/**
 * HTTP handler for Prometheus metrics endpoint.
 * 
 * Exposes metrics at GET /metrics in Prometheus text format.
 */

import type { IncomingMessage, ServerResponse } from 'node:http';
import { getMetricsText, getMetricsContentType } from '../infra/metrics.js';

/**
 * Handle GET /metrics requests for Prometheus scraping.
 */
export async function handleMetricsRequest(
    _req: IncomingMessage,
    res: ServerResponse,
): Promise<void> {
    try {
        const metricsText = await getMetricsText();
        res.writeHead(200, {
            'Content-Type': getMetricsContentType(),
            'Cache-Control': 'no-cache, no-store, must-revalidate',
        });
        res.end(metricsText);
    } catch (error) {
        res.writeHead(500, { 'Content-Type': 'text/plain' });
        res.end('Error collecting metrics');
    }
}

/**
 * Handle GET /health liveness probe.
 * Always returns 200 if the server is responding.
 */
export function handleHealthRequest(
    _req: IncomingMessage,
    res: ServerResponse,
): void {
    res.writeHead(200, { 'Content-Type': 'application/json' });
    res.end(JSON.stringify({
        status: 'ok',
        timestamp: new Date().toISOString(),
    }));
}

/**
 * Readiness check function type.
 * Returns true if the service is ready to accept traffic.
 */
export type ReadinessCheck = () => Promise<boolean> | boolean;

/**
 * Create a readiness handler with custom checks.
 * 
 * @param checks - Array of check functions that must all pass
 */
export function createReadinessHandler(
    checks: ReadinessCheck[] = [],
): (req: IncomingMessage, res: ServerResponse) => Promise<void> {
    return async (_req: IncomingMessage, res: ServerResponse): Promise<void> => {
        try {
            const results = await Promise.all(checks.map((check) => check()));
            const isReady = results.every(Boolean);

            if (isReady) {
                res.writeHead(200, { 'Content-Type': 'application/json' });
                res.end(JSON.stringify({
                    status: 'ready',
                    timestamp: new Date().toISOString(),
                }));
            } else {
                res.writeHead(503, { 'Content-Type': 'application/json' });
                res.end(JSON.stringify({
                    status: 'not_ready',
                    timestamp: new Date().toISOString(),
                }));
            }
        } catch (error) {
            res.writeHead(503, { 'Content-Type': 'application/json' });
            res.end(JSON.stringify({
                status: 'error',
                timestamp: new Date().toISOString(),
            }));
        }
    };
}

/**
 * Simple readiness handler that always returns ready.
 * Use createReadinessHandler for custom checks.
 */
export async function handleReadyRequest(
    req: IncomingMessage,
    res: ServerResponse,
): Promise<void> {
    const handler = createReadinessHandler([]);
    return handler(req, res);
}