package middleware

import (
	"crypto/rand"
	"encoding/hex"
	"log/slog"
	"net/http"
	"time"
)

// responseWriter wraps http.ResponseWriter to capture the status code.
type responseWriter struct {
	http.ResponseWriter
	statusCode int
}

func (rw *responseWriter) WriteHeader(code int) {
	rw.statusCode = code
	rw.ResponseWriter.WriteHeader(code)
}

// generateRequestID creates a short random hex string for request tracing.
func generateRequestID() string {
	b := make([]byte, 8)
	if _, err := rand.Read(b); err != nil {
		return "unknown"
	}
	return hex.EncodeToString(b)
}

// Logging returns middleware that logs each HTTP request with structured fields:
// method, path, status, duration (ms), request-id, and remote address.
func Logging() func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			start := time.Now()
			requestID := generateRequestID()
			rw := &responseWriter{ResponseWriter: w, statusCode: http.StatusOK}

			// Set request ID header for downstream correlation.
			w.Header().Set("X-Request-ID", requestID)

			next.ServeHTTP(rw, r)

			duration := time.Since(start)
			slog.Info("http request",
				"method", r.Method,
				"path", r.URL.Path,
				"status", rw.statusCode,
				"duration_ms", duration.Milliseconds(),
				"duration", duration.String(),
				"request_id", requestID,
				"remote", r.RemoteAddr,
				"user_agent", r.UserAgent(),
			)
		})
	}
}