﻿/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

namespace DotPulsar.Tests.Internal;

using DotPulsar.Internal;
using FluentAssertions;
using System;
using System.Buffers;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
using Xunit;

public class ChunkingPipelineTests
{
    [Fact]
    public async Task Send_GivenSequenceIsUnderChunkSize_ShouldWriteArrayOnce()
    {
        //Arrange
        var a = new byte[] { 0x00, 0x01, 0x02, 0x03 };
        var b = new byte[] { 0x04, 0x05, 0x06, 0x07 };
        var sequence = new SequenceBuilder<byte>().Append(a).Append(b).Build();
        var mockStream = new MockStream();
        var sut = new ChunkingPipeline(mockStream, 9);

        //Act
        await sut.Send(sequence);

        //Assert
        var expected = sequence.ToArray();
        var actual = mockStream.GetReadOnlySequence();
        actual.ToArray().Should().Equal(expected);
        actual.IsSingleSegment.Should().BeTrue();
    }

    [Theory]
    [InlineData(4, 6, 3, 4, 6, 3)]     // No segments can be merged
    [InlineData(1, 6, 4, 7, 4, null)]  // Can merge a and b
    [InlineData(4, 6, 1, 4, 7, null)]  // Can merge b and c
    public async Task Send_GivenSequenceIsOverChunkSize_ShouldWriteMultipleArrays(int length1, int length2, int length3, int expected1, int expected2, int? expected3)
    {
        //Arrange
        var a = Enumerable.Range(0, length1).Select(i => (byte) i).ToArray();
        var b = Enumerable.Range(length1, length2).Select(i => (byte) i).ToArray();
        var c = Enumerable.Range(length1 + length2, length3).Select(i => (byte) i).ToArray();
        var sequence = new SequenceBuilder<byte>().Append(a).Append(b).Append(c).Build();
        var mockStream = new MockStream();
        var sut = new ChunkingPipeline(mockStream, 8);

        //Act
        await sut.Send(sequence);

        //Assert
        var expected = sequence.ToArray();
        var actual = mockStream.GetReadOnlySequence();
        actual.ToArray().Should().Equal(expected);
        GetNumberOfSegments(actual).Should().Be(expected3.HasValue ? 3 : 2);

        var segmentNumber = 0;
        foreach (var segment in actual)
        {
            switch (segmentNumber)
            {
                case 0:
                    segment.Length.Should().Be(expected1);
                    break;
                case 1:
                    segment.Length.Should().Be(expected2);
                    break;
                case 2:
                    expected3.Should().NotBeNull();
                    segment.Length.Should().Be(expected3);
                    break;
            }
            ++segmentNumber;
        }
    }

    private static int GetNumberOfSegments(ReadOnlySequence<byte> sequence)
    {
        var numberOfSegments = 0;
        var enumerator = sequence.GetEnumerator();
        while (enumerator.MoveNext())
            ++numberOfSegments;
        return numberOfSegments;
    }

    private class MockStream : Stream
    {
        private readonly SequenceBuilder<byte> _builder;

        public MockStream() => _builder = new SequenceBuilder<byte>();
        public override bool CanRead => throw new NotImplementedException();
        public override bool CanSeek => throw new NotImplementedException();
        public override bool CanWrite => true;
        public override long Length => throw new NotImplementedException();
        public override long Position { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
        public override void Flush() => throw new NotImplementedException();
        public override int Read(byte[] buffer, int offset, int count) => throw new NotImplementedException();
        public override long Seek(long offset, SeekOrigin origin) => throw new NotImplementedException();
        public override void SetLength(long value) => throw new NotImplementedException();
        public override void Write(byte[] buffer, int offset, int count) => _builder.Append(new ReadOnlyMemory<byte>(buffer, offset, count));
        public ReadOnlySequence<byte> GetReadOnlySequence() => _builder.Build();
    }
}