using System.Net;
using System.Net.Sockets;
using Big.Application;
using Big.Infrastructure;

namespace Big.Tests;

// S-29 (#192, ADR-0036): the clamd INSTREAM adapter, against a fake clamd on a loopback socket. The live
// engine (EICAR → FOUND) is verified by verify-clamav.
public class ClamdDocumentScannerTests
{
    /// <summary>A one-shot fake clamd: reads one INSTREAM request to its zero-length terminator,
    /// records it, and answers <paramref name="reply"/>.</summary>
    private sealed class FakeClamd : IDisposable
    {
        private readonly TcpListener _listener = new(IPAddress.Loopback, 0);
        public Task<byte[]> Received { get; }
        public int Port => ((IPEndPoint)_listener.LocalEndpoint).Port;

        /// <param name="reply">The answer, or null to accept the request and never answer (a hung clamd).</param>
        public FakeClamd(string? reply)
        {
            _listener.Start();
            Received = Serve(reply);
        }

        private async Task<byte[]> Serve(string? reply)
        {
            using var client = await _listener.AcceptTcpClientAsync();
            var stream = client.GetStream();
            var received = new MemoryStream();
            var buffer = new byte[4096];
            while (!EndsWithTerminator(received))
            {
                var n = await stream.ReadAsync(buffer);
                if (n == 0) break;
                received.Write(buffer, 0, n);
            }
            if (reply is null)
                await Task.Delay(TimeSpan.FromSeconds(10)); // long past any test timeout
            else
                await stream.WriteAsync(System.Text.Encoding.ASCII.GetBytes(reply + "\0"));
            return received.ToArray();
        }

        // The request is "zINSTREAM\0" + chunks + a 4-byte zero length; it is complete once it ends in it.
        private static bool EndsWithTerminator(MemoryStream s)
            => s.Length > 14 && s.ToArray()[^4..].All(b => b == 0);

        public void Dispose() => _listener.Stop();
    }

    private static ClamdDocumentScanner ScannerFor(int port) =>
        new(new ClamAvOptions { Host = "127.0.0.1", Port = port, Timeout = TimeSpan.FromSeconds(5) });

    [Fact]
    public async Task Sends_the_document_as_one_length_prefixed_instream_chunk()
    {
        using var clamd = new FakeClamd("stream: OK");

        await ScannerFor(clamd.Port).ScanAsync([1, 2, 3]);

        Assert.Equal("zINSTREAM\0"u8.ToArray().Concat(new byte[] { 0, 0, 0, 3, 1, 2, 3, 0, 0, 0, 0 }),
            await clamd.Received.WaitAsync(TimeSpan.FromSeconds(5)));
    }

    [Theory]
    [InlineData("stream: OK", ScanVerdict.Clean)]
    [InlineData("stream: Eicar-Test-Signature FOUND", ScanVerdict.Infected)]
    [InlineData("INSTREAM size limit exceeded. ERROR", ScanVerdict.Unavailable)]
    public async Task Maps_the_clamd_reply_to_a_verdict(string reply, ScanVerdict expected)
    {
        using var clamd = new FakeClamd(reply);

        Assert.Equal(expected, await ScannerFor(clamd.Port).ScanAsync([1, 2, 3]));
    }

    [Fact]
    public async Task An_unreachable_clamd_is_unavailable_not_an_exception()
    {
        // Grab a free port, then close it, so nothing listens there.
        var listener = new TcpListener(IPAddress.Loopback, 0);
        listener.Start();
        var port = ((IPEndPoint)listener.LocalEndpoint).Port;
        listener.Stop();

        Assert.Equal(ScanVerdict.Unavailable, await ScannerFor(port).ScanAsync([1, 2, 3]));
    }

    [Fact]
    public async Task A_clamd_that_never_answers_is_unavailable_after_the_timeout()
    {
        using var clamd = new FakeClamd(reply: null);
        var scanner = new ClamdDocumentScanner(
            new ClamAvOptions { Host = "127.0.0.1", Port = clamd.Port, Timeout = TimeSpan.FromMilliseconds(300) });

        Assert.Equal(ScanVerdict.Unavailable, await scanner.ScanAsync([1, 2, 3]));
    }

    [Fact]
    public async Task A_cancelled_request_is_cancelled_not_reported_unavailable()
    {
        // The caller giving up is not a scanner outage: it propagates instead of becoming a 503.
        using var clamd = new FakeClamd(reply: null);
        using var cts = new CancellationTokenSource(TimeSpan.FromMilliseconds(300));

        await Assert.ThrowsAnyAsync<OperationCanceledException>(() => ScannerFor(clamd.Port).ScanAsync([1, 2, 3], cts.Token));
    }

    [Fact]
    public async Task Rejects_null_content()
        => await Assert.ThrowsAsync<ArgumentNullException>(() => ScannerFor(1).ScanAsync(null!));

    [Fact]
    public void Defaults_to_the_clamav_service_on_the_clamd_port()
        => Assert.Equal(("clamav", 3310), (new ClamAvOptions().Host, new ClamAvOptions().Port));
}