using System;
using System.Collections.ObjectModel;
using System.Linq;
using System.Reactive;
using System.Reactive.Disposables;
using System.Reactive.Linq;
using System.Threading;
using System.Threading.Tasks;
using AuroraDesk.Core.Entities;
using AuroraDesk.Core.Interfaces;
using AuroraDesk.Presentation.ViewModels.Base;
using Microsoft.Extensions.Logging;
using ReactiveUI;
using Avalonia.Threading;
using System.Reactive.Threading.Tasks;

namespace AuroraDesk.Presentation.ViewModels.Pages;

/// <summary>
/// SSH 多客户端实时交互页面 ViewModel
/// </summary>
public sealed class SshPageViewModel : RoutableViewModel, IDisposable
{
    private readonly ISshSessionService _sshSessionService;
    private readonly ILogger<SshPageViewModel>? _logger;
    private readonly ObservableCollection<SshSessionItemViewModel> _sessions = new();

    private SshSessionItemViewModel? _selectedSession;
    private string _host = "127.0.0.1";
    private int _port = 22;
    private string _userName = "root";
    private string? _password;
    private string? _privateKeyPath;
    private string? _privateKeyPassphrase;
    private string? _displayName;
    private string? _preferredShell;
    private string? _sshExecutablePath;
    private bool _allowAnyHostKey = true;
    private bool _isBusy;
    private string? _statusMessage;
    private SshAuthenticationMode _selectedAuthenticationMode = SshAuthenticationMode.Password;

    public SshPageViewModel(
        IScreen hostScreen,
        ISshSessionService sshSessionService,
        ILogger<SshPageViewModel>? logger = null)
        : base(hostScreen, "ssh-manager")
    {
        _sshSessionService = sshSessionService;
        _logger = logger;

        AddSessionCommand = ReactiveCommand.CreateFromTask(AddSessionAsync,
            this.WhenAnyValue(x => x.IsBusy, busy => !busy));

        RemoveSessionCommand = ReactiveCommand.CreateFromTask<SshSessionItemViewModel>(RemoveSessionAsync);

        SelectPasswordAuthCommand = ReactiveCommand.Create(() =>
        {
            SelectedAuthenticationMode = SshAuthenticationMode.Password;
        });
        SelectPrivateKeyAuthCommand = ReactiveCommand.Create(() =>
        {
            SelectedAuthenticationMode = SshAuthenticationMode.PrivateKey;
        });

        RefreshSnapshotCommand = ReactiveCommand.Create(RefreshSnapshot);

        RefreshSnapshot();
    }

    public ObservableCollection<SshSessionItemViewModel> Sessions => _sessions;

    public SshSessionItemViewModel? SelectedSession
    {
        get => _selectedSession;
        set => this.RaiseAndSetIfChanged(ref _selectedSession, value);
    }

    public string Host
    {
        get => _host;
        set => this.RaiseAndSetIfChanged(ref _host, value);
    }

    public int Port
    {
        get => _port;
        set => this.RaiseAndSetIfChanged(ref _port, value);
    }

    public string UserName
    {
        get => _userName;
        set => this.RaiseAndSetIfChanged(ref _userName, value);
    }

    public string? Password
    {
        get => _password;
        set => this.RaiseAndSetIfChanged(ref _password, value);
    }

    public string? PrivateKeyPath
    {
        get => _privateKeyPath;
        set => this.RaiseAndSetIfChanged(ref _privateKeyPath, value);
    }

    public string? PrivateKeyPassphrase
    {
        get => _privateKeyPassphrase;
        set => this.RaiseAndSetIfChanged(ref _privateKeyPassphrase, value);
    }

    public string? DisplayName
    {
        get => _displayName;
        set => this.RaiseAndSetIfChanged(ref _displayName, value);
    }

    public string? PreferredShell
    {
        get => _preferredShell;
        set => this.RaiseAndSetIfChanged(ref _preferredShell, value);
    }

    public string? SshExecutablePath
    {
        get => _sshExecutablePath;
        set => this.RaiseAndSetIfChanged(ref _sshExecutablePath, value);
    }

    public bool AllowAnyHostKey
    {
        get => _allowAnyHostKey;
        set => this.RaiseAndSetIfChanged(ref _allowAnyHostKey, value);
    }

    public bool IsBusy
    {
        get => _isBusy;
        private set => this.RaiseAndSetIfChanged(ref _isBusy, value);
    }

    public string? StatusMessage
    {
        get => _statusMessage;
        private set => this.RaiseAndSetIfChanged(ref _statusMessage, value);
    }

    public SshAuthenticationMode SelectedAuthenticationMode
    {
        get => _selectedAuthenticationMode;
        private set
        {
            if (_selectedAuthenticationMode == value)
            {
                return;
            }

            this.RaiseAndSetIfChanged(ref _selectedAuthenticationMode, value);
            this.RaisePropertyChanged(nameof(IsPasswordMode));
            this.RaisePropertyChanged(nameof(IsPrivateKeyMode));
        }
    }

    public bool IsPasswordMode => SelectedAuthenticationMode == SshAuthenticationMode.Password;

    public bool IsPrivateKeyMode => SelectedAuthenticationMode == SshAuthenticationMode.PrivateKey;

    public ReactiveCommand<Unit, Unit> AddSessionCommand { get; }

    public ReactiveCommand<SshSessionItemViewModel, Unit> RemoveSessionCommand { get; }

    public ReactiveCommand<Unit, Unit> SelectPasswordAuthCommand { get; }

    public ReactiveCommand<Unit, Unit> SelectPrivateKeyAuthCommand { get; }

    public ReactiveCommand<Unit, Unit> RefreshSnapshotCommand { get; }

    public void Dispose()
    {
        foreach (var session in _sessions.ToArray())
        {
            session.Dispose();
        }
    }

    private async Task AddSessionAsync()
    {
        SshSessionItemViewModel? sessionViewModel = null;
        try
        {
            IsBusy = true;
            StatusMessage = "正在创建 SSH 会话...";

            if (IsPasswordMode && string.IsNullOrWhiteSpace(Password))
            {
                StatusMessage = "请填写密码或切换至私钥登录。";
                return;
            }

            if (IsPrivateKeyMode && string.IsNullOrWhiteSpace(PrivateKeyPath))
            {
                StatusMessage = "请提供私钥路径或切换至密码登录。";
                return;
            }

            var options = new SshSessionOptions(
                Host,
                Port,
                UserName,
                IsPasswordMode ? Password : null,
                IsPrivateKeyMode ? PrivateKeyPath : null,
                IsPrivateKeyMode ? PrivateKeyPassphrase : null,
                DisplayName,
                AllowAnyHostKey,
                PreferredShell,
                SshExecutablePath);

            var info = await _sshSessionService.StartSessionAsync(options, CancellationToken.None).ConfigureAwait(false);

            sessionViewModel = new SshSessionItemViewModel(info, _sshSessionService, _logger);
            sessionViewModel.Initialize();

            var firstStatus = await sessionViewModel
                .WhenAnyValue(x => x.Status)
                .SkipWhile(status => status == SshSessionStatus.Connecting)
                .Take(1)
                .Timeout(TimeSpan.FromSeconds(10))
                .ToTask(CancellationToken.None)
                .ConfigureAwait(false);

            if (firstStatus is SshSessionStatus.Error or SshSessionStatus.Disconnected)
            {
                var latestError = await Dispatcher.UIThread.InvokeAsync(() =>
                    sessionViewModel.Messages.LastOrDefault(m => m.IsError)?.Content);
                sessionViewModel.Dispose();

                StatusMessage = string.IsNullOrWhiteSpace(latestError)
                    ? "创建会话失败：未能保持连接。"
                    : $"创建会话失败：{latestError}";
                return;
            }

            const string handshakeToken = "__aurora_ssh_handshake__";
            var handshakeSent = await _sshSessionService.SendAsync(sessionViewModel.SessionId, $"echo {handshakeToken}", CancellationToken.None).ConfigureAwait(false);
            if (!handshakeSent)
            {
                sessionViewModel.Dispose();
                StatusMessage = "创建会话失败：无法发送握手命令。";
                return;
            }

            try
            {
                await _sshSessionService.ObserveMessages(sessionViewModel.SessionId)
                    .Where(m => m.Direction == SshMessageDirection.Incoming && m.Content.Contains(handshakeToken, StringComparison.Ordinal))
                    .Take(1)
                    .Timeout(TimeSpan.FromSeconds(5))
                    .ToTask(CancellationToken.None)
                    .ConfigureAwait(false);
            }
            catch (TimeoutException)
            {
                sessionViewModel.Dispose();
                StatusMessage = "创建会话失败：握手命令无响应。";
                return;
            }

            await Task.Delay(TimeSpan.FromSeconds(0.5)).ConfigureAwait(false);

            var stableStatus = await Dispatcher.UIThread.InvokeAsync(() => sessionViewModel.Status);
            if (stableStatus is SshSessionStatus.Error or SshSessionStatus.Disconnected)
            {
                var latestError = await Dispatcher.UIThread.InvokeAsync(() =>
                    sessionViewModel.Messages.LastOrDefault(m => m.IsError)?.Content);
                sessionViewModel.Dispose();

                StatusMessage = string.IsNullOrWhiteSpace(latestError)
                    ? "创建会话失败：未能保持连接。"
                    : $"创建会话失败：{latestError}";
                return;
            }

            await Dispatcher.UIThread.InvokeAsync(() =>
            {
                _sessions.Add(sessionViewModel);
                SelectedSession = sessionViewModel;
            });

            StatusMessage = $"会话 {sessionViewModel.DisplayName} 已创建。";
        }
        catch (Exception ex)
        {
            StatusMessage = $"创建会话失败: {ex.Message}";
            _logger?.LogError(ex, "创建 SSH 会话失败。");
            sessionViewModel?.Dispose();
        }
        finally
        {
            IsBusy = false;
        }
    }

    private async Task RemoveSessionAsync(SshSessionItemViewModel? session)
    {
        if (session is null)
        {
            return;
        }

        _logger?.LogInformation("准备移除 SSH 会话 {SessionId}", session.SessionId);
        await _sshSessionService.StopSessionAsync(session.SessionId).ConfigureAwait(false);

        await Dispatcher.UIThread.InvokeAsync(() =>
        {
            _sessions.Remove(session);
            if (ReferenceEquals(SelectedSession, session))
            {
                SelectedSession = _sessions.LastOrDefault();
            }

            session.Dispose();
            StatusMessage = $"会话 {session.DisplayName} 已移除。";
        });
    }

    private void RefreshSnapshot()
    {
        var snapshot = _sshSessionService.GetSessions();

        foreach (var session in _sessions.ToArray())
        {
            if (snapshot.All(x => x.SessionId != session.SessionId))
            {
                session.Dispose();
                _sessions.Remove(session);
            }
        }

        foreach (var info in snapshot)
        {
            if (_sessions.All(x => x.SessionId != info.SessionId))
            {
                var vm = new SshSessionItemViewModel(info, _sshSessionService, _logger);
                vm.Initialize();
                _sessions.Add(vm);
            }
        }

        if (SelectedSession == null || !_sessions.Contains(SelectedSession))
        {
            SelectedSession = _sessions.FirstOrDefault();
        }
    }
}

/// <summary>
/// 表示单个 SSH 会话的视图模型
/// </summary>
public sealed class SshSessionItemViewModel : ReactiveObject, IDisposable
{
    private readonly ISshSessionService _sshSessionService;
    private readonly ILogger? _logger;
    private readonly CompositeDisposable _disposables = new();
    private readonly ObservableCollection<SshMessageEntry> _messages = new();

    private string _displayName;
    private SshSessionStatus _status;
    private string _outgoingText = string.Empty;
    private DateTime _createdAtUtc;

    public SshSessionItemViewModel(SshSessionInfo info, ISshSessionService sshSessionService, ILogger? logger = null)
    {
        _sshSessionService = sshSessionService;
        _logger = logger;
        SessionId = info.SessionId;
        _displayName = info.DisplayName;
        _status = info.Status;
        _createdAtUtc = info.CreatedAtUtc;

        SendCommand = ReactiveCommand.CreateFromTask(SendAsync,
            this.WhenAnyValue(x => x.Status, x => x.OutgoingText,
                (status, text) => status == SshSessionStatus.Connected && !string.IsNullOrWhiteSpace(text)));

        DisconnectCommand = ReactiveCommand.CreateFromTask(DisconnectAsync,
            this.WhenAnyValue(x => x.Status, status => status is SshSessionStatus.Connected or SshSessionStatus.Connecting));
    }

    public Guid SessionId { get; }

    public ObservableCollection<SshMessageEntry> Messages => _messages;

    public string DisplayName
    {
        get => _displayName;
        private set => this.RaiseAndSetIfChanged(ref _displayName, value);
    }

    public SshSessionStatus Status
    {
        get => _status;
        private set => this.RaiseAndSetIfChanged(ref _status, value);
    }

    public string OutgoingText
    {
        get => _outgoingText;
        set => this.RaiseAndSetIfChanged(ref _outgoingText, value);
    }

    public DateTime CreatedAtUtc
    {
        get => _createdAtUtc;
        private set => this.RaiseAndSetIfChanged(ref _createdAtUtc, value);
    }

    public bool IsConnected => Status == SshSessionStatus.Connected;

    public ReactiveCommand<Unit, Unit> SendCommand { get; }

    public ReactiveCommand<Unit, Unit> DisconnectCommand { get; }

    public void Initialize()
    {
        try
        {
            var statusSubscription = _sshSessionService
                .ObserveStatus(SessionId)
                .ObserveOn(RxApp.MainThreadScheduler)
                .Subscribe(status =>
                {
                    Status = status;
                });

            _disposables.Add(statusSubscription);

            var messageSubscription = _sshSessionService
                .ObserveMessages(SessionId)
                .ObserveOn(RxApp.MainThreadScheduler)
                .Subscribe(message =>
                {
                    var entry = SshMessageEntry.FromMessage(message);
                    _messages.Add(entry);
                });

            _disposables.Add(messageSubscription);
        }
        catch (Exception ex)
        {
            _logger?.LogError(ex, "订阅 SSH 会话 {SessionId} 流失败。", SessionId);
        }
    }

    private async Task SendAsync()
    {
        var text = OutgoingText;
        if (string.IsNullOrWhiteSpace(text))
        {
            return;
        }

        var result = await _sshSessionService.SendAsync(SessionId, text, CancellationToken.None).ConfigureAwait(false);
        if (result)
        {
            await Dispatcher.UIThread.InvokeAsync(() =>
            {
                OutgoingText = string.Empty;
            });
        }
    }

    private Task DisconnectAsync()
    {
        return _sshSessionService.StopSessionAsync(SessionId);
    }

    public void Dispose()
    {
        _disposables.Dispose();
    }
}

/// <summary>
/// UI 消息项
/// </summary>
public sealed record SshMessageEntry(
    Guid SessionId,
    string Timestamp,
    SshMessageDirection Direction,
    string Content,
    bool IsError)
{
    public static SshMessageEntry FromMessage(SshMessage message)
    {
        var timestamp = message.Timestamp.ToLocalTime().ToString("HH:mm:ss");
        return new SshMessageEntry(
            message.SessionId,
            timestamp,
            message.Direction,
            message.Content,
            message.IsError);
    }
}

public enum SshAuthenticationMode
{
    Password,
    PrivateKey
}