using System;
using System.Collections;
using System.Collections.Generic;

namespace Substrate.Utility
{
    class LRUCache<TKey, TValue> : IDictionary<TKey, TValue>
    {
        private Dictionary<TKey, TValue> _data;
        private IndexedLinkedList<TKey> _index;

        private int _capacity;

        public LRUCache (int capacity)
        {
            if (_capacity <= 0)
            {
                throw new ArgumentException("Cache capacity must be positive");
            }

            _capacity = capacity;

            _data = new Dictionary<TKey, TValue>();
            _index = new IndexedLinkedList<TKey>();
        }

        #region IDictionary<TKey,TValue> Members

        public void Add (TKey key, TValue value)
        {
            if (_data.ContainsKey(key))
            {
                throw new ArgumentException("Attempted to insert a duplicate key");
            }

            _data[key] = value;
            _index.Add(key);

            if (_data.Count > _capacity)
            {
                _data.Remove(_index.First);
                _index.RemoveFirst();
            }
        }

        public bool ContainsKey (TKey key)
        {
            return _data.ContainsKey(key);
        }

        public ICollection<TKey> Keys
        {
            get { return _data.Keys; }
        }

        public bool Remove (TKey key)
        {
            if (_data.Remove(key))
            {
                _index.Remove(key);
                return true;
            }

            return false;
        }

        public bool TryGetValue (TKey key, out TValue value)
        {
            if (!_data.TryGetValue(key, out value))
            {
                return false;
            }

            _index.Remove(key);
            _index.Add(key);

            return true;
        }

        public ICollection<TValue> Values
        {
            get { return _data.Values; }
        }

        public TValue this[TKey key]
        {
            get
            {
                TValue value = _data[key];
                _index.Remove(key);
                _index.Add(key);
                return value;
            }
            set
            {
                _data[key] = value;
                _index.Remove(key);
                _index.Add(key);

                if (_data.Count > _capacity)
                {
                    _data.Remove(_index.First);
                    _index.RemoveFirst();
                }
            }
        }

        #endregion

        #region ICollection<KeyValuePair<TKey,TValue>> Members

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

        public void Clear ()
        {
            _data.Clear();
            _index.Clear();
        }

        public bool Contains (KeyValuePair<TKey, TValue> item)
        {
            return ((ICollection<KeyValuePair<TKey, TValue>>)_data).Contains(item);
        }

        public void CopyTo (KeyValuePair<TKey, TValue>[] array, int arrayIndex)
        {
            ((ICollection<KeyValuePair<TKey, TValue>>)_data).CopyTo(array, arrayIndex);
        }

        public int Count
        {
            get { return _data.Count; }
        }

        public bool IsReadOnly
        {
            get { return false; }
        }

        public bool Remove (KeyValuePair<TKey, TValue> item)
        {
            if (((ICollection<KeyValuePair<TKey, TValue>>)_data).Remove(item))
            {
                _index.Remove(item.Key);
                return true;
            }

            return false;
        }

        #endregion

        #region IEnumerable<KeyValuePair<TKey,TValue>> Members

        public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator ()
        {
            return _data.GetEnumerator();
        }

        #endregion

        #region IEnumerable Members

        IEnumerator IEnumerable.GetEnumerator ()
        {
            return _data.GetEnumerator();
        }

        #endregion
    }
}