order-parent-child-term.php

<?php

/**
 * Oder Term list by hierarchy.
 *
 * @param  array $terms         Array of terms to be hierarchical sorted
 * @return array $ordered_terms Array ot terms orderd by parent->child relation
 * @author Telmo Teixeira <telmo@widgilabs.com>
 */
function ( array $terms ) {
	// Start by matching the terms array.
	$ordered_terms = $terms;

	$loop_max = count( $ordered_terms ) - 1;

	// The outer loop iterates one time foreach item of the array.
	for ( $x = 0; $x < $loop_max; $x++ ) {
		// keep record of how many ordered items we found in the current iteration.
		$found = 0;

		// The inner loop modifies the array order.
		for ( $i = $loop_max; $i > 0; $i-- ) {
			$curr = $ordered_terms[ $i ];
			$prev = $ordered_terms[ $i - 1 ];

			/**
			 * If the current item is not previous's child they change places.
			 * This forces every item to travel through the array until it finds
			 * it's parent, then it stops.
			 */
			if ( $curr->parent !== $prev->term_id ) {
				// Remove from array.
				array_splice( $ordered_terms, ( $i - 1 ), 1 );

				// Insert after last ordered item (current + found).
				array_splice( $ordered_terms, ( $i + $found ), 0, array( $prev ) );
			} else {
				// +1 already in place found.
				$found++;
			}
		}
	}

	return $ordered_terms;
}