#region License and Terms
// MoreLINQ - Extensions to LINQ to Objects
// Copyright (c) 2008 Jonathan Skeet. All rights reserved.
// 
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// 
//     http://www.apache.org/licenses/LICENSE-2.0
// 
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#endregion

namespace MoreLinq
{
    using System;
    using System.Collections.Generic;

    static partial class MoreEnumerable
    {
        /// <summary>
        /// Executes the given action on each element in the source sequence
        /// and yields it.
        /// </summary>
        /// <typeparam name="T">The type of the elements in the sequence</typeparam>
        /// <param name="source">The sequence of elements</param>
        /// <param name="action">The action to execute on each element</param>
        /// <returns>A sequence with source elements in their original order.</returns>
        /// <remarks>
        /// The returned sequence is essentially a duplicate of
        /// the original, but with the extra action being executed while the
        /// sequence is evaluated. The action is always taken before the element
        /// is yielded, so any changes made by the action will be visible in the
        /// returned sequence. This operator uses deferred execution and streams it results.
        /// </remarks>

        public static IEnumerable<T> Pipe<T>(this IEnumerable<T> source, Action<T> action)
        {
            if (source == null) throw new ArgumentNullException("source");
            if (action == null) throw new ArgumentNullException("action");
            return PipeImpl(source, action);
        }

        private static IEnumerable<T> PipeImpl<T>(this IEnumerable<T> source, Action<T> action)
        {
            foreach (var element in source)
            {
                action(element);
                yield return element;
            }
        }
    }
}
