/*
 * Simple routing to extract a single file from a xz archive
 * Heavily based from doc/examples/02_decompress.c obtained from
 * the official xz git repository: git.tukaani.org/xz.git
 * The license from the original file header follows
 *
 * Author:     Lasse Collin
 * This file has been put into the public domain.
 * You can do whatever you want with this file.
 */


#include <lzma.h>
#include <QDebug>

#include "decompress.h"

XzDecompressor::XzDecompressor(QObject *parent)
    : QObject(parent)
{

}

bool XzDecompressor::decompress(QBuffer *in, QBuffer *out)
{
	lzma_stream strm = LZMA_STREAM_INIT;
	bool success;

	if (!init_decoder(&strm)) {
		return false;
	}

	success = internal_decompress(&strm, in, out);

	// Free the memory allocated for the decoder. This only needs to be
	// done after the last file.
	lzma_end(&strm);

	return success;
}

bool XzDecompressor::init_decoder(lzma_stream *strm)
{
	// Initialize a .xz decoder. The decoder supports a memory usage limit
	// and a set of flags.
	//
	// The memory usage of the decompressor depends on the settings used
	// to compress a .xz file. It can vary from less than a megabyte to
	// a few gigabytes, but in practice (at least for now) it rarely
	// exceeds 65 MiB because that's how much memory is required to
	// decompress files created with "xz -9". Settings requiring more
	// memory take extra effort to use and don't (at least for now)
	// provide significantly better compression in most cases.
	//
	// Memory usage limit is useful if it is important that the
	// decompressor won't consume gigabytes of memory. The need
	// for limiting depends on the application. In this example,
	// no memory usage limiting is used. This is done by setting
	// the limit to UINT64_MAX.
	//
	// The .xz format allows concatenating compressed files as is:
	//
	//     echo foo | xz > foobar.xz
	//     echo bar | xz >> foobar.xz
	//
	// When decompressing normal standalone .xz files, LZMA_CONCATENATED
	// should always be used to support decompression of concatenated
	// .xz files. If LZMA_CONCATENATED isn't used, the decoder will stop
	// after the first .xz stream. This can be useful when .xz data has
	// been embedded inside another file format.
	//
	// Flags other than LZMA_CONCATENATED are supported too, and can
	// be combined with bitwise-or. See lzma/container.h
	// (src/liblzma/api/lzma/container.h in the source package or e.g.
	// /usr/include/lzma/container.h depending on the install prefix)
	// for details.
	lzma_ret ret = lzma_stream_decoder(
			strm, UINT64_MAX, LZMA_CONCATENATED);

	// Return successfully if the initialization went fine.
	if (ret == LZMA_OK)
		return true;

	// Something went wrong. The possible errors are documented in
	// lzma/container.h (src/liblzma/api/lzma/container.h in the source
	// package or e.g. /usr/include/lzma/container.h depending on the
	// install prefix).
	//
	// Note that LZMA_MEMLIMIT_ERROR is never possible here. If you
	// specify a very tiny limit, the error will be delayed until
	// the first headers have been parsed by a call to lzma_code().
	const char *msg;
	switch (ret) {
	case LZMA_MEM_ERROR:
		msg = "Memory allocation failed";
		break;

	case LZMA_OPTIONS_ERROR:
		msg = "Unsupported decompressor flags";
		break;

	default:
		// This is most likely LZMA_PROG_ERROR indicating a bug in
		// this program or in liblzma. It is inconvenient to have a
		// separate error message for errors that should be impossible
		// to occur, but knowing the error code is important for
		// debugging. That's why it is good to print the error code
		// at least when there is no good error message to show.
		msg = "Unknown error, possibly a bug";
		break;
	}

	qDebug() << "Error initializing the decoder:" << msg << "(error code " << ret << ")";
	return false;
}


bool XzDecompressor::internal_decompress(lzma_stream *strm, QBuffer *in, QBuffer *out)
{
	// When LZMA_CONCATENATED flag was used when initializing the decoder,
	// we need to tell lzma_code() when there will be no more input.
	// This is done by setting action to LZMA_FINISH instead of LZMA_RUN
	// in the same way as it is done when encoding.
	//
	// When LZMA_CONCATENATED isn't used, there is no need to use
	// LZMA_FINISH to tell when all the input has been read, but it
	// is still OK to use it if you want. When LZMA_CONCATENATED isn't
	// used, the decoder will stop after the first .xz stream. In that
	// case some unused data may be left in strm->next_in.
	lzma_action action = LZMA_RUN;

	uint8_t inbuf[BUFSIZ];
	uint8_t outbuf[BUFSIZ];
	qint64 bytesAvailable;

	strm->next_in = NULL;
	strm->avail_in = 0;
	strm->next_out = outbuf;
	strm->avail_out = sizeof(outbuf);
	while (true) {
		if (strm->avail_in == 0) {
			strm->next_in = inbuf;
			bytesAvailable = in->bytesAvailable();
			if(bytesAvailable == 0) {
				// Once the end of the input file has been reached,
				// we need to tell lzma_code() that no more input
				// will be coming. As said before, this isn't required
				// if the LZMA_CONCATENATED flag isn't used when
				// initializing the decoder.
				action = LZMA_FINISH;
			} else if(bytesAvailable >= BUFSIZ) {
				in->read((char*) inbuf, BUFSIZ);
				strm->avail_in = BUFSIZ;
			} else {
				in->read((char*) inbuf, bytesAvailable);
				strm->avail_in = bytesAvailable;
			}
		}

		lzma_ret ret = lzma_code(strm, action);

		if (strm->avail_out == 0 || ret == LZMA_STREAM_END) {
			qint64 write_size = sizeof(outbuf) - strm->avail_out;

			if (out->write((char *) outbuf, write_size) != write_size) {
				qDebug() << "Write error";
				return false;
			}

			strm->next_out = outbuf;
			strm->avail_out = sizeof(outbuf);
		}

		if (ret != LZMA_OK) {
			// Once everything has been decoded successfully, the
			// return value of lzma_code() will be LZMA_STREAM_END.
			//
			// It is important to check for LZMA_STREAM_END. Do not
			// assume that getting ret != LZMA_OK would mean that
			// everything has gone well or that when you aren't
			// getting more output it must have successfully
			// decoded everything.
			if (ret == LZMA_STREAM_END)
				return true;

			// It's not LZMA_OK nor LZMA_STREAM_END,
			// so it must be an error code. See lzma/base.h
			// (src/liblzma/api/lzma/base.h in the source package
			// or e.g. /usr/include/lzma/base.h depending on the
			// install prefix) for the list and documentation of
			// possible values. Many values listen in lzma_ret
			// enumeration aren't possible in this example, but
			// can be made possible by enabling memory usage limit
			// or adding flags to the decoder initialization.
			const char *msg;
			switch (ret) {
			case LZMA_MEM_ERROR:
				msg = "Memory allocation failed";
				break;

			case LZMA_FORMAT_ERROR:
				// .xz magic bytes weren't found.
				msg = "The input is not in the .xz format";
				break;

			case LZMA_OPTIONS_ERROR:
				// For example, the headers specify a filter
				// that isn't supported by this liblzma
				// version (or it hasn't been enabled when
				// building liblzma, but no-one sane does
				// that unless building liblzma for an
				// embedded system). Upgrading to a newer
				// liblzma might help.
				//
				// Note that it is unlikely that the file has
				// accidentally became corrupt if you get this
				// error. The integrity of the .xz headers is
				// always verified with a CRC32, so
				// unintentionally corrupt files can be
				// distinguished from unsupported files.
				msg = "Unsupported compression options";
				break;

			case LZMA_DATA_ERROR:
				msg = "Compressed file is corrupt";
				break;

			case LZMA_BUF_ERROR:
				// Typically this error means that a valid
				// file has got truncated, but it might also
				// be a damaged part in the file that makes
				// the decoder think the file is truncated.
				// If you prefer, you can use the same error
				// message for this as for LZMA_DATA_ERROR.
				msg = "Compressed file is truncated or "
						"otherwise corrupt";
				break;

			default:
				// This is most likely LZMA_PROG_ERROR.
				msg = "Unknown error, possibly a bug";
				break;
			}

			qDebug() << "Decoder error:" << msg << "(error code " << ret << ")";
			return false;
		}
	}
}