using System;
using System.Diagnostics;
using System.Security.Permissions;
 
using MS.Internal.WindowsBase;  // for FriendAccessAllowed
 
namespace System.Windows
{
    /// <summary>
    ///
    /// </summary>
    //CASRemoval:[StrongNameIdentityPermissionAttribute(SecurityAction.InheritanceDemand, PublicKey=Microsoft.Internal.BuildInfo.WCP_PUBLIC_KEY_STRING)]
    [FriendAccessAllowed] // Built into Base, used by Core and Framework
    internal class UncommonField<T>
    {
        /// <summary>
        ///     Create a new UncommonField.
        /// </summary>
        public UncommonField() : this(default(T))
        {
        }
 
        /// <summary>
        ///     Create a new UncommonField.
        /// </summary>
        /// <param name="defaultValue">The default value of the field.</param>
        public UncommonField(T defaultValue)
        {
            _defaultValue = defaultValue;
            _hasBeenSet = false;
 
            lock (DependencyProperty.Synchronized)
            {
                _globalIndex = DependencyProperty.GetUniqueGlobalIndex(null, null);
 
                DependencyProperty.RegisteredPropertyList.Add();
            }
        }
 
        /// <summary>
        ///     Write the given value onto a DependencyObject instance.
        /// </summary>
        /// <param name="instance">The DependencyObject on which to set the value.</param>
        /// <param name="value">The value to set.</param>
        public void SetValue(DependencyObject instance, T value)
        {
            if (instance != null)
            {
                EntryIndex entryIndex = instance.LookupEntry(_globalIndex);
 
                // Set the value if it's not the default, otherwise remove the value.
                if (!object.ReferenceEquals(value, _defaultValue))
                {
                    instance.SetEffectiveValue(entryIndex, null /* dp */, _globalIndex, null /* metadata */, value, BaseValueSourceInternal.Local);
                    _hasBeenSet = true;
                }
                else
                {
                    instance.UnsetEffectiveValue(entryIndex, null /* dp */, null /* metadata */);
                }
            }
            else
            {
                throw new ArgumentNullException("instance");
            }
        }
 
        /// <summary>
        ///     Read the value of this field on a DependencyObject instance.
        /// </summary>
        /// <param name="instance">The DependencyObject from which to get the value.</param>
        /// <returns></returns>
        public T GetValue(DependencyObject instance)
        {
            if (instance != null)
            {
                if (_hasBeenSet)
                {
                    EntryIndex entryIndex = instance.LookupEntry(_globalIndex);
 
                    if (entryIndex.Found)
                    {
                        object value = instance.EffectiveValues[entryIndex.Index].LocalValue;
 
                        if (value != DependencyProperty.UnsetValue)
                        {
                            return (T)value;
                        }
                    }
                    return _defaultValue;
                }
                else
                {
                    return _defaultValue;
                }
            }
            else
            {
                throw new ArgumentNullException("instance");
            }
        }
 
 
        /// <summary>
        ///     Clear this field from the given DependencyObject instance.
        /// </summary>
        /// <param name="instance"></param>
        public void ClearValue(DependencyObject instance)
        {
            if (instance != null)
            {
                EntryIndex entryIndex = instance.LookupEntry(_globalIndex);
 
                instance.UnsetEffectiveValue(entryIndex, null /* dp */, null /* metadata */);
            }
            else
            {
                throw new ArgumentNullException("instance");
            }
        }
 
        internal int GlobalIndex
        {
            get
            {
                return _globalIndex;
            }
        }
 
        #region Private Fields
 
        private T _defaultValue;
        private int _globalIndex;
        private bool _hasBeenSet;
 
        #endregion
    }
}