package main

import (
	"context"
	"embed"
	"flag"
	"html/template"
	"log"
	"net/http"
	"os"
	"os/signal"
	"strconv"
	"syscall"
)

//go:embed templates
var templatesFS embed.FS

func main() {
	listen := flag.String("listen", envOr("FRONTEND_LISTEN", ":8080"), "HTTP listen address (env: FRONTEND_LISTEN)")
	target := flag.String("target", envOr("FRONTEND_TARGET", "localhost:9091"), "default gRPC endpoint, aggregator or collector (env: FRONTEND_TARGET)")
	n := flag.Int("n", envOrInt("FRONTEND_N", 25), "default number of table rows (env: FRONTEND_N)")
	refresh := flag.Int("refresh", envOrInt("FRONTEND_REFRESH", 30), "meta-refresh interval in seconds, 0 to disable (env: FRONTEND_REFRESH)")
	flag.Parse()

	funcMap := template.FuncMap{"fmtCount": fmtCount}
	tmpl := template.Must(
		template.New("").Funcs(funcMap).ParseFS(templatesFS, "templates/*.html"),
	)

	h := &Handler{
		defaultTarget: *target,
		defaultN:      *n,
		refreshSecs:   *refresh,
		tmpl:          tmpl,
	}

	srv := &http.Server{Addr: *listen, Handler: h}

	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
	defer stop()

	go func() {
		log.Printf("frontend: listening on %s (default target %s)", *listen, *target)
		if err := srv.ListenAndServe(); err != nil && err != http.ErrServerClosed {
			log.Printf("frontend: %v", err)
			os.Exit(1)
		}
	}()

	<-ctx.Done()
	log.Printf("frontend: shutting down")
	srv.Shutdown(context.Background())
}

func envOr(key, def string) string {
	if v := os.Getenv(key); v != "" {
		return v
	}
	return def
}

func envOrInt(key string, def int) int {
	if v := os.Getenv(key); v != "" {
		if n, err := strconv.Atoi(v); err == nil {
			return n
		}
		log.Printf("frontend: invalid int for %s=%q, using default %d", key, v, def)
	}
	return def
}