile locations
 * that change with the hole at (x0, y) and the play at (x1, y).
 */
static inline uint_fast32_t board_mask_h(int y, int x0, int x1)
{
	uint_fast32_t row = board_row(y);

	if (x0 < x1)
		return (row << x0) & (row >> (4-x1));
	return (row << x1) & (row >> (4-x0));
}

/*
 * Return the board bitmap with set bits indicating tile locations
 * that change with the hole at (x, y0) and the play at (x, y1).
 */
static inline uint_fast32_t board_mask_v(int x, int y0, int y1)
{
	uint_fast32_t col = board_column(x);

	if (y0 < y1)
		return (col << 5*y0) & (col >> 5*(4-y1));
	return (col << 5*y1) & (col >> 5*(4-y0));
}

/*
 * Move the bits in the game bitmaps according to a move at position (x, y),
 * and update the location of the empty position which, if the move was valid
 * is now (x, y).
 *
 * Returns 0 if the move was valid (and board has been updated), -1 otherwise.
 */
int game_do_move(struct board *board, int x, int y);

/*
 * Returns 1 if the game is in a winning position, or 0 otherwise.
 */
int game_check_goal(struct board *board);

/*
 * Initialize the game RNG such that the next call to game_reset will produce a
 * new board that is entirely dependent on the given seed value.
 */
void game_reseed(unsigned long long seed);

/*
 * Shuffle the game and goal tiles to produce a new game state.
 */
void game_reset(struct board *board);

/*
 * Disable new moves and clear all tile bits other than the 9 goal tiles.
 */
void game_finish(struct board *board);

#endif