using System;
using System.Collections.Generic;

namespace DataModel.Helpers
{
    /// <summary>
    /// LINQ helper methods
    /// </summary>
    public static class LinqHelpers
    {
        /// <summary>
        /// Filters for distinct elements by given key
        /// </summary>
        /// <typeparam name="TSource">Source data type</typeparam>
        /// <typeparam name="TKey">Key data type</typeparam>
        /// <param name="source">Source data</param>
        /// <param name="keySelector">Key value function</param>
        /// <returns>Distinct elements from source</returns>
        public static IEnumerable<TSource> DistinctBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
        {
            HashSet<TKey> keys = new HashSet<TKey>();
            foreach (TSource element in source)
            {
                if (keys.Add(keySelector(element)))
                {
                    yield return element;
                }
            }
        }

        /// <summary>
        /// Groups the data into batches of give size
        /// </summary>
        /// <typeparam name="T">Data type of data</typeparam>
        /// <param name="allData">Data to break into batches</param>
        /// <param name="batchSize">Size of batches to create</param>
        /// <returns>Enumerable collection of batches to process</returns>
        public static IEnumerable<List<T>> BatchGroup<T>(this IEnumerable<T> allData, int batchSize)
        {
            List<T> batchGroup = new List<T>();

            //Loop through data and group into batches
            foreach (T data in allData)
            {
                batchGroup.Add(data);

                if (batchGroup.Count == batchSize)
                {
                    //Return batch of data
                    yield return batchGroup;
                    batchGroup = new List<T>();
                }
            }

            //Return remaining data
            yield return batchGroup;
        }
    }
}