Walk the term metadata to get a specific value

term-metadata.php

<?php

/**
 * Get the specified metadata value for the term or from
 * one of it's parent terms.
 *
 * @since 1.0.0
 *
 * @param WP_Term $term Term object
 * @param string $meta_key The meta key to retrieve.
 *
 * @return mixed|null
 */
function get_hierarchichal_term_metadata( WP_Term $term, $meta_key ) {

	if ( ! is_taxonomy_hierarchical( $term->taxonomy ) ) {
		return;
	}

	if ( ! has_parent_term( $term ) ) {
		return;
	}

	return get_term_metadata_recursively( $term, $meta_key );
}

/**
 * Recursively get the term metadata by the specified meta key.
 * 
 * This function walks up the term hierarchical tree, searching for
 * a valid metadata value for the given meta key.
 * 
 * The recursive action stops when:
 *      1. The current term level has the metadata value.
 *      2. The current term level does not have a parent term.
 *
 * @since 1.0.0
 *
 * @param WP_Term $term Term object
 * @param string $meta_key The meta key to retrieve.
 * @param mixed|null $meta
 *
 * @return mixed|null
 */
function get_term_metadata_recursively( WP_Term $term, $meta_key, $meta = null ) {
	$meta = get_term_meta( $term->term_id, $meta_key, true );
	if ( $meta ) {
		return $meta;
	}

	if ( ! has_parent_term( $term ) ) {
		return $meta;
	}

	// Get the parent term
	$parent_term = get_term_by( 'id', $term->parent, $term->taxonomy );
	if ( $parent_term === false ) {
		return $meta;
	}

	// Try again
	return get_term_metadata_recursively( $parent_term, $meta_key, $meta );
}

/**
 * Checks if the term has a parent.
 *
 * @since 1.0.0
 *
 * @param WP_Term $term Term object.
 *
 * @return bool
 */
function has_parent_term( WP_Term $term ) {
	return ( $term->parent > 0 );
}