Converts a duration to human readable format.

function human_readable_duration( $duration = '' ) {
	if ( ( empty( $duration ) || ! is_string( $duration ) ) ) {
		return false;
	}

	$duration = trim( $duration );

	// Remove prepended negative sign.
	if ( '-' === substr( $duration, 0, 1 ) ) {
		$duration = substr( $duration, 1 );
	}

	// Extract duration parts.
	$duration_parts = array_reverse( explode( ':', $duration ) );
	$duration_count = count( $duration_parts );

	$hour   = null;
	$minute = null;
	$second = null;

	if ( 3 === $duration_count ) {
		// Validate HH:ii:ss duration format.
		if ( ! ( (bool) preg_match( '/^([0-9]+):([0-5]?[0-9]):([0-5]?[0-9])$/', $duration ) ) ) {
			return false;
		}
		// Three parts: hours, minutes & seconds.
		list( $second, $minute, $hour ) = $duration_parts;
	} elseif ( 2 === $duration_count ) {
		// Validate ii:ss duration format.
		if ( ! ( (bool) preg_match( '/^([0-5]?[0-9]):([0-5]?[0-9])$/', $duration ) ) ) {
			return false;
		}
		// Two parts: minutes & seconds.
		list( $second, $minute ) = $duration_parts;
	} else {
		return false;
	}

	$human_readable_duration = array();

	// Add the hour part to the string.
	if ( is_numeric( $hour ) ) {
		/* translators: %s: Time duration in hour or hours. */
		$human_readable_duration[] = sprintf( _n( '%s hour', '%s hours', $hour ), (int) $hour );
	}

	// Add the minute part to the string.
	if ( is_numeric( $minute ) ) {
		/* translators: %s: Time duration in minute or minutes. */
		$human_readable_duration[] = sprintf( _n( '%s minute', '%s minutes', $minute ), (int) $minute );
	}

	// Add the second part to the string.
	if ( is_numeric( $second ) ) {
		/* translators: %s: Time duration in second or seconds. */
		$human_readable_duration[] = sprintf( _n( '%s second', '%s seconds', $second ), (int) $second );
	}

	return implode( ', ', $human_readable_duration );
}