package httpserver

import (
	"io/fs"
	"net/http"
)

// spaHandler serves the embedded Vue SPA out of distFS (already rooted at
// web/dist, i.e. index.html is at its top level). Any request path that
// doesn't match a real file falls back to index.html so client-side routes
// (deep links) resolve correctly.
func spaHandler(distFS fs.FS) http.HandlerFunc {
	fileServer := http.FileServer(http.FS(distFS))

	return func(w http.ResponseWriter, r *http.Request) {
		upath := r.URL.Path
		if upath == "" || upath == "/" {
			upath = "index.html"
		} else {
			upath = upath[1:] // strip leading slash for fs.Stat
		}

		if _, err := fs.Stat(distFS, upath); err != nil {
			r = cloneWithPath(r, "/")
		}

		fileServer.ServeHTTP(w, r)
	}
}

// cloneWithPath returns a shallow copy of r with URL.Path replaced, so the
// original request (and its URL) is left untouched.
func cloneWithPath(r *http.Request, path string) *http.Request {
	r2 := r.Clone(r.Context())
	r2.URL.Path = path
	return r2
}