<?php
  
  namespace Guzzle\Http\Message\Header;
  
  use Guzzle\Http\Message\Header;
  
  /**
   * Provides helpful functionality for Cache-Control headers
   */
  class CacheControl extends Header
  {
      /** @var array */
      protected $directives;
  
      public function add($value)
      {
          parent::add($value);
          $this->directives = null;
      }
  
      public function removeValue($searchValue)
      {
          parent::removeValue($searchValue);
          $this->directives = null;
      }
  
      /**
       * Check if a specific cache control directive exists
       *
       * @param string $param Directive to retrieve
       *
       * @return bool
       */
      public function hasDirective($param)
      {
          $directives = $this->getDirectives();
  
          return isset($directives[$param]);
      }
  
      /**
       * Get a specific cache control directive
       *
       * @param string $param Directive to retrieve
       *
       * @return string|bool|null
       */
      public function getDirective($param)
      {
          $directives = $this->getDirectives();
  
          return isset($directives[$param]) ? $directives[$param] : null;
      }
  
      /**
       * Add a cache control directive
       *
       * @param string $param Directive to add
       * @param string $value Value to set
       *
       * @return self
       */
      public function addDirective($param, $value)
      {
          $directives = $this->getDirectives();
          $directives[$param] = $value;
          $this->updateFromDirectives($directives);
  
          return $this;
      }
  
      /**
       * Remove a cache control directive by name
       *
       * @param string $param Directive to remove
       *
       * @return self
       */
      public function removeDirective($param)
      {
          $directives = $this->getDirectives();
          unset($directives[$param]);
          $this->updateFromDirectives($directives);
  
          return $this;
      }
  
      /**
       * Get an associative array of cache control directives
       *
       * @return array
       */
      public function getDirectives()
      {
          if ($this->directives === null) {
              $this->directives = array();
              foreach ($this->parseParams() as $collection) {
                  foreach ($collection as $key => $value) {
                      $this->directives[$key] = $value === '' ? true : $value;
                  }
              }
          }
  
          return $this->directives;
      }
  
      /**
       * Updates the header value based on the parsed directives
       *
       * @param array $directives Array of cache control directives
       */
      protected function updateFromDirectives(array $directives)
      {
          $this->directives = $directives;
          $this->values = array();
  
          foreach ($directives as $key => $value) {
              $this->values[] = $value === true ? $key : "{$key}={$value}";
          }
      }
  }