refactor!: serve the static frontend trough the backend (#520)

Co-authored-by: Alessandro (Ale) Segala <43508+ItalyPaleAle@users.noreply.github.com>

backend/frontend/frontend_included.go

@@ -0,0 +1,77 @@
+//go:build !exclude_frontend
+
+package frontend
+
+import (
+	"embed"
+	"fmt"
+	"io/fs"
+	"net/http"
+	"os"
+	"strings"
+	"time"
+
+	"github.com/gin-gonic/gin"
+)
+
+//go:embed all:dist/*
+var frontendFS embed.FS
+
+func RegisterFrontend(router *gin.Engine) error {
+	distFS, err := fs.Sub(frontendFS, "dist")
+	if err != nil {
+		return fmt.Errorf("failed to create sub FS: %w", err)
+	}
+
+	cacheMaxAge := time.Hour * 24
+	fileServer := NewFileServerWithCaching(http.FS(distFS), int(cacheMaxAge.Seconds()))
+
+	router.NoRoute(func(c *gin.Context) {
+		// Try to serve the requested file
+		path := strings.TrimPrefix(c.Request.URL.Path, "/")
+		if _, err := fs.Stat(distFS, path); os.IsNotExist(err) {
+			// File doesn't exist, serve index.html instead
+			c.Request.URL.Path = "/"
+		}
+
+		fileServer.ServeHTTP(c.Writer, c.Request)
+	})
+
+	return nil
+}
+
+// FileServerWithCaching wraps http.FileServer to add caching headers
+type FileServerWithCaching struct {
+	root                    http.FileSystem
+	lastModified            time.Time
+	cacheMaxAge             int
+	lastModifiedHeaderValue string
+	cacheControlHeaderValue string
+}
+
+func NewFileServerWithCaching(root http.FileSystem, maxAge int) *FileServerWithCaching {
+	return &FileServerWithCaching{
+		root:                    root,
+		lastModified:            time.Now(),
+		cacheMaxAge:             maxAge,
+		lastModifiedHeaderValue: time.Now().UTC().Format(http.TimeFormat),
+		cacheControlHeaderValue: fmt.Sprintf("public, max-age=%d", maxAge),
+	}
+}
+
+func (f *FileServerWithCaching) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	// Check if the client has a cached version
+	if ifModifiedSince := r.Header.Get("If-Modified-Since"); ifModifiedSince != "" {
+		ifModifiedSinceTime, err := time.Parse(http.TimeFormat, ifModifiedSince)
+		if err == nil && f.lastModified.Before(ifModifiedSinceTime.Add(1*time.Second)) {
+			// Client's cached version is up to date
+			w.WriteHeader(http.StatusNotModified)
+			return
+		}
+	}
+
+	w.Header().Set("Last-Modified", f.lastModifiedHeaderValue)
+	w.Header().Set("Cache-Control", f.cacheControlHeaderValue)
+
+	http.FileServer(f.root).ServeHTTP(w, r)
+}