1<?php
2
3namespace Drupal\Core\Asset;
4
5/**
6 * Groups CSS assets.
7 */
8class CssCollectionGrouper implements AssetCollectionGrouperInterface {
9
10  /**
11   * {@inheritdoc}
12   *
13   * Puts multiple items into the same group if they are groupable and if they
14   * are for the same 'media' and 'browsers'. Items of the 'file' type are
15   * groupable if their 'preprocess' flag is TRUE, and items of the 'external'
16   * type are never groupable.
17   *
18   * Also ensures that the process of grouping items does not change their
19   * relative order. This requirement may result in multiple groups for the same
20   * type, media, and browsers, if needed to accommodate other items in between.
21   */
22  public function group(array $css_assets) {
23    $groups = [];
24    // If a group can contain multiple items, we track the information that must
25    // be the same for each item in the group, so that when we iterate the next
26    // item, we can determine if it can be put into the current group, or if a
27    // new group needs to be made for it.
28    $current_group_keys = NULL;
29    // When creating a new group, we pre-increment $i, so by initializing it to
30    // -1, the first group will have index 0.
31    $i = -1;
32    foreach ($css_assets as $item) {
33      // The browsers for which the CSS item needs to be loaded is part of the
34      // information that determines when a new group is needed, but the order
35      // of keys in the array doesn't matter, and we don't want a new group if
36      // all that's different is that order.
37      ksort($item['browsers']);
38
39      // If the item can be grouped with other items, set $group_keys to an
40      // array of information that must be the same for all items in its group.
41      // If the item can't be grouped with other items, set $group_keys to
42      // FALSE. We put items into a group that can be aggregated together:
43      // whether they will be aggregated is up to the _drupal_css_aggregate()
44      // function or an
45      // override of that function specified in hook_css_alter(), but regardless
46      // of the details of that function, a group represents items that can be
47      // aggregated. Since a group may be rendered with a single HTML tag, all
48      // items in the group must share the same information that would need to
49      // be part of that HTML tag.
50      switch ($item['type']) {
51        case 'file':
52          // Group file items if their 'preprocess' flag is TRUE.
53          // Help ensure maximum reuse of aggregate files by only grouping
54          // together items that share the same 'group' value.
55          $group_keys = $item['preprocess'] ? [$item['type'], $item['group'], $item['media'], $item['browsers']] : FALSE;
56          break;
57
58        case 'external':
59          // Do not group external items.
60          $group_keys = FALSE;
61          break;
62      }
63
64      // If the group keys don't match the most recent group we're working with,
65      // then a new group must be made.
66      if ($group_keys !== $current_group_keys) {
67        $i++;
68        // Initialize the new group with the same properties as the first item
69        // being placed into it. The item's 'data', 'weight' and 'basename'
70        // properties are unique to the item and should not be carried over to
71        // the group.
72        $groups[$i] = $item;
73        unset($groups[$i]['data'], $groups[$i]['weight'], $groups[$i]['basename']);
74        $groups[$i]['items'] = [];
75        $current_group_keys = $group_keys ? $group_keys : NULL;
76      }
77
78      // Add the item to the current group.
79      $groups[$i]['items'][] = $item;
80    }
81
82    return $groups;
83  }
84
85}
86