package gateway

import (
	"net/http"
	"path"
	"strings"
)

// spa wraps the API mux with the SPA file server. Requests under /api/ and /ws/
// are served by the API handler; every other path is served from the configured
// frontend filesystem with a fallback to index.html so client-side routes (e.g.
// /chat) resolve in a single-page app.
func (s *Server) spa(api http.Handler) http.Handler {
	fileServer := s.spaFileServer()
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if isAPIRoute(r.URL.Path) {
			api.ServeHTTP(w, r)
			return
		}
		fileServer.ServeHTTP(w, r)
	})
}

// spaFileServer serves static assets, falling back to index.html for paths that
// are not real files in the embedded/external dist.
func (s *Server) spaFileServer() http.Handler {
	fsrv := http.FileServer(http.FS(s.frontend))
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		rel := strings.TrimPrefix(path.Clean(r.URL.Path), "/")
		if rel != "" {
			if f, err := s.frontend.Open(rel); err == nil {
				_ = f.Close()
				fsrv.ServeHTTP(w, r)
				return
			}
		}
		r2 := r.Clone(r.Context())
		r2.URL.Path = "/"
		fsrv.ServeHTTP(w, r2)
	})
}

// isAPIRoute reports whether path belongs to the REST/WS API surface the
// gateway owns, which the SPA handler must leave untouched.
func isAPIRoute(p string) bool {
	return strings.HasPrefix(p, "/api/") || strings.HasPrefix(p, "/ws/")
}