// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Collections.Generic;

namespace System.Linq
{
    public static partial class Enumerable
    {
        public static IEnumerable<TResult> Zip<TFirst, TSecond, TResult>(this IEnumerable<TFirst> first, IEnumerable<TSecond> second, Func<TFirst, TSecond, TResult> resultSelector)
        {
            if (first is null)
            {
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.first);
            }

            if (second is null)
            {
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.second);
            }

            if (resultSelector is null)
            {
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.resultSelector);
            }

            return ZipIterator(first, second, resultSelector);
        }

        public static IEnumerable<(TFirst First, TSecond Second)> Zip<TFirst, TSecond>(this IEnumerable<TFirst> first, IEnumerable<TSecond> second)
        {
            if (first is null)
            {
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.first);
            }

            if (second is null)
            {
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.second);
            }

            return ZipIterator(first, second);
        }

        /// <summary>
        /// Produces a sequence of tuples with elements from the three specified sequences.
        /// </summary>
        /// <typeparam name="TFirst">The type of the elements of the first input sequence.</typeparam>
        /// <typeparam name="TSecond">The type of the elements of the second input sequence.</typeparam>
        /// <typeparam name="TThird">The type of the elements of the third input sequence.</typeparam>
        /// <param name="first">The first sequence to merge.</param>
        /// <param name="second">The second sequence to merge.</param>
        /// <param name="third">The third sequence to merge.</param>
        /// <returns>A sequence of tuples with elements taken from the first, second, and third sequences, in that order.</returns>
        public static IEnumerable<(TFirst First, TSecond Second, TThird Third)> Zip<TFirst, TSecond, TThird>(this IEnumerable<TFirst> first, IEnumerable<TSecond> second, IEnumerable<TThird> third)
        {
            if (first is null)
            {
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.first);
            }

            if (second is null)
            {
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.second);
            }

            if (third is null)
            {
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.third);
            }

            return ZipIterator(first, second, third);
        }

        private static IEnumerable<(TFirst First, TSecond Second)> ZipIterator<TFirst, TSecond>(IEnumerable<TFirst> first, IEnumerable<TSecond> second)
        {
            using IEnumerator<TFirst> e1 = first.GetEnumerator();
            using IEnumerator<TSecond> e2 = second.GetEnumerator();
            while (e1.MoveNext() && e2.MoveNext())
            {
                yield return (e1.Current, e2.Current);
            }
        }

        private static IEnumerable<TResult> ZipIterator<TFirst, TSecond, TResult>(IEnumerable<TFirst> first, IEnumerable<TSecond> second, Func<TFirst, TSecond, TResult> resultSelector)
        {
            using IEnumerator<TFirst> e1 = first.GetEnumerator();
            using IEnumerator<TSecond> e2 = second.GetEnumerator();
            while (e1.MoveNext() && e2.MoveNext())
            {
                yield return resultSelector(e1.Current, e2.Current);
            }
        }

        private static IEnumerable<(TFirst First, TSecond Second, TThird Third)> ZipIterator<TFirst, TSecond, TThird>(IEnumerable<TFirst> first, IEnumerable<TSecond> second, IEnumerable<TThird> third)
        {
            using IEnumerator<TFirst> e1 = first.GetEnumerator();
            using IEnumerator<TSecond> e2 = second.GetEnumerator();
            using IEnumerator<TThird> e3 = third.GetEnumerator();
            while (e1.MoveNext() && e2.MoveNext() && e3.MoveNext())
            {
                yield return (e1.Current, e2.Current, e3.Current);
            }
        }
    }
}