EO_Replacement_Variable( 'currentdate', __( 'Current date', 'wordpress-seo' ), __( 'Replaced with the current date', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'currentyear', __( 'Current year', 'wordpress-seo' ), __( 'Replaced with the current year', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'currentmonth', __( 'Current month', 'wordpress-seo' ), __( 'Replaced with the current month', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'currentday', __( 'Current day', 'wordpress-seo' ), __( 'Replaced with the current day', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'post_year', __( 'Post year', 'wordpress-seo' ), __( 'Replaced with the year the post was published', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'post_month', __( 'Post month', 'wordpress-seo' ), __( 'Replaced with the month the post was published', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'post_day', __( 'Post day', 'wordpress-seo' ), __( 'Replaced with the day the post was published', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'author_first_name', __( 'Author first name', 'wordpress-seo' ), __( 'Replaced with the first name of the author', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'author_last_name', __( 'Author last name', 'wordpress-seo' ), __( 'Replaced with the last name of the author', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'permalink', __( 'Permalink', 'wordpress-seo' ), __( 'Replaced with the permalink', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'post_content', __( 'Post Content', 'wordpress-seo' ), __( 'Replaced with the post content', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'category_title', __( 'Category Title', 'wordpress-seo' ), __( 'Current or first category title', 'wordpress-seo' ) ),
		];

		foreach ( $replacement_variables as $replacement_variable ) {
			self::register_help_text( 'basic', $replacement_variable );
		}
	}

	/**
	 * Set/translate the help texts for the WPSEO standard advanced variables.
	 *
	 * @return void
	 */
	private static function set_advanced_help_texts() {
		$replacement_variables = [
			new WPSEO_Replacement_Variable( 'pt_single', __( 'Post type (singular)', 'wordpress-seo' ), __( 'Replaced with the content type single label', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'pt_plural', __( 'Post type (plural)', 'wordpress-seo' ), __( 'Replaced with the content type plural label', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'modified', __( 'Modified', 'wordpress-seo' ), __( 'Replaced with the post/page modified time', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'id', __( 'ID', 'wordpress-seo' ), __( 'Replaced with the post/page ID', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'name', __( 'Name', 'wordpress-seo' ), __( 'Replaced with the post/page author\'s \'nicename\'', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'user_description', __( 'User description', 'wordpress-seo' ), __( 'Replaced with the post/page author\'s \'Biographical Info\'', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'page', __( 'Page', 'wordpress-seo' ), __( 'Replaced with the current page number with context (i.e. page 2 of 4)', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'pagetotal', __( 'Pagetotal', 'wordpress-seo' ), __( 'Replaced with the current page total', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'pagenumber', __( 'Pagenumber', 'wordpress-seo' ), __( 'Replaced with the current page number', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'caption', __( 'Caption', 'wordpress-seo' ), __( 'Attachment caption', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'focuskw', __( 'Focus keyword', 'wordpress-seo' ), __( 'Replaced with the posts focus keyphrase', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'term404', __( 'Term404', 'wordpress-seo' ), __( 'Replaced with the slug which caused the 404', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'cf_<custom-field-name>', '<custom-field-name> ' . __( '(custom field)', 'wordpress-seo' ), __( 'Replaced with a posts custom field value', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'ct_<custom-tax-name>', '<custom-tax-name> ' . __( '(custom taxonomy)', 'wordpress-seo' ), __( 'Replaced with a posts custom taxonomies, comma separated.', 'wordpress-seo' ) ),
			new WPSEO_Replacement_Variable( 'ct_desc_<custom-tax-name>', '<custom-tax-name> ' . __( 'description (custom taxonomy)', 'wordpress-seo' ), __( 'Replaced with a custom taxonomies description', 'wordpress-seo' ) ),
		];

		foreach ( $replacement_variables as $replacement_variable ) {
			self::register_help_text( 'advanced', $replacement_variable );
		}
	}

	/* *********************** GENERAL HELPER METHODS ************************** */

	/**
	 * Remove the '%%' delimiters from a variable string.
	 *
	 * @param string $text Variable string to be cleaned.
	 *
	 * @return string
	 */
	private static function remove_var_delimiter( $text ) {
		return trim( $text, '%' );
	}

	/**
	 * Add the '%%' delimiters to a variable string.
	 *
	 * @param string $text Variable string to be delimited.
	 *
	 * @return string
	 */
	private static function add_var_delimiter( $text ) {
		return '%%' . $text . '%%';
	}

	/**
	 * Retrieve a post's terms, comma delimited.
	 *
	 * @param int    $id            ID of the post to get the terms for.
	 * @param string $taxonomy      The taxonomy to get the terms for this post from.
	 * @param bool   $return_single If true, return the first term.
	 *
	 * @return string Either a single term or a comma delimited string of terms.
	 */
	public function get_terms( $id, $taxonomy, $return_single = false ) {
		$output = '';

		// If we're on a specific tag, category or taxonomy page, use that.
		if ( ! empty( $this->args->term_id ) ) {
			$output = $this->args->name;
		}
		elseif ( ! empty( $id ) && ! empty( $taxonomy ) ) {
			$terms = get_the_terms( $id, $taxonomy );
			if ( is_array( $terms ) && $terms !== [] ) {
				foreach ( $terms as $term ) {
					if ( $return_single ) {
						$output = $term->name;
						break;
					}
					else {
						$output .= $term->name . ', ';
					}
				}
				$output = rtrim( trim( $output ), ',' );
			}
		}
		unset( $terms, $term );

		/**
		 * Allows filtering of the terms list used to replace %%category%%, %%tag%%
		 * and %%ct_<custom-tax-name>%% variables.
		 *
		 * @param string $output   Comma-delimited string containing the terms.
		 * @param string $taxonomy The taxonomy of the terms.
		 */
		return apply_filters( 'wpseo_terms', $output, $taxonomy );
	}

	/**
	 * Gets a taxonomy term hierarchy including the term to get the parents for.
	 *
	 * @return string
	 */
	private function get_term_hierarchy() {
		if ( ! is_taxonomy_hierarchical( $this->args->taxonomy ) ) {
			return '';
		}

		$separator = ' ' . $this->retrieve_sep() . ' ';

		$args = [
			'format'    => 'name',
			'separator' => $separator,
			'link'      => false,
			'inclusive' => true,
		];

		return rtrim(
			get_term_parents_list( $this->args->term_id, $this->args->taxonomy, $args ),
			$separator
		);
	}

	/**
	 * Retrieves the term ancestors hierarchy.
	 *
	 * @return string|null The term ancestors hierarchy.
	 */
	private function retrieve_term_hierarchy() {
		$replacement = null;

		if ( ! empty( $this->args->term_id ) && ! empty( $this->args->taxonomy ) ) {
			$hierarchy = $this->get_term_hierarchy();

			if ( $hierarchy !== '' ) {
				$replacement = esc_html( $hierarchy );
			}
		}

		return $replacement;
	}
}