<?php
// $Id: esi.module,v 1.1 2010-08-24 21:23:36 dstuart Exp $
/**
 * @file esi.module
 *   Adds support for ESI (Edge-Side-Include) integration, allowing blocks to be\
 *   delivered by ESI, with support for per-block cache times.
 */

// Default interval for rotating the seed key: defaults to change-daily.
define('ESI__DEFAULT_SEED_KEY_ROTATION_INTERVAL', 86400);

// Default ESI setting for blocks: enabled
define('ESI__BLOCK_CONFIG_DEFAULT__IS_ENABLED', TRUE);

// Default TTL for blocks: 5 minutes
define('ESI__BLOCK_CONFIG_DEFAULT__TTL', 300);


/**
 * Implementation of hook_theme
 */
function esi_theme() {
  return array(
    'esi_tag' => array(
      'arguments' => array('block' => array()),
      'file' => 'esi.theme.inc',
    ),
  );
}

/**
 * Implementation of hook_theme_registry_alter.
 * Override theme('blocks') to apply our ESI handler.
 */
function esi_theme_registry_alter(&$theme_registry) {
  // override the default theme function for theme('blocks').
  $path = drupal_get_path('module', 'esi');
  $theme_registry['blocks']['function'] = 'esi__theme_blocks';
  $theme_registry['blocks']['file'] = 'esi.theme.inc';
  $theme_registry['blocks']['include files'] = array( "./{$path}/esi.theme.inc");
  $theme_registry['blocks']['theme path']  = $path;
  $theme_registry['blocks']['theme paths'] = array($path);
}


/**
 * Implementation of hook_menu.
 *   Define a menu-handler.
 */
function esi_menu() {
  return array(
    'esi/block/%' => array(
      'title' => 'ESI handler',
      'page callback' => 'esi__block_handler',
      'page arguments' => array(2),
      'access callback' => TRUE,
      'type' => MENU_CALLBACK
    )
  );
}


/**
 * Implementation of hook_cron.
 * Every interval, rotate the seed (used to generate the role-cookie).
 * (Each rotation will invalidate the varnish-cache for cached pre-role blocks).
 */
function esi_cron() {
  $age = time() - variable_get('esi_seed_key_last_changed', 0);
  $interval = variable_get('esi_seed_key_rotation_interval', ESI__DEFAULT_SEED_KEY_ROTATION_INTERVAL);
  if($age > $interval) {
    require_once(dirname(__FILE__) . '/esi.inc');
    _esi__rotate_seed_key();
  }
}


/**
 * Implementation of hook_user.
 *   For maximum cache-efficiency, the proxy must be able to identify the roles
 *   held by a user.  A cookie is used which provides a consistent hash for
 *   all users who share the same roles.
 *   For security, the hash uses a random seed which is rotated (by hook_cron)
 *   at regular intervals - defaults to daily.
 */
function esi_user($op, &$edit, &$account, $category = NULL) {
  // only respond to login/logout.
  if(!($op == 'login' || $op == 'logout')) {
    return;
  }

  // Drupal session cookies use the name 'SESS' followed by an MD5 hash.
  // The role-cookie is the same, prefixes with the letter 'R'.
  $cookie = array('name' => 'R'.session_name());

  if($op == 'login') {
    require_once(dirname(__FILE__) . '/esi.inc');
    $hash = _esi__get_roles_hash(array_keys($account->roles));
    $lifespan = min(variable_get('esi_seed_key_rotation_interval', ESI__DEFAULT_SEED_KEY_ROTATION_INTERVAL), ini_get('session.cookie_lifetime'));
    $cookie += array(
      'value' => $hash,
      'expire' => time() + $lifespan,
    );
  }
  else {
    $cookie += array(
      'value' => 'deleted',
      'expire' => 1,
    );
  }
  setcookie($cookie['name'], $cookie['value'], $cookie['expire']);
}


/**
 * Implementation of hook_form_FORM_ID_alter
 * for block_admin_configure
 *   Add ESI-configuration options to the block-config pages.
 */
function esi_form_block_admin_configure_alter(&$form, $form_state) {
  // TODO: describe how the cache configs can be configured as defaults in code.

  // load our helper functions
  require_once(dirname(__FILE__) . '/esi.inc');

  $module = $form['module']['#value'];
  $delta  = $form['delta']['#value'];
  $config = _esi__block_settings($module, $delta);
  
  $element['esi_config'] = array(
    '#type' => 'fieldset',
    '#title' => t('ESI settings'),
    '#description' => t('Control how this block is cached on an ESI-enabled reverse proxy.'),
    '#tree' => TRUE,
  );
  
  $element['esi_config']['enabled'] = array(
    '#type' => 'checkbox',
    '#title' => t('Enable ESI'),
    '#default_value' => $config->enabled,
  );

  $options = _esi__ttl_options($config->ttl);
  $element['esi_config']['ttl'] = array(
    '#type' => 'select',
    '#title' => t('TTL'),
    '#description' => t('Time-to-live on the proxy-cache.'),
    '#options' => $options,
    '#default_value' => $config->ttl,
  );

  // inject our ESI config-fieldset onto the form,
  // just after the 'block_settings' fieldset.
  $i = 1;
  foreach($form as $key => $value) {
    if($key == 'block_settings') {
      break;
    }
    $i++;
  }
  $f = array_slice($form, 0, $i);
  $f += $element;
  $f += array_slice($form, $i);
  $form = $f;

  // add a submit-handler to save our config.
  $form['#submit'][] = 'esi__block_config_save';
}

/**
 * Form-submit handler for ESI settings in block-config
 */
function esi__block_config_save($form, $form_state) {
  require_once(dirname(__FILE__) . '/esi.inc');

  $module = $form_state['values']['module'];
  $delta  = $form_state['values']['delta'];

  $config = new stdClass;
  $config->enabled = $form_state['values']['esi_config']['enabled'];
  $config->ttl     = $form_state['values']['esi_config']['ttl'];

  _esi__block_settings($module, $delta, $config);
}


/**
 * Menu handler for ESIs
 *
 * Render a particular block.
 */
function esi__block_handler($bid, $page = NULL) {
  require_once(dirname(__FILE__)  . '/esi.inc');

  /**
   * Expect the bid format to be theme:region:module:delta
   * Fail if this doesn't match.
   */
  if(!substr_count($bid, ':') == 3) {
    return FALSE;
  }
  list($theme, $region, $module, $delta) = explode(':', $bid);
  
  // Block content may change per-page.
  // If this is true for the current block, the origin page url should be
  // provided as an argument.
  if ($page) {
    $_GET['q'] = base64_decode($page);
  }

  // theme set-up.
  // we need to do this manually, because output is echo'd instead of returned.
  init_theme();

  // get the block into a format that can be passed to view-blockk.
  $block = _esi__get_block($theme, $region, $module, $delta);
  $output = theme('block', $block);
  /**
   * Pass PER-USER or PER-ROLE cache info to varnish.
   *
   * No-cache is header (TTL) controlled.
   * Per-page is passed as a url argument
   */
  if($block->cache == BLOCK_NO_CACHE) {
    header("Cache-Control: no-cache, max-age=0");
  }
  elseif($block->cache & BLOCK_CACHE_PER_USER) {
    // "Cache-control: private" advises proxies that the content is
    // user-specific.  Most proxies will not cache this data - a clever proxy
    // config may make this cacheable.
    header("Cache-Control: private");
    header("X-BLOCK-CACHE: " . BLOCK_CACHE_PER_USER);
  }
  elseif($block->cache & BLOCK_CACHE_PER_ROLE) {
    header("Cache-Control: private");
    header("X-BLOCK-CACHE: " . BLOCK_CACHE_PER_ROLE);
  }

  // For all cacheable blocks, set the TTL based on the block config.
  if($block->cache != BLOCK_NO_CACHE) {
    $config = _esi__block_settings($module, $delta);
    header("Cache-Control: max-age={$config->ttl}");
  }

  echo $output;  
  return null;
}