package middleware

import (
	"encoding/json"
	"log/slog"
	"net/http"
	"runtime/debug"
)

// Recoverer turns panics into 500 JSON responses without leaking the stack to
// clients. The full stack is logged at error level.
func Recoverer(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		defer func() {
			if rv := recover(); rv != nil {
				slog.Error("panic recovered",
					"path", r.URL.Path,
					"method", r.Method,
					"err", rv,
					"stack", string(debug.Stack()),
				)
				if !headerWritten(w) {
					w.Header().Set("Content-Type", "application/json")
					w.WriteHeader(http.StatusInternalServerError)
					_ = json.NewEncoder(w).Encode(map[string]string{
						"error":  "InternalError",
						"detail": "internal server error",
					})
				}
			}
		}()
		next.ServeHTTP(w, r)
	})
}

// headerWritten is best-effort; if the response is hijacked we skip writing.
func headerWritten(w http.ResponseWriter) bool {
	if rw, ok := w.(interface{ Status() int }); ok {
		return rw.Status() != 0
	}
	return false
}