using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;

namespace JiShe.CollectBus.Common.Extensions
{    
    /// <summary> 
    /// Extension methods for <see cref="IEnumerable{T}"/>.
    /// </summary>
    public static class EnumerableExtensions
    {
        /// <summary>
        /// Concatenates the members of a constructed <see cref="IEnumerable{T}"/> collection of type System.String, using the specified separator between each member.
        /// This is a shortcut for string.Join(...)
        /// </summary>
        /// <param name="source">A collection that contains the strings to concatenate.</param>
        /// <param name="separator">The string to use as a separator. separator is included in the returned string only if values has more than one element.</param>
        /// <returns>A string that consists of the members of values delimited by the separator string. If values has no members, the method returns System.String.Empty.</returns>
        [Description("Enumerable转换String")]
        public static string JoinAsString(this IEnumerable<string> source, string separator)
        {
            return string.Join(separator, source);
        }

        /// <summary>
        /// Concatenates the members of a collection, using the specified separator between each member.
        /// This is a shortcut for string.Join(...)
        /// </summary>
        /// <param name="source">A collection that contains the objects to concatenate.</param>
        /// <param name="separator">The string to use as a separator. separator is included in the returned string only if values has more than one element.</param>
        /// <typeparam name="T">The type of the members of values.</typeparam>
        /// <returns>A string that consists of the members of values delimited by the separator string. If values has no members, the method returns System.String.Empty.</returns>
        public static string JoinAsString<T>(this IEnumerable<T> source, string separator)
        {
            return string.Join(separator, source);
        }

        /// <summary>
        /// Filters a <see cref="IEnumerable{T}"/> by given predicate if given condition is true.
        /// </summary>
        /// <param name="source">Enumerable to apply filtering</param>
        /// <param name="condition">A boolean value</param>
        /// <param name="predicate">Predicate to filter the enumerable</param>
        /// <returns>Filtered or not filtered enumerable based on <paramref name="condition"/></returns>
        [Description("Enumerable筛选")]
        public static IEnumerable<T> WhereIf<T>(this IEnumerable<T> source, bool condition, Func<T, bool> predicate)
        {
            return condition
                ? source.Where(predicate)
                : source;
        }

        /// <summary>
        /// Filters a <see cref="IEnumerable{T}"/> by given predicate if given condition is true.
        /// </summary>
        /// <param name="source">Enumerable to apply filtering</param>
        /// <param name="condition">A boolean value</param>
        /// <param name="predicate">Predicate to filter the enumerable</param>
        /// <returns>Filtered or not filtered enumerable based on <paramref name="condition"/></returns>
        public static IEnumerable<T> WhereIf<T>(this IEnumerable<T> source, bool condition, Func<T, int, bool> predicate)
        {
            return condition
                ? source.Where(predicate)
                : source;
        }

        /// <summary>
        /// 分批
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="source"></param>
        /// <param name="batchSize"></param>
        /// <returns></returns>
        public static IEnumerable<IEnumerable<T>> Batch<T>(
        this IEnumerable<T> source,
        int batchSize)
        {
            var buffer = new List<T>(batchSize);
            foreach (var item in source)
            {
                buffer.Add(item);
                if (buffer.Count == batchSize)
                {
                    yield return buffer;
                    buffer = new List<T>(batchSize);
                }
            }
            if (buffer.Count > 0)
                yield return buffer;
        }

        //public static IEnumerable<IEnumerable<T>> Batch<T>(this IEnumerable<T> source, int batchSize)
        //{
        //    if (batchSize <= 0)
        //        throw new ArgumentOutOfRangeException(nameof(batchSize));

        //    using var enumerator = source.GetEnumerator();
        //    while (enumerator.MoveNext())
        //    {
        //        yield return GetBatch(enumerator, batchSize);
        //    }
        //}

        //private static IEnumerable<T> GetBatch<T>(IEnumerator<T> enumerator, int batchSize)
        //{
        //    do
        //    {
        //        yield return enumerator.Current;
        //        batchSize--;
        //    } while (batchSize > 0 && enumerator.MoveNext());
        //}
    }
}