// Standard C
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// System
#include <unistd.h>

// zlib
#include <zlib.h>

static void
usage(void)
{
	(void) fprintf(stderr, "compress [-d] infile outfile\n");
}

static void
error(const char *msg)
{
	perror(msg);
	exit(EXIT_FAILURE);
}

size_t
get_filesize(FILE *file)
{
	long current_pos = ftell(file);
	if ( current_pos == -1 ) {
		error("ftell() failed");
	}

	if ( fseek(file, 0, SEEK_END) != 0 ) {
		error("fseek() failed");
	}

	long size = ftell(file);
	if ( size == -1 ) {
		error("ftell() failed");
	}

	if ( fseek(file, current_pos, SEEK_SET) != 0 ) {
		error("fseek() failed");
	}

	return (size_t) size;
}

void
do_compress(FILE *in_file, FILE *out_file, int compress_level)
{
	size_t in_size = get_filesize(in_file);

	(void) fwrite(&in_size, sizeof in_size, 1, out_file);

	unsigned char *in_data = malloc(in_size);
	(void) fread(in_data, 1, in_size, in_file);

	size_t         out_size = compressBound(in_size);
	unsigned char *out_data = malloc(out_size);

	const int error = compress2(out_data, &out_size,
	                            in_data, in_size,
	                            compress_level);

	if ( !error ) {
		(void) fwrite(out_data, 1, out_size, out_file);
	}
	else {
		(void) fprintf(stderr, "Error: %s\n", zError(error));
	}

	free(out_data);
	free(in_data);
}

void
do_uncompress(FILE *in_file, FILE *out_file)
{
	size_t in_size = get_filesize(in_file);

	unsigned char *in_data = malloc(in_size);
	(void) fread(in_data, 1, in_size, in_file);

	size_t out_size = 0;
	memcpy(&out_size, in_data, sizeof out_size);

	unsigned char *out_data = malloc(out_size);

	const size_t compressed_data_size = in_size - sizeof(size_t);
	size_t       consumed_size        = compressed_data_size;

	const int error = uncompress2(out_data, &out_size,
	                              in_data + sizeof(size_t),
	                              &consumed_size);

	if ( !error ) {
		if ( compressed_data_size != consumed_size ) {
			(void) fputs("Warning: Trailing data detected.\n", stderr);
		}

		(void) fwrite(out_data, 1, out_size, out_file);
	}
	else {
		(void) fprintf(stderr, "Error: %s\n", zError(error));
	}

	free(out_data);
	free(in_data);
}

int
main(int argc, char *argv[])
{
	enum {
		COMPRESSION_STD  = 5,
		COMPRESSION_BEST = 9
	};

	int decompress     = 0;
	int compress_level = COMPRESSION_STD;

	int opt = 0;
	while ( (opt = getopt(argc, argv, "dl")) != -1 ) {
		switch ( opt ) {
		case 'd':
			decompress = 1;
			break;

		case 'l':
			compress_level = COMPRESSION_BEST;
			break;

		case '?':
		default:
			usage();
			return EXIT_SUCCESS;
		}
	}
	argc -= optind;
	argv += optind;

	if ( argc != 2 ) {
		usage();
	}

	FILE *in_file  = fopen(argv[0], "rb");
	FILE *out_file = fopen(argv[1], "wb");

	if ( !decompress ) {
		do_compress(in_file, out_file, compress_level);
	}
	else {
		do_uncompress(in_file, out_file);
	}

	(void) fclose(out_file);
	(void) fclose(in_file);

	return EXIT_SUCCESS;
}