* @return array $attrs
	 */
	private function remove_link_class( $attrs ) {
		if ( ! $this->remove_class || empty( $attrs['class'] ) || strpos( $attrs['class'], 'rank-math-link' ) === false ) {
			return $attrs;
		}

		$this->is_dirty = true;
		$attrs['class'] = str_replace( 'rank-math-link', '', $attrs['class'] );

		if ( ! trim( $attrs['class'] ) ) {
			unset( $attrs['class'] );
		}

		return $attrs;
	}

	/**
	 * Set External attributs
	 *
	 * @since 1.0.44.2
	 *
	 * @param array $attrs Array of link attributes.
	 *
	 * @return array $attrs
	 */
	private function set_external_attrs( $attrs ) {
		if ( ! $this->add_attributes ) {
			return $attrs;
		}

		// Skip if there is no href or it's a hash link like "#id".
		// Skip if relative link.
		// Skip for same domain ignoring sub-domain if any.
		if ( ! Url::is_external( $attrs['href'] ) ) {
			return $attrs;
		}

		if ( $this->should_add_nofollow( $attrs['href'] ) ) {
			if ( $this->nofollow_link || ( $this->nofollow_image && $this->is_valid_image( $attrs['href'] ) ) ) {
				$this->is_dirty = true;
				$this->set_rel_attribute( $attrs, 'nofollow', ( isset( $attrs['rel'] ) && ! Str::contains( 'dofollow', $attrs['rel'] ) && ! Str::contains( 'nofollow', $attrs['rel'] ) ) );
			}
		}

		if ( $this->new_window_link && ! isset( $attrs['target'] ) ) {
			$this->is_dirty  = true;
			$attrs['target'] = '_blank';
		}

		if ( $this->add_noopener && $this->do_filter( 'noopener/domain', Url::get_domain( $attrs['href'] ) ) ) {
			$this->is_dirty = true;
			$this->set_rel_attribute( $attrs, 'noopener', ( isset( $attrs['rel'] ) && ! Str::contains( 'noopener', $attrs['rel'] ) ) );
		}

		if ( Url::is_affiliate( $attrs['href'] ) ) {
			$this->is_dirty = true;
			$this->set_rel_attribute( $attrs, 'sponsored', ( isset( $attrs['rel'] ) && ! Str::contains( 'sponsored', $attrs['rel'] ) ) );
		}

		return $attrs;
	}

	/**
	 * Check if we need to add nofollow for this link, based on "nofollow_domains" & "nofollow_exclude_domains"
	 *
	 * @param  string $url Link URL.
	 * @return bool
	 */
	private function should_add_nofollow( $url ) {
		if ( ! $this->nofollow_link && ! $this->nofollow_image ) {
			return false;
		}

		$include_domains = $this->get_nofollow_domains( 'include' );
		$exclude_domains = $this->get_nofollow_domains( 'exclude' );
		$parent_domain   = Url::get_domain( $url );
		$parent_domain   = preg_replace( '/^www\./', '', $parent_domain );

		// Check if domain is in list.
		if ( ! empty( $include_domains ) ) {
			return in_array( $parent_domain, $include_domains, true );
		}

		// Check if domain is NOT in list.
		if ( ! empty( $exclude_domains ) && in_array( $parent_domain, $exclude_domains, true ) ) {
			return false;
		}

		return true;
	}

	/**
	 * Get domain for nofollow
	 *
	 * @param  string $type Type either include or exclude.
	 * @return array
	 */
	private function get_nofollow_domains( $type ) {
		static $rank_math_nofollow_domains;

		if ( isset( $rank_math_nofollow_domains[ $type ] ) ) {
			return $rank_math_nofollow_domains[ $type ];
		}

		$setting = 'include' === $type ? 'nofollow_domains' : 'nofollow_exclude_domains';
		$domains = Helper::get_settings( "general.{$setting}" );
		$domains = Str::to_arr_no_empty( $domains );

		// Strip off www. prefixes.
		$domains = array_map(
			function( $domain ) {
				$domain = preg_replace( '#^http(s)?://#', '', trim( $domain, '/' ) );
				return preg_replace( '/^www\./', '', $domain );
			},
			$domains
		);

		$rank_math_nofollow_domains[ $type ] = $domains;

		return $rank_math_nofollow_domains[ $type ];
	}

	/**
	 * Is a valid image url.
	 *
	 * @param string $url Image url.
	 *
	 * @return boolean
	 */
	private function is_valid_image( $url ) {
		foreach ( [ '.jpg', '.jpeg', '.png', '.gif' ] as $ext ) {
			if ( Str::contains( $ext, $url ) ) {
				return true;
			}
		}

		return false;
	}
}