/* SPDX-License-Identifier: GPL-3.0-or-later */
/* Copyright (C) 2021 KikooDX */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "level.h"

static const int kble_fmt_version = 0;

static int read_byte(FILE *file);
static int read_byte_group(FILE *file, int number);

void level_read(struct Level *level, char *path) {
	FILE *file = NULL;
	int byte = 0;
	int width = 0;
	int height = 0;
	int tile_size = 0;
	int level_size = 0;
	int tile = 0;
	int i = 0;

	/* open file in read mode */
	file = fopen(path, "rb");
	if (file == NULL) {
		fprintf(stderr, "ERROR: Cannot open input file %s\n", path);
		exit(EXIT_FAILURE);
	}

	/* check KBLE format version */
	byte = read_byte(file);
	if (byte != kble_fmt_version) {
		fprintf(stderr, "ERROR: KBLE format version doesn't match ; "
			"expected %d, got %d\n", kble_fmt_version, byte);
		exit(EXIT_FAILURE);
	}

	/* get tile size (in bytes) */
	tile_size = read_byte(file);
	/* get width */
	width = read_byte_group(file, 2);
	/* get height */
	height = read_byte_group(file, 2);

	/* allocate memory for data */
	level_size = width * height;
	if (level->data == NULL) {
		level->data = malloc(level_size * sizeof(int));
	} else {
		level->data = realloc(level->data, level_size * sizeof(int));
	}
	/* check for allocation failure */
	if (level->data == NULL) {
		fprintf(stderr, "ERROR: memory allocation failure\n");
		exit(EXIT_FAILURE);
	}

	/* read file content */
	for (i = 0; i < level_size; i += 1) {
		tile = read_byte_group(file, tile_size);
		level->data[i] = tile;
	}

	/* close file */
	fclose(file);
}

void level_free(struct Level *level) {
	free(level->data);
}

/* Read a single byte safely (handles EOF). */
static int read_byte(FILE *file) {
	const int byte = getc(file);
	if (byte == EOF) {
		fprintf(stderr, "ERROR: unexpected EOF\n");
		exit(EXIT_FAILURE);
	}
	return byte;
}

/* Read multiple bytes and "merge" them into one integer. */
static int read_byte_group(FILE *file, int number) {
	int byte = 0;
	int merged = 0;
	int i = 0;
	int shift = number * 8;
	for (i = 0; i < number; i += 1) {
		shift -= 8;
		byte = read_byte(file);
		merged |= byte << shift;
	}
	return merged;
}