package api

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

// spaFS holds the built Vite SPA.
// The directory backend/internal/api/webapp/ is populated by the Docker
// multi-stage build (node → copy dist → go build).
// A placeholder file keeps the embed valid when building without Docker.

//go:embed webapp
var spaFS embed.FS

// SPAHandler serves the Vite SPA under the given prefix (e.g. "/app").
// Static assets (paths with file extensions) are served directly.
// All other paths fall back to index.html for client-side routing.
func SPAHandler(prefix string) http.Handler {
	sub, err := fs.Sub(spaFS, "webapp")
	if err != nil {
		return http.NotFoundHandler()
	}
	fileServer := http.FileServer(http.FS(sub))

	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// Strip the mount prefix to get the file path
		path := strings.TrimPrefix(r.URL.Path, prefix)
		if path == "" || path == "/" {
			// Serve index.html
			r2 := r.Clone(r.Context())
			r2.URL.Path = "/index.html"
			fileServer.ServeHTTP(w, r2)
			return
		}

		// Has a file extension → serve asset directly (JS, CSS, fonts, …)
		if filepath.Ext(path) != "" {
			r2 := r.Clone(r.Context())
			r2.URL.Path = path
			fileServer.ServeHTTP(w, r2)
			return
		}

		// SPA route → serve index.html
		r2 := r.Clone(r.Context())
		r2.URL.Path = "/index.html"
		fileServer.ServeHTTP(w, r2)
	})
}