package sdkserver

import (
	"net/http"
	"os"
	"path/filepath"
	"regexp"
	"strings"

	"gac-hkrpg-go/internal/common"
)

// Route name is part of this server's HTTP interface, not a machine URL.
const luaOverlayRoute = "/gacy-lua-overlay"

var luaBundleName = regexp.MustCompile(`^(?:M_LuaV|LuaV_[0-9a-f]{32}|[0-9a-f]{32})\.bytes$`)

// Dispatch outside ServeMux: a subtree registration conflicts with the
// product-name wildcard used by the existing login endpoints in newer Go.
func withLuaOverlay(next http.Handler, cfg common.LuaOverlayConfig) http.Handler {
	if !cfg.Enabled {
		return next
	}
	overlay := luaOverlayHandler(cfg)
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if strings.HasPrefix(r.URL.Path, luaOverlayRoute+"/") {
			overlay(w, r)
			return
		}
		next.ServeHTTP(w, r)
	})
}

// Serve only the Lua updater's known flat namespace. Stage files win, then the
// local hotfix and shipping files; no filesystem path or remote URL is derived
// from untrusted input. The original caches remain untouched.
func luaOverlayHandler(cfg common.LuaOverlayConfig) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodGet && r.Method != http.MethodHead {
			w.WriteHeader(http.StatusMethodNotAllowed)
			return
		}
		path := strings.TrimPrefix(r.URL.Path, luaOverlayRoute+"/")
		path = strings.TrimPrefix(path, "client/Windows/")
		if !luaBundleName.MatchString(path) {
			http.NotFound(w, r)
			return
		}
		for _, root := range []string{cfg.StageDir, cfg.HotfixDir, cfg.StreamingDir} {
			file, err := os.Open(filepath.Join(root, path))
			if os.IsNotExist(err) {
				continue
			}
			if err != nil {
				http.Error(w, "Lua overlay read failed", http.StatusInternalServerError)
				return
			}
			info, err := file.Stat()
			if err != nil || !info.Mode().IsRegular() {
				file.Close()
				http.Error(w, "Lua overlay file invalid", http.StatusInternalServerError)
				return
			}
			w.Header().Set("Content-Type", "application/octet-stream")
			http.ServeContent(w, r, path, info.ModTime(), file)
			file.Close()
			return
		}
		http.NotFound(w, r)
	}
}