using System.Diagnostics;
using System.Net.Sockets;
using System.Text;

namespace Housing.Services;

public sealed class TcpStartSignalWatcher
{
    private readonly StartSignalSettings _settings;

    public TcpStartSignalWatcher(StartSignalSettings settings)
    {
        _settings = settings;
    }

    public async Task WaitForStartAsync(CancellationToken cancellationToken = default)
    {
        if (string.IsNullOrWhiteSpace(_settings.Host))
        {
            throw new InvalidOperationException("Hardware.ini [StartSignal] Host 값을 LAN 장비 IP로 설정하세요.");
        }

        using var client = new TcpClient();
        await ConnectAsync(client, cancellationToken);

        using var stream = client.GetStream();
        var stopwatch = Stopwatch.StartNew();

        if (string.IsNullOrWhiteSpace(_settings.ReadCommand))
        {
            await WaitForEventMessageAsync(stream, stopwatch, cancellationToken);
            return;
        }

        await WaitForPolledResponseAsync(stream, stopwatch, cancellationToken);
    }

    private async Task ConnectAsync(TcpClient client, CancellationToken cancellationToken)
    {
        try
        {
            using var timeout = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
            if (_settings.TimeoutMilliseconds > 0)
            {
                timeout.CancelAfter(_settings.TimeoutMilliseconds);
            }

            await client.ConnectAsync(_settings.Host, _settings.Port, timeout.Token);
        }
        catch (OperationCanceledException ex) when (!cancellationToken.IsCancellationRequested)
        {
            throw new TimeoutException($"LAN 시작 신호 장비 연결 시간 초과: {_settings.Host}:{_settings.Port}", ex);
        }
        catch (SocketException ex)
        {
            throw new InvalidOperationException($"LAN 시작 신호 장비 연결 실패: {_settings.Host}:{_settings.Port}, {ex.Message}", ex);
        }
    }

    private async Task WaitForEventMessageAsync(NetworkStream stream, Stopwatch stopwatch, CancellationToken cancellationToken)
    {
        while (true)
        {
            ThrowIfTimedOut(stopwatch, "LAN 메시지 수신 대기");

            var response = await ReadResponseAsync(stream, cancellationToken);
            if (_settings.IsActive(response))
            {
                return;
            }
        }
    }

    private async Task WaitForPolledResponseAsync(NetworkStream stream, Stopwatch stopwatch, CancellationToken cancellationToken)
    {
        if (_settings.RequireInactiveBeforeStart)
        {
            while (_settings.IsActive(await QueryAsync(stream, cancellationToken)))
            {
                ThrowIfTimedOut(stopwatch, "기존 LAN 시작 상태 해제 대기");
                await DelayAsync(cancellationToken);
            }
        }

        while (!_settings.IsActive(await QueryAsync(stream, cancellationToken)))
        {
            ThrowIfTimedOut(stopwatch, "LAN 시작 응답 대기");
            await DelayAsync(cancellationToken);
        }
    }

    private async Task<string> QueryAsync(NetworkStream stream, CancellationToken cancellationToken)
    {
        var command = _settings.ReadCommand.Trim() + _settings.GetTerminator();
        var bytes = Encoding.ASCII.GetBytes(command);
        await stream.WriteAsync(bytes, cancellationToken);
        await stream.FlushAsync(cancellationToken);
        return await ReadResponseAsync(stream, cancellationToken);
    }

    private async Task<string> ReadResponseAsync(NetworkStream stream, CancellationToken cancellationToken)
    {
        var buffer = new byte[1024];
        var response = new StringBuilder();

        using var timeout = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
        timeout.CancelAfter(_settings.ReadTimeoutMilliseconds);

        try
        {
            while (true)
            {
                var count = await stream.ReadAsync(buffer, timeout.Token);
                if (count == 0)
                {
                    break;
                }

                var chunk = Encoding.ASCII.GetString(buffer, 0, count);
                response.Append(chunk);
                if (chunk.Contains('\n') || chunk.Contains('\r') || !stream.DataAvailable)
                {
                    break;
                }
            }
        }
        catch (OperationCanceledException) when (!cancellationToken.IsCancellationRequested)
        {
            return response.ToString();
        }

        return response.ToString();
    }

    private async Task DelayAsync(CancellationToken cancellationToken)
    {
        await Task.Delay(_settings.PollIntervalMilliseconds, cancellationToken);
    }

    private void ThrowIfTimedOut(Stopwatch stopwatch, string state)
    {
        if (_settings.TimeoutMilliseconds <= 0 ||
            stopwatch.ElapsedMilliseconds <= _settings.TimeoutMilliseconds)
        {
            return;
        }

        throw new TimeoutException(
            $"LAN 시작 신호 대기 시간 초과: {state}, 대상={_settings.Host}:{_settings.Port}, 제한={_settings.TimeoutMilliseconds}ms");
    }
}