// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Collections.Concurrent;
using System.Diagnostics.CodeAnalysis;
using System.Linq;
using Microsoft.AspNetCore.Components.RenderTree;
using Microsoft.AspNetCore.Components.Web;
using Microsoft.AspNetCore.SignalR;
using Microsoft.Extensions.Internal;
using Microsoft.Extensions.Logging;
using static Microsoft.AspNetCore.Internal.LinkerFlags;

namespace Microsoft.AspNetCore.Components.Server.Circuits;

#pragma warning disable CA1852 // Seal internal types
internal partial class RemoteRenderer : WebRenderer
#pragma warning restore CA1852 // Seal internal types
{
    private static readonly Task CanceledTask = Task.FromCanceled(new CancellationToken(canceled: true));

    private readonly CircuitClientProxy _client;
    private readonly CircuitOptions _options;
    private readonly IServerComponentDeserializer _serverComponentDeserializer;
    private readonly ILogger _logger;
    internal readonly ConcurrentQueue<UnacknowledgedRenderBatch> _unacknowledgedRenderBatches = new ConcurrentQueue<UnacknowledgedRenderBatch>();
    private long _nextRenderId = 1;
    private bool _disposing;

    /// <summary>
    /// Notifies when a rendering exception occurred.
    /// </summary>
    public event EventHandler<Exception>? UnhandledException;

    /// <summary>
    /// Creates a new <see cref="RemoteRenderer"/>.
    /// </summary>
    public RemoteRenderer(
        IServiceProvider serviceProvider,
        ILoggerFactory loggerFactory,
        CircuitOptions options,
        CircuitClientProxy client,
        IServerComponentDeserializer serverComponentDeserializer,
        ILogger logger,
        RemoteJSRuntime jsRuntime,
        CircuitJSComponentInterop jsComponentInterop)
        : base(serviceProvider, loggerFactory, jsRuntime.ReadJsonSerializerOptions(), jsComponentInterop)
    {
        _client = client;
        _options = options;
        _serverComponentDeserializer = serverComponentDeserializer;
        _logger = logger;

        ElementReferenceContext = jsRuntime.ElementReferenceContext;
    }

    public override Dispatcher Dispatcher { get; } = Dispatcher.CreateDefault();

    public Task AddComponentAsync(Type componentType, ParameterView parameters, string domElementSelector)
    {
        var componentId = AddRootComponent(componentType, domElementSelector);
        return RenderRootComponentAsync(componentId, parameters);
    }

    protected override int GetWebRendererId() => (int)WebRendererId.Server;

    protected override void AttachRootComponentToBrowser(int componentId, string domElementSelector)
    {
        var attachComponentTask = _client.SendAsync("JS.AttachComponent", componentId, domElementSelector);
        _ = CaptureAsyncExceptions(attachComponentTask);
    }

    internal Type GetExistingComponentType(int componentId) =>
        GetComponentState(componentId).Component.GetType();

    protected override void ProcessPendingRender()
    {
        if (_unacknowledgedRenderBatches.Count >= _options.MaxBufferedUnacknowledgedRenderBatches)
        {
            // If we got here it means we are at max capacity, so we don't want to actually process the queue,
            // as we have a client that is not acknowledging render batches fast enough (something we consider needs
            // to be fast).
            // The result is something as follows:
            // Lets imagine an extreme case where the server produces a new batch every millisecond.
            // Lets say the client is able to ACK a batch every 100 milliseconds.
            // When the app starts the client might see the sequence 0->(MaxUnacknowledgedRenderBatches-1) and then
            // after 100 milliseconds it sees it jump to 1xx, then to 2xx where xx is something between {0..99} the
            // reason for this is that the server slows down rendering new batches to as fast as the client can consume
            // them.
            // Similarly, if a client were to send events at a faster pace than the server can consume them, the server
            // would still process the events, but would not produce new renders until it gets an ack that frees up space
            // for a new render.
            // We should never see UnacknowledgedRenderBatches.Count > _options.MaxBufferedUnacknowledgedRenderBatches

            // But if we do, it's safer to simply disable the rendering in that case too instead of allowing batches to
            Log.FullUnacknowledgedRenderBatchesQueue(_logger);

            return;
        }

        base.ProcessPendingRender();
    }

    /// <inheritdoc />
    protected override void HandleException(Exception exception)
    {
        if (exception is AggregateException aggregateException)
        {
            foreach (var innerException in aggregateException.Flatten().InnerExceptions)
            {
                Log.UnhandledExceptionRenderingComponent(_logger, innerException);
            }
        }
        else
        {
            Log.UnhandledExceptionRenderingComponent(_logger, exception);
        }

        UnhandledException?.Invoke(this, exception);
    }

    /// <inheritdoc />
    protected override void Dispose(bool disposing)
    {
        _disposing = true;
        while (_unacknowledgedRenderBatches.TryDequeue(out var entry))
        {
            entry.CompletionSource.TrySetCanceled();
            entry.Data.Dispose();
        }
        base.Dispose(true);
    }

    /// <inheritdoc />
    protected override Task UpdateDisplayAsync(in Microsoft.AspNetCore.Components.RenderTree.RenderBatch batch)
    {
        if (_disposing)
        {
            // We are being disposed, so do no work.
            return CanceledTask;
        }

        // Note that we have to capture the data as a byte[] synchronously here, because
        // SignalR's SendAsync can wait an arbitrary duration before serializing the params.
        // The RenderBatch buffer will get reused by subsequent renders, so we need to
        // snapshot its contents now.
        var arrayBuilder = new ArrayBuilder<byte>(2048);
        using var memoryStream = new ArrayBuilderMemoryStream(arrayBuilder);
        UnacknowledgedRenderBatch pendingRender;
        try
        {
            using (var renderBatchWriter = new RenderBatchWriter(memoryStream, false))
            {
                renderBatchWriter.Write(in batch);
            }

            var renderId = Interlocked.Increment(ref _nextRenderId);

            pendingRender = new UnacknowledgedRenderBatch(
                renderId,
                arrayBuilder,
                new TaskCompletionSource(),
                ValueStopwatch.StartNew());

            // Buffer the rendered batches no matter what. We'll send it down immediately when the client
            // is connected or right after the client reconnects.

            _unacknowledgedRenderBatches.Enqueue(pendingRender);
        }
        catch
        {
            // if we throw prior to queueing the write, dispose the builder.
            arrayBuilder.Dispose();
            throw;
        }

        // Fire and forget the initial send for this batch (if connected). Otherwise it will be sent
        // as soon as the client reconnects.
        var _ = WriteBatchBytesAsync(pendingRender);

        return pendingRender.CompletionSource.Task;
    }

    public Task ProcessBufferedRenderBatches()
    {
        // All the batches are sent in order based on the fact that SignalR
        // provides ordering for the underlying messages and that the batches
        // are always in order.
        return Task.WhenAll(_unacknowledgedRenderBatches.Select(WriteBatchBytesAsync));
    }

    private async Task WriteBatchBytesAsync(UnacknowledgedRenderBatch pending)
    {
        // Send the render batch to the client
        // If the "send" operation fails (synchronously or asynchronously) or the client
        // gets disconnected simply give up. This likely means that
        // the circuit went offline while sending the data, so simply wait until the
        // client reconnects back or the circuit gets evicted because it stayed
        // disconnected for too long.

        try
        {
            if (!_client.Connected)
            {
                // If we detect that the client is offline. Simply stop trying to send the payload.
                // When the client reconnects we'll resend it.
                return;
            }

            Log.BeginUpdateDisplayAsync(_logger, pending.BatchId, pending.Data.Count, _client.ConnectionId);
            var segment = new ArraySegment<byte>(pending.Data.Buffer, 0, pending.Data.Count);
            await _client.SendAsync("JS.RenderBatch", pending.BatchId, segment);
        }
        catch (Exception e)
        {
            Log.SendBatchDataFailed(_logger, e);
        }

        // We don't have to remove the entry from the list of pending batches if we fail to send it or the client fails to
        // acknowledge that it received it. We simply keep it in the queue until we receive another ack from the client for
        // a later batch (clientBatchId > thisBatchId) or the circuit becomes disconnected and we ultimately get evicted and
        // disposed.
    }

    public Task OnRenderCompletedAsync(long incomingBatchId, string? errorMessageOrNull)
    {
        if (_disposing)
        {
            // Disposing so don't do work.
            return Task.CompletedTask;
        }

        // When clients send acks we know for sure they received and applied the batch.
        // We send batches right away, and hold them in memory until we receive an ACK.
        // If one or more client ACKs get lost (e.g., with long polling, client->server delivery is not guaranteed)
        // we might receive an ack for a higher batch.
        // We confirm all previous batches at that point (because receiving an ack is guarantee
        // from the client that it has received and successfully applied all batches up to that point).

        // If receive an ack for a previously acknowledged batch, its an error, as the messages are
        // guaranteed to be delivered in order, so a message for a render batch of 2 will never arrive
        // after a message for a render batch for 3.
        // If that were to be the case, it would just be enough to relax the checks here and simply skip
        // the message.

        // A batch might get lost when we send it to the client, because the client might disconnect before receiving and processing it.
        // In this case, once it reconnects the server will re-send any unacknowledged batches, some of which the
        // client might have received and even believe it did send back an acknowledgement for. The client handles
        // those by re-acknowledging.

        // Even though we're not on the renderer sync context here, it's safe to assume ordered execution of the following
        // line (i.e., matching the order in which we received batch completion messages) based on the fact that SignalR
        // synchronizes calls to hub methods. That is, it won't issue more than one call to this method from the same hub
        // at the same time on different threads.

        if (!_unacknowledgedRenderBatches.TryPeek(out var nextUnacknowledgedBatch) || incomingBatchId < nextUnacknowledgedBatch.BatchId)
        {
            Log.ReceivedDuplicateBatchAck(_logger, incomingBatchId);
            return Task.CompletedTask;
        }
        else
        {
            var lastBatchId = nextUnacknowledgedBatch.BatchId;
            // Order is important here so that we don't prematurely dequeue the last nextUnacknowledgedBatch
            while (_unacknowledgedRenderBatches.TryPeek(out nextUnacknowledgedBatch) && nextUnacknowledgedBatch.BatchId <= incomingBatchId)
            {
                lastBatchId = nextUnacknowledgedBatch.BatchId;
                // At this point the queue is definitely not full, we have at least emptied one slot, so we allow a further
                // full queue log entry the next time it fills up.
                _unacknowledgedRenderBatches.TryDequeue(out _);
                ProcessPendingBatch(errorMessageOrNull, nextUnacknowledgedBatch);
            }

            if (lastBatchId < incomingBatchId)
            {
                // This exception is due to a bad client input, so we mark it as such to prevent logging it as a warning and
                // flooding the logs with warnings.
                throw new InvalidOperationException($"Received an acknowledgement for batch with id '{incomingBatchId}' when the last batch produced was '{lastBatchId}'.");
            }

            // Normally we will not have pending renders, but it might happen that we reached the limit of
            // available buffered renders and new renders got queued.
            // Invoke ProcessBufferedRenderRequests so that we might produce any additional batch that is
            // missing.

            // We return the task in here, but the caller doesn't await it.
            return Dispatcher.InvokeAsync(() =>
            {
                // Now we're on the sync context, check again whether we got disposed since this
                // work item was queued. If so there's nothing to do.
                if (!_disposing)
                {
                    ProcessPendingRender();
                }
            });
        }
    }

    protected override IComponent ResolveComponentForRenderMode([DynamicallyAccessedMembers(Component)] Type componentType, int? parentComponentId, IComponentActivator componentActivator, IComponentRenderMode renderMode)
        => renderMode switch
        {
            InteractiveServerRenderMode or InteractiveAutoRenderMode => componentActivator.CreateInstance(componentType),
            _ => throw new NotSupportedException($"Cannot create a component of type '{componentType}' because its render mode '{renderMode}' is not supported by interactive server-side rendering."),
        };

    private void ProcessPendingBatch(string? errorMessageOrNull, UnacknowledgedRenderBatch entry)
    {
        var elapsedTime = entry.ValueStopwatch.GetElapsedTime();
        if (errorMessageOrNull == null)
        {
            Log.CompletingBatchWithoutError(_logger, entry.BatchId, elapsedTime);
        }
        else
        {
            Log.CompletingBatchWithError(_logger, entry.BatchId, errorMessageOrNull, elapsedTime);
        }

        entry.Data.Dispose();
        CompleteRender(entry.CompletionSource, errorMessageOrNull);
    }

    private static void CompleteRender(TaskCompletionSource pendingRenderInfo, string? errorMessageOrNull)
    {
        if (errorMessageOrNull == null)
        {
            pendingRenderInfo.TrySetResult();
        }
        else
        {
            pendingRenderInfo.TrySetException(new InvalidOperationException(errorMessageOrNull));
        }
    }

    internal readonly struct UnacknowledgedRenderBatch
    {
        public UnacknowledgedRenderBatch(long batchId, ArrayBuilder<byte> data, TaskCompletionSource completionSource, ValueStopwatch valueStopwatch)
        {
            BatchId = batchId;
            Data = data;
            CompletionSource = completionSource;
            ValueStopwatch = valueStopwatch;
        }

        public long BatchId { get; }
        public ArrayBuilder<byte> Data { get; }
        public TaskCompletionSource CompletionSource { get; }
        public ValueStopwatch ValueStopwatch { get; }
    }

    private async Task CaptureAsyncExceptions(Task task)
    {
        try
        {
            await task;
        }
        catch (Exception exception)
        {
            UnhandledException?.Invoke(this, exception);
        }
    }

    private static partial class Log
    {
        [LoggerMessage(100, LogLevel.Warning, "Unhandled exception rendering component: {Message}", EventName = "ExceptionRenderingComponent")]
        private static partial void UnhandledExceptionRenderingComponent(ILogger logger, string message, Exception exception);

        public static void UnhandledExceptionRenderingComponent(ILogger logger, Exception exception)
            => UnhandledExceptionRenderingComponent(logger, exception.Message, exception);

        [LoggerMessage(101, LogLevel.Debug, "Sending render batch {BatchId} of size {DataLength} bytes to client {ConnectionId}.", EventName = "BeginUpdateDisplayAsync")]
        public static partial void BeginUpdateDisplayAsync(ILogger logger, long batchId, int dataLength, string connectionId);

        [LoggerMessage(102, LogLevel.Debug, "Buffering remote render because the client on connection {ConnectionId} is disconnected.", EventName = "SkipUpdateDisplayAsync")]
        public static partial void BufferingRenderDisconnectedClient(ILogger logger, string connectionId);

        [LoggerMessage(103, LogLevel.Information, "Sending data for batch failed: {Message}", EventName = "SendBatchDataFailed")]
        private static partial void SendBatchDataFailed(ILogger logger, string message, Exception exception);

        public static void SendBatchDataFailed(ILogger logger, Exception exception)
            => SendBatchDataFailed(logger, exception.Message, exception);

        [LoggerMessage(104, LogLevel.Debug, "Completing batch {BatchId} with error: {ErrorMessage} in {ElapsedMilliseconds}ms.", EventName = "CompletingBatchWithError")]
        private static partial void CompletingBatchWithError(ILogger logger, long batchId, string errorMessage, double elapsedMilliseconds);

        public static void CompletingBatchWithError(ILogger logger, long batchId, string errorMessage, TimeSpan elapsedTime)
            => CompletingBatchWithError(logger, batchId, errorMessage, elapsedTime.TotalMilliseconds);

        [LoggerMessage(105, LogLevel.Debug, "Completing batch {BatchId} without error in {ElapsedMilliseconds}ms.", EventName = "CompletingBatchWithoutError")]
        private static partial void CompletingBatchWithoutError(ILogger logger, long batchId, double elapsedMilliseconds);

        public static void CompletingBatchWithoutError(ILogger logger, long batchId, TimeSpan elapsedTime)
            => CompletingBatchWithoutError(logger, batchId, elapsedTime.TotalMilliseconds);

        [LoggerMessage(106, LogLevel.Debug, "Received a duplicate ACK for batch id '{IncomingBatchId}'.", EventName = "ReceivedDuplicateBatchAcknowledgement")]
        public static partial void ReceivedDuplicateBatchAck(ILogger logger, long incomingBatchId);

        [LoggerMessage(107, LogLevel.Debug, "The queue of unacknowledged render batches is full.", EventName = "FullUnacknowledgedRenderBatchesQueue")]
        public static partial void FullUnacknowledgedRenderBatchesQueue(ILogger logger);
    }
}

internal readonly struct PendingRender
{
    public PendingRender(int componentId, RenderFragment renderFragment)
    {
        ComponentId = componentId;
        RenderFragment = renderFragment;
    }

    public int ComponentId { get; }
    public RenderFragment RenderFragment { get; }
}
