import { NextResponse } from 'next/server';
import client from 'prom-client';

// Force Node.js runtime for this route
export const runtime = 'nodejs';
export const dynamic = 'force-dynamic';

// Singleton pattern to avoid duplicate metric registration
const globalForProm = globalThis as unknown as {
  promRegistry: client.Registry | undefined;
  metricsInitialized: boolean | undefined;
};

function getRegistry(): client.Registry {
  if (!globalForProm.promRegistry) {
    globalForProm.promRegistry = new client.Registry();
  }
  return globalForProm.promRegistry;
}

function initializeMetrics(register: client.Registry) {
  if (globalForProm.metricsInitialized) {
    return;
  }

  // Add default metrics (CPU, memory, etc.)
  client.collectDefaultMetrics({ register });

  // Custom metrics
  new client.Counter({
    name: 'http_requests_total',
    help: 'Total number of HTTP requests',
    labelNames: ['method', 'path', 'status'],
    registers: [register],
  });

  new client.Histogram({
    name: 'http_request_duration_seconds',
    help: 'Duration of HTTP requests in seconds',
    labelNames: ['method', 'path'],
    buckets: [0.1, 0.3, 0.5, 0.7, 1, 3, 5, 7, 10],
    registers: [register],
  });

  globalForProm.metricsInitialized = true;
}

export async function GET() {
  try {
    const register = getRegistry();
    initializeMetrics(register);

    const metrics = await register.metrics();
    return new NextResponse(metrics, {
      status: 200,
      headers: {
        'Content-Type': register.contentType,
      },
    });
  } catch (error) {
    console.error('Metrics error:', error);
    return NextResponse.json({ error: 'Failed to get metrics' }, { status: 500 });
  }
}