wordpress-oop-shortcode-example.php

class MyCitations_Plugin {
  /**
   * @var int
   */
  private $citeID;
  
  /**
   * @var array
   */
  private $citationList;
    
  public function __construct() {
    $this->citeID = 0;
  }
  
  /**
   * Method to call to load actions and shortcodes.
   */
  public function load() {
    add_shortcode( 'cite', array($this,'cite') );
    add_shortcode( 'print_citations', array($this,'printCitations') );
    add_filter( 'the_content', array($this,'theContent') );
  }
    
  /** 
   * Adds a citation when this shortcode is used.
   *
   * @param $atts array Allows "description" and "source" - a URL
   * @param $content The text for which a citation is made.
   */
  public function cite($atts, $content='') {
    $citeID = ++$this->citeID;
    
    if (isset($atts['description']) || isset($atts['source'])) {
      $this->addCitation($citeID, $atts);
      return $content . sprintf('<sup><a name="text-%1$s"></a> <a href="#citation-%1$s">[%1$s]</a></sup>, $citeID);
    } else {
      //do nothing
      return $content;     
  }
  
  /**
   * Adds a citation to to a footer string.
   *
   * @param int $citeID The index for this citation.
   * @param array $atts An array of attributes that matches the [cite] shortcode.
   */
  protected function addCitation($citeID, $atts)
  {    
    $text = '';
    if (isset($atts['description'])) {
      $text .= $atts['description'] . ' ';
    }
    if (isset($atts['source'])) {
      $text .= sprintf('<a href="%1$s">[%1$s]</a>', $atts['source']);
    }
    $this->citationList .= sprintf('<div><a name="citation-%1$d"></a>' .
        '<a href="#text-%1$d" alt="Citation Origin">%1$d</a><cite>%2$s</cite></div>', $citeID, $text);
  }
  
  /**
   * Returns a list of citations, if there are any.
   *
   * @param 
  public function printCitations()
  {
    if ($this->citationList) {
      return "<div class='citations'>" . $this->citationList . "</div>";
    }
    return '';
  }
  
  public function theContent($content)
  {
    return $content . '[print-citations]';
  }
}