website/main.go

package main

import (
	"embed"
	"flag"
	"fmt"
	"html/template"
	"io/fs"
	"log/slog"
	"net/http"
	"os"
	"strings"
	"time"
)

//go:embed web/static/*
var staticFS embed.FS

//go:embed web/html/*
var htmlTemplates embed.FS

func main() {
	var (
		address  string
		profiles links
		services links
	)

	flag.StringVar(&address, "address", "0.0.0.0:8080", "The address that the web server will listen on")
	flag.Var(&services, "service", "A list of service links")
	flag.Var(&profiles, "profile", "A list of profile links")

	flag.Parse()

	setupLogging()

	mux, err := routes(services, profiles)
	if err != nil {
		slog.Error("Unable to create the Mux", "error", err)
		os.Exit(1)
	}

	server := http.Server{
		Addr:              address,
		Handler:           mux,
		ReadHeaderTimeout: 1 * time.Second,
		ReadTimeout:       5 * time.Second,
	}

	slog.Info("Starting web application.", "address", address)

	err = server.ListenAndServe()
	if err != nil {
		slog.Error("Failed to run the web application", "error", err)
	}
}

func routes(services, profiles links) (*http.ServeMux, error) {
	mux := http.NewServeMux()

	staticRootFS, err := fs.Sub(staticFS, "web/static")
	if err != nil {
		return nil, fmt.Errorf("unable to create the static root file system; %w", err)
	}

	fileServer := http.FileServer(http.FS(staticRootFS))
	mux.Handle("/static/", http.StripPrefix("/static", neuter(fileServer)))

	mux.HandleFunc("/", landing(services, profiles))

	return mux, nil
}

func neuter(next http.Handler) http.Handler {
	return http.HandlerFunc(func(writer http.ResponseWriter, request *http.Request) {
		if strings.HasSuffix(request.URL.Path, "/") {
			notFound(writer)

			return
		}

		next.ServeHTTP(writer, request)
	})
}

func landing(services, profiles links) func(http.ResponseWriter, *http.Request) {
	return func(writer http.ResponseWriter, request *http.Request) {
		if request.URL.Path != "/" {
			notFound(writer)

			return
		}

		if request.Method != http.MethodGet {
			writer.Header().Set("Allow", http.MethodGet)
			clientError(writer, http.StatusMethodNotAllowed)

			return
		}

		tmpl, err := template.New("base").ParseFS(htmlTemplates, "web/html/base.tmpl.html")
		if err != nil {
			serverError(writer, fmt.Errorf("error parsing the HTML template; %w", err))

			return
		}

		links := struct {
			Services links
			Profiles links
		}{
			Services: services,
			Profiles: profiles,
		}

		if err = tmpl.Execute(writer, &links); err != nil {
			serverError(writer, fmt.Errorf("error rendering the HTML templates; %w", err))
		}
	}
}

func notFound(w http.ResponseWriter) {
	clientError(w, http.StatusNotFound)
}

func clientError(w http.ResponseWriter, status int) {
	http.Error(w, http.StatusText(status), status)
}

func serverError(w http.ResponseWriter, err error) {
	slog.Error(err.Error())

	http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
}

func setupLogging() {
	opts := slog.HandlerOptions{
		AddSource: false,
	}

	logger := slog.New(slog.NewJSONHandler(os.Stdout, &opts))

	slog.SetDefault(logger)
}