/* 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 size);
static void write_byte(FILE *file, unsigned char byte);
static void write_byte_group(FILE *file, int value, int size);

void level_read(struct Level *level, char *path) {
	FILE *file = NULL;
	int byte = 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 */
	level->width = read_byte_group(file, 2);
	/* get height */
	level->height = read_byte_group(file, 2);

	/* allocate memory for data */
	level_size = level->width * level->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);
}

void level_write(struct Level level, char *path) {
	FILE *file = NULL;
	int tile = 0;
	int tile_size = 0;
	int max_tile_size = 1;
	int i = 0;
	const int level_size = level.width * level.height;

	/* open file in write mode */
	file = fopen(path, "wb");
	if (file == NULL) {
		fprintf(stderr, "ERROR: cannot open output file %s\n", path);
		exit(EXIT_FAILURE);
	}

	/* find longest value in data (in bytes) */
	for (i = 0; i < level_size; i += 1) {
		tile = level.data[i];
		tile_size = 1;
		while (tile >>= 8)
			tile_size += 1;
		if (tile_size > max_tile_size)
			max_tile_size = tile_size;
	}

	/* write KBLE format version */
	write_byte(file, kble_fmt_version);
	/* write tile size (in bytes) */
	write_byte(file, max_tile_size);
	/* write width */
	write_byte_group(file, level.width, 2);
	/* write height */
	write_byte_group(file, level.height, 2);

	/* write level content */
	for (i = 0; i < level_size; i += 1) {
		write_byte_group(file, level.data[i], max_tile_size);
	}

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

/* Read a single byte safely (handle EOF). */
static int read_byte(FILE *file) {
	const int byte = fgetc(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 size) {
	int byte = 0;
	int merged = 0;
	int i = 0;
	int shift = size * 8;
	for (i = 0; i < size; i += 1) {
		shift -= 8;
		byte = read_byte(file);
		merged |= byte << shift;
	}
	return merged;
}

/* Write a single byte safely (handle EOF). */
static void write_byte(FILE *file, unsigned char byte) {
	const int result = fputc(byte, file);
	if (result == EOF) {
		fprintf(stderr, "ERROR: file write error\n");
		exit(EXIT_FAILURE);
	}
}

/* Write an integer as multiple bytes. */
static void write_byte_group(FILE *file, int value, int size) {
	int byte = 0;
	int shift = size * 8;
	int i = 0;
	const int mask = (1 << 8) - 1;
	for (i = 0; i < size; i += 1) {
		shift -= 8;
		byte = value >> shift;
		byte &= mask;
		write_byte(file, byte);
	}
}