Shrlalgo.RvKits/WPFluent/Controls/PasswordBox/PasswordHelper.cs

using System.Diagnostics;
namespace WPFluent.Controls;

public partial class PasswordBox
{
    private class PasswordHelper
    {
        private string currentPassword;
        private string currentText;
        private string newPasswordValue;
        private readonly PasswordBox passwordBox;

        public PasswordHelper(PasswordBox passwordBox)
        {
            this.passwordBox = passwordBox;
            currentText = string.Empty;
            newPasswordValue = string.Empty;
            currentPassword = string.Empty;
        }

        private bool IsDeleteOption()
        {
            Debug.Assert(currentText == passwordBox.Text, "_currentText == _passwordBox.Text");
            Debug.Assert(currentPassword == passwordBox.Password, "_currentPassword == _passwordBox.Password");

            return currentText.Length < currentPassword.Length;
        }

        private void UpdatePasswordWithInputCharacter(int insertIndex, string insertValue)
        {
            Debug.Assert(currentText == passwordBox.Text, "_currentText == _passwordBox.Text");

            if(currentText.Length == newPasswordValue.Length)
            {
                // If it's a direct character replacement, remove the existing one before inserting the new one.
                newPasswordValue = newPasswordValue.Remove(insertIndex, 1).Insert(insertIndex, insertValue);
            }
            else
            {
                newPasswordValue = newPasswordValue.Insert(insertIndex, insertValue);
            }
        }

        public string GetNewPassword()
        {
            currentPassword = GetPassword();
            newPasswordValue = currentPassword;
            currentText = passwordBox.Text;
            var selectionIndex = passwordBox.SelectionStart;
            var passwordChar = passwordBox.PasswordChar;
            var newCharacters = currentText.Replace(passwordChar.ToString(), string.Empty);
            bool isDeleted = false;

            if(IsDeleteOption())
            {
                newPasswordValue = currentPassword.Remove(selectionIndex, currentPassword.Length - currentText.Length);
                isDeleted = true;
            }

            switch(newCharacters.Length)
            {
                case > 1:
                {
                    var index = currentText.IndexOf(newCharacters[0]);

                    newPasswordValue =
                            index > newPasswordValue.Length - 1
                        ? $"{newPasswordValue}{newCharacters}"
                        : newPasswordValue.Insert(index, newCharacters);
                    break;
                }

                case 1:
                {
                    for(int i = 0; i < currentText.Length; i++)
                    {
                        if(currentText[i] == passwordChar)
                        {
                            continue;
                        }

                        UpdatePasswordWithInputCharacter(i, currentText[i].ToString());
                        break;
                    }

                    break;
                }

                case 0 when !isDeleted:
                {
                    // The input is a PasswordChar, which is to be inserted at the designated position.
                    int insertIndex = selectionIndex - 1;
                    UpdatePasswordWithInputCharacter(insertIndex, passwordChar.ToString());
                    break;
                }
            }

            return newPasswordValue;
        }

        public string GetPassword() => passwordBox.Password ?? string.Empty;
    }
}