// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Internal;
using Microsoft.Extensions.Logging;
 
namespace Microsoft.Extensions.Http.Logging
{
    /// <summary>
    /// Handles logging of the lifecycle for an HTTP request within a log scope.
    /// </summary>
    public class LoggingScopeHttpMessageHandler : DelegatingHandler
    {
        private readonly ILogger _logger;
        private readonly HttpClientFactoryOptions? _options;
 
        private static readonly Func<string, bool> _shouldNotRedactHeaderValue = (header) => false;
 
        /// <summary>
        /// Initializes a new instance of the <see cref="LoggingScopeHttpMessageHandler"/> class with a specified logger.
        /// </summary>
        /// <param name="logger">The <see cref="ILogger"/> to log to.</param>
        /// <exception cref="ArgumentNullException"><paramref name="logger"/> is <see langword="null"/>.</exception>
        public LoggingScopeHttpMessageHandler(ILogger logger)
        {
            ThrowHelper.ThrowIfNull(logger);
 
            _logger = logger;
        }
 
        /// <summary>
        /// Initializes a new instance of the <see cref="LoggingScopeHttpMessageHandler"/> class with a specified logger and options.
        /// </summary>
        /// <param name="logger">The <see cref="ILogger"/> to log to.</param>
        /// <param name="options">The <see cref="HttpClientFactoryOptions"/> used to configure the <see cref="LoggingScopeHttpMessageHandler"/> instance.</param>
        /// <exception cref="ArgumentNullException"><paramref name="logger"/> or <paramref name="options"/> is <see langword="null"/>.</exception>
        public LoggingScopeHttpMessageHandler(ILogger logger, HttpClientFactoryOptions options)
        {
            ThrowHelper.ThrowIfNull(logger);
            ThrowHelper.ThrowIfNull(options);
 
            _logger = logger;
            _options = options;
        }
 
        private Task<HttpResponseMessage> SendCoreAsync(HttpRequestMessage request, bool useAsync, CancellationToken cancellationToken)
        {
            ThrowHelper.ThrowIfNull(request);
            return Core(request, useAsync, cancellationToken);
 
            async Task<HttpResponseMessage> Core(HttpRequestMessage request, bool useAsync, CancellationToken cancellationToken)
            {
                var stopwatch = ValueStopwatch.StartNew();
 
                Func<string, bool> shouldRedactHeaderValue = _options?.ShouldRedactHeaderValue ?? _shouldNotRedactHeaderValue;
 
                using (Log.BeginRequestPipelineScope(_logger, request))
                {
                    Log.RequestPipelineStart(_logger, request, shouldRedactHeaderValue);
                    HttpResponseMessage response = useAsync
                        ? await base.SendAsync(request, cancellationToken).ConfigureAwait(false)
#if NET
                        : base.Send(request, cancellationToken);
#else
                        : throw new NotImplementedException("Unreachable code");
#endif
                    Log.RequestPipelineEnd(_logger, response, stopwatch.GetElapsedTime(), shouldRedactHeaderValue);
 
                    return response;
                }
            }
        }
 
        /// <inheritdoc />
        /// <remarks>Logs the request to and response from the sent <see cref="HttpRequestMessage"/>.</remarks>
        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
            => SendCoreAsync(request, useAsync: true, cancellationToken);
 
#if NET
        /// <inheritdoc />
        /// <remarks>Logs the request to and response from the sent <see cref="HttpRequestMessage"/>.</remarks>
        protected override HttpResponseMessage Send(HttpRequestMessage request, CancellationToken cancellationToken)
            => SendCoreAsync(request, useAsync: false, cancellationToken).GetAwaiter().GetResult();
#endif
 
        // Used in tests
        internal static class Log
        {
            public static class EventIds
            {
                public static readonly EventId PipelineStart = new EventId(100, "RequestPipelineStart");
                public static readonly EventId PipelineEnd = new EventId(101, "RequestPipelineEnd");
 
                public static readonly EventId RequestHeader = new EventId(102, "RequestPipelineRequestHeader");
                public static readonly EventId ResponseHeader = new EventId(103, "RequestPipelineResponseHeader");
            }
 
            private static readonly Func<ILogger, HttpMethod, string?, IDisposable?> _beginRequestPipelineScope = LoggerMessage.DefineScope<HttpMethod, string?>("HTTP {HttpMethod} {Uri}");
 
            private static readonly Action<ILogger, HttpMethod, string?, Exception?> _requestPipelineStart = LoggerMessage.Define<HttpMethod, string?>(
                LogLevel.Information,
                EventIds.PipelineStart,
                "Start processing HTTP request {HttpMethod} {Uri}");
 
            private static readonly Action<ILogger, double, int, Exception?> _requestPipelineEnd = LoggerMessage.Define<double, int>(
                LogLevel.Information,
                EventIds.PipelineEnd,
                "End processing HTTP request after {ElapsedMilliseconds}ms - {StatusCode}");
 
            public static IDisposable? BeginRequestPipelineScope(ILogger logger, HttpRequestMessage request)
            {
                return _beginRequestPipelineScope(logger, request.Method, GetUriString(request.RequestUri));
            }
 
            public static void RequestPipelineStart(ILogger logger, HttpRequestMessage request, Func<string, bool> shouldRedactHeaderValue)
            {
                _requestPipelineStart(logger, request.Method, GetUriString(request.RequestUri), null);
 
                if (logger.IsEnabled(LogLevel.Trace))
                {
                    logger.Log(
                        LogLevel.Trace,
                        EventIds.RequestHeader,
                        new HttpHeadersLogValue(HttpHeadersLogValue.Kind.Request, request.Headers, request.Content?.Headers, shouldRedactHeaderValue),
                        null,
                        (state, ex) => state.ToString());
                }
            }
 
            public static void RequestPipelineEnd(ILogger logger, HttpResponseMessage response, TimeSpan duration, Func<string, bool> shouldRedactHeaderValue)
            {
                _requestPipelineEnd(logger, duration.TotalMilliseconds, (int)response.StatusCode, null);
 
                if (logger.IsEnabled(LogLevel.Trace))
                {
                    logger.Log(
                        LogLevel.Trace,
                        EventIds.ResponseHeader,
                        new HttpHeadersLogValue(HttpHeadersLogValue.Kind.Response, response.Headers, response.Content?.Headers, shouldRedactHeaderValue),
                        null,
                        (state, ex) => state.ToString());
                }
            }
 
            private static string? GetUriString(Uri? requestUri)
            {
                return requestUri?.IsAbsoluteUri == true
                    ? requestUri.AbsoluteUri
                    : requestUri?.ToString();
            }
        }
    }
}