resolve_block_template() WordPress Function

function resolve_block_template( $template_type, $template_hierarchy, $fallback_template ) {
	if ( ! $template_type ) {
		return null;
	}

	if ( empty( $template_hierarchy ) ) {
		$template_hierarchy = array( $template_type );
	}

	$slugs = array_map(
		'_strip_template_file_suffix',
		$template_hierarchy
	);

	// Find all potential templates 'wp_template' post matching the hierarchy.
	$query     = array(
		'theme'    => wp_get_theme()->get_stylesheet(),
		'slug__in' => $slugs,
	);
	$templates = get_block_templates( $query );

	// Order these templates per slug priority.
	// Build map of template slugs to their priority in the current hierarchy.
	$slug_priorities = array_flip( $slugs );

	usort(
		$templates,
		static function ( $template_a, $template_b ) use ( $slug_priorities ) {
			return $slug_priorities[ $template_a->slug ] - $slug_priorities[ $template_b->slug ];
		}
	);

	$theme_base_path        = get_stylesheet_directory() . DIRECTORY_SEPARATOR;
	$parent_theme_base_path = get_template_directory() . DIRECTORY_SEPARATOR;

	// Is the active theme a child theme, and is the PHP fallback template part of it?
	if (
		strpos( $fallback_template, $theme_base_path ) === 0 &&
		strpos( $fallback_template, $parent_theme_base_path ) === false
	) {
		$fallback_template_slug = substr(
			$fallback_template,
			// Starting position of slug.
			strpos( $fallback_template, $theme_base_path ) + strlen( $theme_base_path ),
			// Remove '.php' suffix.
			-4
		);

		// Is our candidate block template's slug identical to our PHP fallback template's?
		if (
			count( $templates ) &&
			$fallback_template_slug === $templates[0]->slug &&
			'theme' === $templates[0]->source
		) {
			// Unfortunately, we cannot trust $templates[0]->theme, since it will always
			// be set to the active theme's slug by _build_block_template_result_from_file(),
			// even if the block template is really coming from the active theme's parent.
			// (The reason for this is that we want it to be associated with the active theme
			// -- not its parent -- once we edit it and store it to the DB as a wp_template CPT.)
			// Instead, we use _get_block_template_file() to locate the block template file.
			$template_file = _get_block_template_file( 'wp_template', $fallback_template_slug );
			if ( $template_file && get_template() === $template_file['theme'] ) {
				// The block template is part of the parent theme, so we
				// have to give precedence to the child theme's PHP template.
				array_shift( $templates );
			}
		}
	}

	return count( $templates ) ? $templates[0] : null;
}