ByteDecoder/RoyalLibrary

using System;
using System.Collections.Generic;
using ByteDecoder.Common.GuardClauses;

namespace ByteDecoder.RoyalLibrary
{
    /// <summary>
    /// 
    /// </summary>
    public static class RoyalExtensions
    {
        /// <summary>
        /// Deferred execution returning a LINQ sequence of elements, after applying the selector on each sequence element
        /// </summary>
        /// <typeparam name="TInput">Element type</typeparam>
        /// <typeparam name="TResult">Result data type</typeparam>
        /// <param name="source">Input LINQ sequence</param>
        /// <param name="element">Applied action to transform each collection element</param>
        /// <returns></returns>
        public static IEnumerable<TResult> Map<TInput, TResult>(this IEnumerable<TInput> source, Func<TInput, TResult> element)
        {
            Guard.Break.IfArgumentIsNull(source, nameof(source));
            Guard.Break.IfArgumentIsNull(element, nameof(element));

            foreach (var item in source)
            {
                yield return element(item);
            }
        }

        /// <summary>
        /// Returns the element with the Max property value, based on the selector of IComparable type
        /// in the sequence of elements
        /// </summary>
        /// <typeparam name="TElement"></typeparam>
        /// <typeparam name="TData"></typeparam>
        /// <param name="source"></param>
        /// <param name="selector"></param>
        /// <returns></returns>
        public static TElement MaxElement<TElement, TData>(this IEnumerable<TElement> source,
          Func<TElement, TData> selector) where TData : IComparable<TData>
        {
            Guard.Break.IfArgumentIsNull(source, nameof(source));
            Guard.Break.IfArgumentIsNull(selector, nameof(selector));

            var firstElement = true;
            var result = default(TElement);
            var maxValue = default(TData);

            foreach (var element in source)
            {
                var candidate = selector(element);
                if (!firstElement && (candidate.CompareTo(maxValue) <= 0)) continue;
                firstElement = false;
                maxValue = candidate;
                result = element;
            }
            return result;
        }
    }
}