// 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.IO;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Server.Kestrel.Internal.Infrastructure;

namespace Microsoft.AspNetCore.Server.Kestrel.Internal.Http
{
    class FrameRequestStream : Stream
    {
        private MessageBody _body;
        private FrameStreamState _state;
        private Exception _error;

        public FrameRequestStream()
        {
            _state = FrameStreamState.Closed;
        }

        public override bool CanRead => true;

        public override bool CanSeek => false;

        public override bool CanWrite => false;

        public override long Length
        {
            get
            {
                throw new NotSupportedException();
            }
        }

        public override long Position
        {
            get
            {
                throw new NotSupportedException();
            }
            set
            {
                throw new NotSupportedException();
            }
        }

        public override void Flush()
        {
            // No-op.
        }

        public override Task FlushAsync(CancellationToken cancellationToken)
        {
            // No-op.
            return TaskUtilities.CompletedTask;
        }

        public override long Seek(long offset, SeekOrigin origin)
        {
            throw new NotSupportedException();
        }

        public override void SetLength(long value)
        {
            throw new NotSupportedException();
        }

        public override int Read(byte[] buffer, int offset, int count)
        {
            // ValueTask uses .GetAwaiter().GetResult() if necessary
            return ReadAsync(buffer, offset, count).Result;
        }

#if NET451
        public override IAsyncResult BeginRead(byte[] buffer, int offset, int count, AsyncCallback callback, object state)
        {
            ValidateState(default(CancellationToken));

            var task = ReadAsync(buffer, offset, count, default(CancellationToken), state);
            if (callback != null)
            {
                task.ContinueWith(t => callback.Invoke(t));
            }
            return task;
        }

        public override int EndRead(IAsyncResult asyncResult)
        {
            return ((Task<int>)asyncResult).GetAwaiter().GetResult();
        }

        private Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken, object state)
        {
            ValidateState(cancellationToken);

            var tcs = new TaskCompletionSource<int>(state);
            var task = _body.ReadAsync(new ArraySegment<byte>(buffer, offset, count), cancellationToken);
            task.AsTask().ContinueWith((task2, state2) =>
            {
                var tcs2 = (TaskCompletionSource<int>)state2;
                if (task2.IsCanceled)
                {
                    tcs2.SetCanceled();
                }
                else if (task2.IsFaulted)
                {
                    tcs2.SetException(task2.Exception);
                }
                else
                {
                    tcs2.SetResult(task2.Result);
                }
            }, tcs, cancellationToken);
            return tcs.Task;
        }
#endif

        public override Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
        {
            var task = ValidateState(cancellationToken);
            if (task == null)
            {
                // Needs .AsTask to match Stream's Async method return types
                return _body.ReadAsync(new ArraySegment<byte>(buffer, offset, count), cancellationToken).AsTask();
            }
            return task;
        }

        public override void Write(byte[] buffer, int offset, int count)
        {
            throw new NotSupportedException();
        }

        public void StartAcceptingReads(MessageBody body)
        {
            // Only start if not aborted
            if (_state == FrameStreamState.Closed)
            {
                _state = FrameStreamState.Open;
                _body = body;
            }
        }

        public void PauseAcceptingReads()
        {
            _state = FrameStreamState.Closed;
        }

        public void ResumeAcceptingReads()
        {
            if (_state == FrameStreamState.Closed)
            {
                _state = FrameStreamState.Open;
            }
        }

        public void StopAcceptingReads()
        {
            // Can't use dispose (or close) as can be disposed too early by user code
            // As exampled in EngineTests.ZeroContentLengthNotSetAutomaticallyForCertainStatusCodes
            _state = FrameStreamState.Closed;
            _body = null;
        }

        public void Abort(Exception error = null)
        {
            // We don't want to throw an ODE until the app func actually completes.
            // If the request is aborted, we throw an TaskCanceledException instead,
            // unless error is not null, in which case we throw it.
            if (_state != FrameStreamState.Closed)
            {
                _state = FrameStreamState.Aborted;
                _error = error;
            }
        }

        private Task<int> ValidateState(CancellationToken cancellationToken)
        {
            switch (_state)
            {
                case FrameStreamState.Open:
                    if (cancellationToken.IsCancellationRequested)
                    {
                        return TaskUtilities.GetCancelledZeroTask(cancellationToken);
                    }
                    break;
                case FrameStreamState.Closed:
                    throw new ObjectDisposedException(nameof(FrameRequestStream));
                case FrameStreamState.Aborted:
                    return _error != null ?
                        TaskUtilities.GetFaultedTask(_error) :
                        TaskUtilities.GetCancelledZeroTask();
            }
            return null;
        }
    }
}