import { getToken } from './auth';

type EventHandler = (data: string) => void;

let eventSource: EventSource | null = null;
let lastEventTime: string | null = null;
const handlers: Map<string, EventHandler[]> = new Map();

export function onSseEvent(eventType: string, handler: EventHandler): () => void {
	if (!handlers.has(eventType)) {
		handlers.set(eventType, []);
	}
	handlers.get(eventType)!.push(handler);

	// Return unsubscribe function
	return () => {
		const list = handlers.get(eventType);
		if (list) {
			const idx = list.indexOf(handler);
			if (idx >= 0) list.splice(idx, 1);
		}
	};
}

export function connectSse(): void {
	const token = getToken();
	if (!token || eventSource) return;

	// EventSource doesn't support custom headers, so pass token as query param
	// The backend will need to accept this — or we use a polyfill / fetch-based SSE
	// For simplicity, use native EventSource with token in URL
	eventSource = new EventSource(`/api/v1/stream?token=${encodeURIComponent(token)}`);

	eventSource.onopen = () => {
		lastEventTime = new Date().toISOString();
	};

	eventSource.addEventListener('new-upload', (e) => dispatch('new-upload', e.data));
	eventSource.addEventListener('upload-processed', (e) => dispatch('upload-processed', e.data));
	eventSource.addEventListener('like-update', (e) => dispatch('like-update', e.data));
	eventSource.addEventListener('new-comment', (e) => dispatch('new-comment', e.data));
	eventSource.addEventListener('export-available', (e) => dispatch('export-available', e.data));

	eventSource.onerror = () => {
		// EventSource auto-reconnects, but we track the time for delta-fetch
		disconnectSse();
		// Reconnect after a short delay
		setTimeout(connectSse, 3000);
	};
}

export function disconnectSse(): void {
	if (eventSource) {
		eventSource.close();
		eventSource = null;
	}
}

export function getLastEventTime(): string | null {
	return lastEventTime;
}

export function setLastEventTime(time: string): void {
	lastEventTime = time;
}

function dispatch(eventType: string, data: string): void {
	lastEventTime = new Date().toISOString();
	const list = handlers.get(eventType);
	if (list) {
		for (const handler of list) {
			handler(data);
		}
	}
}

// Page Visibility API integration
if (typeof document !== 'undefined') {
	document.addEventListener('visibilitychange', () => {
		if (document.hidden) {
			disconnectSse();
		} else {
			connectSse();
		}
	});
}