// Package webassets serves the compiled frontend without giving transport code filesystem access.
package webassets

import (
	"io/fs"
	"net/http"
	"os"
	"path/filepath"
	"strings"
)

func New(root string) http.Handler {
	files := os.DirFS(root)
	fileServer := http.FileServer(http.FS(files))

	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		requested := strings.TrimPrefix(filepath.Clean(r.URL.Path), string(filepath.Separator))
		if requested == "." {
			requested = "index.html"
		}
		if _, err := fs.Stat(files, requested); err == nil {
			fileServer.ServeHTTP(w, r)
			return
		}
		if _, err := fs.Stat(files, "index.html"); err == nil {
			r.URL.Path = "/"
			fileServer.ServeHTTP(w, r)
			return
		}
		http.Error(w, "Drive web assets are not built", http.StatusServiceUnavailable)
	})
}