system/classes/stackitem.php

<?php
namespace Habari;
class StackItem
{
  static $items = array();
  public $dependencies = array();
  public $resource = '';

  public function __construct($name, $version, $resource)
  {
    $this->name = $name;
    $this->version = $version;
    $this->resource = $resource;
  }

  public function __toString()
  {
    if(is_callable($this->resource)) {
      $fn = $this->resource;
      return $fn($this);
    }
    return $this->resource;
  }

  public function __get($name)
  {
    switch($name) {
      case 'resource':
        return Plugins::filter('get_stackitem_resource', $this->resource, $this);
    }
    trigger_error(_t('Requested property @name does not exist.', array('@name' => $name)), E_NOTICE);
    return null;
  }

  public function add_dependency($itemname, $version = null)
  {
    if($itemname instanceof StackItem) {
      $this->dependencies[] = $itemname;
    }
    else {
      $this->dependencies[] = array('name' => $itemname, 'version' => $version);
    }
    return $this;
  }

  public function get_dependencies()
  {
    $results = array();
    foreach($this->dependencies as $dependency) {
      if(is_array($dependency)) {
        $stackitem = self::get($dependency['name'], $dependency['version']);
        if($stackitem instanceof StackItem) {
          $results[$dependency['name']] = $stackitem;
        }
      }
      else {
        $results[$dependency->name] = $dependency;
      }
    }
    return array_filter($results);
  }

  public function in_stack_index($stack)
  {
    return isset($stack[$this->name]);
  }

  public static function register($name, $resource = '', $version = 0) {
    // @todo add a hook here to register StackItem contents on demand
    $item = new StackItem($name, $version, $resource);
    if(!isset(self::$items[$name])) {
      self::$items[$name] = array();
    }
    self::$items[$name][$version] = $item;
    uksort(self::$items[$name], function($a, $b) {
      return version_compare($a, $b);
    });
    return $item;
  }

  public static function get($name, $version = null) {
    if(isset(self::$items[$name])) {
      $result = array_reduce(self::$items[$name], function(&$result, $item) use ($version) {
        // If there was no result yet
        if(is_null($result)) {
          // If the version requested was omitted
          // or the version of this item is greater than or equal to the version requested
          if(is_null($version) || version_compare($version, $item->version) >= 0) {
            // return this item
            return $item;
          }
        }
        else {
          // If this item has a higher version than the one we already have
          if(version_compare($result->version, $item->version) < 0) {
            // return this item, which is more current
            return $item;
          }
        }
        // Otherwise, return the result we already have
        return $result;
      }, null);
      return $result;
    }
    return null;
  }
}