// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Reflection;
using System.Security.Claims;
using System.Threading;
using System.Threading.Channels;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.SignalR.Core;
using Microsoft.AspNetCore.SignalR.Core.Internal;
using Microsoft.AspNetCore.SignalR.Internal;
using Microsoft.AspNetCore.SignalR.Internal.Protocol;
using Microsoft.AspNetCore.Sockets;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Internal;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;

namespace Microsoft.AspNetCore.SignalR
{
    public class HubEndPoint<THub> : IInvocationBinder where THub : Hub
    {
        private readonly Dictionary<string, HubMethodDescriptor> _methods = new Dictionary<string, HubMethodDescriptor>(StringComparer.OrdinalIgnoreCase);

        private readonly HubLifetimeManager<THub> _lifetimeManager;
        private readonly IHubContext<THub> _hubContext;
        private readonly ILoggerFactory _loggerFactory;
        private readonly ILogger<HubEndPoint<THub>> _logger;
        private readonly IServiceScopeFactory _serviceScopeFactory;
        private readonly IHubProtocolResolver _protocolResolver;
        private readonly HubOptions _hubOptions;
        private readonly IUserIdProvider _userIdProvider;

        public HubEndPoint(HubLifetimeManager<THub> lifetimeManager,
                           IHubProtocolResolver protocolResolver,
                           IHubContext<THub> hubContext,
                           IOptions<HubOptions> hubOptions,
                           ILoggerFactory loggerFactory,
                           IServiceScopeFactory serviceScopeFactory,
                           IUserIdProvider userIdProvider)
        {
            _protocolResolver = protocolResolver;
            _lifetimeManager = lifetimeManager;
            _hubContext = hubContext;
            _loggerFactory = loggerFactory;
            _hubOptions = hubOptions.Value;
            _logger = loggerFactory.CreateLogger<HubEndPoint<THub>>();
            _serviceScopeFactory = serviceScopeFactory;
            _userIdProvider = userIdProvider;

            DiscoverHubMethods();
        }

        public async Task OnConnectedAsync(ConnectionContext connection)
        {
            var connectionContext = new HubConnectionContext(connection, _hubOptions.KeepAliveInterval, _loggerFactory);

            if (!await connectionContext.NegotiateAsync(_hubOptions.NegotiateTimeout, _protocolResolver, _userIdProvider))
            {
                return;
            }

            // We don't need to hold this task, it's also held internally and awaited by DisposeAsync.
            _ = connectionContext.StartAsync();

            try
            {
                await _lifetimeManager.OnConnectedAsync(connectionContext);
                await RunHubAsync(connectionContext);
            }
            finally
            {
                await _lifetimeManager.OnDisconnectedAsync(connectionContext);

                await connectionContext.DisposeAsync();
            }
        }


        private async Task RunHubAsync(HubConnectionContext connection)
        {
            await HubOnConnectedAsync(connection);

            try
            {
                await DispatchMessagesAsync(connection);
            }
            catch (Exception ex)
            {
                _logger.ErrorProcessingRequest(ex);
                await HubOnDisconnectedAsync(connection, ex);
                throw;
            }

            await HubOnDisconnectedAsync(connection, null);
        }

        private async Task HubOnConnectedAsync(HubConnectionContext connection)
        {
            try
            {
                using (var scope = _serviceScopeFactory.CreateScope())
                {
                    var hubActivator = scope.ServiceProvider.GetRequiredService<IHubActivator<THub>>();
                    var hub = hubActivator.Create();
                    try
                    {
                        InitializeHub(hub, connection);
                        await hub.OnConnectedAsync();
                    }
                    finally
                    {
                        hubActivator.Release(hub);
                    }
                }
            }
            catch (Exception ex)
            {
                _logger.ErrorInvokingHubMethod("OnConnectedAsync", ex);
                throw;
            }
        }

        private async Task HubOnDisconnectedAsync(HubConnectionContext connection, Exception exception)
        {
            try
            {
                // We wait on abort to complete, this is so that we can guarantee that all callbacks have fired
                // before OnDisconnectedAsync

                try
                {
                    // Ensure the connection is aborted before firing disconnect
                    await connection.AbortAsync();
                }
                catch (Exception ex)
                {
                    _logger.AbortFailed(ex);
                }

                using (var scope = _serviceScopeFactory.CreateScope())
                {
                    var hubActivator = scope.ServiceProvider.GetRequiredService<IHubActivator<THub>>();
                    var hub = hubActivator.Create();
                    try
                    {
                        InitializeHub(hub, connection);
                        await hub.OnDisconnectedAsync(exception);
                    }
                    finally
                    {
                        hubActivator.Release(hub);
                    }
                }
            }
            catch (Exception ex)
            {
                _logger.ErrorInvokingHubMethod("OnDisconnectedAsync", ex);
                throw;
            }
        }

        private async Task DispatchMessagesAsync(HubConnectionContext connection)
        {
            // Since we dispatch multiple hub invocations in parallel, we need a way to communicate failure back to the main processing loop.
            // This is done by aborting the connection.

            try
            {
                while (await connection.Input.WaitToReadAsync(connection.ConnectionAbortedToken))
                {
                    while (connection.Input.TryRead(out var buffer))
                    {
                        if (connection.ProtocolReaderWriter.ReadMessages(buffer, this, out var hubMessages))
                        {
                            foreach (var hubMessage in hubMessages)
                            {
                                switch (hubMessage)
                                {
                                    case InvocationMessage invocationMessage:
                                        _logger.ReceivedHubInvocation(invocationMessage);

                                        // Don't wait on the result of execution, continue processing other
                                        // incoming messages on this connection.
                                        _ = ProcessInvocation(connection, invocationMessage, isStreamedInvocation: false);
                                        break;

                                    case StreamInvocationMessage streamInvocationMessage:
                                        _logger.ReceivedStreamHubInvocation(streamInvocationMessage);

                                        // Don't wait on the result of execution, continue processing other
                                        // incoming messages on this connection.
                                        _ = ProcessInvocation(connection, streamInvocationMessage, isStreamedInvocation: true);
                                        break;

                                    case CancelInvocationMessage cancelInvocationMessage:
                                        // Check if there is an associated active stream and cancel it if it exists.
                                        // The cts will be removed when the streaming method completes executing
                                        if (connection.ActiveRequestCancellationSources.TryGetValue(cancelInvocationMessage.InvocationId, out var cts))
                                        {
                                            _logger.CancelStream(cancelInvocationMessage.InvocationId);
                                            cts.Cancel();
                                        }
                                        else
                                        {
                                            // Stream can be canceled on the server while client is canceling stream.
                                            _logger.UnexpectedCancel();
                                        }
                                        break;

                                    case PingMessage _:
                                        // We don't care about pings
                                        break;

                                    // Other kind of message we weren't expecting
                                    default:
                                        _logger.UnsupportedMessageReceived(hubMessage.GetType().FullName);
                                        throw new NotSupportedException($"Received unsupported message: {hubMessage}");
                                }
                            }
                        }
                    }
                }
            }
            catch (OperationCanceledException)
            {
                // If there's an exception, bubble it to the caller
                connection.AbortException?.Throw();
            }
        }

        private async Task ProcessInvocation(HubConnectionContext connection,
            HubMethodInvocationMessage hubMethodInvocationMessage, bool isStreamedInvocation)
        {
            try
            {
                // If an unexpected exception occurs then we want to kill the entire connection
                // by ending the processing loop
                if (!_methods.TryGetValue(hubMethodInvocationMessage.Target, out var descriptor))
                {
                    // Send an error to the client. Then let the normal completion process occur
                    _logger.UnknownHubMethod(hubMethodInvocationMessage.Target);
                    await SendMessageAsync(connection, CompletionMessage.WithError(
                        hubMethodInvocationMessage.InvocationId, $"Unknown hub method '{hubMethodInvocationMessage.Target}'"));
                }
                else
                {
                    await Invoke(descriptor, connection, hubMethodInvocationMessage, isStreamedInvocation);
                }
            }
            catch (Exception ex)
            {
                // Abort the entire connection if the invocation fails in an unexpected way
                connection.Abort(ex);
            }
        }

        private async Task SendMessageAsync(HubConnectionContext connection, HubMessage hubMessage)
        {
            while (await connection.Output.Writer.WaitToWriteAsync())
            {
                if (connection.Output.Writer.TryWrite(hubMessage))
                {
                    return;
                }
            }

            // Output is closed. Cancel this invocation completely
            _logger.OutboundChannelClosed();
            throw new OperationCanceledException("Outbound channel was closed while trying to write hub message");
        }

        private async Task Invoke(HubMethodDescriptor descriptor, HubConnectionContext connection,
            HubMethodInvocationMessage hubMethodInvocationMessage, bool isStreamedInvocation)
        {
            var methodExecutor = descriptor.MethodExecutor;

            using (var scope = _serviceScopeFactory.CreateScope())
            {
                if (!await IsHubMethodAuthorized(scope.ServiceProvider, connection.User, descriptor.Policies))
                {
                    _logger.HubMethodNotAuthorized(hubMethodInvocationMessage.Target);
                    await SendInvocationError(hubMethodInvocationMessage, connection,
                        $"Failed to invoke '{hubMethodInvocationMessage.Target}' because user is unauthorized");
                    return;
                }

                if (!await ValidateInvocationMode(methodExecutor.MethodReturnType, isStreamedInvocation, hubMethodInvocationMessage, connection))
                {
                    return;
                }

                var hubActivator = scope.ServiceProvider.GetRequiredService<IHubActivator<THub>>();
                var hub = hubActivator.Create();

                try
                {
                    InitializeHub(hub, connection);

                    var result = await ExecuteHubMethod(methodExecutor, hub, hubMethodInvocationMessage.Arguments);

                    if (isStreamedInvocation)
                    {
                        var enumerator = GetStreamingEnumerator(connection, hubMethodInvocationMessage.InvocationId, methodExecutor, result, methodExecutor.MethodReturnType);
                        _logger.StreamingResult(hubMethodInvocationMessage.InvocationId, methodExecutor.MethodReturnType.FullName);
                        await StreamResultsAsync(hubMethodInvocationMessage.InvocationId, connection, enumerator);
                    }
                    else if (!hubMethodInvocationMessage.NonBlocking)
                    {
                        _logger.SendingResult(hubMethodInvocationMessage.InvocationId, methodExecutor.MethodReturnType.FullName);
                        await SendMessageAsync(connection, CompletionMessage.WithResult(hubMethodInvocationMessage.InvocationId, result));
                    }
                }
                catch (TargetInvocationException ex)
                {
                    _logger.FailedInvokingHubMethod(hubMethodInvocationMessage.Target, ex);
                    await SendInvocationError(hubMethodInvocationMessage, connection, ex.InnerException.Message);
                }
                catch (Exception ex)
                {
                    _logger.FailedInvokingHubMethod(hubMethodInvocationMessage.Target, ex);
                    await SendInvocationError(hubMethodInvocationMessage, connection, ex.Message);
                }
                finally
                {
                    hubActivator.Release(hub);
                }
            }
        }

        private static async Task<object> ExecuteHubMethod(ObjectMethodExecutor methodExecutor, THub hub, object[] arguments)
        {
            // ReadableChannel is awaitable but we don't want to await it.
            if (methodExecutor.IsMethodAsync && !IsChannel(methodExecutor.MethodReturnType, out _))
            {
                if (methodExecutor.MethodReturnType == typeof(Task))
                {
                    await (Task)methodExecutor.Execute(hub, arguments);
                }
                else
                {
                    return await methodExecutor.ExecuteAsync(hub, arguments);
                }
            }
            else
            {
                return methodExecutor.Execute(hub, arguments);
            }

            return null;
        }

        private async Task SendInvocationError(HubMethodInvocationMessage hubMethodInvocationMessage,
            HubConnectionContext connection, string errorMessage)
        {
            if (hubMethodInvocationMessage.NonBlocking)
            {
                return;
            }

            await SendMessageAsync(connection, CompletionMessage.WithError(hubMethodInvocationMessage.InvocationId, errorMessage));
        }

        private void InitializeHub(THub hub, HubConnectionContext connection)
        {
            hub.Clients = new HubCallerClients(_hubContext.Clients, connection.ConnectionId);
            hub.Context = new HubCallerContext(connection);
            hub.Groups = _hubContext.Groups;
        }

        private static bool IsChannel(Type type, out Type payloadType)
        {
            var channelType = type.AllBaseTypes().FirstOrDefault(t => t.IsGenericType && t.GetGenericTypeDefinition() == typeof(ChannelReader<>));
            if (channelType == null)
            {
                payloadType = null;
                return false;
            }
            else
            {
                payloadType = channelType.GetGenericArguments()[0];
                return true;
            }
        }

        private async Task StreamResultsAsync(string invocationId, HubConnectionContext connection, IAsyncEnumerator<object> enumerator)
        {
            string error = null;

            try
            {
                while (await enumerator.MoveNextAsync())
                {
                    // Send the stream item
                    await SendMessageAsync(connection, new StreamItemMessage(invocationId, enumerator.Current));
                }
            }
            catch (Exception ex)
            {
                // If the streaming method was canceled we don't want to send a HubException message - this is not an error case
                if (!(ex is OperationCanceledException && connection.ActiveRequestCancellationSources.TryGetValue(invocationId, out var cts)
                    && cts.IsCancellationRequested))
                {
                    error = ex.Message;
                }
            }
            finally
            {
                await SendMessageAsync(connection, new CompletionMessage(invocationId, error: error, result: null, hasResult: false));

                if (connection.ActiveRequestCancellationSources.TryRemove(invocationId, out var cts))
                {
                    cts.Dispose();
                }
            }
        }

        private async Task<bool> ValidateInvocationMode(Type resultType, bool isStreamedInvocation,
            HubMethodInvocationMessage hubMethodInvocationMessage, HubConnectionContext connection)
        {
            var isStreamedResult = IsStreamed(resultType);
            if (isStreamedResult && !isStreamedInvocation)
            {
                if (!hubMethodInvocationMessage.NonBlocking)
                {
                    _logger.StreamingMethodCalledWithInvoke(hubMethodInvocationMessage);
                    await SendMessageAsync(connection, CompletionMessage.WithError(hubMethodInvocationMessage.InvocationId,
                        $"The client attempted to invoke the streaming '{hubMethodInvocationMessage.Target}' method in a non-streaming fashion."));
                }

                return false;
            }

            if (!isStreamedResult && isStreamedInvocation)
            {
                _logger.NonStreamingMethodCalledWithStream(hubMethodInvocationMessage);
                await SendMessageAsync(connection, CompletionMessage.WithError(hubMethodInvocationMessage.InvocationId,
                    $"The client attempted to invoke the non-streaming '{hubMethodInvocationMessage.Target}' method in a streaming fashion."));

                return false;
            }

            return true;
        }

        private static bool IsStreamed(Type resultType)
        {
            var observableInterface = IsIObservable(resultType) ?
                resultType :
                resultType.GetInterfaces().FirstOrDefault(IsIObservable);

            if (observableInterface != null)
            {
                return true;
            }

            if (IsChannel(resultType, out _))
            {
                return true;
            }

            return false;
        }

        private IAsyncEnumerator<object> GetStreamingEnumerator(HubConnectionContext connection, string invocationId, ObjectMethodExecutor methodExecutor, object result, Type resultType)
        {
            if (result != null)
            {
                var observableInterface = IsIObservable(resultType) ?
                    resultType :
                    resultType.GetInterfaces().FirstOrDefault(IsIObservable);
                if (observableInterface != null)
                {
                    return AsyncEnumeratorAdapters.FromObservable(result, observableInterface, CreateCancellation());
                }

                if (IsChannel(resultType, out var payloadType))
                {
                    return AsyncEnumeratorAdapters.FromChannel(result, payloadType, CreateCancellation());
                }
            }

            _logger.InvalidReturnValueFromStreamingMethod(methodExecutor.MethodInfo.Name);
            throw new InvalidOperationException($"The value returned by the streaming method '{methodExecutor.MethodInfo.Name}' is null, does not implement the IObservable<> interface or is not a ReadableChannel<>.");

            CancellationToken CreateCancellation()
            {
                var streamCts = new CancellationTokenSource();
                connection.ActiveRequestCancellationSources.TryAdd(invocationId, streamCts);
                return CancellationTokenSource.CreateLinkedTokenSource(connection.ConnectionAbortedToken, streamCts.Token).Token;
            }
        }

        private static bool IsIObservable(Type iface)
        {
            return iface.IsGenericType && iface.GetGenericTypeDefinition() == typeof(IObservable<>);
        }

        private void DiscoverHubMethods()
        {
            var hubType = typeof(THub);
            var hubTypeInfo = hubType.GetTypeInfo();

            foreach (var methodInfo in HubReflectionHelper.GetHubMethods(hubType))
            {
                var methodName =
                    methodInfo.GetCustomAttribute<HubMethodNameAttribute>()?.Name ??
                    methodInfo.Name;

                if (_methods.ContainsKey(methodName))
                {
                    throw new NotSupportedException($"Duplicate definitions of '{methodName}'. Overloading is not supported.");
                }

                var executor = ObjectMethodExecutor.Create(methodInfo, hubTypeInfo);
                var authorizeAttributes = methodInfo.GetCustomAttributes<AuthorizeAttribute>(inherit: true);
                _methods[methodName] = new HubMethodDescriptor(executor, authorizeAttributes);

                _logger.HubMethodBound(methodName);
            }
        }

        private async Task<bool> IsHubMethodAuthorized(IServiceProvider provider, ClaimsPrincipal principal, IList<IAuthorizeData> policies)
        {
            // If there are no policies we don't need to run auth
            if (!policies.Any())
            {
                return true;
            }

            var authService = provider.GetRequiredService<IAuthorizationService>();
            var policyProvider = provider.GetRequiredService<IAuthorizationPolicyProvider>();

            var authorizePolicy = await AuthorizationPolicy.CombineAsync(policyProvider, policies);
            // AuthorizationPolicy.CombineAsync only returns null if there are no policies and we check that above
            Debug.Assert(authorizePolicy != null);

            var authorizationResult = await authService.AuthorizeAsync(principal, authorizePolicy);
            // Only check authorization success, challenge or forbid wouldn't make sense from a hub method invocation
            return authorizationResult.Succeeded;
        }

        Type IInvocationBinder.GetReturnType(string invocationId)
        {
            return typeof(object);
        }

        Type[] IInvocationBinder.GetParameterTypes(string methodName)
        {
            HubMethodDescriptor descriptor;
            if (!_methods.TryGetValue(methodName, out descriptor))
            {
                return Type.EmptyTypes;
            }
            return descriptor.ParameterTypes;
        }

        // REVIEW: We can decide to move this out of here if we want pluggable hub discovery
        private class HubMethodDescriptor
        {
            public HubMethodDescriptor(ObjectMethodExecutor methodExecutor, IEnumerable<IAuthorizeData> policies)
            {
                MethodExecutor = methodExecutor;
                ParameterTypes = methodExecutor.MethodParameters.Select(p => p.ParameterType).ToArray();
                Policies = policies.ToArray();
            }

            public ObjectMethodExecutor MethodExecutor { get; }

            public Type[] ParameterTypes { get; }

            public IList<IAuthorizeData> Policies { get; }
        }
    }
}