thermograph/frontend/server/main.go

// thermograph-frontend: the SSR frontend service — server-rendered content
// pages (climate hub / per-city / month / records / glossary / about), the
// interactive tool's SPA shells, and every static asset. All climate data
// comes from the backend's content API over HTTP (internal/contentapi); this
// process holds no data of its own.
//
// Go port of app.py: configuration, the route wiring (internal/content for
// the content.py routes, internal/handlers for the SPA shells + static
// assets), and the process lifecycle uvicorn used to own (listen, access
// logs, graceful shutdown).
package main

import (
	"context"
	"errors"
	"log/slog"
	"mime"
	"net"
	"net/http"
	"os"
	"os/signal"
	"syscall"
	"time"

	"thermograph/frontend/internal/config"
	"thermograph/frontend/internal/content"
	"thermograph/frontend/internal/contentapi"
	"thermograph/frontend/internal/contentdata"
	"thermograph/frontend/internal/handlers"
	"thermograph/frontend/internal/render"
)

func main() {
	logger := slog.New(slog.NewJSONHandler(os.Stdout, nil))
	slog.SetDefault(logger)

	// Fail loud at boot on bad configuration or content (missing backend URL,
	// garbage TTL, malformed glossary/pages YAML) — the Python raised at
	// import for the same cases: a missing backend URL or a bad content edit
	// should break the boot, not silently 500 on the first request.
	cfg, err := config.Load()
	if err != nil {
		fatal(logger, "config", err)
	}

	client := contentapi.New(contentapi.Options{
		BaseURL:    cfg.APIBaseInternal,
		BasePrefix: cfg.Base, // backend runs under the same THERMOGRAPH_BASE
		APIVersion: cfg.APIVersion,
		TTL:        cfg.SSRCacheTTL,
	})

	glossary, err := contentdata.LoadGlossary(cfg.ContentDir)
	if err != nil {
		fatal(logger, "glossary", err)
	}
	pages, err := contentdata.LoadPages(cfg.ContentDir)
	if err != nil {
		fatal(logger, "pages", err)
	}

	// Templates parse once, at boot, with the full FuncMap (html/template
	// resolves function names at parse time) — the Go analogue of the Jinja
	// environment's auto_reload=False.
	engine, err := render.New(content.FuncMap(cfg))
	if err != nil {
		fatal(logger, "templates", err)
	}

	// The PWA manifest is served as a static file; register its media type so
	// the file server labels it correctly (not in Go's default mime table).
	if err := mime.AddExtensionType(".webmanifest", "application/manifest+json"); err != nil {
		fatal(logger, "mime", err)
	}

	// app.py-layer routes: SPA shells + static assets + the bare-BASE redirect.
	app := handlers.New(handlers.Options{
		Base:         cfg.Base,
		StaticDir:    cfg.StaticDir,
		GoogleVerify: cfg.GoogleVerify,
		BingVerify:   cfg.BingVerify,
		Log:          logger,
	})

	// content.py-layer routes. content.New takes a *log.Logger; bridge it into
	// slog so its lines (IndexNow boot warning, render failures) land on
	// stdout structured like everything else.
	contentHandlers, err := content.New(cfg, client, engine, glossary, pages,
		slog.NewLogLogger(logger.Handler(), slog.LevelWarn))
	if err != nil {
		fatal(logger, "content", err)
	}

	mux := http.NewServeMux()

	// Liveness probe: the process is up and serving. Deliberately does no I/O
	// — no call to the backend — so it stays cheap and reliable for a tight
	// healthcheck interval. Readiness (backend reachable) is a separate concern.
	mux.HandleFunc("GET /healthz", func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "application/json")
		_, _ = w.Write([]byte(`{"status":"ok"}`))
	})

	// Register order does not matter for precedence (most-specific pattern
	// wins), but content registration performs the eager IndexNow key fetch —
	// same point in boot as the Python's content.register(app). Its lazy
	// fallback route needs the static handler to delegate non-key requests to.
	contentHandlers.Register(mux, app.Static())
	app.Register(mux)

	srv := &http.Server{
		Addr:              net.JoinHostPort("", cfg.Port), // 0.0.0.0:PORT, like uvicorn --host 0.0.0.0
		Handler:           accessLog(logger, mux),
		ReadHeaderTimeout: 10 * time.Second,
	}

	// Graceful shutdown on SIGINT/SIGTERM: stop accepting, drain in-flight
	// requests, then exit — what uvicorn did for the Python process.
	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
	defer stop()

	errCh := make(chan error, 1)
	go func() {
		logger.Info("thermograph-frontend listening", "port", cfg.Port, "base", cfg.Base)
		errCh <- srv.ListenAndServe()
	}()

	select {
	case err := <-errCh:
		if !errors.Is(err, http.ErrServerClosed) {
			fatal(logger, "serve", err)
		}
	case <-ctx.Done():
		shutdownCtx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
		defer cancel()
		if err := srv.Shutdown(shutdownCtx); err != nil {
			logger.Error("shutdown", "err", err)
			os.Exit(1)
		}
		logger.Info("shut down cleanly")
	}
}

func fatal(logger *slog.Logger, stage string, err error) {
	logger.Error(stage, "err", err)
	os.Exit(1)
}

// accessLog is the uvicorn access log's replacement: one structured line per
// request on stdout.
func accessLog(logger *slog.Logger, next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()
		rec := &statusRecorder{ResponseWriter: w, status: http.StatusOK}
		next.ServeHTTP(rec, r)
		logger.Info("request",
			"method", r.Method,
			"path", r.URL.Path,
			"status", rec.status,
			"dur_ms", time.Since(start).Milliseconds(),
		)
	})
}

// statusRecorder captures the response status for the access log.
type statusRecorder struct {
	http.ResponseWriter
	status int
}

func (rec *statusRecorder) WriteHeader(status int) {
	rec.status = status
	rec.ResponseWriter.WriteHeader(status)
}