Fix clarifications for unlinked problems

Closes: #3032

Author: meisterT

webapp/src/Controller/Jury/ClarificationController.php

@@ -193,7 +193,12 @@ public function viewAction(Request $request, int $id): Response
             $clarcontest = $contest->getShortname();
             $data['subjectlink'] = null;
             if ($clar->getProblem()) {
-                $concernssubject = $contest->getCid() . "-" . $clar->getProblem()->getProbid();
+                if ($clar->getContestProblem()) {
+                    $concernssubject = $contest->getCid() . "-" . $clar->getProblem()->getProbid();
+                } else {
+                    // Very special case, this problem is unlinked.
+                    $concernssubject = "";
+                }
                 $data['subjectlink'] = $this->generateUrl('jury_problem', ['probId' => $clar->getProblem()->getProbid()]);
             } elseif ($clar->getCategory()) {
                 $concernssubject = $contest->getCid() . "-" . $clar->getCategory();

webapp/src/Twig/TwigExtension.php

@@ -1179,9 +1179,59 @@ public function fileTypeIcon(string $type): string
         return 'fas fa-file-' . $iconName;
     }
 
-    public function problemBadge(ContestProblem $problem, bool $grayedOut = false): string
+    private function relativeLuminance(string $rgb): float
     {
-        $rgb = Utils::convertToHex($problem->getColor() ?? '#ffffff');
+        // See https://en.wikipedia.org/wiki/Relative_luminance
+        [$r, $g, $b] = Utils::parseHexColor($rgb);
+
+        [$lr, $lg, $lb] = [
+            pow($r / 255, 2.4),
+            pow($g / 255, 2.4),
+            pow($b / 255, 2.4),
+        ];
+
+        return 0.2126 * $lr + 0.7152 * $lg + 0.0722 * $lb;
+    }
+
+    private function apcaContrast(string $fgColor, string $bgColor): float
+    {
+        // Based on WCAG 3.x (https://www.w3.org/TR/wcag-3.0/)
+        $luminanceForeground = $this->relativeLuminance($fgColor);
+        $luminanceBackground = $this->relativeLuminance($bgColor);
+
+        $contrast = ($luminanceBackground > $luminanceForeground)
+            ? (pow($luminanceBackground, 0.56) - pow($luminanceForeground, 0.57)) * 1.14
+            : (pow($luminanceBackground, 0.65) - pow($luminanceForeground, 0.62)) * 1.14;
+
+        return round($contrast * 100, 2);
+    }
+
+    /**
+     * @return array{string, string}
+     */
+    private function hexToForegroundAndBorder(string $rgb): array
+    {
+        $background = Utils::parseHexColor($rgb);
+
+        // Pick a border that's a bit darker.
+        $darker = $background;
+        $darker[0] = max($darker[0] - 64, 0);
+        $darker[1] = max($darker[1] - 64, 0);
+        $darker[2] = max($darker[2] - 64, 0);
+        $border    = Utils::rgbToHex($darker);
+
+        // Pick the text color with the biggest absolute contrast.
+        $contrastWithWhite = $this->apcaContrast('#ffffff', $rgb);
+        $contrastWithBlack = $this->apcaContrast('#000000', $rgb);
+
+        $foreground = (abs($contrastWithBlack) > abs($contrastWithWhite)) ? '#000000' : '#ffffff';
+
+        return [$foreground, $border];
+    }
+
+    public function problemBadge(?ContestProblem $problem, bool $grayedOut = false): string
+    {
+        $rgb = Utils::convertToHex($problem?->getColor() ?? '#ffffff');
         if ($grayedOut || empty($rgb)) {
             $rgb = Utils::convertToHex('whitesmoke');
         }
@@ -1197,7 +1247,7 @@ public function problemBadge(ContestProblem $problem, bool $grayedOut = false):
             $rgb,
             $border,
             $foreground,
-            $problem->getShortname()
+            $problem?->getShortname() ?? '?'
         );
     }