using System;

namespace ShiftArrayElements
{
    public static class Shifter
    {
        /// <summary>
        /// Shifts elements in a <see cref="source"/> array using <see cref="iterations"/> array for getting directions and iterations (see README.md for detailed instructions).
        /// </summary>
        /// <param name="source">A source array.</param>
        /// <param name="iterations">An array with iterations.</param>
        /// <returns>An array with shifted elements.</returns>
        /// <exception cref="ArgumentNullException">source array is null.</exception>
        /// <exception cref="ArgumentNullException">iterations array is null.</exception>
        public static int[] Shift(int[] source, int[] iterations)
        {
            // #2. Implement the method using "for" statements and Array.Copy method.
            if (source is null)
            {
                throw new ArgumentNullException(nameof(source));
            }

            if (iterations is null)
            {
                throw new ArgumentNullException(nameof(iterations));
            }

            int sumEven = 0;
            int sumOdd = 0;
            for (int i = 0; i < iterations.Length; i += 2)
            {
                sumEven += iterations[i];
            }

            for (int i = 1; i < iterations.Length; i += 2)
            {
                sumOdd += iterations[i];
            }

            int iteration;

            if (sumEven > sumOdd)
            {
                iteration = sumEven - sumOdd;
                ShiftLeft(source, iteration);
            }
            else if (sumEven == sumOdd)
            {
                return source;
            }
            else
            {
                iteration = sumOdd - sumEven;
                ShiftRight(source, iteration);
            }

            return source;
        }

        private static void ShiftLeft(int[] array, int iterations = 1)
        {
            for (int i = 0; i < iterations; i++)
            {
                int firstElemen = array[0];
                for (int k = 0; k < array.Length - 1; k++)
                {
                    array[k] = array[k + 1];
                }

                array[^1] = firstElemen;
            }
        }

        private static void ShiftRight(int[] array, int iterations = 1)
        {
            for (int i = 0; i < iterations; i++)
            {
                int lastElement = array[^1];
                for (int k = array.Length - 1; k > 0; k--)
                {
                    array[k] = array[k - 1];
                }

                array[0] = lastElement;
            }
        }
    }
}