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import { useState, useEffect, useCallback, useRef } from 'react';
import type { SLOResult } from '@/lib/observability';
import { clientLogger } from '@/lib/logging/clientLogger';
/**
* Metrics summary from the stream
*/
export interface MetricsSummary {
totalRequests: number;
successRate: number;
avgDuration: number;
errorCount: number;
}
/**
* Error log entry
*/
export interface ErrorLogEntry {
id: string;
category: string;
message: string;
createdAt: string;
}
/**
* Alert entry
*/
export interface Alert {
sloName: string;
status: string;
}
/**
* Connection status
*/
export type ConnectionStatus = 'connecting' | 'connected' | 'reconnecting' | 'disconnected' | 'polling';
/**
* SSE Message structure
*/
interface SSEMessage {
type: string;
data: unknown;
timestamp: number;
}
/**
* Real-time metrics state
*/
export interface RealtimeMetricsState {
slos: SLOResult[];
metrics: MetricsSummary | null;
recentErrors: ErrorLogEntry[];
alerts: Alert[];
lastUpdate: Date | null;
status: ConnectionStatus;
error: string | null;
}
/**
* Hook options
*/
export interface UseRealtimeMetricsOptions {
/** Enable incident mode (faster updates) */
incidentMode?: boolean;
/** Polling fallback interval in ms (default: 30000) */
pollingInterval?: number;
/** Auto-reconnect on disconnect */
autoReconnect?: boolean;
/** Max reconnection attempts */
maxReconnectAttempts?: number;
/** Callback when alerts are received */
onAlert?: (alerts: Alert[]) => void;
/** Callback when connection status changes */
onStatusChange?: (status: ConnectionStatus) => void;
}
/**
* Hook return type
*/
export interface UseRealtimeMetricsReturn extends RealtimeMetricsState {
/** Manually reconnect */
reconnect: () => void;
/** Disconnect from stream */
disconnect: () => void;
/** Check if using polling fallback */
isPolling: boolean;
}
/**
* Default state
*/
const defaultState: RealtimeMetricsState = {
slos: [],
metrics: null,
recentErrors: [],
alerts: [],
lastUpdate: null,
status: 'connecting',
error: null,
};
/**
* useRealtimeMetrics Hook
*
* Provides real-time metrics updates via Server-Sent Events (SSE)
* with automatic fallback to polling if SSE is not supported.
*/
export function useRealtimeMetrics(
options: UseRealtimeMetricsOptions = {}
): UseRealtimeMetricsReturn {
const {
incidentMode = false,
pollingInterval = 30000,
autoReconnect = true,
maxReconnectAttempts = 5,
onAlert,
onStatusChange,
} = options;
const [state, setState] = useState<RealtimeMetricsState>(defaultState);
const [isPolling, setIsPolling] = useState(false);
const eventSourceRef = useRef<EventSource | null>(null);
const pollingIntervalRef = useRef<NodeJS.Timeout | null>(null);
const reconnectAttemptsRef = useRef(0);
const reconnectTimeoutRef = useRef<NodeJS.Timeout | null>(null);
const isVisibleRef = useRef(true);
/**
* Update connection status
*/
const updateStatus = useCallback(
(status: ConnectionStatus) => {
setState((prev) => ({ ...prev, status }));
onStatusChange?.(status);
},
[onStatusChange]
);
/**
* Handle incoming SSE message
*/
const handleMessage = useCallback(
(event: MessageEvent) => {
try {
const message: SSEMessage = JSON.parse(event.data);
const { type, data, timestamp } = message;
setState((prev) => {
const updates: Partial<RealtimeMetricsState> = {
lastUpdate: new Date(timestamp),
error: null,
};
switch (type) {
case 'slo_update':
updates.slos = data as SLOResult[];
break;
case 'metrics_update':
updates.metrics = data as MetricsSummary;
break;
case 'error_update':
updates.recentErrors = data as ErrorLogEntry[];
break;
case 'alert':
updates.alerts = data as Alert[];
onAlert?.(data as Alert[]);
break;
case 'connected':
updates.status = 'connected';
reconnectAttemptsRef.current = 0;
break;
case 'heartbeat':
// Just update timestamp
break;
}
return { ...prev, ...updates };
});
} catch (error) {
clientLogger.error('Failed to parse realtime metrics message', error instanceof Error ? error : new Error(String(error)));
}
},
[onAlert]
);
/**
* Fallback polling fetch
*/
const fetchMetrics = useCallback(async () => {
try {
const response = await fetch('/api/admin/monitoring/stream?poll=true');
if (!response.ok) throw new Error('Failed to fetch metrics');
// For polling, we need to fetch data differently
// This is a simplified approach - in production you'd have a separate endpoint
const slosRes = await fetch('/api/admin/monitoring/slo-history?mode=trends');
if (slosRes.ok) {
const slosData = await slosRes.json();
setState((prev) => ({
...prev,
slos: slosData.slos || [],
lastUpdate: new Date(),
error: null,
}));
}
} catch (error) {
setState((prev) => ({
...prev,
error: error instanceof Error ? error.message : 'Failed to fetch metrics',
}));
}
}, []);
/**
* Start polling fallback
*/
const startPolling = useCallback(() => {
setIsPolling(true);
updateStatus('polling');
// Initial fetch
fetchMetrics();
// Set up interval
pollingIntervalRef.current = setInterval(fetchMetrics, pollingInterval);
}, [fetchMetrics, pollingInterval, updateStatus]);
/**
* Stop polling
*/
const stopPolling = useCallback(() => {
if (pollingIntervalRef.current) {
clearInterval(pollingIntervalRef.current);
pollingIntervalRef.current = null;
}
setIsPolling(false);
}, []);
/**
* Connect to SSE stream
*/
const connect = useCallback(() => {
// Don't connect if page is not visible
if (!isVisibleRef.current) return;
// Clean up existing connection
if (eventSourceRef.current) {
eventSourceRef.current.close();
}
// Check if SSE is supported
if (typeof EventSource === 'undefined') {
clientLogger.warn('SSE not supported, falling back to polling');
startPolling();
return;
}
updateStatus('connecting');
const url = `/api/admin/monitoring/stream${incidentMode ? '?incident=true' : ''}`;
const eventSource = new EventSource(url);
eventSourceRef.current = eventSource;
// Handle all event types
const eventTypes = ['slo_update', 'metrics_update', 'error_update', 'alert', 'heartbeat', 'connected'];
eventTypes.forEach((eventType) => {
eventSource.addEventListener(eventType, handleMessage);
});
eventSource.onerror = () => {
eventSource.close();
eventSourceRef.current = null;
if (autoReconnect && reconnectAttemptsRef.current < maxReconnectAttempts) {
reconnectAttemptsRef.current++;
updateStatus('reconnecting');
// Exponential backoff
const delay = Math.min(1000 * Math.pow(2, reconnectAttemptsRef.current), 30000);
reconnectTimeoutRef.current = setTimeout(connect, delay);
} else if (reconnectAttemptsRef.current >= maxReconnectAttempts) {
// Fall back to polling
clientLogger.warn('Max reconnect attempts reached, falling back to polling');
startPolling();
} else {
updateStatus('disconnected');
setState((prev) => ({ ...prev, error: 'Connection lost' }));
}
};
}, [autoReconnect, handleMessage, incidentMode, maxReconnectAttempts, startPolling, updateStatus]);
/**
* Disconnect from stream
*/
const disconnect = useCallback(() => {
if (eventSourceRef.current) {
eventSourceRef.current.close();
eventSourceRef.current = null;
}
if (reconnectTimeoutRef.current) {
clearTimeout(reconnectTimeoutRef.current);
reconnectTimeoutRef.current = null;
}
stopPolling();
updateStatus('disconnected');
}, [stopPolling, updateStatus]);
/**
* Manual reconnect
*/
const reconnect = useCallback(() => {
reconnectAttemptsRef.current = 0;
stopPolling();
connect();
}, [connect, stopPolling]);
/**
* Handle visibility change
*/
useEffect(() => {
const handleVisibilityChange = () => {
isVisibleRef.current = document.visibilityState === 'visible';
if (isVisibleRef.current) {
// Reconnect when page becomes visible
if (state.status === 'disconnected' || !eventSourceRef.current) {
reconnect();
}
} else {
// Disconnect when page is hidden to save resources
disconnect();
}
};
document.addEventListener('visibilitychange', handleVisibilityChange);
return () => document.removeEventListener('visibilitychange', handleVisibilityChange);
}, [disconnect, reconnect, state.status]);
/**
* Initial connection
*/
useEffect(() => {
connect();
return () => {
disconnect();
};
// eslint-disable-next-line react-hooks/exhaustive-deps
}, [incidentMode]);
return {
...state,
reconnect,
disconnect,
isPolling,
};
}
export default useRealtimeMetrics;
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