ap_parse_search_string( string $str )

function ap_parse_search_string( $str ) {
	$output = array();

	// Split by space.
	$bits = explode( ' ', $str );

	// Process pairs.
	foreach ( $bits as $id => $pair ) {
		// Split the pair.
		$pair_bits = explode( ':', $pair );

		// This was actually a pair.
		if ( count( $pair_bits ) === 2 ) {
			$values    = explode( ',', $pair_bits[1] );
			$sanitized = array();

			if ( is_array( $values ) && ! empty( $values ) ) {
				foreach ( $values as $value ) {
					if ( ! empty( $value ) ) {
						$sanitized[] = sanitize_text_field( $value );
					}
				}
			}

			if ( count( $sanitized ) > 0 ) {
				// Use left part of pair as index and push right part to array.
				if ( ! empty( $pair_bits[0] ) ) {
					$output[ sanitize_text_field( $pair_bits[0] ) ] = $sanitized;
				}
			}

			if ( isset( $bits[ $id ] ) ) {
				// Remove this pair from $bits.
				unset( $bits[ $id ] );
			}
		} else {
			// Exit the loop.
			break;
		}
	}

	// Rebuild query with remains of $bits.
	$output['q'] = sanitize_text_field( implode( ' ', $bits ) );

	return $output;
}