Find if featured image on page has changed - php

Question

While looking into this question I came up with the following solution that is called from canDelete() in an extension to File:
protected function isFileInUse()
{
$owner = $this->getOwner();
$dataObjectSubClasses = ClassInfo::subclassesFor('DataObject');
$classesWithFileHasOne = [];
foreach ($dataObjectSubClasses as $subClass) {
$hasOnes = array_flip($subClass::create()->hasOne());
if (array_key_exists($owner->class, $hasOnes)) {
$classesWithFileHasOne[$subClass] = $hasOnes[$owner->class];
}
}
$threshold = (Director::get_current_page()->class == 'AssetAdmin') ? 1 : 2;
$uses = 0;
foreach ($classesWithFileHasOne as $class => $relation) {
$uses += count($class::get()->filter("{$relation}ID", $this->owner->ID));
if ($uses >= $threshold) {
return true;
}
}
return false;
}
There is one edge case I can't get around though. If, say, a featured image is changed on a blog post then if there is exactly one other use of the same image then with this approach it will still allow it to be deleted. This is because until the page is saved the current change doesn't count towards uses of the image.
The threshold is set differently in CMS Pages and the Media Manager to allow an image to be deleted from within the page that is using it.
Is there a way that I can access the containing page (or other element - we're using Elemental) from within my File extension to see if its associated image has changed?

Answer 1

This is the solution I eventually came up with. I'm not entirely happy with having to inspect the request but couldn't see any other solution:
public function canDelete($member = null)
{
return !$this->isFileInUse();
}
/**
* Check if the file is in use anywhere on the site
* #return bool True if the file is in use
*/
protected function isFileInUse()
{
$owner = $this->getOwner();
$dataObjectSubClasses = ClassInfo::subclassesFor('DataObject');
$classesWithFileHasOne = [];
foreach ($dataObjectSubClasses as $subClass) {
$hasOnes = array_flip($subClass::create()->hasOne());
if (array_key_exists($owner->class, $hasOnes)) {
$classesWithFileHasOne[$subClass] = $hasOnes[$owner->class];
}
}
$threshold = ($this->isAssetAdmin() || ($this->isFileAttach($classesWithFileHasOne))) ? 1 : 2;
$uses = 0;
foreach ($classesWithFileHasOne as $class => $relation) {
$uses += count($class::get()->filter("{$relation}ID", $this->owner->ID));
if ($uses >= $threshold) {
return true;
}
}
return false;
}
/**
* Are we in the asset manager rather than editing a Page or Element?
* #return bool
*/
protected function isAssetAdmin()
{
return 'AssetAdmin' === Director::get_current_page()->class;
}
/**
* Is the current action attaching a file to a field that we're interested in?
* #param array $classesWithFileHasOne Classes with a relationship we're interested in and the name of the
* relevant field
* #return bool
*/
protected function isFileAttach($classesWithFileHasOne)
{
$controller = Controller::curr();
$field = $controller->request->allParams()['FieldName'];
return (preg_match('/attach$/', $controller->requestParams['url']) &&
($controller->action == 'EditForm')
&& (in_array($field, array_values($classesWithFileHasOne))));
}