using Microsoft.Extensions.Logging;
using System.Diagnostics;
using System.IO.Pipes;
using System.Text.Json;

namespace LightlessSync.FileCache;

internal sealed class ExternalCompactionExecutor : ICompactionExecutor, IDisposable
{
    private readonly ILogger<ExternalCompactionExecutor> _logger;
    private readonly ICompactorContext _context;
    private readonly TimeSpan _timeout = TimeSpan.FromMinutes(5);
    private readonly string _pipeName;
    private Process? _workerProcess;
    private bool _disposed;
    private readonly object _sync = new();

    public ExternalCompactionExecutor(ILogger<ExternalCompactionExecutor> logger, ICompactorContext context)
    {
        _logger = logger;
        _context = context;
        _pipeName = $"LightlessCompactor-{Environment.ProcessId}";
    }

    public bool TryCompact(string filePath)
    {
        if (string.IsNullOrWhiteSpace(filePath) || !File.Exists(filePath))
            return false;

        if (!EnsureWorkerRunning())
            return false;

        try
        {
            var request = new CompactorRequest
            {
                Type = "compact",
                Path = filePath
            };

            return SendRequest(request, out var response) && response?.Success == true;
        }
        catch (Exception ex)
        {
            _logger.LogWarning(ex, "External compactor failed for {file}", filePath);
            return false;
        }
    }

    public void Dispose()
    {
        if (_disposed)
            return;

        _disposed = true;

        try
        {
            SendRequest(new CompactorRequest { Type = "shutdown" }, out _);
        }
        catch
        {
            // ignore
        }

        lock (_sync)
        {
            if (_workerProcess is null)
                return;

            TryKill(_workerProcess);
            _workerProcess.Dispose();
            _workerProcess = null;
        }
    }

    private bool EnsureWorkerRunning()
    {
        lock (_sync)
        {
            if (_workerProcess is { HasExited: false })
                return true;

            _workerProcess?.Dispose();
            _workerProcess = null;

            var workerPath = ResolveWorkerPath();
            if (string.IsNullOrEmpty(workerPath))
                return false;

            var args = BuildArguments();
            var startInfo = new ProcessStartInfo
            {
                FileName = workerPath,
                Arguments = args,
                CreateNoWindow = true,
                UseShellExecute = false,
                RedirectStandardOutput = true,
                RedirectStandardError = true
            };

            var process = new Process { StartInfo = startInfo };
            if (!process.Start())
                return false;

            TrySetLowPriority(process);
            _ = DrainAsync(process.StandardOutput, "stdout");
            _ = DrainAsync(process.StandardError, "stderr");

            _workerProcess = process;
            return true;
        }
    }

    private bool SendRequest(CompactorRequest request, out CompactorResponse? response)
    {
        response = null;
        using var pipe = new NamedPipeClientStream(".", _pipeName, PipeDirection.InOut, PipeOptions.Asynchronous);

        try
        {
            pipe.Connect((int)_timeout.TotalMilliseconds);
        }
        catch (Exception ex)
        {
            _logger.LogDebug(ex, "Compactor pipe connection failed.");
            return false;
        }

        using var writer = new StreamWriter(pipe) { AutoFlush = true };
        using var reader = new StreamReader(pipe);

        var payload = JsonSerializer.Serialize(request);
        writer.WriteLine(payload);

        var readTask = reader.ReadLineAsync();
        if (!readTask.Wait(_timeout))
        {
            _logger.LogWarning("Compactor pipe timed out waiting for response.");
            return false;
        }

        var line = readTask.Result;
        if (string.IsNullOrWhiteSpace(line))
            return false;

        try
        {
            response = JsonSerializer.Deserialize<CompactorResponse>(line);
            return response is not null;
        }
        catch (Exception ex)
        {
            _logger.LogDebug(ex, "Failed to parse compactor response.");
            return false;
        }
    }

    private string? ResolveWorkerPath()
    {
        var baseDir = AppContext.BaseDirectory;
        var exeName = OperatingSystem.IsWindows() || _context.IsWine
            ? "LightlessCompactorWorker.exe"
            : "LightlessCompactorWorker";
        var path = Path.Combine(baseDir, exeName);
        return File.Exists(path) ? path : null;
    }

    private string BuildArguments()
    {
        var args = new List<string> { "--pipe", Quote(_pipeName), "--parent", Environment.ProcessId.ToString() };
        if (_context.IsWine)
            args.Add("--wine");
        return string.Join(' ', args);
    }

    private static string Quote(string value)
    {
        if (string.IsNullOrEmpty(value))
            return "\"\"";

        if (!value.Contains('"', StringComparison.Ordinal))
            return "\"" + value + "\"";

        return "\"" + value.Replace("\"", "\\\"", StringComparison.Ordinal) + "\"";
    }

    private static void TrySetLowPriority(Process process)
    {
        try
        {
            if (OperatingSystem.IsWindows())
                process.PriorityClass = ProcessPriorityClass.BelowNormal;
        }
        catch
        {
            // ignore
        }
    }

    private async Task DrainAsync(StreamReader reader, string label)
    {
        try
        {
            string? line;
            while ((line = await reader.ReadLineAsync().ConfigureAwait(false)) != null)
            {
                if (_logger.IsEnabled(LogLevel.Trace))
                    _logger.LogTrace("Compactor {label}: {line}", label, line);
            }
        }
        catch
        {
            // ignore
        }
    }

    private static void TryKill(Process process)
    {
        try
        {
            process.Kill(entireProcessTree: true);
        }
        catch
        {
            // ignore
        }
    }

    private sealed class CompactorRequest
    {
        public string Type { get; init; } = "compact";
        public string? Path { get; init; }
    }

    private sealed class CompactorResponse
    {
        public bool Success { get; init; }
        public string? Error { get; init; }
    }
}