using System.Net;
using ErsatzTV.Infrastructure.Streaming;
using Microsoft.Extensions.Logging;
using NSubstitute;
using NUnit.Framework;
using Shouldly;

namespace ErsatzTV.Infrastructure.Tests.Streaming;

[TestFixture]
public class HttpRemoteStreamProberTests
{
    private const string Url = "http://localhost:8409/media/jellyfin/abc123";

    [Test]
    public async Task Should_Report_Unavailable_On_404_From_The_Media_Server()
    {
        // a media-server 404 arrives after our /media/... endpoint redirected, so the response's
        // final request uri is the media server's, not the probe url
        HttpRemoteStreamProber prober = ProberReturning(
            HttpStatusCode.NotFound,
            finalUri: "http://jellyfin:8096/Videos/abc123/stream?static=true");

        bool result = await prober.IsAvailable(Url, CancellationToken.None);

        result.ShouldBeFalse();
    }

    // ersatztv#473 review finding: our OWN /media/{provider}/... endpoint 404s when the media source
    // is unconfigured or momentarily missing. Failing closed there would blank every item on that
    // source, which is exactly what the fail-open contract exists to prevent.
    [Test]
    public async Task Should_Fail_Open_On_404_That_Was_Not_Redirected()
    {
        HttpRemoteStreamProber prober = ProberReturning(HttpStatusCode.NotFound, finalUri: Url);

        bool result = await prober.IsAvailable(Url, CancellationToken.None);

        result.ShouldBeTrue();
    }

    // a plex key can contain spaces/unicode; pin that an un-redirected 404 on such a url still fails
    // OPEN. (This passes against a naive string comparison too - Uri.ToString() unescapes - so it
    // guards the behaviour, not the implementation choice.)
    [Test]
    public async Task Should_Fail_Open_On_404_For_An_Unredirected_Url_Needing_Escaping()
    {
        const string plexUrl = "http://localhost:8409/media/plex/1/library/parts/1/a file.mkv";
        HttpRemoteStreamProber prober = ProberReturning(HttpStatusCode.NotFound, finalUri: plexUrl);

        bool result = await prober.IsAvailable(plexUrl, CancellationToken.None);

        result.ShouldBeTrue();
    }

    [TestCase(HttpStatusCode.OK)]
    [TestCase(HttpStatusCode.PartialContent)]
    [TestCase(HttpStatusCode.NoContent)]
    public async Task Should_Report_Available_On_Success(HttpStatusCode statusCode)
    {
        HttpRemoteStreamProber prober = ProberReturning(statusCode);

        bool result = await prober.IsAvailable(Url, CancellationToken.None);

        result.ShouldBeTrue();
    }

    // the fail-open contract: a probe that cannot answer must never block a tune that would
    // otherwise have worked. these cases exist so a future refactor can't silently invert it.
    [TestCase(HttpStatusCode.InternalServerError)]
    [TestCase(HttpStatusCode.BadGateway)]
    [TestCase(HttpStatusCode.Unauthorized)]
    [TestCase(HttpStatusCode.Forbidden)]
    public async Task Should_Fail_Open_On_Other_Status_Codes(HttpStatusCode statusCode)
    {
        HttpRemoteStreamProber prober = ProberReturning(statusCode);

        bool result = await prober.IsAvailable(Url, CancellationToken.None);

        result.ShouldBeTrue();
    }

    // a server that ignores `Range: bytes=0-0` answers 200 with the WHOLE FILE. The probe must not
    // read it -- buffering a video on the streaming hot path would be far worse than the aborted
    // socket the drain was added to avoid. (Review finding against the first fix commit.)
    [Test]
    public async Task Should_Not_Read_The_Body_When_The_Server_Ignores_The_Range_Request()
    {
        var body = new TrackingStream(64 * 1024 * 1024);
        var response = new HttpResponseMessage(HttpStatusCode.OK) { Content = new StreamContent(body) };

        var prober = new HttpRemoteStreamProber(
            new StubHttpClientFactory(new FixedResponseHttpMessageHandler(response)),
            Substitute.For<ILogger<HttpRemoteStreamProber>>());

        bool result = await prober.IsAvailable(Url, CancellationToken.None);

        result.ShouldBeTrue();
        body.BytesRead.ShouldBe(0);
    }

    // the counterpart: when the server DID honour the range, the one byte is read so the connection
    // goes back to the pool rather than being aborted
    [Test]
    public async Task Should_Drain_The_Single_Byte_When_The_Server_Honours_The_Range_Request()
    {
        var body = new TrackingStream(1);
        var response = new HttpResponseMessage(HttpStatusCode.PartialContent)
        {
            Content = new StreamContent(body)
        };

        var prober = new HttpRemoteStreamProber(
            new StubHttpClientFactory(new FixedResponseHttpMessageHandler(response)),
            Substitute.For<ILogger<HttpRemoteStreamProber>>());

        bool result = await prober.IsAvailable(Url, CancellationToken.None);

        result.ShouldBeTrue();
        body.BytesRead.ShouldBe(1);
    }

    [Test]
    public async Task Should_Fail_Open_On_Transport_Failure()
    {
        var prober = new HttpRemoteStreamProber(
            new StubHttpClientFactory(new ThrowingHttpMessageHandler(new HttpRequestException("no route to host"))),
            Substitute.For<ILogger<HttpRemoteStreamProber>>());

        bool result = await prober.IsAvailable(Url, CancellationToken.None);

        result.ShouldBeTrue();
    }

    [Test]
    public async Task Should_Fail_Open_On_Timeout()
    {
        var prober = new HttpRemoteStreamProber(
            new StubHttpClientFactory(new ThrowingHttpMessageHandler(new TaskCanceledException("timed out"))),
            Substitute.For<ILogger<HttpRemoteStreamProber>>());

        bool result = await prober.IsAvailable(Url, CancellationToken.None);

        result.ShouldBeTrue();
    }

    // caller cancellation (shutdown / client disconnect) is a genuine signal, NOT a probe failure --
    // swallowing it would let the handler go on building an ffmpeg command on a dead token.
    [Test]
    public async Task Should_Propagate_Caller_Cancellation()
    {
        HttpRemoteStreamProber prober = ProberReturning(HttpStatusCode.OK);

        using var cts = new CancellationTokenSource();
        await cts.CancelAsync();

        await Should.ThrowAsync<OperationCanceledException>(() => prober.IsAvailable(Url, cts.Token));
    }

    private static HttpRemoteStreamProber ProberReturning(HttpStatusCode statusCode, string finalUri = null) =>
        new(
            new StubHttpClientFactory(new StatusCodeHttpMessageHandler(statusCode, finalUri)),
            Substitute.For<ILogger<HttpRemoteStreamProber>>());

    private sealed class StubHttpClientFactory(HttpMessageHandler handler) : IHttpClientFactory
    {
        public HttpClient CreateClient(string name) => new(handler, disposeHandler: false);
    }

    private sealed class StatusCodeHttpMessageHandler(HttpStatusCode statusCode, string finalUri = null)
        : HttpMessageHandler
    {
        protected override Task<HttpResponseMessage> SendAsync(
            HttpRequestMessage request,
            CancellationToken cancellationToken)
        {
            cancellationToken.ThrowIfCancellationRequested();

            // HttpClient rewrites RequestMessage.RequestUri to the final hop when it follows a
            // redirect; finalUri lets a test stand in for "the media server answered this".
            if (finalUri is not null)
            {
                request.RequestUri = new Uri(finalUri);
            }

            return Task.FromResult(new HttpResponseMessage(statusCode) { RequestMessage = request });
        }
    }

    private sealed class FixedResponseHttpMessageHandler(HttpResponseMessage response) : HttpMessageHandler
    {
        protected override Task<HttpResponseMessage> SendAsync(
            HttpRequestMessage request,
            CancellationToken cancellationToken)
        {
            cancellationToken.ThrowIfCancellationRequested();
            response.RequestMessage = request;
            return Task.FromResult(response);
        }
    }

    /// <summary>A readable stream that records how many bytes were actually pulled from it.</summary>
    private sealed class TrackingStream(long length) : Stream
    {
        public int BytesRead { get; private set; }

        public override bool CanRead => true;
        public override bool CanSeek => false;
        public override bool CanWrite => false;
        public override long Length => length;

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

        public override int Read(byte[] buffer, int offset, int count)
        {
            if (BytesRead >= length)
            {
                return 0;
            }

            int toRead = (int)Math.Min(count, length - BytesRead);
            Array.Clear(buffer, offset, toRead);
            BytesRead += toRead;
            return toRead;
        }

        public override void Flush()
        {
        }

        public override long Seek(long offset, SeekOrigin origin) => throw new NotSupportedException();
        public override void SetLength(long value) => throw new NotSupportedException();
        public override void Write(byte[] buffer, int offset, int count) => throw new NotSupportedException();
    }

    private sealed class ThrowingHttpMessageHandler(Exception exception) : HttpMessageHandler
    {
        protected override Task<HttpResponseMessage> SendAsync(
            HttpRequestMessage request,
            CancellationToken cancellationToken) =>
            Task.FromException<HttpResponseMessage>(exception);
    }
}