package mw

import (
	"fmt"
	"log/slog"
	"net/http"
	"time"
)

const (
	logRequest  = "request"
	logResponse = "response"
	logMethod   = "method"
	logURI      = "uri"
	logStatus   = "status"
	logSize     = "size"
	logDuration = "duration"
)

// LoggingMiddleware returns a middleware that logs the request and response,
// each in a loggroup.
//
// The request group contains the request method and URI.
// The response group contains the response status, size and duration.
func LoggingMiddleware(l *slog.Logger) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			startTime := time.Now()

			lwr := &loggingResponseWriter{
				ResponseWriter: w,
				data:           &responseData{status: http.StatusOK, size: 0},
			}

			next.ServeHTTP(lwr, r)

			l.InfoContext(r.Context(), "HTTP request answered",
				slog.Group(
					logRequest,
					slog.String(logMethod, r.Method),
					slog.String(logURI, r.RequestURI),
				),
				slog.Group(
					logResponse,
					slog.Int(logStatus, lwr.data.status),
					slog.Int(logSize, lwr.data.size),
					slog.Duration(logDuration, time.Since(startTime)),
				),
			)
		})
	}
}

// Struct for holding response details.
type responseData struct {
	status int
	size   int
}

// loggingResponseWriter is a wrapper for http.ResponseWriter that records the
// size of data sent and the status code of the response.
type loggingResponseWriter struct {
	http.ResponseWriter // compose original http.ResponseWriter
	data                *responseData
}

// Write implements http.ResponseWriter.
func (r *loggingResponseWriter) Write(b []byte) (int, error) {
	size, err := r.ResponseWriter.Write(b)
	r.data.size += size

	if err != nil {
		return size, fmt.Errorf("cannot forward data: %w", err)
	}

	return size, nil
}

// WriteHeader implements http.ResponseWriter.
func (r *loggingResponseWriter) WriteHeader(statusCode int) {
	r.ResponseWriter.WriteHeader(statusCode)
	r.data.status = statusCode
}