'use strict';

import {parentPort} from 'node:worker_threads';
import {decompress as lzmaDecompress} from 'lzma1';
import {ZstdCodec} from 'zstd-codec';

let zstdStreamingPromise = null;

function getZstd() {
	if (!zstdStreamingPromise) {
		zstdStreamingPromise = new Promise(resolve => ZstdCodec.run(zstd => resolve(new zstd.Streaming())));
	}
	return zstdStreamingPromise;
}

/** Rebuilds a full 13-byte "alone" LZMA header from libzim's truncated 5-byte one (unknown size). */
function toLzmaAloneStream(body) {
	const header = Buffer.concat([body.subarray(0, 5), Buffer.alloc(8, 0xff)]);
	return Buffer.concat([header, body.subarray(5)]);
}

parentPort.on('message', async ({id, compType, body}) => {
	try {
		const buf = Buffer.from(body);
		const data = compType === 4
			? Buffer.from(lzmaDecompress(toLzmaAloneStream(buf)))
			: Buffer.from((await getZstd()).decompress(new Uint8Array(buf)));
		parentPort.postMessage({id, data}, [data.buffer]);
	} catch (e) {
		parentPort.postMessage({id, error: e.message});
	}
});