using System;

namespace PrimeFactorsTask
{
    public static class PrimeFactors
    {
        /// <summary>
        /// Compute the prime factors of a given natural number.
        /// A prime number is only evenly divisible by itself and 1.
        /// Note that 1 is not a prime number.
        /// </summary>
        /// <param name="number">Source number.</param>
        /// <returns>Prime factors of a given natural number.</returns>
        /// <exception cref="ArgumentException">Thrown when number less or equal 0.</exception>
        /// <example>
        /// 60 => {2, 2, 3, 5}
        /// 8 => {2, 2, 2}
        /// 12 => {2, 2, 3}
        /// 901255 => {5, 17, 23, 461}
        /// 93819012551 => {11, 9539, 894119}
        /// </example>
        public static int[] GetFactors(int number)
        {
            if (number <= 0)
            {
                throw new ArgumentException("Argument out of range", nameof(number));
            }

            int numberOfDividers = 0;
            int[] dividers = new int[numberOfDividers];
            while (number != 1)
            {
                for (int i = 2; i <= number; i++)
                {
                    if (number % i == 0 && IsPrime(i))
                    {
                        int[] copy = dividers;
                        numberOfDividers++;
                        dividers = new int[numberOfDividers];
                        Array.Copy(copy, 0, dividers, 0, numberOfDividers - 1);
                        dividers[numberOfDividers - 1] = i;
                        number /= i;
                        break;
                    }
                }
            }

            return dividers;
        }

        private static bool IsPrime(int number)
        {
            if (number == 0 || number == 1)
            {
                return false;
            }
            else
            {
                for (int i = 2; i <= number / 2; i++)
                {
                    if (number % i == 0)
                    {
                        return false;
                    }
                }
            }

            return true;
        }
    }
}