using System;
using System.Collections.ObjectModel;
using System.Windows;
using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using HC_APTBS.Services;
using HC_APTBS.Views.Dialogs;

namespace HC_APTBS.ViewModels.Dialogs
{
    /// <summary>
    /// ViewModel for the user management dialog.
    /// Invokes incremental methods on <see cref="IConfigurationService"/>
    /// (<c>AddUser</c>, <c>RemoveUser</c>, <c>ChangeUserPassword</c>) so that
    /// hashes of untouched accounts are preserved. Each action persists immediately;
    /// the dialog has no Accept/Cancel split — Close simply dismisses the window.
    /// </summary>
    public sealed partial class UserManageViewModel : ObservableObject
    {
        private readonly IConfigurationService _config;
        private readonly ILocalizationService _loc;

        /// <summary>Creates the ViewModel and populates <see cref="Users"/> from the service.</summary>
        public UserManageViewModel(IConfigurationService config, ILocalizationService loc)
        {
            _config = config;
            _loc    = loc;
            ReloadUsers();
        }

        // ── Bindable state ────────────────────────────────────────────────────

        /// <summary>Usernames currently stored in the configuration.</summary>
        public ObservableCollection<string> Users { get; } = new();

        /// <summary>Currently selected username in the DataGrid, or null when nothing is selected.</summary>
        [ObservableProperty]
        [NotifyCanExecuteChangedFor(nameof(RemoveCommand))]
        [NotifyCanExecuteChangedFor(nameof(ChangePasswordCommand))]
        private string? _selectedUser;

        /// <summary>Raised to close the owning dialog window.</summary>
        public event Action? RequestClose;

        // ── Commands ──────────────────────────────────────────────────────────

        /// <summary>Prompts for a username and password, then adds the user via the service.</summary>
        [RelayCommand]
        private void Add()
        {
            var prompt = new UserPromptDialog(
                _loc.GetString("Dialog.UserManage.Prompt.AddTitle"),
                usernameVisible: true)
            {
                Owner = Application.Current?.Windows.Count > 0
                    ? GetActiveWindow()
                    : null
            };

            if (prompt.ShowDialog() != true)
                return;

            string username = prompt.EnteredUsername?.Trim() ?? string.Empty;
            string password = prompt.EnteredPassword ?? string.Empty;

            if (string.IsNullOrEmpty(username) || string.IsNullOrEmpty(password))
            {
                ShowError("Dialog.UserManage.Error.Empty", "Dialog.UserManage.Error.EmptyTitle");
                return;
            }
            if (username.IndexOfAny(new[] { ':', ',' }) >= 0)
            {
                ShowError("Dialog.UserManage.Error.InvalidChars", "Dialog.UserManage.Error.InvalidCharsTitle");
                return;
            }

            if (!_config.AddUser(username, password))
            {
                ShowError("Dialog.UserManage.Error.Duplicate", "Dialog.UserManage.Error.DuplicateTitle");
                return;
            }

            ReloadUsers();
            SelectedUser = username;
        }

        /// <summary>Removes the selected user after confirmation, refusing when only one user remains.</summary>
        [RelayCommand(CanExecute = nameof(HasSelection))]
        private void Remove()
        {
            string user = SelectedUser!;
            var confirm = MessageBox.Show(
                string.Format(_loc.GetString("Dialog.UserManage.Confirm.Remove"), user),
                _loc.GetString("Dialog.UserManage.Confirm.RemoveTitle"),
                MessageBoxButton.YesNo,
                MessageBoxImage.Question);

            if (confirm != MessageBoxResult.Yes)
                return;

            if (!_config.RemoveUser(user))
            {
                ShowError("Dialog.UserManage.Error.LastUser", "Dialog.UserManage.Error.LastUserTitle");
                return;
            }

            ReloadUsers();
        }

        /// <summary>Prompts for a new password for the selected user and applies it.</summary>
        [RelayCommand(CanExecute = nameof(HasSelection))]
        private void ChangePassword()
        {
            string user = SelectedUser!;

            var prompt = new UserPromptDialog(
                string.Format(_loc.GetString("Dialog.UserManage.Prompt.ChangeTitle"), user),
                usernameVisible: false,
                prefillUsername: user)
            {
                Owner = GetActiveWindow()
            };

            if (prompt.ShowDialog() != true)
                return;

            string newPassword = prompt.EnteredPassword ?? string.Empty;
            if (string.IsNullOrEmpty(newPassword))
            {
                ShowError("Dialog.UserManage.Error.Empty", "Dialog.UserManage.Error.EmptyTitle");
                return;
            }

            if (!_config.ChangeUserPassword(user, newPassword))
            {
                ShowError("Dialog.UserManage.Error.Empty", "Dialog.UserManage.Error.EmptyTitle");
                return;
            }
        }

        /// <summary>Closes the dialog.</summary>
        [RelayCommand]
        private void Close() => RequestClose?.Invoke();

        // ── Helpers ───────────────────────────────────────────────────────────

        private bool HasSelection() => !string.IsNullOrEmpty(SelectedUser);

        /// <summary>Reloads the user list from the service, preserving selection when possible.</summary>
        private void ReloadUsers()
        {
            string? previous = SelectedUser;
            Users.Clear();
            foreach (var name in _config.GetUsers())
                Users.Add(name);

            SelectedUser = (previous != null && Users.Contains(previous)) ? previous : null;
        }

        private void ShowError(string messageKey, string titleKey)
        {
            MessageBox.Show(
                _loc.GetString(messageKey),
                _loc.GetString(titleKey),
                MessageBoxButton.OK,
                MessageBoxImage.Stop);
        }

        /// <summary>Returns the topmost active window for use as a dialog owner, or null if none.</summary>
        private static Window? GetActiveWindow()
        {
            foreach (Window w in Application.Current.Windows)
            {
                if (w.IsActive) return w;
            }
            return Application.Current.MainWindow;
        }
    }
}