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

namespace NATS.Server.Tests;

public class ParserTests
{
    private static async Task<List<ParsedCommand>> ParseAsync(string input)
    {
        var pipe = new Pipe();
        var commands = new List<ParsedCommand>();

        // Write input to pipe
        var bytes = Encoding.ASCII.GetBytes(input);
        await pipe.Writer.WriteAsync(bytes);
        pipe.Writer.Complete();

        // Parse from pipe
        var parser = new NatsParser(maxPayload: NatsProtocol.MaxPayloadSize);
        while (true)
        {
            var result = await pipe.Reader.ReadAsync();
            var buffer = result.Buffer;

            while (parser.TryParse(ref buffer, out var cmd))
                commands.Add(cmd);

            pipe.Reader.AdvanceTo(buffer.Start, buffer.End);

            if (result.IsCompleted)
                break;
        }

        return commands;
    }

    [Fact]
    public async Task Parse_PING()
    {
        var cmds = await ParseAsync("PING\r\n");
        Assert.Single(cmds);
        Assert.Equal(CommandType.Ping, cmds[0].Type);
    }

    [Fact]
    public async Task Parse_PONG()
    {
        var cmds = await ParseAsync("PONG\r\n");
        Assert.Single(cmds);
        Assert.Equal(CommandType.Pong, cmds[0].Type);
    }

    [Fact]
    public async Task Parse_CONNECT()
    {
        var cmds = await ParseAsync("CONNECT {\"verbose\":false,\"echo\":true}\r\n");
        Assert.Single(cmds);
        Assert.Equal(CommandType.Connect, cmds[0].Type);
        Assert.Contains("verbose", Encoding.ASCII.GetString(cmds[0].Payload.ToArray()));
    }

    [Fact]
    public async Task Parse_SUB_without_queue()
    {
        var cmds = await ParseAsync("SUB foo 1\r\n");
        Assert.Single(cmds);
        Assert.Equal(CommandType.Sub, cmds[0].Type);
        Assert.Equal("foo", cmds[0].Subject);
        Assert.Null(cmds[0].Queue);
        Assert.Equal("1", cmds[0].Sid);
    }

    [Fact]
    public async Task Parse_SUB_with_queue()
    {
        var cmds = await ParseAsync("SUB foo workers 1\r\n");
        Assert.Single(cmds);
        Assert.Equal(CommandType.Sub, cmds[0].Type);
        Assert.Equal("foo", cmds[0].Subject);
        Assert.Equal("workers", cmds[0].Queue);
        Assert.Equal("1", cmds[0].Sid);
    }

    [Fact]
    public async Task Parse_UNSUB()
    {
        var cmds = await ParseAsync("UNSUB 1\r\n");
        Assert.Single(cmds);
        Assert.Equal(CommandType.Unsub, cmds[0].Type);
        Assert.Equal("1", cmds[0].Sid);
        Assert.Equal(-1, cmds[0].MaxMessages);
    }

    [Fact]
    public async Task Parse_UNSUB_with_max()
    {
        var cmds = await ParseAsync("UNSUB 1 5\r\n");
        Assert.Single(cmds);
        Assert.Equal(CommandType.Unsub, cmds[0].Type);
        Assert.Equal("1", cmds[0].Sid);
        Assert.Equal(5, cmds[0].MaxMessages);
    }

    [Fact]
    public async Task Parse_PUB_with_payload()
    {
        var cmds = await ParseAsync("PUB foo 5\r\nHello\r\n");
        Assert.Single(cmds);
        Assert.Equal(CommandType.Pub, cmds[0].Type);
        Assert.Equal("foo", cmds[0].Subject);
        Assert.Null(cmds[0].ReplyTo);
        Assert.Equal("Hello", Encoding.ASCII.GetString(cmds[0].Payload.ToArray()));
    }

    [Fact]
    public async Task Parse_PUB_with_reply()
    {
        var cmds = await ParseAsync("PUB foo reply 5\r\nHello\r\n");
        Assert.Single(cmds);
        Assert.Equal(CommandType.Pub, cmds[0].Type);
        Assert.Equal("foo", cmds[0].Subject);
        Assert.Equal("reply", cmds[0].ReplyTo);
        Assert.Equal("Hello", Encoding.ASCII.GetString(cmds[0].Payload.ToArray()));
    }

    [Fact]
    public async Task Parse_multiple_commands()
    {
        var cmds = await ParseAsync("PING\r\nPONG\r\nSUB foo 1\r\n");
        Assert.Equal(3, cmds.Count);
        Assert.Equal(CommandType.Ping, cmds[0].Type);
        Assert.Equal(CommandType.Pong, cmds[1].Type);
        Assert.Equal(CommandType.Sub, cmds[2].Type);
    }

    [Fact]
    public async Task Parse_PUB_zero_payload()
    {
        var cmds = await ParseAsync("PUB foo 0\r\n\r\n");
        Assert.Single(cmds);
        Assert.Equal(CommandType.Pub, cmds[0].Type);
        Assert.Empty(cmds[0].Payload.ToArray());
    }

    [Fact]
    public async Task Parse_case_insensitive()
    {
        var cmds = await ParseAsync("ping\r\npub FOO 3\r\nabc\r\n");
        Assert.Equal(2, cmds.Count);
        Assert.Equal(CommandType.Ping, cmds[0].Type);
        Assert.Equal(CommandType.Pub, cmds[1].Type);
    }

    [Fact]
    public async Task Parse_HPUB()
    {
        // HPUB subject 12 17\r\nNATS/1.0\r\n\r\nHello\r\n
        var header = "NATS/1.0\r\n\r\n";
        var payload = "Hello";
        var total = header.Length + payload.Length;
        var cmds = await ParseAsync($"HPUB foo {header.Length} {total}\r\n{header}{payload}\r\n");
        Assert.Single(cmds);
        Assert.Equal(CommandType.HPub, cmds[0].Type);
        Assert.Equal("foo", cmds[0].Subject);
        Assert.Equal(header.Length, cmds[0].HeaderSize);
    }

    [Fact]
    public async Task Parse_INFO()
    {
        var cmds = await ParseAsync("INFO {\"server_id\":\"test\"}\r\n");
        Assert.Single(cmds);
        Assert.Equal(CommandType.Info, cmds[0].Type);
    }
}