using System.Buffers.Binary;
using Google.Protobuf;
using MxGateway.Contracts;
using MxGateway.Contracts.Proto;
using MxGateway.Server.Workers;

namespace MxGateway.Tests.Gateway.Workers;

public sealed class WorkerFrameProtocolTests
{
    private const string SessionId = "session-1";

    [Fact]
    public async Task WriteAndReadAsync_WithValidEnvelope_RoundTripsFrame()
    {
        WorkerFrameProtocolOptions options = new(SessionId);
        await using MemoryStream stream = new();
        WorkerEnvelope original = CreateEnvelope();

        WorkerFrameWriter writer = new(stream, options);
        await writer.WriteAsync(original);
        stream.Position = 0;

        WorkerFrameReader reader = new(stream, options);
        WorkerEnvelope parsed = await reader.ReadAsync();

        Assert.Equal(original, parsed);
    }

    [Fact]
    public async Task ReadAsync_WithPartialReads_ReassemblesFrame()
    {
        WorkerFrameProtocolOptions options = new(SessionId);
        WorkerEnvelope original = CreateEnvelope();
        byte[] frame = CreateFrame(original);
        await using ChunkedReadStream stream = new(frame, chunkSize: 2);

        WorkerFrameReader reader = new(stream, options);
        WorkerEnvelope parsed = await reader.ReadAsync();

        Assert.Equal(original, parsed);
        Assert.True(stream.ReadCallCount > 2);
    }

    [Fact]
    public async Task ReadAsync_WithZeroLengthFrame_ThrowsMalformedLength()
    {
        WorkerFrameProtocolOptions options = new(SessionId);
        await using MemoryStream stream = new(new byte[sizeof(uint)]);

        WorkerFrameReader reader = new(stream, options);
        WorkerFrameProtocolException exception =
            await Assert.ThrowsAsync<WorkerFrameProtocolException>(
                async () => await reader.ReadAsync());

        Assert.Equal(WorkerFrameProtocolErrorCode.MalformedLength, exception.ErrorCode);
    }

    [Fact]
    public async Task ReadAsync_WithOversizedLength_ThrowsBeforePayloadAllocation()
    {
        WorkerFrameProtocolOptions options = new(SessionId, GatewayContractInfo.WorkerProtocolVersion, maxMessageBytes: 16);
        byte[] lengthPrefix = new byte[sizeof(uint)];
        BinaryPrimitives.WriteUInt32LittleEndian(lengthPrefix, 17);
        await using MemoryStream stream = new(lengthPrefix);

        WorkerFrameReader reader = new(stream, options);
        WorkerFrameProtocolException exception =
            await Assert.ThrowsAsync<WorkerFrameProtocolException>(
                async () => await reader.ReadAsync());

        Assert.Equal(WorkerFrameProtocolErrorCode.MessageTooLarge, exception.ErrorCode);
    }

    [Fact]
    public async Task ReadAsync_WithWrongProtocolVersion_ThrowsProtocolVersionMismatch()
    {
        WorkerFrameProtocolOptions options = new(SessionId);
        WorkerEnvelope envelope = CreateEnvelope();
        envelope.ProtocolVersion++;
        await using MemoryStream stream = new(CreateFrame(envelope));

        WorkerFrameReader reader = new(stream, options);
        WorkerFrameProtocolException exception =
            await Assert.ThrowsAsync<WorkerFrameProtocolException>(
                async () => await reader.ReadAsync());

        Assert.Equal(WorkerFrameProtocolErrorCode.ProtocolVersionMismatch, exception.ErrorCode);
    }

    [Fact]
    public async Task ReadAsync_WithWrongSessionId_ThrowsSessionMismatch()
    {
        WorkerFrameProtocolOptions options = new(SessionId);
        WorkerEnvelope envelope = CreateEnvelope();
        envelope.SessionId = "different-session";
        await using MemoryStream stream = new(CreateFrame(envelope));

        WorkerFrameReader reader = new(stream, options);
        WorkerFrameProtocolException exception =
            await Assert.ThrowsAsync<WorkerFrameProtocolException>(
                async () => await reader.ReadAsync());

        Assert.Equal(WorkerFrameProtocolErrorCode.SessionMismatch, exception.ErrorCode);
    }

    [Fact]
    public async Task ReadAsync_WithMalformedPayload_ThrowsInvalidEnvelope()
    {
        WorkerFrameProtocolOptions options = new(SessionId);
        byte[] frame = CreateFrame([0x80]);
        await using MemoryStream stream = new(frame);

        WorkerFrameReader reader = new(stream, options);
        WorkerFrameProtocolException exception =
            await Assert.ThrowsAsync<WorkerFrameProtocolException>(
                async () => await reader.ReadAsync());

        Assert.Equal(WorkerFrameProtocolErrorCode.InvalidEnvelope, exception.ErrorCode);
    }

    [Fact]
    public async Task ReadAsync_WithMissingEnvelopeBody_ThrowsInvalidEnvelope()
    {
        WorkerFrameProtocolOptions options = new(SessionId);
        WorkerEnvelope envelope = CreateEnvelope();
        envelope.ClearBody();
        await using MemoryStream stream = new(CreateFrame(envelope));

        WorkerFrameReader reader = new(stream, options);
        WorkerFrameProtocolException exception =
            await Assert.ThrowsAsync<WorkerFrameProtocolException>(
                async () => await reader.ReadAsync());

        Assert.Equal(WorkerFrameProtocolErrorCode.InvalidEnvelope, exception.ErrorCode);
    }

    [Fact]
    public async Task WriteAsync_WithOversizedEnvelope_ThrowsMessageTooLarge()
    {
        WorkerFrameProtocolOptions options = new(SessionId, GatewayContractInfo.WorkerProtocolVersion, maxMessageBytes: 8);
        await using MemoryStream stream = new();

        WorkerFrameWriter writer = new(stream, options);
        WorkerFrameProtocolException exception =
            await Assert.ThrowsAsync<WorkerFrameProtocolException>(
                async () => await writer.WriteAsync(CreateEnvelope()));

        Assert.Equal(WorkerFrameProtocolErrorCode.MessageTooLarge, exception.ErrorCode);
        Assert.Equal(0, stream.Length);
    }

    private static WorkerEnvelope CreateEnvelope()
    {
        return new WorkerEnvelope
        {
            ProtocolVersion = GatewayContractInfo.WorkerProtocolVersion,
            SessionId = SessionId,
            Sequence = 1,
            CorrelationId = "correlation-1",
            WorkerHello = new WorkerHello
            {
                ProtocolVersion = GatewayContractInfo.WorkerProtocolVersion,
                Nonce = "nonce",
                WorkerProcessId = 1234,
                WorkerVersion = "test-worker",
            },
        };
    }

    private static byte[] CreateFrame(IMessage message)
    {
        return CreateFrame(message.ToByteArray());
    }

    private static byte[] CreateFrame(byte[] payload)
    {
        byte[] frame = new byte[sizeof(uint) + payload.Length];
        BinaryPrimitives.WriteUInt32LittleEndian(frame.AsSpan(0, sizeof(uint)), (uint)payload.Length);
        payload.CopyTo(frame.AsSpan(sizeof(uint)));

        return frame;
    }

    private sealed class ChunkedReadStream : MemoryStream
    {
        private readonly int _chunkSize;

        public ChunkedReadStream(
            byte[] buffer,
            int chunkSize)
            : base(buffer)
        {
            _chunkSize = chunkSize;
        }

        public int ReadCallCount { get; private set; }

        public override ValueTask<int> ReadAsync(
            Memory<byte> buffer,
            CancellationToken cancellationToken = default)
        {
            ReadCallCount++;
            int requestedCount = Math.Min(buffer.Length, _chunkSize);

            return base.ReadAsync(buffer[..requestedCount], cancellationToken);
        }
    }
}