/**
 * Represents a sandbox for executing code in a controlled environment.
 */
export default class Sandbox {
	#callbacks = new Map();
	#worker = null;
	constructor() {}

	/**
	 * Executes the provided code and invokes the callback function with the result.
	 * @param {string} code - The code to be executed.
	 * @param {function} cb - The callback function to be invoked with the result.
	 * @returns {string} - The unique identifier for the execution.
	 * @throws {Error} - If the callback is not a function or if the code is not a string.
	 */
	execute(code, cb) {
		if (typeof cb !== 'function')
			throw new Error('Callback must be a function');
		if (typeof code !== 'string') throw new Error('Code must be a string');
		if (code == '') throw new Error('Code cannot be empty');

		const uniqueId = Math.random().toString(36).substring(2, 9);
		if (!this.#worker) this.#startup(code, cb);
		this.#callbacks.set(uniqueId, cb);
		this.#worker.postMessage({ code, id: uniqueId });

		return uniqueId;
	}

	/**
	 * Handles incoming messages and invokes the corresponding callback.
	 * @param {Event} event - The message event.
	 */
	#onMessage(event) {
		for (let [id, cb] of this.#callbacks) {
			if (event.data.id === id) {
				cb(event.data);
				this.#callbacks.delete(id);
				break;
			}
		}
	}

	/**
	 * Stops the execution of a callback with the given ID.
	 * @param {string} id - The ID of the callback to stop.
	 */
	stop(id) {
		this.#callbacks.delete(id);
		if (this.#callbacks.size === 0) {
			this.#terminate();
		}
	}

	/**
	 * Starts the sandbox by initializing the worker and setting up the event listener for messages.
	 *
	 * @param {string} code - The code to be executed in the sandbox.
	 * @param {function} cb - The callback function to be called when a message is received from the worker.
	 */
	#startup(code, cb) {
		if (this.#worker) return; // Already started
		const workerCode = workerFunction
			.toString()
			.replace(/^[^{]*{\s*/, '')
			.replace(/\s*}[^}]*$/, '');
		const workerBlob = new Blob(workerCode, {
			type: 'text/javascript',
		});
		const workerUrl = URL.createObjectURL(workerBlob);
		this.#worker = new Worker(workerUrl);
		this.#worker.addEventListener('message', this.#onMessage.bind(this));
	}

	/**
	 * Terminates the worker and clears the callbacks.
	 */
	#terminate() {
		this.#worker.terminate();
		this.#callbacks.clear();
	}
}

/**
 * Gets inserted into the web worker for executing code.
 * 	Executes the code received from the event data in a sandboxed environment.
 * @function workerFunction
 */
function workerFunction() {
	self.onmessage = (event) => {
		// Get the code from the event data
		const { id, code } = event.data;

		// Define the sandbox API
		const sandbox = {
			console: {
				log: (...args) => {
					self.postMessage({ type: 'log', data: args, id });
				},
				error: (...args) => {
					self.postMessage({ type: 'error', data: args, id });
				},
				warn: (...args) => {
					self.postMessage({ type: 'warn', data: args, id });
				},
			},
			setTimeout: (callback, delay) => {
				const timeoutId = setTimeout(() => {
					callback();
					sandbox.timeouts.delete(timeoutId);
				}, delay);
				sandbox.timeouts.set(timeoutId, true);
				return timeoutId;
			},
			clearTimeout: (timeoutId) => {
				clearTimeout(timeoutId);
				sandbox.timeouts.delete(timeoutId);
			},
			setInterval: (callback, interval) => {
				const intervalId = setInterval(callback, interval);
				sandbox.intervals.set(intervalId, Date.now());
				return intervalId;
			},
			clearInterval: (intervalId) => {
				clearInterval(intervalId);
				sandbox.intervals.delete(intervalId);
			},
			timeouts: new Map(),
			intervals: new Map(),
			// overwrite self.postMessage to always send the public id with the message
			postMessage: (data) => {
				self.postMessage({ ...data, id });
			},
		};

		Object.freeze(sandbox);

		const sbCode = [
			'try {',
			'  ' + code,
			'} catch (error) {',
			'  self.postMessage({ type: "fatal", data: [error] });',
			'}',
		].join('\n');

		// Wrap the code in a function and execute it in the context of the sandbox
		const func = new Function('sandbox', `with (sandbox) { ${sbCode} }`);
		func(sandbox);
	};
}