package webui

import (
	"io/fs"
	"mime"
	"net/http"
	"path"
	"strconv"
	"strings"
)

// Handler отдаёт статику SvelteKit (embed) и index.html для клиентских маршрутов SPA.
func Handler() http.Handler {
	root, err := fs.Sub(static, "static")
	if err != nil {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			http.NotFound(w, r)
		})
	}

	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodGet && r.Method != http.MethodHead {
			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
			return
		}

		name := strings.TrimPrefix(path.Clean(r.URL.Path), "/")
		if name == "." || name == "" {
			name = "index.html"
		}

		b, err := fs.ReadFile(root, name)
		if err != nil {
			if path.Ext(name) != "" {
				http.NotFound(w, r)
				return
			}
			b, err = fs.ReadFile(root, "index.html")
			if err != nil {
				http.NotFound(w, r)
				return
			}
			name = "index.html"
		}

		ct := mime.TypeByExtension(path.Ext(name))
		if ct == "" {
			ct = "application/octet-stream"
		}
		if strings.HasPrefix(ct, "text/") && !strings.Contains(ct, "charset") {
			ct = ct + "; charset=utf-8"
		}
		w.Header().Set("Content-Type", ct)
		if name == "index.html" {
			w.Header().Set("Cache-Control", "no-cache")
		} else {
			w.Header().Set("Cache-Control", "public, max-age=31536000, immutable")
		}

		if r.Method == http.MethodHead {
			w.Header().Set("Content-Length", strconv.Itoa(len(b)))
			w.WriteHeader(http.StatusOK)
			return
		}
		w.WriteHeader(http.StatusOK)
		_, _ = w.Write(b)
	})
}