package httpx

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

const basename = "/"

type NotFoundHandler struct {
	fs         http.FileSystem
	fileServer http.Handler
}

// NewNotFoundHandler 静态资源服务：命中即返回文件，否则回退到 index.html（前端 SPA 路由）
func NewNotFoundHandler(fs http.FileSystem) NotFoundHandler {
	return NotFoundHandler{
		fs:         fs,
		fileServer: http.FileServer(fs),
	}
}

func (n NotFoundHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if strings.HasPrefix(r.URL.Path, "/api/") {
		http.Error(w, "not found", http.StatusNotFound)
		return
	}
	filePath := strings.TrimPrefix(path.Clean(r.URL.Path), basename)
	if len(filePath) == 0 {
		filePath = basename
	}

	file, err := n.fs.Open(filePath)
	switch {
	case err == nil:
		n.fileServer.ServeHTTP(w, r)
		_ = file.Close()
		return
	case os.IsNotExist(err):
		r.URL.Path = "/" // vue app 虚拟路由统一回 index.html
		n.fileServer.ServeHTTP(w, r)
		return
	default:
		http.Error(w, "not found", http.StatusNotFound)
		return
	}
}