<?php

/**
 * @file
 * Plugin definition for the ROT13 encryption method.
 */

$plugin = array(
  'title' => t('ROT13'),
  'description' => t('A simple letter substitution cipher that replaces each letter with the letter 13 letters after it in the alphabet.'),
  'encrypt callback' => 'encrypt_encryption_methods_rot13',
  'settings form' => 'encrypt_ro13_method_settings_form',
);

/**
 * Callback for Encrypt implementation: ROT13.
 *
 * This method uses the ROT13 method of character substitution. The key
 * is ignored.
 */
function encrypt_encryption_methods_rot13($op, $text, $key, $options = array()) {
  $processed_text = '';

  // Caching length operations to speed up for loops.
  $text_length = strlen($text);

  // Loop through each character.
  for ($i = 0; $i < $text_length; $i++) {
    $char = substr($text, $i, 1);

    // Encrypt or decrypt the character.
    $char = str_rot13($char);
    $processed_text .= $char;
  }

  return $processed_text;
}

/**
 * Settings form for the ROT13 encryption method.
 */
function encrypt_ro13_method_settings_form($defaults) {
  $form = array();

  $form['unused'] = array(
    '#type' => 'textfield',
    '#title' => t('Unused'),
    '#description' => t('This field is not used.'),
    '#default_value' => isset($defaults['unused']) ? $defaults['unused'] : '',
    '#required' => TRUE,
  );

  return $form;
}