import { NextResponse } from "next/server";
import { Registry, Gauge } from "prom-client";
import { query } from "@/lib/db";

export const runtime = "nodejs";

/**
 * Prometheus-compatible metrics endpoint.
 *
 * Usage in prometheus.yml:
 *   - job_name: 'admin-metrics'
 *     scrape_interval: 60s
 *     static_configs:
 *       - targets: ['admin:3000']
 *     metrics_path: '/api/metrics/prometheus'
 */
export async function GET() {
  const register = new Registry();

  const gauge = new Gauge({
    name: "platform_entity_count",
    help: "Platform entity counts by time window",
    labelNames: ["entity", "window"] as const,
    registers: [register],
  });

  const entities = [
    { name: "users", table: '"user"' },
    { name: "workspaces", table: "workspace" },
    { name: "projects", table: "project" },
    { name: "repos", table: "repo" },
    { name: "rooms", table: "room" },
    { name: "skills", table: "project_skill" },
  ];

  const results = await Promise.all(
    entities.map(async ({ name, table }) => {
      const res = await query<{
        total: string;
        new_27h: string;
        new_7d: string;
        new_30d: string;
      }>(
        `SELECT
          COUNT(*) AS total,
          COUNT(*) FILTER (WHERE created_at >= NOW() - INTERVAL '27 hours') AS new_27h,
          COUNT(*) FILTER (WHERE created_at >= NOW() - INTERVAL '7 days') AS new_7d,
          COUNT(*) FILTER (WHERE created_at >= NOW() - INTERVAL '30 days') AS new_30d
         FROM ${table}`
      );
      const row = res.rows[0];
      return {
        name,
        total: parseInt(row.total, 10),
        new_27h: parseInt(row.new_27h, 10),
        new_7d: parseInt(row.new_7d, 10),
        new_30d: parseInt(row.new_30d, 10),
      };
    })
  );

  for (const r of results) {
    gauge.set({ entity: r.name, window: "total" }, r.total);
    gauge.set({ entity: r.name, window: "27h" }, r.new_27h);
    gauge.set({ entity: r.name, window: "7d" }, r.new_7d);
    gauge.set({ entity: r.name, window: "30d" }, r.new_30d);
  }

  const metrics = await register.metrics();

  return new NextResponse(metrics, {
    headers: { "Content-Type": register.contentType },
  });
}