﻿/*
 * Copyright © 2010, Denys Vuika
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *  http://www.apache.org/licenses/LICENSE-2.0
 *  
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

using System.Globalization;
using System.Windows.Data;

namespace System.Windows.Controls.WpfPropertyGrid
{
  /// <summary>
  /// Converts a null value into a string representation.
  /// </summary>
  public class NullValueConverter : IValueConverter
  {
    /// <summary>
    /// Default Null presentation. The default value is "(null)".
    /// </summary>
    public const string NullString = "(null)";

    #region IValueConverter Members

    /// <summary>
    /// Converts a value.
    /// </summary>
    /// <param name="value">The value produced by the binding source.</param>
    /// <param name="targetType">The type of the binding target property.</param>
    /// <param name="parameter">The converter parameter to use.</param>
    /// <param name="culture">The culture to use in the converter.</param>
    /// <returns>
    /// A converted value. If the method returns null, the valid null value is used.
    /// </returns>
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
      if (value == null)
        return parameter ?? NullString;
      else
        return value;
    }

    /// <summary>
    /// Converts a value.
    /// </summary>
    /// <param name="value">The value that is produced by the binding target.</param>
    /// <param name="targetType">The type to convert to.</param>
    /// <param name="parameter">The converter parameter to use.</param>
    /// <param name="culture">The culture to use in the converter.</param>
    /// <returns>
    /// A converted value. If the method returns null, the valid null value is used.
    /// </returns>
    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
      if (value == null) return null;

      string stringValue = value.ToString();
      if (string.IsNullOrEmpty(stringValue)) return null;

      bool isNull = (parameter != null) ? stringValue == (string)parameter : stringValue == NullString;
      return (isNull) ? null : value;
    }

    #endregion
  }
}
