using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;

namespace System.Linq
{
	public static partial class Enumerable
	{
		// Count / LongCount

		public static int Count<TSource> (this IEnumerable<TSource> source)
		{
			if (source is ICollection<TSource>) return ((ICollection<TSource>)source).Count;
			if (source is ICollection) return ((ICollection)source).Count;

			int count = 0;
			foreach (TSource element in source) count++;
			return count;
		}

		public static int Count<TSource> (this IEnumerable<TSource> source, Func<TSource, bool> predicate)
		{
			if (source == null) throw new ArgumentNullException ("source");
			if (predicate == null) throw new ArgumentNullException ("predicate");

			int count = 0;
			foreach (TSource element in source)
				if (predicate (element))
					count++;

			return count;
		}

		public static long LongCount<TSource> (this IEnumerable<TSource> source)
		{
			if (source is ICollection<TSource>) return ((ICollection<TSource>)source).Count;
			if (source is ICollection) return ((ICollection)source).Count;

			long count = 0;
			foreach (TSource element in source) count++;
			return count;
		}

		public static long LongCount<TSource> (this IEnumerable<TSource> source, Func<TSource, bool> predicate)
		{
			if (source == null) throw new ArgumentNullException ("source");
			if (predicate == null) throw new ArgumentNullException ("predicate");

			long count = 0;
			foreach (TSource element in source)
				if (predicate (element))
					count++;

			return count;
		}

		// Min

		public static TSource Min<TSource> (this IEnumerable<TSource> source) 
		{
			if (!source.Any () && default (TSource) == null) return default (TSource);
			return source.Aggregate ((accum, element) => Comparer<TSource>.Default.Compare (accum, element) < 0 ? accum : element);
		}

		public static TSource? Min<TSource> (this IEnumerable<TSource?> source)
			where TSource : struct
		{
			if (!source.Any ()) return default (TSource?);
			return source.Aggregate ((accum, element) => Comparer<TSource?>.Default.Compare (accum, element) < 0 ? accum : element);
		}

		public static TResult Min<TSource, TResult> (this IEnumerable<TSource> source, Func<TSource, TResult> selector)
		{
			return source.Select (selector).Min ();
		}

		// Max

		public static TSource Max<TSource> (this IEnumerable<TSource> source) 
		{
			if (!source.Any () && default (TSource) == null) return default (TSource);
			return source.Aggregate ((accum, element) => Comparer<TSource>.Default.Compare (accum, element) > 0 ? accum : element);
		}

		public static TSource? Max<TSource> (this IEnumerable<TSource?> source)
			where TSource : struct
		{
			if (!source.Any ()) return default (TSource?);
			return source.Aggregate ((accum, element) => Comparer<TSource?>.Default.Compare (accum, element) > 0 ? accum : element);
		}

		public static TResult Max<TSource, TResult> (this IEnumerable<TSource> source, Func<TSource, TResult> selector)
		{
			return source.Select (selector).Max ();
		}

		// Aggregate

		public static TSource Aggregate<TSource> (this IEnumerable<TSource> source, Func<TSource, TSource, TSource> func)
		{
			if (source == null) throw new ArgumentNullException ("source");
			if (func == null) throw new ArgumentNullException ("func");

			bool noElements = true;
			TSource runningValue = default (TSource);

			foreach (TSource element in source)
			{
				if (noElements)
				{
					noElements = false;
					runningValue = element;
				}
				else
					runningValue = func (runningValue, element);
			}

			if (noElements) ThrowNoElements ();
			return runningValue;
		}

		public static TAccumulate Aggregate<TSource, TAccumulate> (
			this IEnumerable<TSource> source,
			TAccumulate seed,
			Func<TAccumulate, TSource, TAccumulate> func)
		{
			return source.Aggregate (seed, func, x => x);
		}

		public static TResult Aggregate<TSource, TAccumulate, TResult> (
			this IEnumerable<TSource> source, TAccumulate seed,
			Func<TAccumulate, TSource, TAccumulate> func,
			Func<TAccumulate, TResult> resultSelector)
		{
			if (source == null) throw new ArgumentNullException ("source");
			if (func == null) throw new ArgumentNullException ("func");
			if (resultSelector == null) throw new ArgumentNullException ("resultSelector");

			TAccumulate runningValue = seed;

			foreach (TSource element in source)
				runningValue = func (runningValue, element);

			return resultSelector (runningValue);
		}

	}
}