한 포스트의 중간 텀을 구한다.

get_mid_term.php

/**
 * 말단 텀 이외에 찍힌 것 제거
 *
 * @param int    $post_id
 * @param string $taxonomy
 *
 * @return WP_Term[]
 */
function get_mid_terms( int $post_id, string $taxonomy = 'category' ): array {
	$terms = wp_get_object_terms( $post_id, $taxonomy );
	$terms = array_combine( wp_list_pluck( $terms, 'term_id' ), $terms );

	$result = [];

	if ( is_array( $terms ) && count( $terms ) > 1 ) {
		$parents   = [];
		$mid_terms = [];

		// Build parents links
		foreach ( $terms as $term ) {
			$parents[ $term->term_id ] = $term->parent;

			$ancestors = get_ancestors( $term->term_id, $taxonomy, 'taxonomy' );
			if ( $ancestors ) {
				for ( $i = 1; $i < count( $ancestors ); ++ $i ) {
					$parents[ $ancestors[ $i ] ] = $ancestors[ $i + 1 ] ?? 0;
				}
			}
		}

		// Calc mid terms
		foreach ( $terms as $term ) {
			$p = $parents[ $term->term_id ] ?? 0;
			while ( $p ) {
				if ( isset( $terms[ $p ] ) ) {
					$mid_terms[] = $p;
				}
				$p = $parents[ $p ] ?? 0;
			}
		}

		// Populate terms
		foreach ( array_unique( $mid_terms ) as $term_id ) {
			if ( isset( $terms[ $term_id ] ) ) {
				$result[] = $terms[ $term_id ];
			}
		}
	}

	return $result;
}