// 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.Buffers;
using System.Buffers.Binary;
using System.Collections.Generic;
using System.IO.Pipelines;
using System.Net.Http.HPack;
using Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http2;

namespace Microsoft.AspNetCore.Testing
{
    internal static class PipeWriterHttp2FrameExtensions
    {
        public static void WriteSettings(this PipeWriter writer, Http2PeerSettings clientSettings)
        {
            var frame = new Http2Frame();
            frame.PrepareSettings(Http2SettingsFrameFlags.NONE);
            var settings = clientSettings.GetNonProtocolDefaults();
            var payload = new byte[settings.Count * Http2FrameReader.SettingSize];
            frame.PayloadLength = payload.Length;
            Http2FrameWriter.WriteSettings(settings, payload);
            Http2FrameWriter.WriteHeader(frame, writer);
            writer.Write(payload);
        }

        public static void WriteStartStream(this PipeWriter writer, int streamId, Http2HeadersEnumerator headers, byte[] headerEncodingBuffer, bool endStream, Http2Frame frame = null)
        {
            frame ??= new Http2Frame();
            frame.PrepareHeaders(Http2HeadersFrameFlags.NONE, streamId);

            var buffer = headerEncodingBuffer.AsSpan();
            var done = HPackHeaderWriter.BeginEncodeHeaders(headers, buffer, out var length);
            frame.PayloadLength = length;

            if (done)
            {
                frame.HeadersFlags = Http2HeadersFrameFlags.END_HEADERS;
            }

            if (endStream)
            {
                frame.HeadersFlags |= Http2HeadersFrameFlags.END_STREAM;
            }

            Http2FrameWriter.WriteHeader(frame, writer);
            writer.Write(buffer.Slice(0, length));

            while (!done)
            {
                frame.PrepareContinuation(Http2ContinuationFrameFlags.NONE, streamId);

                done = HPackHeaderWriter.ContinueEncodeHeaders(headers, buffer, out length);
                frame.PayloadLength = length;

                if (done)
                {
                    frame.ContinuationFlags = Http2ContinuationFrameFlags.END_HEADERS;
                }

                Http2FrameWriter.WriteHeader(frame, writer);
                writer.Write(buffer.Slice(0, length));
            }
        }

        public static void WriteStartStream(this PipeWriter writer, int streamId, Span<byte> headerData, bool endStream, Http2Frame frame = null)
        {
            frame ??= new Http2Frame();
            frame.PrepareHeaders(Http2HeadersFrameFlags.NONE, streamId);
            frame.PayloadLength = headerData.Length;
            frame.HeadersFlags = Http2HeadersFrameFlags.END_HEADERS;

            if (endStream)
            {
                frame.HeadersFlags |= Http2HeadersFrameFlags.END_STREAM;
            }

            Http2FrameWriter.WriteHeader(frame, writer);
            writer.Write(headerData);
        }

        public static void WriteData(this PipeWriter writer, int streamId, Memory<byte> data, bool endStream, Http2Frame frame = null)
        {
            frame ??= new Http2Frame();
            frame.PrepareData(streamId);
            frame.PayloadLength = data.Length;
            frame.DataFlags = endStream ? Http2DataFrameFlags.END_STREAM : Http2DataFrameFlags.NONE;

            Http2FrameWriter.WriteHeader(frame, writer);
            writer.Write(data.Span);
        }

        public static void WriteWindowUpdateAsync(this PipeWriter writer, int streamId, int sizeIncrement, Http2Frame frame = null)
        {
            frame ??= new Http2Frame();
            frame.PrepareWindowUpdate(streamId, sizeIncrement);
            Http2FrameWriter.WriteHeader(frame, writer);
            BinaryPrimitives.WriteUInt32BigEndian(writer.GetSpan(4), (uint)sizeIncrement);
            writer.Advance(4);
        }
    }
}