#include <stdbool.h>
#include <string.h> // memset()
#include "sok.h"

#define UNUSED(a) ((void) (a))

#define VALID_POS(pos) ( \
  (pos).x < SOK_LEVEL_MAX_WIDTH && \
  (pos).y < SOK_LEVEL_MAX_HEIGHT \
)

#define POINTS_EQUAL(a, b) ( \
  ((a).x == (b).x) && \
  ((a).y == (b).y) \
)

static bool
ctx_is_wall(
  const sok_ctx_t * const ctx,
  const sok_pos_t pos
) {
  return ctx->level.walls[pos.y * ctx->level.size.x + pos.x];
}

static void
ctx_set_wall(
  sok_ctx_t * const ctx,
  const sok_pos_t pos
) {
  ctx->level.walls[pos.y * ctx->level.size.x + pos.x] = true;
}

static void
ctx_clear_walls(
  sok_ctx_t * const ctx
) {
  memset(ctx->level.walls, 0, SOK_LEVEL_MAX_WIDTH * SOK_LEVEL_MAX_HEIGHT);
}

static bool
on_size(
  const sok_level_parser_t * const parser,
  const sok_pos_t pos
) {
  sok_ctx_t *ctx = (sok_ctx_t*) parser->user_data;

  if (!VALID_POS(pos)) {
    // size out of bounds
    return false;
  }

  // save width and height
  ctx->level.size = pos;

  // return success
  return true;
}

static bool
on_home(
  const sok_level_parser_t * const parser,
  const sok_pos_t pos
) {
  sok_ctx_t *ctx = (sok_ctx_t*) parser->user_data;

  if (!VALID_POS(pos)) {
    // position out of bounds
    return false;
  }

  // save start position
  ctx->level.home = pos;

  // return success
  return true;
}

static bool
on_wall(
  const sok_level_parser_t * const parser,
  const sok_pos_t pos
) {
  sok_ctx_t *ctx = (sok_ctx_t*) parser->user_data;

  if (!VALID_POS(pos)) {
    // position out of bounds
    return false;
  }

  // save wall
  ctx_set_wall(ctx, pos);

  // return sucess
  return true;
}

static bool
on_goal(
  const sok_level_parser_t * const parser,
  const sok_pos_t pos
) {
  sok_ctx_t *ctx = (sok_ctx_t*) parser->user_data;

  if (!VALID_POS(pos)) {
    // position out of bounds
    return false;
  }

  if (ctx->level.num_goals >= SOK_LEVEL_MAX_GOALS - 1) {
    // too many goals
    return false;
  }

  // save goal
  ctx->level.goals[ctx->level.num_goals++] = pos;

  // return sucess
  return true;
}

static bool
on_box(
  const sok_level_parser_t * const parser,
  const sok_pos_t pos
) {
  sok_ctx_t *ctx = (sok_ctx_t*) parser->user_data;

  if (!VALID_POS(pos)) {
    // position out of bounds
    return false;
  }

  if (ctx->level.num_boxes >= SOK_LEVEL_MAX_BOXES - 1) {
    // too many boxes
    return false;
  }

  // save box
  ctx->level.boxes[ctx->level.num_boxes++] = pos;

  // return sucess
  return true;
}

static bool
on_junk(
  const sok_level_parser_t * const parser,
  const size_t ofs,
  const char tile
) {
  UNUSED(parser);
  UNUSED(ofs);
  UNUSED(tile);

  // TODO

  // return sucess
  return true;
}

static const sok_level_parser_cbs_t
LEVEL_PARSER_CBS = {
  .on_size = on_size,
  .on_home = on_home,
  .on_wall = on_wall,
  .on_goal = on_goal,
  .on_box  = on_box,
  .on_junk = on_junk,
};

static size_t
pos_find(
  const sok_pos_t pos,
  const sok_pos_t * const set,
  const size_t len
) {
  for (size_t i = 0; i < len; i++) {
    if (POINTS_EQUAL(pos, set[i])) {
      return i;
    }
  }

  return len;
}

static size_t
sok_ctx_count_goals_left(
  sok_ctx_t * const ctx
) {
  const size_t num_boxes = ctx->level.num_boxes;
  size_t r = 0;

  for (size_t i = 0; i < ctx->level.num_goals; i++) {
    r += pos_find(
      ctx->level.goals[i],
      ctx->boxes,
      num_boxes
    ) < num_boxes ? 0 : 1;
  }

  return r;
}

/*
 * static bool
 * sok_ctx_has_corner_boxes(
 *   const sok_ctx_t * const ctx
 * ) {
 *   for (size_t i = 0; i < ctx->level.num_boxes; i++) {
 *     // right
 *     const bool r = ctx_is_wall(ctx, (sok_pos_t) {
 *       .x = ctx->boxes[i].x + 1,
 *       .y = ctx->boxes[i].y,
 *     });
 *
 *     // top-right
 *     const bool tr = ctx_is_wall(ctx, (sok_pos_t) {
 *       .x = ctx->boxes[i].x + 1,
 *       .y = ctx->boxes[i].y - 1,
 *     });
 *
 *     // top
 *     const bool t = ctx_is_wall(ctx, (sok_pos_t) {
 *       .x = ctx->boxes[i].x,
 *       .y = ctx->boxes[i].y - 1,
 *     });
 *
 *     // top-left
 *     const bool tl = ctx_is_wall(ctx, (sok_pos_t) {
 *       .x = ctx->boxes[i].x - 1,
 *       .y = ctx->boxes[i].y - 1,
 *     });
 *
 *     // left
 *     const bool l = ctx_is_wall(ctx, (sok_pos_t) {
 *       .x = ctx->boxes[i].x - 1,
 *       .y = ctx->boxes[i].y,
 *     });
 *
 *     // bottom-left
 *     const bool bl = ctx_is_wall(ctx, (sok_pos_t) {
 *       .x = ctx->boxes[i].x - 1,
 *       .y = ctx->boxes[i].y + 1,
 *     });
 *
 *     // bottom
 *     const bool b = ctx_is_wall(ctx, (sok_pos_t) {
 *       .x = ctx->boxes[i].x,
 *       .y = ctx->boxes[i].y + 1,
 *     });
 *
 *     const bool br = ctx_is_wall(ctx, (sok_pos_t) {
 *       .x = ctx->boxes[i].x + 1,
 *       .y = ctx->boxes[i].y + 1,
 *     });
 *
 *     if (
 *       (r && tr && t) || // top-right
 *       (t && tl && l) || // top-left
 *       (l && bl && b) || // bottom-left
 *       (b && br && r)    // bottom-right
 *     ) {
 *       // return
 *       return true;
 *     }
 *   }
 *
 *   return false;
 * }
 */

void
sok_ctx_init(sok_ctx_t * const ctx, void *user_data) {
  memset(ctx, 0, sizeof(sok_ctx_t));
  ctx->user_data = user_data;
}

bool
sok_ctx_set_level(
  sok_ctx_t * const ctx,
  const char * const str
) {

  // clear level
  ctx->level.num_goals = 0;
  ctx->level.num_boxes = 0;
  ctx_clear_walls(ctx);

  // parse level
  sok_level_parser_t parser;
  sok_level_parser_init(&parser, &LEVEL_PARSER_CBS, ctx);
  if (!sok_level_parser_parse(&parser, str, strlen(str))) {
    // return failure
    return false;
  }

  // init moves, player, and boxes
  ctx->num_moves = 0;
  ctx->home = ctx->level.home;
  memcpy(ctx->boxes, ctx->level.boxes, ctx->level.num_boxes * sizeof(sok_pos_t));

  // count number of goals left and check whether there are
  ctx->num_goals_left = sok_ctx_count_goals_left(ctx);
  // ctx->is_lost = sok_ctx_is_lost(ctx);

  // return success
  return true;
}

static bool
tile_is_floor(
  const sok_ctx_t * const ctx,
  const sok_pos_t pos
) {
  return (
    (pos.x < SOK_LEVEL_MAX_WIDTH - 1) &&
    (pos.y < SOK_LEVEL_MAX_HEIGHT - 1) &&
    !ctx_is_wall(ctx, pos)
  );
}

static bool
tile_is_box(
  const sok_ctx_t * const ctx,
  const sok_pos_t pos
) {
  const size_t num_boxes = ctx->level.num_boxes;
  return pos_find(pos, ctx->boxes, num_boxes) < num_boxes;
}

static bool
tile_is_goal(
  const sok_ctx_t * const ctx,
  const sok_pos_t pos
) {
  const size_t num_goals = ctx->level.num_goals;
  return pos_find(pos, ctx->level.goals, num_goals) < num_goals;
}

static bool
sok_ctx_push_move(
  sok_ctx_t * const ctx,
  const sok_dir_t dir,
  const bool is_push
) {
  if (ctx->num_moves >= SOK_CTX_MAX_MOVES - 1) {
    return false;
  }

  ctx->moves[ctx->num_moves].pos = ctx->home;
  ctx->moves[ctx->num_moves].dir = dir;
  ctx->moves[ctx->num_moves].is_push = is_push;
  ctx->num_moves++;

  return true;
}

static bool
sok_ctx_pop_move(
  sok_ctx_t * const ctx,
  sok_move_t * const ret
) {
  if (!ctx->num_moves) {
    // return failure
    return false;
  }

  // decriment moves
  ctx->num_moves--;

  if (ret) {
    // save popped move
    *ret = ctx->moves[ctx->num_moves];
  }

  // return success
  return true;
}

static bool
sok_ctx_move_box(
  sok_ctx_t * const ctx,
  const sok_pos_t old_pos,
  const sok_pos_t new_pos
) {
  const size_t num_boxes = ctx->level.num_boxes,
               box_ofs = pos_find(old_pos, ctx->boxes, num_boxes);

  if (box_ofs < num_boxes) {
    // update box and goal count
    ctx->boxes[box_ofs] = new_pos;
    ctx->num_goals_left = sok_ctx_count_goals_left(ctx);
    // ctx->is_lost = sok_ctx_has_corner_boxes(ctx);

    // return success
    return true;
  }

  // return failure
  return false;
}

bool
sok_ctx_is_done(
  const sok_ctx_t * const ctx
) {
  return ctx->num_goals_left == 0;
}

/*
 * bool
 * sok_ctx_is_lost(
 *   const sok_ctx_t * const ctx
 * ) {
 *   return ctx->is_lost;
 * }
 */

bool
sok_ctx_move(
  sok_ctx_t * const ctx,
  const sok_dir_t dir
) {
  if (ctx->num_moves >= SOK_CTX_MAX_MOVES - 1) {
    // no more move slots available
    return false;
  }

  const sok_pos_t ps[2] = {{
    .x = ctx->home.x + ((dir == SOK_DIR_LEFT) ? -1 : ((dir == SOK_DIR_RIGHT) ? 1 : 0)),
    .y = ctx->home.y + ((dir == SOK_DIR_UP) ? -1 : ((dir == SOK_DIR_DOWN) ? 1 : 0))
  }, {
    .x = ctx->home.x + ((dir == SOK_DIR_LEFT) ? -2 : ((dir == SOK_DIR_RIGHT) ? 2 : 0)),
    .y = ctx->home.y + ((dir == SOK_DIR_UP) ? -2 : ((dir == SOK_DIR_DOWN) ? 2 : 0))
  }};

  const bool can_move = (
    (dir == SOK_DIR_UP) ? (ctx->home.y > 0) :
    ((dir == SOK_DIR_DOWN) ? (ctx->home.y < SOK_LEVEL_MAX_HEIGHT - 1) :
    ((dir == SOK_DIR_LEFT) ? (ctx->home.x > 0) :
    ((dir == SOK_DIR_RIGHT) ? (ctx->home.x < SOK_LEVEL_MAX_WIDTH - 1) :
    false
  ))));

  const bool can_push = (
    (dir == SOK_DIR_UP) ? (ctx->home.y > 1) :
    ((dir == SOK_DIR_DOWN) ? (ctx->home.y < SOK_LEVEL_MAX_HEIGHT - 2) :
    ((dir == SOK_DIR_LEFT) ? (ctx->home.x > 1) :
    ((dir == SOK_DIR_RIGHT) ? (ctx->home.x < SOK_LEVEL_MAX_WIDTH - 2) :
    false
  ))));

  if (
    can_move &&
    tile_is_floor(ctx, ps[0]) &&
    !tile_is_box(ctx, ps[0])
  ) {
    // push move
    if (!sok_ctx_push_move(ctx, dir, false)) {
      return false;
    }

    // update position
    ctx->home.x += (dir == SOK_DIR_LEFT) ? -1 : ((dir == SOK_DIR_RIGHT) ? 1 : 0);
    ctx->home.y += (dir == SOK_DIR_UP) ? -1 : ((dir == SOK_DIR_DOWN) ? 1 : 0);

    // return success
    return true;
  } else if (
    can_push &&
    tile_is_floor(ctx, ps[0]) &&
    tile_is_box(ctx, ps[0]) &&
    tile_is_floor(ctx, ps[1]) &&
    !tile_is_box(ctx, ps[1])
  ) {
    // push move
    if (!sok_ctx_push_move(ctx, dir, true)) {
      return false;
    }

    // move box
    if (!sok_ctx_move_box(ctx, ps[0], ps[1])) {
      return false;
    }

    // update position
    ctx->home.x += (dir == SOK_DIR_LEFT) ? -1 : ((dir == SOK_DIR_RIGHT) ? 1 : 0);
    ctx->home.y += (dir == SOK_DIR_UP) ? -1 : ((dir == SOK_DIR_DOWN) ? 1 : 0);


    // return success
    return true;
  }

  // return failure
  return false;
}

bool
sok_ctx_undo(
  sok_ctx_t * const ctx
) {
  sok_move_t move;
  if (!sok_ctx_pop_move(ctx, &move)) {
    // return failure
    return false;
  }

  if (move.is_push) {
    const sok_pos_t box_pos = {
      .x = move.pos.x + ((move.dir == SOK_DIR_LEFT) ? -2 : ((move.dir == SOK_DIR_RIGHT) ? 2 : 0)),
      .y = move.pos.y + ((move.dir == SOK_DIR_UP) ? -2 : ((move.dir == SOK_DIR_DOWN) ? 2 : 0)),
    };

    sok_ctx_move_box(ctx, box_pos, ctx->home);
  }

  // update position
  ctx->home = move.pos;

  // return success
  return true;
}

bool sok_ctx_walk(
  const sok_ctx_t * const ctx,
  const sok_ctx_walk_cbs_t * const cbs,
  void * const data
) {
  if (!cbs) {
    return false;
  }

  if (cbs->on_size) {
    // emit size
    if (!cbs->on_size(ctx, ctx->level.size, data)) {
      return false;
    }
  }

  if (cbs->on_home) {
    const bool has_goal = tile_is_goal(ctx, ctx->home);

    // emit home
    if (!cbs->on_home(ctx, ctx->home, has_goal, data)) {
      return false;
    }
  }

  if (cbs->on_walls_start && !cbs->on_walls_start(ctx, data)) {
    return false;
  }

  if (cbs->on_wall) {
    // walk walls
    for (size_t i = 0; i < (ctx->level.size.x * ctx->level.size.y); i++) {
      const sok_pos_t pos = {
        .y = i / ctx->level.size.x,
        .x = i % ctx->level.size.x,
      };

      if (ctx_is_wall(ctx, pos)) {
        // emit wall
        if (!cbs->on_wall(ctx, pos, data)) {
          return false;
        }
      }
    }
  }

  if (cbs->on_walls_end && !cbs->on_walls_end(ctx, data)) {
    return false;
  }

  if (cbs->on_goals_start && !cbs->on_goals_start(ctx, data)) {
    return false;
  }

  if (cbs->on_goal) {
    // walk goals
    for (size_t i = 0; i < ctx->level.num_goals; i++) {
      const bool has_player = POINTS_EQUAL(ctx->level.goals[i], ctx->home);
      const bool has_box = tile_is_box(ctx, ctx->level.goals[i]);

      // emit goal
      if (!cbs->on_goal(ctx, ctx->level.goals[i], has_player, has_box, data)) {
        return false;
      }
    }
  }

  if (cbs->on_goals_end && !cbs->on_goals_end(ctx, data)) {
    return false;
  }

  if (cbs->on_boxes_start && !cbs->on_boxes_start(ctx, data)) {
    return false;
  }

  if (cbs->on_box) {
    // walk boxes
    for (size_t i = 0; i < ctx->level.num_boxes; i++) {
      const bool has_goal = tile_is_goal(ctx, ctx->boxes[i]);

      // emit box
      if (!cbs->on_box(ctx, ctx->boxes[i], has_goal, data)) {
        return false;
      }
    }
  }

  if (cbs->on_boxes_end && !cbs->on_boxes_end(ctx, data)) {
    return false;
  }

  if (cbs->on_moves_start && !cbs->on_moves_start(ctx, data)) {
    return false;
  }

  if (cbs->on_move) {
    // walk moves
    for (size_t i = 0; i < ctx->num_moves; i++) {
      // emit move
      if (!cbs->on_move(ctx, ctx->moves[i], data)) {
        return false;
      }
    }
  }

  if (cbs->on_moves_end && !cbs->on_moves_end(ctx, data)) {
    return false;
  }

  // return success
  return true;
}