Utopia-Canteen-System/ViewModels/ScannerViewModel.cs

using DebounceTimer = System.Timers.Timer;
using System.Windows;
using System.Windows.Threading;
using System.Windows.Input;
using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using UtopiaCanteenSystem.Services;

namespace UtopiaCanteenSystem.ViewModels;

/// <summary>
/// ViewModel for ScannerView: RFID input, scan command, scanner status, current scan time.
/// Supports both Enter-to-submit and debounce-to-submit for keyboard-wedge scanners.
/// </summary>
public partial class ScannerViewModel : ObservableObject
{
    private const int DebounceMs = 200;
    private const int CooldownTickSeconds = 1;
    private static readonly TimeSpan ScannerInactivityTimeout = TimeSpan.FromSeconds(10);

    private readonly IRfidService _rfidService;
    private readonly INavigationService _navigation;
    private readonly AppSession _session;
    private readonly Dispatcher _uiDispatcher;
    private readonly DebounceTimer _debounceTimer;
    private readonly DispatcherTimer _cooldownTimer;
    private DateTime? _cooldownEndsUtc;
    private int _lastDisplayedCooldownSeconds = -1;
    private readonly DispatcherTimer _scannerStatusTimer;
    private DateTime? _lastScanActivityUtc;
    private readonly object _submitLock = new();
    private bool _isSubmitting;

    [ObservableProperty]
    [NotifyPropertyChangedFor(nameof(IsWatermarkVisible))]
    private string _cardIdInput = string.Empty;

    /// <summary>True when CardIdInput is empty; used to show/hide the "Scan Card ID" watermark.</summary>
    public bool IsWatermarkVisible => string.IsNullOrWhiteSpace(CardIdInput);

    [ObservableProperty]
    [NotifyPropertyChangedFor(nameof(ScannerStatusDisplay))]
    private string _scannerStatus = "Disconnected";

    public string ScannerStatusDisplay =>
        string.Equals(ScannerStatus, "Connected", StringComparison.Ordinal) ? "Connected" : "waiting for scan...";

    [ObservableProperty]
    private string _currentScanTime = DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss");

    [ObservableProperty]
    private string _message = string.Empty;

    [ObservableProperty]
    private bool _isSuccess;

    public ScannerViewModel(IRfidService rfidService, INavigationService navigation, AppSession session)
    {
        _rfidService = rfidService;
        _navigation = navigation;
        _session = session;

        _uiDispatcher = Application.Current?.Dispatcher ?? Dispatcher.CurrentDispatcher;
        _debounceTimer = new DebounceTimer(DebounceMs)
        {
            AutoReset = false
        };
        _debounceTimer.Elapsed += (_, _) =>
        {
            // Timer runs on a background thread; marshal back to UI thread.
            _uiDispatcher.BeginInvoke(() =>
            {
                lock (_submitLock)
                {
                    if (_isSubmitting)
                        return;
                }

                // If something already cleared the input (e.g., Enter submit), do nothing.
                if (string.IsNullOrWhiteSpace(CardIdInput))
                    return;

                if (ScanCommand.CanExecute(null))
                    ScanCommand.Execute(null);
            }, DispatcherPriority.Background);
        };

        _cooldownTimer = new DispatcherTimer
        {
            Interval = TimeSpan.FromSeconds(CooldownTickSeconds)
        };
        _cooldownTimer.Tick += (_, _) => UpdateCooldownMessage();

        _scannerStatusTimer = new DispatcherTimer
        {
            Interval = TimeSpan.FromSeconds(1)
        };
        _scannerStatusTimer.Tick += (_, _) => UpdateScannerStatusFromActivity();
        _scannerStatusTimer.Start();

        RefreshScannerStatus();
        RefreshTime();
    }

    partial void OnCardIdInputChanged(string value)
    {
        // Clear any previous message once a new scan starts.
        if (!string.IsNullOrWhiteSpace(value) && !string.IsNullOrEmpty(Message))
            Message = string.Empty;

        // If the user starts scanning again, don't keep overwriting their feedback with an old countdown.
        StopCooldownCountdown();

        // Keyboard-wedge scanners "type" into the TextBox. Any incoming characters means activity/connected.
        if (!string.IsNullOrWhiteSpace(value))
        {
            _lastScanActivityUtc = DateTime.UtcNow;
            ScannerStatus = "Connected";
        }

        RestartDebounceTimer();
    }

    private void RestartDebounceTimer()
    {
        _debounceTimer.Stop();

        // Only auto-submit when we have a non-empty value.
        if (string.IsNullOrWhiteSpace(CardIdInput))
            return;

        _debounceTimer.Start();
    }

    public void RefreshScannerStatus()
    {
        // Default: waiting for activity.
        ScannerStatus = "Disconnected";
    }

    public void RefreshTime()
    {
        CurrentScanTime = DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss");
    }

    [RelayCommand]
    private void Logout()
    {
        _session.Logout();
        _navigation.NavigateToAdminLogin();
    }

    /// <summary>Processes the current CardIdInput as a scan and navigates to dashboard on success.</summary>
    [RelayCommand]
    private void Scan()
    {
        lock (_submitLock)
        {
            if (_isSubmitting)
                return;
            _isSubmitting = true;
        }

        try
        {
            // Ensure any pending debounce doesn't fire after an explicit submit.
            _debounceTimer.Stop();
            StopCooldownCountdown();

            Message = string.Empty;
            IsSuccess = false;

            // Keep CardId as string (preserves leading zeros).
            var cardId = CardIdInput?.Trim() ?? string.Empty;

            // Avoid showing "empty" errors if something triggered submit after we already cleared input.
            if (string.IsNullOrWhiteSpace(cardId))
                return;

            var result = _rfidService.ProcessScanDetailed(cardId);
            IsSuccess = result.Success;
            Message = result.Message;

            // Always clear input after attempt so the next scan starts cleanly.
            CardIdInput = string.Empty;

            if (!result.Success && result.CooldownSecondsRemaining > 0)
            {
                StartCooldownCountdown(result.CooldownSecondsRemaining);
                return;
            }

            if (result.Success)
            {
                _navigation.StartDashboardSession();
                _navigation.NavigateToDashboard();
            }
        }
        finally
        {
            lock (_submitLock)
            {
                _isSubmitting = false;
            }
        }
    }

    private void StartCooldownCountdown(int seconds)
    {
        if (seconds <= 0)
            return;

        _cooldownEndsUtc = DateTime.UtcNow.AddSeconds(seconds);
        _lastDisplayedCooldownSeconds = -1;
        UpdateCooldownMessage(); // immediate update
        _cooldownTimer.Start();
    }

    private void StopCooldownCountdown()
    {
        _cooldownTimer.Stop();
        _cooldownEndsUtc = null;
        _lastDisplayedCooldownSeconds = -1;
    }

    private void UpdateCooldownMessage()
    {
        if (_cooldownEndsUtc is null)
            return;

        var remaining = (int)Math.Ceiling((_cooldownEndsUtc.Value - DateTime.UtcNow).TotalSeconds);
        if (remaining <= 0)
        {
            StopCooldownCountdown();
            Message = "You can scan now.";
            IsSuccess = true;
            return;
        }

        // Avoid redundant PropertyChanged churn.
        if (remaining == _lastDisplayedCooldownSeconds)
            return;
        _lastDisplayedCooldownSeconds = remaining;

        var unit = remaining == 1 ? "second" : "seconds";
        Message = $"Please wait {remaining} {unit}…";
        IsSuccess = false;
    }

    private void UpdateScannerStatusFromActivity()
    {
        if (_lastScanActivityUtc is null)
        {
            if (!string.Equals(ScannerStatus, "Disconnected", StringComparison.Ordinal))
                ScannerStatus = "Disconnected";
            return;
        }

        var inactiveFor = DateTime.UtcNow - _lastScanActivityUtc.Value;
        if (inactiveFor > ScannerInactivityTimeout)
        {
            if (!string.Equals(ScannerStatus, "Disconnected", StringComparison.Ordinal))
                ScannerStatus = "Disconnected";
        }
    }

    ~ScannerViewModel()
    {
        _scannerStatusTimer.Stop();
        _cooldownTimer.Stop();
        _debounceTimer.Stop();
    }
}