package httpapi

import (
	"io/fs"
	"net/http"
	"path"
	"strings"

	"github.com/mithral/vellum/web"
)

// mountWeb serves the embedded single-page app at the root path.
//
// Unknown non-API paths fall back to index.html so client-side routes work on
// reload. API paths never fall back: a typo in an endpoint returns JSON, not
// an HTML page.
func (s *Server) mountWeb() {
	sub, err := fs.Sub(web.Dist, "dist")
	if err != nil {
		s.mux.HandleFunc("/", s.handleNotFound)
		return
	}
	index, err := fs.ReadFile(sub, "index.html")
	if err != nil {
		// Frontend not built into this binary. Keep JSON 404s rather than
		// pretending the app exists.
		s.log.Warn("web UI not embedded; run the frontend build to include it")
		s.mux.HandleFunc("/", s.handleNotFound)
		return
	}

	files := http.FileServer(http.FS(sub))
	s.mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		if isAPIPath(r.URL.Path) {
			s.handleNotFound(w, r)
			return
		}
		if r.URL.Path == "/" || r.URL.Path == "" {
			serveIndex(w, index)
			return
		}
		name := strings.TrimPrefix(path.Clean(r.URL.Path), "/")
		if f, err := sub.Open(name); err == nil {
			_ = f.Close()
			files.ServeHTTP(w, r)
			return
		}
		// SPA route: hand back the shell and let the client router decide.
		serveIndex(w, index)
	})
}

func serveIndex(w http.ResponseWriter, index []byte) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.Header().Set("Cache-Control", "no-cache")
	_, _ = w.Write(index)
}

func isAPIPath(p string) bool {
	return p == "/healthz" || strings.HasPrefix(p, "/api/")
}