functions/hook to remove physical files of Wordpress subimages that PressThumb will generate dynamically (Pagely specific)

readme.txt

Note: this code is specific to Wordpress running on Pagely with the PressThumb
service enabled.

Adding this code to your theme's functions.php file will allow uploaded media
to generate subimages and the metadata associated with them, but then remove
the physical files generated for those subimages (aka intermediate image sizes).

By leaving the metadata, this allows the rest of Wordpress and it's plugins to
continue referencing them as they'd expect.  So, you can simply leave the custom
image sizes in Wordpress (and theme/plugins) as they are and your disk usage 
won't be overblown.

After the code is added, newly uploaded media's subimage assets will be removed.
If you have existing uploaded media and want to remove the subimage assets, you
can do so through a wp-cli shell:

$ wp shell
wp> pressthumb__remove_files_of_subimages_for_all_attachments()
wp> exit

functions.php

<?php

/**
 * Remove the phsyical files created for the intermediate image sizes but
 * after they're created to ensure the metadata is generated and saved for
 * the attachment. The PressThumb service dynamically creates these images
 * outside of Wordpress, so we can save disk space by removing them.
 *
 * Note: will interfere with any thumbnail regeration attempts
 */
add_filter( 'wp_generate_attachment_metadata', 'pressthumb__remove_files_of_attachment_subimages', 99, 3 );
function pressthumb__remove_files_of_attachment_subimages( $metadata, $attachment_id, $context ) {
	$pressthumb_pattern = '![^/]+\-[1-9][0-9]+x[1-9][0-9]+\.(jpe?g|png)$!';
	$attachment_path = get_attached_file( $attachment_id );
	$base_dir = dirname( $attachment_path );

	if ( !empty( $metadata['sizes'] ) ) {
		foreach( $metadata['sizes'] as $size => $image ) {
			// PDF attachments have a preview image in the array under the 'full' key.
			// The other intermediate images are all based on it, so we need to skip it.
			if ( 'full' === $size ) {
				continue;
			}
			// images scaled in wordpress keep originals around in the postmata key _wp_attachment_backup_sizes,
			// but we should keep the one with the 'original-full' key. we only see this when this
			// function is called by pressthumb__remove_files_of_subimages_for_all_attachments
			if ( 'full-orig' === $size ) {
				continue;
			}

			// only remove files that match the pattern for PressThumb to generate them on the fly
			if ( !empty( $image['file'] ) && preg_match( $pressthumb_pattern, $image['file'] ) ) {
				$file_path = path_join( $base_dir, $image['file'] );
				if ( file_exists( $file_path ) ) {
					@unlink( $file_path );
				}
			}
		}
	}
	return $metadata;
}

/**
 * Removes physical files of image versions that PressThumb generates
 * outside of Wordpress
 */
function pressthumb__remove_files_of_subimages_for_all_attachments() {
	$args = array(
		'post_type' => 'attachment',
		'post_mime_type__in' => array(
			'application/pdf',
			'image/jpeg',
			'image/png',
		),
		'fields' => 'ids',
		'posts_per_page' => -1,
	);

	$attachment_ids = get_posts( $args );

	foreach ( $attachment_ids as $attachment_id ) {
		$metadata = wp_get_attachment_metadata( $attachment_id );
		pressthumb__remove_files_of_attachment_subimages( $metadata, $attachment_id, null );
		// check for backup images too
		$metadata = get_post_meta( $attachment_id, '_wp_attachment_backup_sizes', true );
		if ( !empty( $metadata ) ) {
			pressthumb__remove_files_of_attachment_subimages( array( 'sizes' => $metadata ), $attachment_id, null );
		}
	}
}