wp7 BaseDictionary<TKey, TValue>

/// <summary>
/// Represents a dictionary mapping keys to values.
/// </summary>
/// 
/// <remarks>
/// Provides the plumbing for the portions of IDictionary<TKey,
/// TValue> which can reasonably be implemented without any
/// dependency on the underlying representation of the dictionary.
/// </remarks>
[DebuggerDisplay("Count = {Count}")]
[DebuggerTypeProxy(PREFIX + "DictionaryDebugView`2" + SUFFIX)]
public abstract class BaseDictionary<TKey, TValue> : IDictionary<TKey, TValue> {
    private const string PREFIX = "System.Collections.Generic.Mscorlib_";
    private const string SUFFIX =",mscorlib,Version=2.0.0.0,Culture=neutral,PublicKeyToken=b77a5c561934e089";

    private KeyCollection keys;
    private ValueCollection values;

    protected BaseDictionary() { }

    public abstract int Count { get; }
    public abstract void Clear();
    public abstract void Add(TKey key, TValue value);
    public abstract bool ContainsKey(TKey key);
    public abstract bool Remove(TKey key);
    public abstract bool TryGetValue(TKey key, out TValue value);
    public abstract IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator();
    protected abstract void SetValue(TKey key, TValue value);

    public bool IsReadOnly {
        get { return false; }
    }

    public ICollection<TKey> Keys {
        get {
            if (this.keys == null)
                this.keys = new KeyCollection(this);

            return this.keys;
        }
    }

    public ICollection<TValue> Values {
        get {
            if (this.values == null)
                this.values = new ValueCollection(this);

            return this.values;
        }
    }

    public TValue this[TKey key] {
        get {
            TValue value;
            if (!this.TryGetValue(key, out value))
                throw new KeyNotFoundException();

            return value;
        }
        set {
            SetValue(key, value);
        }
    }

    public void Add(KeyValuePair<TKey, TValue> item) {
        this.Add(item.Key, item.Value);
    }

    public bool Contains(KeyValuePair<TKey, TValue> item) {
        TValue value;
        if (!this.TryGetValue(item.Key, out value))
            return false;

        return EqualityComparer<TValue>.Default.Equals(value, item.Value);
    }

    public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex) {
        Copy(this, array, arrayIndex);
    }

    public bool Remove(KeyValuePair<TKey, TValue> item) {
        if (!this.Contains(item))
            return false;

        return this.Remove(item.Key);
    }

    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {
        return this.GetEnumerator();
    }

    private abstract class Collection<T> : ICollection<T> {
        protected readonly IDictionary<TKey, TValue> dictionary;

        protected Collection(IDictionary<TKey, TValue> dictionary) {
            this.dictionary = dictionary;
        }

        public int Count {
            get { return this.dictionary.Count; }
        }

        public bool IsReadOnly {
            get { return true; }
        }

        public void CopyTo(T[] array, int arrayIndex) {
            Copy(this, array, arrayIndex);
        }

        public virtual bool Contains(T item) {
            foreach (T element in this)
                if (EqualityComparer<T>.Default.Equals(element, item))
                    return true;
            return false;
        }

        public IEnumerator<T> GetEnumerator() {
            foreach (KeyValuePair<TKey, TValue> pair in this.dictionary)
                yield return GetItem(pair);
        }

        protected abstract T GetItem(KeyValuePair<TKey, TValue> pair);

        public bool Remove(T item) {
            throw new NotSupportedException("Collection is read-only.");
        }

        public void Add(T item) {
            throw new NotSupportedException("Collection is read-only.");
        }

        public void Clear() {
            throw new NotSupportedException("Collection is read-only.");
        }

        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {
            return this.GetEnumerator();
        }
    }

    [DebuggerDisplay("Count = {Count}")]
    [DebuggerTypeProxy(PREFIX + "DictionaryKeyCollectionDebugView`2" + SUFFIX)]
    private class KeyCollection : Collection<TKey> {
        public KeyCollection(IDictionary<TKey, TValue> dictionary)
            : base(dictionary) { }

        protected override TKey GetItem(KeyValuePair<TKey, TValue> pair) {
            return pair.Key;
        }
        public override bool Contains(TKey item) {
            return this.dictionary.ContainsKey(item);
        }
    }

    [DebuggerDisplay("Count = {Count}")]
    [DebuggerTypeProxy(PREFIX + "DictionaryValueCollectionDebugView`2" + SUFFIX)]
    private class ValueCollection : Collection<TValue> {
        public ValueCollection(IDictionary<TKey, TValue> dictionary)
            : base(dictionary) { }

        protected override TValue GetItem(KeyValuePair<TKey, TValue> pair) {
            return pair.Value;
        }
    }

    private static void Copy<T>(ICollection<T> source, T[] array, int arrayIndex) {
        if (array == null)
            throw new ArgumentNullException("array");

        if (arrayIndex < 0 || arrayIndex > array.Length)
            throw new ArgumentOutOfRangeException("arrayIndex");

        if ((array.Length - arrayIndex) < source.Count)
            throw new ArgumentException("Destination array is not large enough. Check array.Length and arrayIndex.");

        foreach (T item in source)
            array[arrayIndex++] = item;
    }
}