/**
 * Simple Gzip compression/decompression.
 *
 * 2007  Vladimir Panteleev <thecybershadow@gmail.com>
 */

module Gzip;

static import zlib = std.zlib;
static import stdcrc32 = crc32;
debug import std.stdio, std.file;

private enum
{
	FTEXT = 1,
	FHCRC = 2,
	FEXTRA = 4,
	FNAME = 8,
	FCOMMENT = 16
}

uint crc32(void[] data)
{
	uint crc = stdcrc32.init_crc32();
	foreach(v;cast(ubyte[])data)
		crc = stdcrc32.update_crc32(v, crc);
	return ~crc;
}

void[] compress(void[] data)
{
	ubyte[] header;
	header.length = 10;
	header[0] = 0x1F;
	header[1] = 0x8B;
	header[2] = 0x08;
	header[3..8] = 0;  // TODO: set MTIME
	header[8] = 4;
	header[9] = 3;     // TODO: set OS
	uint[2] footer = [crc32(data), data.length];
	ubyte[] compressed = cast(ubyte[])zlib.compress(data, 9);
	return header ~ compressed[2..$-4] ~ cast(ubyte[])footer;
}

void[] uncompress(void[] data)
{
	assert(data.length>=10);
	ubyte[] header = cast(ubyte[])data[0..10];
	assert(header[0] == 0x1F);
	assert(header[1] == 0x8B);
	assert(header[2] == 0x08);
	assert(header[3] == 0);  // TODO: support (skipping of) extra fields
	void[] uncompressed = zlib.uncompress(data[header.length..$-8], 0, -15);
	assert(uncompressed.length == *cast(uint*)(&data[$-4]));
	return uncompressed;
}