export interface SSEEvent {
	type: string;
	data: unknown;
}

export interface SSEClientOptions {
	path: string;
	onEvent: (event: SSEEvent) => void;
	onReconnect?: () => void;
}

// Wrapper над EventSource с экспоненциальным backoff и догоном через REST.
export class SSEClient {
	private es: EventSource | null = null;
	private stopped = false;
	private attempt = 0;
	private readonly knownEvents = [
		'photo.created',
		'photo.updated',
		'photo.deleted',
		'comment.created',
		'like.added',
		'like.removed',
		'member.joined',
		'member.left',
		'member.updated',
		'album.updated',
		'album.deleted',
		'notification'
	];

	constructor(private opts: SSEClientOptions) {}

	connect(token: string) {
		this.stopped = false;
		this.open(token);
	}

	private open(token: string) {
		if (this.stopped) return;
		const url = `${this.opts.path}?token=${encodeURIComponent(token)}`;
		this.es = new EventSource(url);

		this.es.onopen = () => {
			if (this.attempt > 0) {
				this.opts.onReconnect?.();
			}
			this.attempt = 0;
		};

		for (const name of this.knownEvents) {
			this.es.addEventListener(name, (ev) => {
				let data: unknown = null;
				try {
					data = JSON.parse((ev as MessageEvent).data);
				} catch {
					data = (ev as MessageEvent).data;
				}
				this.opts.onEvent({ type: name, data });
			});
		}

		this.es.onerror = () => {
			this.es?.close();
			this.es = null;
			if (this.stopped) return;
			const delay = Math.min(1000 * 2 ** this.attempt, 30000);
			this.attempt += 1;
			setTimeout(() => this.open(token), delay);
		};
	}

	close() {
		this.stopped = true;
		this.es?.close();
		this.es = null;
	}
}