feat: add GitHub repository dashboard with Prometheus metrics

ghtracker authenticates as a GitHub App and scans a configured list of repositories on a schedule. It serves a dashboard, a JSON state endpoint, a health probe and Prometheus metrics.

The dashboard lists only items that need attention: failing workflows, pull requests that wait too long or fail their checks, stale issues and projects that failed to scan. It has search, dynamic filters and a button that rescans on demand. The Vue app is embedded in the Go binary.

The client protects the GitHub rate limit with conditional requests, a request reserve and Retry-After handling.

main.go

@@ -0,0 +1,101 @@
+// Command ghtracker serves a dashboard and Prometheus metrics for a list of GitHub repositories.
+package main
+
+import (
+	"context"
+	"embed"
+	"errors"
+	"flag"
+	"fmt"
+	"io/fs"
+	"log/slog"
+	"net/http"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/collectors"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+
+	"github.com/lukaszraczylo/ghtracker/internal/collector"
+	"github.com/lukaszraczylo/ghtracker/internal/config"
+	"github.com/lukaszraczylo/ghtracker/internal/gh"
+	"github.com/lukaszraczylo/ghtracker/internal/metrics"
+	"github.com/lukaszraczylo/ghtracker/internal/web"
+)
+
+// distFS holds the built UI; dist/.gitkeep keeps the pattern valid before the first UI build.
+//
+//go:embed all:dist
+var distFS embed.FS
+
+// version is set at release time with -ldflags "-X main.version=...".
+var version = "dev"
+
+const (
+	httpTimeout     = 30 * time.Second
+	shutdownTimeout = 10 * time.Second
+	headerTimeout   = 10 * time.Second
+)
+
+func main() {
+	cfgPath := flag.String("config", "config.yaml", "path to the YAML config file")
+	showVersion := flag.Bool("version", false, "print the version and exit")
+	flag.Parse()
+	if *showVersion {
+		fmt.Println(version)
+		return
+	}
+	log := slog.New(slog.NewTextHandler(os.Stderr, nil))
+	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
+	defer stop()
+	if err := run(ctx, *cfgPath, log); err != nil {
+		stop()
+		log.Error("fatal", "err", err)
+		os.Exit(1)
+	}
+}
+
+func run(ctx context.Context, cfgPath string, log *slog.Logger) error {
+	cfg, err := config.Load(cfgPath)
+	if err != nil {
+		return err
+	}
+	hc := &http.Client{Timeout: httpTimeout}
+	auth, err := gh.NewAppAuth(cfg.GitHub.AppID, cfg.GitHub.PrivateKeyPEM, cfg.GitHub.APIURL, cfg.GitHub.InstallationID, hc)
+	if err != nil {
+		return err
+	}
+	client := gh.NewClient(cfg.GitHub.APIURL, auth, hc, cfg.MaxItems)
+	coll := collector.New(client, cfg, log)
+
+	reg := prometheus.NewRegistry()
+	reg.MustRegister(collectors.NewGoCollector(), collectors.NewProcessCollector(collectors.ProcessCollectorOpts{}),
+		metrics.New(coll, client.RateLimitRemaining))
+	ui, err := fs.Sub(distFS, "dist")
+	if err != nil {
+		return err
+	}
+	srv := web.New(coll, promhttp.HandlerFor(reg, promhttp.HandlerOpts{}), ui, *cfg.ManualRefresh, log)
+
+	go coll.Run(ctx)
+
+	hs := &http.Server{Addr: cfg.Listen, Handler: srv.Handler(), ReadHeaderTimeout: headerTimeout}
+	errc := make(chan error, 1)
+	go func() { errc <- hs.ListenAndServe() }()
+	log.Info("listening", "version", version, "addr", cfg.Listen, "repos", len(cfg.Repos), "refresh", cfg.RefreshInterval)
+
+	select {
+	case err := <-errc:
+		return err
+	case <-ctx.Done():
+	}
+	sctx, cancel := context.WithTimeout(context.Background(), shutdownTimeout)
+	defer cancel()
+	if err := hs.Shutdown(sctx); err != nil && !errors.Is(err, http.ErrServerClosed) {
+		return err
+	}
+	return nil
+}