gmafactory.js

const { buf } = require("crc-32");
const { readFile, stat } = require("fs").promises;
const { createWriteStream } = require("fs");

const addon_data = JSON.stringify(require("./addon.json"));

class GMAFile {
	constructor(fname) {
		this.stream = createWriteStream(fname);
		this.current_length = 8; // crc32 + 0 (uint)
		this.length = this.current_length;

		this.write(Buffer.from("GMAD"));
		this.write(Buffer.from("\x03"));
		this.write(Buffer.alloc(8));
		this.write(Buffer.alloc(8));
		this.write(Buffer.alloc(1));
		this.write(Buffer.from("pluto.gg content"));
		this.write(Buffer.alloc(1));
		this.write(Buffer.from(addon_data));
		this.write(Buffer.alloc(1));
		this.write(Buffer.from("Meepen"));
		this.write(Buffer.alloc(1));
		this.write(Buffer.from("\x01\x00\x00\x00"));
		this.filenames = [];
	}

	write(data) {
		this.current_length += data.length;
		this.length += data.length;
		this.crc32 = buf(data, this.crc32);
		this.stream.write(data);
	}

	async addFile(fname) {
		this.filenames.push(fname);

		let size = (await stat(fname)).size;
		this.length += size;

		let num = Buffer.alloc(4);
		num.writeUInt32LE(this.filenames.length);
		this.write(num);

		let name = Buffer.from(fname.toLowerCase())
		this.write(name);

		let size_buffer = Buffer.alloc(13);
		size_buffer.writeUInt32LE(size, 1);
		size_buffer.writeInt32LE(buf(await readFile(fname)), 9);
		this.write(size_buffer);
	}

	async finalize() {
		this.write(Buffer.alloc(4));

		for (let fname of this.filenames) {
			let data = await readFile(fname);
			this.write(data);
		}

		let last_crc = Buffer.alloc(4);
		last_crc.writeInt32LE(this.crc32);
		this.write(last_crc);

		this.stream.end();
	}
}