/**
 * Extract a gzipped tarball (e.g. a GitHub repository archive) fully in
 * memory. Bounded so a hostile or oversized archive can't exhaust the Worker.
 */

import { createGzipDecoder, unpackTar } from "modern-tar";

const MAX_DECOMPRESSED_BYTES = 50 * 1024 * 1024;
const MAX_TAR_FILES = 5000;
const MAX_FILE_BYTES = 5 * 1024 * 1024;
const LEADING_DOT_SLASH = /^\.\//;

async function collectStream(
	stream: ReadableStream<Uint8Array>,
	limit: number,
): Promise<Uint8Array> {
	const reader = stream.getReader();
	const chunks: Uint8Array[] = [];
	let total = 0;
	try {
		for (;;) {
			const { done, value } = await reader.read();
			if (done) break;
			total += value.length;
			if (total > limit) throw new Error(`Archive exceeds ${limit} bytes decompressed`);
			chunks.push(value);
		}
	} finally {
		reader.releaseLock();
	}
	const out = new Uint8Array(total);
	let offset = 0;
	for (const c of chunks) {
		out.set(c, offset);
		offset += c.length;
	}
	return out;
}

/**
 * Files in the archive, keyed by path with the archive's single top-level
 * directory removed (GitHub archives are `owner-repo-sha/…`). Only regular
 * files whose path matches `keep` (when given) are returned.
 */
export async function extractTarball(
	data: ArrayBuffer,
	keep?: (path: string) => boolean,
): Promise<Map<string, Uint8Array>> {
	// Decompress fully first: piping straight into the tar decoder deadlocks in
	// workerd (the decoder's pull waits on a pipe stalled on its own drain).
	const decompressed = await collectStream(
		new Response(data).body!.pipeThrough(createGzipDecoder()),
		MAX_DECOMPRESSED_BYTES,
	);
	let count = 0;
	const entries = await unpackTar(decompressed, {
		strip: 0,
		filter: (header) => {
			if (header.type !== "file") return false;
			if (header.size > MAX_FILE_BYTES) return false;
			const name = header.name.replace(LEADING_DOT_SLASH, "");
			const rel = name.includes("/") ? name.slice(name.indexOf("/") + 1) : name;
			if (keep && !keep(rel)) return false;
			if (++count > MAX_TAR_FILES) throw new Error(`Archive has more than ${MAX_TAR_FILES} files`);
			return true;
		},
	});
	const files = new Map<string, Uint8Array>();
	for (const e of entries) {
		if (!e.data || !e.header.name) continue;
		const name = e.header.name.replace(LEADING_DOT_SLASH, "");
		files.set(name.includes("/") ? name.slice(name.indexOf("/") + 1) : name, e.data);
	}
	return files;
}