package server

import (
	"net/http"
	"strings"

	"glchat/internal/httpx"
)

// methodOfPattern splits a Go 1.22 routing pattern such as "GET /api/v1/meta"
// into its method and path parts. Patterns without a method apply to all.
func methodOfPattern(pattern string) (method, path string) {
	if i := strings.IndexByte(pattern, ' '); i > 0 {
		return pattern[:i], pattern[i+1:]
	}
	return "", pattern
}

func (s *Server) routeExists(method, path string) bool {
	for _, pattern := range s.patterns {
		patternMethod, patternPath := methodOfPattern(pattern)
		if patternMethod == "" || patternMethod == method {
			continue
		}
		if patternPath == path {
			return true
		}
		if strings.HasSuffix(patternPath, "/") && strings.HasPrefix(path, patternPath) {
			return true
		}
	}
	return false
}

// reservedPrefixes are handled by the API, the gateway or the file CDN; an
// unknown path under them is a real 404 and must not receive the SPA shell.
var reservedPrefixes = []string{"/api/", "/gateway", "/files/", "/rtc"}

func isReservedPath(path string) bool {
	for _, prefix := range reservedPrefixes {
		if path == strings.TrimSuffix(prefix, "/") || strings.HasPrefix(path, prefix) {
			return true
		}
	}
	return false
}

func (s *Server) handleFallback(w http.ResponseWriter, r *http.Request) {
	if s.routeExists(r.Method, r.URL.Path) {
		httpx.WriteErrorStatus(w, http.StatusMethodNotAllowed, httpx.CodeBadRequest, "method not allowed")
		return
	}
	if isReservedPath(r.URL.Path) {
		httpx.WriteError(w, httpx.NewError(httpx.CodeNotFound, "resource not found"))
		return
	}
	if r.Method == http.MethodGet || r.Method == http.MethodHead {
		s.static.serve(w, r)
		return
	}
	httpx.WriteError(w, httpx.NewError(httpx.CodeNotFound, "resource not found"))
}