DocumentOrganizer/Diligent.WebAPI.Business/Helper/StringGenerator.cs

namespace Diligent.WebAPI.Business.Helper
{
    public static class StringGenerator
    {
        public static string GenerateRandomPassword(PasswordOptions opts = null)
        {
            if (opts == null) opts = new PasswordOptions()
            {
                RequiredLength = 8,
                RequiredUniqueChars = 4,
                RequireDigit = true,
                RequireLowercase = true,
                RequireNonAlphanumeric = true,
                RequireUppercase = true
            };

            if(opts.RequiredLength < 4)
                opts.RequiredLength = 4;

            string[] randomChars = new[] {
                "ABCDEFGHJKLMNOPQRSTUVWXYZ",    // uppercase
                "abcdefghijkmnopqrstuvwxyz",    // lowercase
                "0123456789",                   // digits
                "!@$?_-"                        // non-alphanumeric
            };

            Random rand = new(Environment.TickCount);
            List<char> chars = new List<char>();

            if (opts.RequireUppercase)
                chars.Insert(rand.Next(0, chars.Count),
                    randomChars[0][rand.Next(0, randomChars[0].Length)]);

            if (opts.RequireLowercase)
                chars.Insert(rand.Next(0, chars.Count),
                    randomChars[1][rand.Next(0, randomChars[1].Length)]);

            if (opts.RequireDigit)
                chars.Insert(rand.Next(0, chars.Count),
                    randomChars[2][rand.Next(0, randomChars[2].Length)]);

            if (opts.RequireNonAlphanumeric)
                chars.Insert(rand.Next(0, chars.Count),
                    randomChars[3][rand.Next(0, randomChars[3].Length)]);

            for (int i = chars.Count; i < opts.RequiredLength
                 || chars.Distinct().Count() < opts.RequiredUniqueChars; i++)
            {
                string rcs = randomChars[rand.Next(0, randomChars.Length)];
                chars.Insert(rand.Next(0, chars.Count),
                    rcs[rand.Next(0, rcs.Length)]);
            }

            return new string(chars.ToArray());
        }
    }
}