using System.Buffers;
using System.IO.Pipelines;
using System.Reflection;
using System.Text;
using NATS.Server.Protocol;

namespace NATS.Server.Core.Tests.ProtocolParity;

public class ParserSpanRetentionTests
{
    [Fact]
    public void TryParseView_exposes_PUB_fields_as_byte_views()
    {
        var parser = new NatsParser();
        ReadOnlySequence<byte> buffer = new(Encoding.ASCII.GetBytes("PUB foo reply 5\r\nHello\r\n"));

        var parsed = TryParseView(parser, ref buffer, out var view);

        parsed.ShouldBeTrue();
        GetCommandType(view).ShouldBe(CommandType.Pub);
        GetAscii(view, "Subject").ShouldBe("foo");
        GetAscii(view, "ReplyTo").ShouldBe("reply");
        GetAscii(view, "Payload").ShouldBe("Hello");
        GetPropertyType(view, "Subject").ShouldNotBe(typeof(string));
        GetPropertyType(view, "ReplyTo").ShouldNotBe(typeof(string));
    }

    [Fact]
    public void TryParseView_exposes_HPUB_fields_as_byte_views()
    {
        const string header = "NATS/1.0\r\n\r\n";
        const string payload = "Hello";
        var total = header.Length + payload.Length;
        var parser = new NatsParser();
        ReadOnlySequence<byte> buffer = new(Encoding.ASCII.GetBytes(
            $"HPUB foo reply {header.Length} {total}\r\n{header}{payload}\r\n"));

        var parsed = TryParseView(parser, ref buffer, out var view);

        parsed.ShouldBeTrue();
        GetCommandType(view).ShouldBe(CommandType.HPub);
        GetAscii(view, "Subject").ShouldBe("foo");
        GetAscii(view, "ReplyTo").ShouldBe("reply");
        GetAscii(view, "Payload").ShouldBe(header + payload);
        GetInt(view, "HeaderSize").ShouldBe(header.Length);
        GetPropertyType(view, "Payload").ShouldNotBe(typeof(byte[]));
    }

    [Fact]
    public void TryParseView_exposes_CONNECT_payload_as_byte_view()
    {
        const string json = "{\"verbose\":false,\"echo\":true}";
        var parser = new NatsParser();
        ReadOnlySequence<byte> buffer = new(Encoding.ASCII.GetBytes($"CONNECT {json}\r\n"));

        var parsed = TryParseView(parser, ref buffer, out var view);

        parsed.ShouldBeTrue();
        GetCommandType(view).ShouldBe(CommandType.Connect);
        GetAscii(view, "Payload").ShouldBe(json);
        GetPropertyType(view, "Payload").ShouldNotBe(typeof(byte[]));
    }

    [Fact]
    public void TryParseView_exposes_INFO_payload_as_byte_view()
    {
        const string json = "{\"server_id\":\"test\"}";
        var parser = new NatsParser();
        ReadOnlySequence<byte> buffer = new(Encoding.ASCII.GetBytes($"INFO {json}\r\n"));

        var parsed = TryParseView(parser, ref buffer, out var view);

        parsed.ShouldBeTrue();
        GetCommandType(view).ShouldBe(CommandType.Info);
        GetAscii(view, "Payload").ShouldBe(json);
        GetPropertyType(view, "Payload").ShouldNotBe(typeof(byte[]));
    }

    [Fact]
    public async Task TryParseView_preserves_split_payload_state_across_reads()
    {
        var parser = new NatsParser();
        var pipe = new Pipe();

        await pipe.Writer.WriteAsync(Encoding.ASCII.GetBytes("PUB foo 5\r\nHe"));

        var first = await pipe.Reader.ReadAsync();
        var firstBuffer = first.Buffer;
        TryParseView(parser, ref firstBuffer, out _).ShouldBeFalse();
        pipe.Reader.AdvanceTo(firstBuffer.Start, firstBuffer.End);

        await pipe.Writer.WriteAsync(Encoding.ASCII.GetBytes("llo\r\n"));
        pipe.Writer.Complete();

        var second = await pipe.Reader.ReadAsync();
        var secondBuffer = second.Buffer;
        TryParseView(parser, ref secondBuffer, out var view).ShouldBeTrue();
        GetCommandType(view).ShouldBe(CommandType.Pub);
        GetAscii(view, "Subject").ShouldBe("foo");
        GetAscii(view, "Payload").ShouldBe("Hello");
        pipe.Reader.AdvanceTo(secondBuffer.Start, secondBuffer.End);
    }

    private static bool TryParseView(NatsParser parser, ref ReadOnlySequence<byte> buffer, out object view)
    {
        var method = typeof(NatsParser).GetMethod(
            "TryParseView",
            BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);

        method.ShouldNotBeNull("NatsParser should expose a byte-first TryParseView API.");

        object?[] args =
        [
            buffer,
            null,
        ];

        var parsed = (bool)method!.Invoke(parser, args)!;
        buffer = (ReadOnlySequence<byte>)args[0]!;
        view = args[1]!;
        return parsed;
    }

    private static CommandType GetCommandType(object view) =>
        (CommandType)GetRequiredProperty(view, "Type").GetValue(view)!;

    private static int GetInt(object view, string propertyName) =>
        (int)GetRequiredProperty(view, propertyName).GetValue(view)!;

    private static Type GetPropertyType(object view, string propertyName) =>
        GetRequiredProperty(view, propertyName).PropertyType;

    private static string GetAscii(object view, string propertyName)
    {
        var property = GetRequiredProperty(view, propertyName);
        var value = property.GetValue(view);

        return value switch
        {
            ReadOnlyMemory<byte> memory => Encoding.ASCII.GetString(memory.Span),
            ReadOnlySequence<byte> sequence => Encoding.ASCII.GetString(sequence.ToArray()),
            byte[] bytes => Encoding.ASCII.GetString(bytes),
            null => string.Empty,
            _ => throw new InvalidOperationException(
                $"Unsupported property type for {propertyName}: {property.PropertyType}"),
        };
    }

    private static PropertyInfo GetRequiredProperty(object view, string propertyName)
    {
        var property = view.GetType().GetProperty(propertyName, BindingFlags.Instance | BindingFlags.Public);
        property.ShouldNotBeNull($"Expected property {propertyName} on {view.GetType().Name}.");
        return property!;
    }
}