// Command ffd-metrics is the long-running metrics daemon for the federated
// forge indexer.
//
// It reads the same SQLite store the indexer writes to and exposes the state
// of the index to Prometheus at /metrics. It is intended to be run as a
// separate systemd service; it performs no scraping of its own.
package main

import (
	"context"
	"errors"
	"flag"
	"fmt"
	"net/http"
	"os"
	"os/signal"
	"syscall"
	"time"

	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promhttp"
	"go.yaml.in/yaml/v4"

	"git.xengi.de/ffd/indexer/config"
	"git.xengi.de/ffd/indexer/internal/version"
	"git.xengi.de/ffd/indexer/metrics"
	"git.xengi.de/ffd/indexer/store"
)

func main() {
	configPath := flag.String("config", "config.yaml", "path to the configuration file")
	showVersion := flag.Bool("version", false, "print version and commit, then exit")
	flag.Parse()

	if *showVersion {
		version.PrintFull()
		return
	}

	data, err := os.ReadFile(*configPath)
	if err != nil {
		panic(err)
	}
	var cfg config.Config
	if err := yaml.Unmarshal(data, &cfg); err != nil {
		panic(err)
	}

	// The daemon shares the indexer's database; both processes may be open on
	// it at once (the SQLite driver handles that with WAL-safe read queries).
	db, err := store.Open(cfg.DbPath)
	if err != nil {
		panic(err)
	}
	defer func() { _ = db.Close() }()

	registry := prometheus.NewRegistry()
	registry.MustRegister(metrics.NewCollector(db))

	mux := http.NewServeMux()
	mux.Handle("/metrics", promhttp.HandlerFor(registry, promhttp.HandlerOpts{}))

	srv := &http.Server{
		Addr:              cfg.Metrics.Listen,
		Handler:           mux,
		ReadHeaderTimeout: 5 * time.Second,
	}

	// Shut down cleanly on SIGTERM/SIGINT.
	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGTERM, os.Interrupt)
	defer stop()

	errCh := make(chan error, 1)
	go func() {
		fmt.Printf("ffd-metrics listening on %s\n", srv.Addr)
		errCh <- srv.ListenAndServe()
	}()

	select {
	case err := <-errCh:
		if err != nil && !errors.Is(err, http.ErrServerClosed) {
			fmt.Fprintf(os.Stderr, "metrics server: %v\n", err)
			os.Exit(1)
		}
	case <-ctx.Done():
		fmt.Println("shutting down")
		shutdownCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
		defer cancel()
		if err := srv.Shutdown(shutdownCtx); err != nil {
			fmt.Fprintf(os.Stderr, "shutdown: %v\n", err)
		}
	}
}