package web

import (
	"crypto/rand"
	"encoding/hex"
	"log"
	"net/http"
	"net/url"
	"path/filepath"
	"runtime/debug"
	"strings"
)

// registerRoutes is set by internal/web/handlers's init() (via RegisterRoutes),
// avoiding an import cycle: handlers imports web for *App, so web cannot import
// handlers back — it calls into this hook instead.
var registerRoutes func(*App, *http.ServeMux)

// RegisterRoutes installs the application's route-registration callback. Called
// once from the handlers package's init().
func RegisterRoutes(fn func(*App, *http.ServeMux)) {
	registerRoutes = fn
}

// Handler builds the full HTTP handler: routing, static assets, session
// load/save, panic recovery, request-id tagging and base-URL prefix handling.
func (a *App) Handler() http.Handler {
	mux := http.NewServeMux()
	if registerRoutes != nil {
		registerRoutes(a, mux)
	}

	staticDir := filepath.Join(a.Cfg.WebDir, "static")
	mux.Handle("GET /static/", http.StripPrefix("/static/", http.FileServer(http.Dir(staticDir))))

	var h http.Handler = mux
	h = a.recoverer(h)
	h = a.requestID(h)
	h = a.Sessions.LoadAndSave(h)
	h = a.stripBasePrefix(h)
	return h
}

// recoverer converts panics in handlers into a 500 response instead of crashing
// the server.
func (a *App) recoverer(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		defer func() {
			if rec := recover(); rec != nil {
				log.Printf("panic: %v\n%s", rec, debug.Stack())
				http.Error(w, "Внутренняя ошибка сервера.", http.StatusInternalServerError)
			}
		}()
		next.ServeHTTP(w, r)
	})
}

// requestID tags every response with a short correlation id (X-Request-Id),
// useful for grepping logs; purely optional/best-effort.
func (a *App) requestID(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		id := r.Header.Get("X-Request-Id")
		if id == "" {
			b := make([]byte, 8)
			_, _ = rand.Read(b)
			id = hex.EncodeToString(b)
		}
		w.Header().Set("X-Request-Id", id)
		next.ServeHTTP(w, r)
	})
}

// stripBasePrefix strips the configured APP_BASE_URL path prefix (if any) from
// incoming requests before they reach the router, so route patterns stay
// prefix-free. Requests that arrive without the prefix (e.g. an internal
// container health check hitting 127.0.0.1 directly) are passed through
// unchanged rather than 404ing.
func (a *App) stripBasePrefix(next http.Handler) http.Handler {
	prefix := strings.Trim(a.Cfg.BaseURL, "/")
	if prefix == "" {
		return next
	}
	p := "/" + prefix
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if r.URL.Path == p || strings.HasPrefix(r.URL.Path, p+"/") {
			trimmed := strings.TrimPrefix(r.URL.Path, p)
			if trimmed == "" {
				trimmed = "/"
			}
			r2 := new(http.Request)
			*r2 = *r
			u2 := new(url.URL)
			*u2 = *r.URL
			u2.Path = trimmed
			r2.URL = u2
			next.ServeHTTP(w, r2)
			return
		}
		next.ServeHTTP(w, r)
	})
}