edit

XLAB2/AccountingBookEditWindowViewModel.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Windows.Input;
+
+namespace XLAB2
+{
+    internal sealed class AccountingBookEditWindowViewModel : ObservableObject
+    {
+        private readonly IReadOnlyList<GroupOption> _existingItems;
+        private readonly string _originalKey;
+        private string _bookNumber;
+        private string _key;
+        private string _validationMessage;
+
+        public AccountingBookEditWindowViewModel(GroupOption seed, bool isNew, IReadOnlyList<GroupOption> existingItems)
+        {
+            var source = seed ?? new GroupOption();
+            _existingItems = existingItems ?? Array.Empty<GroupOption>();
+            _originalKey = Normalize(source.Key);
+            IsNew = isNew;
+            BookNumber = source.Title ?? string.Empty;
+            Key = source.Key ?? string.Empty;
+
+            ConfirmCommand = new RelayCommand(Confirm);
+            CancelCommand = new RelayCommand(Cancel);
+        }
+
+        public event EventHandler<bool?> CloseRequested;
+
+        public string BookNumber
+        {
+            get { return _bookNumber; }
+            set { SetProperty(ref _bookNumber, value); }
+        }
+
+        public ICommand CancelCommand { get; private set; }
+
+        public ICommand ConfirmCommand { get; private set; }
+
+        public bool IsNew { get; private set; }
+
+        public string Key
+        {
+            get { return _key; }
+            set { SetProperty(ref _key, value); }
+        }
+
+        public string Title
+        {
+            get { return IsNew ? "Новая книга учета" : "Редактирование книги учета"; }
+        }
+
+        public string ValidationMessage
+        {
+            get { return _validationMessage; }
+            private set { SetProperty(ref _validationMessage, value); }
+        }
+
+        public GroupOption ToResult()
+        {
+            return new GroupOption
+            {
+                Key = Normalize(Key) ?? string.Empty,
+                Title = Normalize(BookNumber) ?? string.Empty
+            };
+        }
+
+        private void Cancel(object parameter)
+        {
+            RaiseCloseRequested(false);
+        }
+
+        private void Confirm(object parameter)
+        {
+            var normalizedKey = Normalize(Key);
+            if (normalizedKey == null)
+            {
+                ValidationMessage = "Укажите ключ книги учета.";
+                return;
+            }
+
+            var normalizedBookNumber = Normalize(BookNumber);
+            if (normalizedBookNumber == null)
+            {
+                ValidationMessage = "Укажите номер книги учета.";
+                return;
+            }
+
+            var duplicateKey = _existingItems.FirstOrDefault(delegate(GroupOption item)
+            {
+                return item != null
+                       && !IsCurrentItem(item)
+                       && string.Equals(Normalize(item.Key), normalizedKey, StringComparison.OrdinalIgnoreCase);
+            });
+            if (duplicateKey != null)
+            {
+                ValidationMessage = string.Format("Ключ книги учета \"{0}\" уже существует.", normalizedKey);
+                return;
+            }
+
+            var duplicateBookNumber = _existingItems.FirstOrDefault(delegate(GroupOption item)
+            {
+                return item != null
+                       && !IsCurrentItem(item)
+                       && string.Equals(Normalize(item.Title), normalizedBookNumber, StringComparison.OrdinalIgnoreCase);
+            });
+            if (duplicateBookNumber != null)
+            {
+                ValidationMessage = string.Format("Книга учета \"{0}\" уже существует.", normalizedBookNumber);
+                return;
+            }
+
+            ValidationMessage = string.Empty;
+            RaiseCloseRequested(true);
+        }
+
+        private bool IsCurrentItem(GroupOption item)
+        {
+            return !IsNew
+                   && string.Equals(Normalize(item == null ? null : item.Key), _originalKey, StringComparison.OrdinalIgnoreCase);
+        }
+
+        private static string Normalize(string value)
+        {
+            return string.IsNullOrWhiteSpace(value) ? null : value.Trim();
+        }
+
+        private void RaiseCloseRequested(bool? dialogResult)
+        {
+            var handler = CloseRequested;
+            if (handler != null)
+            {
+                handler(this, dialogResult);
+            }
+        }
+    }
+}