Resolve #3450120 "Make consistent"

Closes #3450120

src/Plugin/Filter/FootnotesFilter.php

@@ -7,7 +7,6 @@ use Drupal\Component\Render\PlainTextOutput;
 use Drupal\Component\Serialization\Json;
 use Drupal\Component\Utility\Crypt;
 use Drupal\Component\Utility\Html;
-use Drupal\Component\Utility\Random;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
 use Drupal\Core\Render\Markup;
@@ -351,17 +350,13 @@ class FootnotesFilter extends FilterBase implements ContainerFactoryPluginInterf
     }
 
     // Build the render array for the footnote.
-    $random = new Random();
-    $random_string = $random->name(12);
-    $text_id = Crypt::hashBase64($text);
-    $text_id = str_replace('_', '', $text_id);
     $footnote = [
       'value' => $value,
       'backlink_value' => $value,
       'text' => $text instanceof MarkupInterface ? $text : Markup::create($text),
       'text_clean' => PlainTextOutput::renderFromHtml((string) $text),
-      'fn_id' => 'footnote' . $value . '_' . $text_id . '_' . $random_string,
-      'ref_id' => 'footnoteref' . $value . '_' . $text_id . '_' . $random_string,
+      'fn_id' => 'footnote' . $value,
+      'ref_id' => 'footnoteref' . $value,
       'instance' => 1,
       'is_auto' => $is_auto,
       'is_same_text' => TRUE,
@@ -374,14 +369,31 @@ class FootnotesFilter extends FilterBase implements ContainerFactoryPluginInterf
     }
 
     // Record the target text.
-    $this->storedFootnotes[$key][$footnote['fn_id']] = $footnote;
+    $fn_id = $footnote['fn_id'];
+    $counter = 1;
+    while (isset($this->storedFootnotes[$key][$fn_id])) {
+      $fn_id = $footnote['fn_id'] . '-' . $counter;
+      $counter++;
+    }
+    $this->storedFootnotes[$key][$fn_id] = $footnote;
 
     // If there are multiple stored footnotes, set the backlink value.
     if (count($this->storedFootnotes[$key]) > 1) {
       $alphabet = range('a', 'z');
       $counter = 0;
+      $stored_sub_keys = array_keys($this->storedFootnotes[$key]);
+      $first_sub_key = reset($stored_sub_keys);
       foreach ($this->storedFootnotes[$key] as &$stored_footnote) {
         $stored_footnote['backlink_value'] = $stored_footnote['value'] . $alphabet[$counter];
+
+        // Set reference and footnote ID's to be relative to the first footnote.
+        // So any subsequent footnotes after a first one like this:
+        // - #footnote1.
+        // Would become:
+        // - #footnote1-1.
+        // - #footnote1-2.
+        $stored_footnote['fn_id'] = $this->storedFootnotes[$key][$first_sub_key]['fn_id'] . '-' . $counter;
+        $stored_footnote['ref_id'] = $this->storedFootnotes[$key][$first_sub_key]['ref_id'] . '-' . $counter;
         $counter++;
       }