using System.Collections.Generic;

namespace Modbus.Utility
{
    /// <summary>
    /// Functional utility methods.
    /// </summary>
    public static class FunctionalUtility
    {
        /// <summary>
        /// Memoizes the given function.
        /// </summary>
        public static Func<T> Memoize<T>(Func<T> generator)
        {
            bool hasValue = false;
            T returnValue = default(T);
            return delegate
            {
                if (!hasValue)
                {
                    returnValue = generator();
                    hasValue = true;
                }

                return returnValue;
            };
        }

        /// <summary>
        /// Memoizes the given function.
        /// </summary>
        public static Func<TInput, TOutput> Memoize<TInput, TOutput>(Func<TInput, TOutput> generator)
        {
            return Memoize(generator, delegate(TInput input) { return input; });
        }

        /// <summary>
        /// Memoizes the given function.
        /// </summary>
        public static Func<TInput, TOutput> Memoize<TInput, TKey, TOutput>(Func<TInput, TOutput> generator, Func<TInput, TKey> keySelector)
        {
            Dictionary<TKey, TOutput> cache = new Dictionary<TKey, TOutput>();
            return delegate(TInput input)
            {
                TOutput output;
                if (!cache.TryGetValue(keySelector(input), out output))
                {
                    output = generator(input);
                    cache.Add(keySelector(input), output);
                }

                return output;
            };
        }
    }
}