using System.IO.Pipes;
using System.Security.AccessControl;
using System.Security.Principal;
using System.Text;
using System.Text.Json;
using KronaStaffTerminal.Models;

namespace KronaStaffTerminal.Services;

public sealed class IpcRequest
{
    public string Command { get; set; } = "";
    public string? Payload { get; set; }
}

public sealed class IpcResponse
{
    public bool Success { get; set; }
    public string? ErrorMessage { get; set; }
    public IpcServiceStatus? Status { get; set; }
    public int? SyncedCount { get; set; }
    public string? Payload { get; set; }
}

public sealed class IpcServiceStatus
{
    public bool ServiceRunning { get; set; } = true;
    public string ServiceVersion { get; set; } = "0.3.0";
    public bool ScannerInSession0Supported { get; set; }
    public string ScannerDiagnostic { get; set; } = "";
    public int PendingSyncCount { get; set; }
    public DateTimeOffset? LastSyncUtc { get; set; }
    public string? LastSyncError { get; set; }
    public string LicenseStatus { get; set; } = "Active";
}

public static class TerminalIpcConstants
{
    public const string PipeName = "KronaStaffTerminalPipe";
    public const string PipeServerName = ".";
}

public sealed class TerminalIpcClient
{
    public async Task<bool> IsServiceAvailableAsync(CancellationToken cancellationToken = default)
    {
        var response = await SendCommandAsync("Ping", null, cancellationToken);
        return response?.Success == true;
    }

    public async Task<IpcServiceStatus?> GetStatusAsync(CancellationToken cancellationToken = default)
    {
        var response = await SendCommandAsync("GetStatus", null, cancellationToken);
        return response?.Status;
    }

    public async Task<bool> EnqueueAttendanceAsync(AttendanceRecord record, CancellationToken cancellationToken = default)
    {
        var payload = JsonSerializer.Serialize(record);
        var response = await SendCommandAsync("EnqueueAttendance", payload, cancellationToken);
        return response?.Success == true;
    }

    public async Task<AttendanceSyncResult?> TriggerSyncAsync(CancellationToken cancellationToken = default)
    {
        var response = await SendCommandAsync("TriggerSync", null, cancellationToken);
        if (response?.Success == true && !string.IsNullOrWhiteSpace(response.Payload))
        {
            return JsonSerializer.Deserialize<AttendanceSyncResult>(response.Payload);
        }
        return null;
    }

    public async Task<IpcResponse?> SendCommandAsync(string command, string? payload, CancellationToken cancellationToken = default)
    {
        try
        {
            await using var pipe = new NamedPipeClientStream(TerminalIpcConstants.PipeServerName, TerminalIpcConstants.PipeName, PipeDirection.InOut, PipeOptions.Asynchronous);
            using var timeoutCts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
            timeoutCts.CancelAfter(TimeSpan.FromSeconds(2));

            await pipe.ConnectAsync(timeoutCts.Token);

            var request = new IpcRequest { Command = command, Payload = payload };
            var json = JsonSerializer.Serialize(request);
            var bytes = Encoding.UTF8.GetBytes(json);
            var lengthPrefix = BitConverter.GetBytes(bytes.Length);
            await pipe.WriteAsync(lengthPrefix, cancellationToken);
            await pipe.WriteAsync(bytes, cancellationToken);
            await pipe.FlushAsync(cancellationToken);

            var respLenBytes = new byte[4];
            var read = await pipe.ReadAsync(respLenBytes, cancellationToken);
            if (read < 4) return null;
            var respLen = BitConverter.ToInt32(respLenBytes);
            if (respLen is <= 0 or > 10 * 1024 * 1024) return null;

            var respBytes = new byte[respLen];
            var totalRead = 0;
            while (totalRead < respLen)
            {
                var r = await pipe.ReadAsync(respBytes.AsMemory(totalRead), cancellationToken);
                if (r == 0) return null;
                totalRead += r;
            }

            var responseJson = Encoding.UTF8.GetString(respBytes);
            if (string.IsNullOrWhiteSpace(responseJson)) return null;

            return JsonSerializer.Deserialize<IpcResponse>(responseJson);
        }
        catch (Exception ex) when (ex is IOException or TimeoutException or OperationCanceledException)
        {
            // Service not running or unreachable
            return null;
        }
    }
}

public sealed class TerminalIpcServer : IDisposable
{
    private readonly Func<IpcRequest, Task<IpcResponse>> _handler;
    private CancellationTokenSource? _cancellation;
    private Task? _listenTask;
    private bool _disposed;

    public TerminalIpcServer(Func<IpcRequest, Task<IpcResponse>> handler)
    {
        _handler = handler;
    }

    public void Start()
    {
        _cancellation = new CancellationTokenSource();
        _listenTask = Task.Run(() => ListenLoopAsync(_cancellation.Token));
    }

    private async Task ListenLoopAsync(CancellationToken token)
    {
        while (!token.IsCancellationRequested)
        {
            NamedPipeServerStream? server = null;
            try
            {
                server = CreatePipeServer();
                await server.WaitForConnectionAsync(token);

                // Handle client in background task so server can accept next client
                var clientStream = server;
                _ = Task.Run(() => HandleClientAsync(clientStream, token), token);
            }
            catch (OperationCanceledException)
            {
                server?.Dispose();
                break;
            }
            catch (Exception ex)
            {
                CrashLogService.WriteDiagnostic($"IPC server loop error: {ex.Message}");
                server?.Dispose();
                await Task.Delay(500, token);
            }
        }
    }

    private async Task HandleClientAsync(NamedPipeServerStream stream, CancellationToken token)
    {
        await using (stream)
        {
            try
            {
                var reqLenBytes = new byte[4];
                var read = await stream.ReadAsync(reqLenBytes, token);
                if (read < 4) return;
                var reqLen = BitConverter.ToInt32(reqLenBytes);
                if (reqLen is <= 0 or > 10 * 1024 * 1024) return;

                var reqBytes = new byte[reqLen];
                var totalRead = 0;
                while (totalRead < reqLen)
                {
                    var r = await stream.ReadAsync(reqBytes.AsMemory(totalRead), token);
                    if (r == 0) return;
                    totalRead += r;
                }

                var line = Encoding.UTF8.GetString(reqBytes);
                if (string.IsNullOrWhiteSpace(line)) return;

                var request = JsonSerializer.Deserialize<IpcRequest>(line);
                var response = request is not null
                    ? await _handler(request)
                    : new IpcResponse { Success = false, ErrorMessage = "Invalid request" };

                var responseJson = JsonSerializer.Serialize(response);
                var responseBytes = Encoding.UTF8.GetBytes(responseJson);
                var lengthPrefix = BitConverter.GetBytes(responseBytes.Length);
                
                await stream.WriteAsync(lengthPrefix, token);
                await stream.WriteAsync(responseBytes, token);
                await stream.FlushAsync(token);
            }
            catch (Exception ex) when (ex is not OperationCanceledException)
            {
                CrashLogService.WriteDiagnostic($"IPC client handle error: {ex.Message}");
            }
        }
    }

    private static NamedPipeServerStream CreatePipeServer()
    {
        var pipeSecurity = new PipeSecurity();
        var systemSid = new SecurityIdentifier(WellKnownSidType.LocalSystemSid, null);
        var adminSid = new SecurityIdentifier(WellKnownSidType.BuiltinAdministratorsSid, null);
        var usersSid = new SecurityIdentifier(WellKnownSidType.AuthenticatedUserSid, null);

        pipeSecurity.AddAccessRule(new PipeAccessRule(systemSid, PipeAccessRights.FullControl, AccessControlType.Allow));
        pipeSecurity.AddAccessRule(new PipeAccessRule(adminSid, PipeAccessRights.FullControl, AccessControlType.Allow));
        pipeSecurity.AddAccessRule(new PipeAccessRule(usersSid, PipeAccessRights.ReadWrite, AccessControlType.Allow));

        return NamedPipeServerStreamAcl.Create(
            @"global\" + TerminalIpcConstants.PipeName,
            PipeDirection.InOut,
            NamedPipeServerStream.MaxAllowedServerInstances,
            PipeTransmissionMode.Byte,
            PipeOptions.Asynchronous,
            inBufferSize: 4096,
            outBufferSize: 4096,
            pipeSecurity);
    }

    public void Dispose()
    {
        if (_disposed) return;
        _disposed = true;
        _cancellation?.Cancel();
        _cancellation?.Dispose();
    }
}