fix: groupmentions have poor contrast on some backgrounds

extensions/mentions/js/src/forum/utils/textFormatter.js

@@ -1,6 +1,7 @@
 import app from 'flarum/forum/app';
 import username from 'flarum/common/helpers/username';
 import extractText from 'flarum/common/utils/extractText';
+import isDark from 'flarum/common/utils/isDark';
 
 export function filterUserMentions(tag) {
   let user;
@@ -40,6 +41,7 @@ export function filterGroupMentions(tag) {
       tag.setAttribute('groupname', extractText(group.namePlural()));
       tag.setAttribute('icon', group.icon());
       tag.setAttribute('color', group.color());
+      tag.setAttribute('class', isDark(group.color()) ? 'GroupMention--light' : 'GroupMention--dark');
 
       return true;
     }

extensions/mentions/less/forum.less

@@ -98,15 +98,39 @@
   .Button--color(@tooltip-color, @tooltip-bg);
 }
 .GroupMention {
-  color: @body-bg;
+  & when (@config-dark-mode = false) {
+    &,
+    &:hover,
+    &:active {
+      color: @text-on-light;
+    }
+  }
+  & when (@config-dark-mode = true) {
+    &,
+    &:hover,
+    &:active {
+      color: @text-on-dark;
+    }
+  }
 
-  .icon {
-    margin-left: 5px;
+  &--light {
+    &,
+    &:hover,
+    &:active {
+      color: @text-on-light;
+    }
   }
 
-  &:hover,
-  &:active {
-    color: @body-bg;
+  &--dark {
+    &,
+    &:hover,
+    &:active {
+      color: @text-on-dark;
+    }
+  }
+
+  .icon {
+    margin-left: 5px;
   }
 }
 .MentionsDropdown .Badge {

extensions/mentions/src/ConfigureMentions.php

@@ -14,6 +14,7 @@
 use Flarum\Post\CommentPost;
 use Flarum\Settings\SettingsRepositoryInterface;
 use Flarum\User\User;
+use Illuminate\Support\Str;
 use s9e\TextFormatter\Configurator;
 
 class ConfigureMentions
@@ -147,12 +148,13 @@ private function configureGroupMentions(Configurator $config)
         $tag->attributes->add('groupname');
         $tag->attributes->add('icon');
         $tag->attributes->add('color');
+        $tag->attributes->add('class');
         $tag->attributes->add('id')->filterChain->append('#uint');
 
         $tag->template = '
             <xsl:choose>
                 <xsl:when test="@deleted != 1">
-                    <span class="GroupMention" style="background: {@color}">@<xsl:value-of select="@groupname"/><i class="icon {@icon}"></i></span>
+                    <span class="GroupMention {@class}" style="background: {@color}">@<xsl:value-of select="@groupname"/><i class="icon {@icon}"></i></span>
                 </xsl:when>
                 <xsl:otherwise>
                     <span class="GroupMention GroupMention--deleted" style="background: {@color}">@<xsl:value-of select="@groupname"/><i class="icon {@icon}"></i></span>
@@ -177,10 +179,40 @@ public static function addGroupId($tag)
             $tag->setAttribute('groupname', $group->name_plural);
             $tag->setAttribute('icon', $group->icon ?? 'fas fa-at');
             $tag->setAttribute('color', $group->color);
+            if (! empty($group->color)) {
+                $tag->setAttribute('class', self::isDark($group->color) ? 'GroupMention--light' : 'GroupMention--dark');
+            } else {
+                $tag->setAttribute('class', '');
+            }
 
             return true;
         }
 
         $tag->invalidate();
     }
+
+    /**
+     * The `isDark` utility converts a hex color to rgb, and then calcul a YIQ
+     * value in order to get the appropriate brightness value (is it dark or is it
+     * light?) See https://www.w3.org/TR/AERT/#color-contrast for references. A YIQ
+     * value >= 128 is a light color.
+     */
+    public static function isDark(?string $hexColor): bool
+    {
+        if (! $hexColor) {
+            return false;
+        }
+
+        $hexNumbers = Str::replace('#', '', $hexColor);
+        if (Str::length($hexNumbers) === 3) {
+            $hexNumbers += $hexNumbers;
+        }
+
+        $r = hexdec(Str::substr($hexNumbers, 0, 2));
+        $g = hexdec(Str::subStr($hexNumbers, 2, 2));
+        $b = hexdec(Str::subStr($hexNumbers, 4, 2));
+        $yiq = ($r * 299 + $g * 587 + $b * 114) / 1000;
+
+        return $yiq >= 128 ? false : true;
+    }
 }

extensions/mentions/tests/integration/api/GroupMentionsTest.php

@@ -84,7 +84,7 @@ public function rendering_a_valid_group_mention_works()
 
         $response = json_decode($response->getBody(), true);
 
-        $this->assertStringContainsString('<p>One of the <span style="background:#80349E" class="GroupMention">@Mods<i class="icon fas fa-bolt"></i></span> will look at this</p>', $response['data']['attributes']['contentHtml']);
+        $this->assertStringContainsString('<p>One of the <span style="background:#80349E" class="GroupMention ">@Mods<i class="icon fas fa-bolt"></i></span> will look at this</p>', $response['data']['attributes']['contentHtml']);
         $this->assertNotNull(CommentPost::find($response['data']['id'])->mentionsGroups->find(4));
     }