using System;
using System.Collections.Generic;
using JD.Kernel.StaticHelpers;

namespace JD.Collections
{
    /// <summary>
    /// Base framework for a keyed cache.
    /// </summary>
    public class KeyedCacheBase<TKey, TValue> : IEnumerable<KeyValuePair<TKey, TValue>>
    {
        private Dictionary<TKey, TValue> m_cache = new Dictionary<TKey, TValue>();

        /// <summary>
        /// Returns the value for the key, (if not cached, will use the provider).
        /// </summary>
        /// <param name="key"></param>
        /// <param name="provider"></param>
        /// <returns></returns>
        protected TValue this[TKey key, Converter<TKey, TValue> provider]
        {
            get
            {
                Throw.IfNull(provider, "provider");

                TValue result;
                lock (m_cache)
                {
                    if (!m_cache.TryGetValue(key, out result))
                    {
                        result = provider(key);
                        if (!m_cache.ContainsKey(key))
                        {
                            m_cache.Add(key, result);
                        }
                    }
                }
                return result;
            }
        }

        /// <summary>
        /// Clears the cache.
        /// </summary>
        public void Clear()
        {
            m_cache.Clear();
        }

        /// <summary>
        /// Adds in the cache
        /// </summary>
        /// <param name="key"></param>
        /// <param name="value"></param>
        public void Add(TKey key, TValue value)
        {
            m_cache.Add(key, value);
        }

        /// <summary>
        /// True if the key is cached.
        /// </summary>
        /// <param name="key"></param>
        /// <returns></returns>
        public bool Contains(TKey key)
        {
            return m_cache.ContainsKey(key);
        }

        /// <summary>
        /// Lists all the values.
        /// </summary>
        public IEnumerable<TValue> Values
        {
            get { return m_cache.Values; }
        }

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

        /// <summary>
        /// Enumerates the entries.
        /// </summary>
        /// <returns></returns>
        public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
        {
            return m_cache.GetEnumerator();
        }

        #endregion

        #region IEnumerable Members

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

        #endregion
    }
}