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Add guardrails against transparent background color #919

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Add guardrails against transparent background color #919

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62 changes: 61 additions & 1 deletion src/Lms/Canvas/CanvasLms.php
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@

namespace App\Lms\Canvas;

use DOMDocument;
use App\Entity\ContentItem;
use App\Entity\Course;
use App\Entity\FileItem;
Expand Down Expand Up @@ -213,7 +214,15 @@ public function updateCourseContent(Course $course, User $user): array
$url = "courses/{$course->getLmsCourseId()}/pages/{$lmsContent['id']}";
$pageResponse = $canvasApi->apiGet($url);
$pageObj = $pageResponse->getContent();

/*Check if HTML has any transparent elements, and if so, update them to inherit the parent
background color*/
$html = $this->updateTransparentElements($pageObj['body']);
if (!empty($html) && $html !== $pageObj['body']){
$pageObj['body'] = $html;
$pageUrl = $pageObj['html_url'];
$options['wiki_page[body]'] = $html;
$canvasApi->apiPut($url, ['body' => $options]);
}
if (!empty($pageObj['body'])) {
$lmsContent['body'] = $pageObj['body'];
}
Expand Down Expand Up @@ -492,6 +501,57 @@ public function getContentTypes()
* PROTECTED FUNCTIONS
**********************/

/* Updates HTML elements with transparent backgrounds to inherit parent background colors
to better deal with color contrast issues */
protected function updateTransparentElements($html) {
$pageHtml = new DOMDocument;
$pageHtml->loadHTML($html);
$elements = $pageHtml->getElementsByTagName('p');

$html = "";

foreach($elements as $element) {
$style = $element->getAttribute('style');
if (strpos($style, 'background-color: transparent;') !== false) {
$html = $this->inheritStyle($element);
}
}

return $html;
}

protected function inheritStyle($element) {
$currElement = $element;
$parentStyles = [];
while(property_exists($currElement->parentNode, 'tagName')) {
$style = $currElement->getAttribute('style');
preg_match('/background-color:\s*([^;]+);/', $style, $matches);
if (isset($matches[1]) && $matches[1] !== 'transparent') {
array_push($parentStyles, $matches[1]);
}

$currElement = $currElement->parentNode;
}

$style = $element->getAttribute('style');

//If the element has no parent elements, then let its background color be the default background color.
//Else, set its background color to equal its first parent element's color
if (empty($parentStyles)) {
$newStyle = preg_replace('/background-color:\s*[^;]+;/', 'background-color: white;', $style);
}
else{
$color = 'background-color: ' . $parentStyles[0];
$newStyle = preg_replace('/background-color:\s*[^;]+;/', $color, $style);
}

$element->setAttribute('style', $newStyle);

$dom = $element->ownerDocument;

return $dom->saveHTML();
}

protected function getAccountInfo(User $user, $accountId)
{
$url = "accounts/${accountId}";
Expand Down
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