ClassLibrary

namespace Ch04Ex02PrimeFactorsLib;
using System.Linq;
using System.Reflection.Metadata;
using System.Runtime.ConstrainedExecution;
using System.Security.Cryptography.X509Certificates;
using static System.Console;
public class PFLib
{
    public List<string> primeFactors(double userinput)
    {
        int[] primeNumbers =
        {
        2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97,
        101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199,
        211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331,
        337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397, 401, 409, 419, 421, 431, 433, 439, 443, 449, 457,
        461, 463, 467, 479, 487, 491, 499, 503, 509, 521, 523, 541, 547, 557, 563, 569, 571, 577, 587, 593, 599,
        601, 607, 613, 617, 619, 631, 641, 643, 647, 653, 659, 661, 673, 677, 683, 691, 701, 709, 719, 727, 733,
        739, 743, 751, 757, 761, 769, 773, 787, 797, 809, 811, 821, 823, 827, 829, 839, 853, 857, 859, 863, 877,
        881, 883, 887, 907, 911, 919, 929, 937, 941, 947, 953, 967, 971, 977, 983, 991, 997
        };


        List<int> magicNumbers = new List<int>();

        foreach (int n in primeNumbers)
        {
            if (n == userinput)
            {
                magicNumbers.Add(n);
            }
            else if (n != userinput)
            {
                if (userinput % n == 0)
                {
                    magicNumbers.Add(n);
                }
                else if (userinput % n != 0)
                {
                    continue;
                }
            }
        }

        List<string> finalProduct = magicNumbers.ConvertAll<string>(x => x.ToString());

        if (finalProduct.Count == 1 && !finalProduct.Contains(Convert.ToString(userinput)))
        {
            foreach (string y in finalProduct)
            {
                Write($"The only prime factor of {userinput} is " + (y) + ".");
            }
        }
        else if (finalProduct.Count == 1 && finalProduct.Contains(Convert.ToString(userinput)))
        {
            Write($"{userinput} is a prime number!");
        }
        else if (finalProduct.Count == 2)
        {
            Write($"The two prime factors of {userinput} are " + (finalProduct.First()) + " and " + (finalProduct.Last()) + ".");
        }
        else if (finalProduct.Count >= 3)
        {
            Write($"The prime factors of {userinput} are ");
            foreach (string s in finalProduct)
            {
                if (s != finalProduct.Last())
                    Write((s) + ", ");
            }
            Write("and " + (finalProduct.Last()) + ".");
        }
        return finalProduct;
    }
}