/**
 * SSE client helper with auto-reconnect and exponential backoff.
 *
 * Provides type-safe event handling for Docker Watcher's real-time
 * event streams (deploy logs and instance status changes).
 */

// ── Types ──────────────────────────────────────────────────────────

export type SSEEventType = 'deploy_log' | 'instance_status' | 'deploy_status';

export interface SSEEvent<T = unknown> {
	type: SSEEventType;
	payload: T;
}

export interface DeployLogPayload {
	deploy_id: string;
	message: string;
	level: 'info' | 'warn' | 'error';
}

export interface InstanceStatusPayload {
	instance_id: string;
	project_id: string;
	stage_id: string;
	status: string;
}

export interface DeployStatusPayload {
	deploy_id: string;
	project_id: string;
	stage_id: string;
	image_tag: string;
	status: string;
	error?: string;
}

type SSEPayload = DeployLogPayload | InstanceStatusPayload | DeployStatusPayload;

export interface SSEOptions {
	/** Called for each SSE event received. */
	onEvent: (event: SSEEvent<SSEPayload>) => void;
	/** Called when the connection is established. */
	onOpen?: () => void;
	/** Called when the connection is lost. Receives the retry attempt number. */
	onError?: (attempt: number) => void;
	/** Called when reconnection is given up (max retries exceeded). */
	onGiveUp?: () => void;
	/** Maximum number of reconnect attempts. 0 = infinite. Default: 0 */
	maxRetries?: number;
	/** Initial backoff delay in ms. Default: 1000 */
	initialDelay?: number;
	/** Maximum backoff delay in ms. Default: 30000 */
	maxDelay?: number;
}

// ── SSE Connection ─────────────────────────────────────────────────

export interface SSEConnection {
	/** Close the connection and stop reconnecting. */
	close: () => void;
}

/**
 * Creates an SSE connection to the given URL with auto-reconnect.
 *
 * Uses exponential backoff with jitter for reconnection.
 * Returns an object with a `close` method to cleanly shut down.
 */
export function connectSSE(url: string, options: SSEOptions): SSEConnection {
	const {
		onEvent,
		onOpen,
		onError,
		onGiveUp,
		maxRetries = 0,
		initialDelay = 1000,
		maxDelay = 30000
	} = options;

	let eventSource: EventSource | null = null;
	let retryCount = 0;
	let retryTimeout: ReturnType<typeof setTimeout> | null = null;
	let closed = false;

	function connect(): void {
		if (closed) return;

		eventSource = new EventSource(url);

		eventSource.onopen = () => {
			retryCount = 0;
			onOpen?.();
		};

		eventSource.onmessage = (messageEvent: MessageEvent) => {
			try {
				const parsed: SSEEvent<SSEPayload> = JSON.parse(messageEvent.data);
				onEvent(parsed);
			} catch {
				// Ignore malformed events.
			}
		};

		eventSource.onerror = () => {
			eventSource?.close();
			eventSource = null;

			if (closed) return;

			retryCount++;
			onError?.(retryCount);

			if (maxRetries > 0 && retryCount > maxRetries) {
				onGiveUp?.();
				return;
			}

			// Exponential backoff with jitter.
			const delay = Math.min(initialDelay * Math.pow(2, retryCount - 1), maxDelay);
			const jitter = delay * 0.2 * Math.random();
			const totalDelay = delay + jitter;

			retryTimeout = setTimeout(connect, totalDelay);
		};
	}

	connect();

	return {
		close() {
			closed = true;
			if (retryTimeout !== null) {
				clearTimeout(retryTimeout);
				retryTimeout = null;
			}
			eventSource?.close();
			eventSource = null;
		}
	};
}

// ── Convenience Factories ──────────────────────────────────────────

/**
 * Connect to deploy log SSE stream for a specific deploy.
 * Streams existing logs first, then real-time updates.
 */
export function connectDeployLogs(
	deployId: string,
	callbacks: {
		onLog: (log: DeployLogPayload) => void;
		onStatus?: (status: DeployStatusPayload) => void;
		onOpen?: () => void;
		onError?: (attempt: number) => void;
	}
): SSEConnection {
	return connectSSE(`/api/deploys/${deployId}/logs`, {
		onEvent(event) {
			if (event.type === 'deploy_log') {
				callbacks.onLog(event.payload as DeployLogPayload);
			} else if (event.type === 'deploy_status') {
				callbacks.onStatus?.(event.payload as DeployStatusPayload);
			}
		},
		onOpen: callbacks.onOpen,
		onError: callbacks.onError
	});
}

/**
 * Connect to the global events SSE stream.
 * Receives instance status changes and deploy status updates.
 */
export function connectGlobalEvents(callbacks: {
	onInstanceStatus?: (payload: InstanceStatusPayload) => void;
	onDeployStatus?: (payload: DeployStatusPayload) => void;
	onOpen?: () => void;
	onError?: (attempt: number) => void;
}): SSEConnection {
	return connectSSE('/api/events', {
		onEvent(event) {
			if (event.type === 'instance_status') {
				callbacks.onInstanceStatus?.(event.payload as InstanceStatusPayload);
			} else if (event.type === 'deploy_status') {
				callbacks.onDeployStatus?.(event.payload as DeployStatusPayload);
			}
		},
		onOpen: callbacks.onOpen,
		onError: callbacks.onError
	});
}