using System;
using System.Collections.Generic;

namespace JD.Core
{
    /// <summary>
    /// A simple implementation of a cache that will compute a variation only once.
    /// </summary>
    public class Cache<TKey, TValue>
    {
        private readonly Dictionary<TKey, TValue> _dictionary = new Dictionary<TKey, TValue>();

        /// <summary>
        /// Looks into its cache first, when the result is not present uses the <paramref name="computeResult"/> to compute the result.
        /// </summary>
        public TValue GetOrCompute(TKey key, Func<TKey, TValue> computeResult)
        {
            TValue result;
            if (!TryGetValue(key, out result))
            {
                result = computeResult(key);
                lock (_dictionary)
                {
                    _dictionary[key] = result;
                }
            }
            return result;
        }

        private bool TryGetValue(TKey key, out TValue result)
        {
            lock (_dictionary)
            {
                return _dictionary.TryGetValue(key, out result);
            }
        }
    }
}