/**
	 * Recursively merge a variable number of arrays, using the left array as base,
	 * giving priority to the right array.
	 *
	 * Difference with native array_merge_recursive():
	 * array_merge_recursive converts values with duplicate keys to arrays rather than
	 * overwriting the value in the first array with the duplicate value in the second array.
	 *
	 * array_merge_recursive_distinct does not change the data types of the values in the arrays.
	 * Matching keys' values in the second array overwrite those in the first array, as is the
	 * case with array_merge.
	 *
	 * Freely based on information found on http://www.php.net/manual/en/function.array-merge-recursive.php
	 *
	 * {@internal Should be moved to a general utility class.}}
	 *
	 * @return array
	 */
	public static function array_merge_recursive_distinct() {

		$arrays = func_get_args();
		if ( count( $arrays ) < 2 ) {
			if ( $arrays === [] ) {
				return [];
			}
			else {
				return $arrays[0];
			}
		}

		$merged = array_shift( $arrays );

		foreach ( $arrays as $array ) {
			foreach ( $array as $key => $value ) {
				if ( is_array( $value ) && ( isset( $merged[ $key ] ) && is_array( $merged[ $key ] ) ) ) {
					$merged[ $key ] = self::array_merge_recursive_distinct( $merged[ $key ], $value );
				}
				else {
					$merged[ $key ] = $value;
				}
			}
			unset( $key, $value );
		}

		return $merged;
	}

	/**
	 * Counts the total of all the keywords being used for posts except the given one.
	 *
	 * @param string  $keyword The keyword to be counted.
	 * @param integer $post_id The id of the post to which the keyword belongs.
	 *
	 * @return array
	 */
	public static function keyword_usage( $keyword, $post_id ) {

		if ( empty( $keyword ) ) {
			return [];
		}

		/**
		 * The indexable repository.
		 *
		 * @var Indexable_Repository
		 */
		$repository = YoastSEO()->classes->get( Indexable_Repository::class );

		$post_ids = $repository->query()
			->select( 'object_id' )
			->where( 'primary_focus_keyword', $keyword )
			->where( 'object_type', 'post' )
			->where_not_equal( 'object_id', $post_id )
			->limit( 2 )
			->find_array();

		$callback = function ( $row ) {
			return (int) $row['object_id'];
		};
		$post_ids = array_map( $callback, $post_ids );

		/*
		 * If Yoast SEO Premium is active, get the additional keywords as well.
		 * We only check for the additional keywords if we've not already found two.
		 * In that case there's no use for an additional query as we already know
		 * that the keyword has been used multiple times before.
		 */
		if ( YoastSEO()->helpers->product->is_premium() && count( $post_ids ) < 2 ) {
			$query = [
				'meta_query'     => [
					[
						'key'     => '_yoast_wpseo_focuskeywords',
						'value'   => sprintf( '"keyword":"%s"', $keyword ),
						'compare' => 'LIKE',
					],
				],
				'post__not_in'   => [ $post_id ],
				'fields'         => 'ids',
				'post_type'      => 'any',

				/*
				 * We only need to return zero, one or two results:
				 * - Zero: keyword hasn't been used before
				 * - One: Keyword has been used once before
				 * - Two or more: Keyword has been used twice or more before
				 */
				'posts_per_page' => 2,
			];
			$get_posts = new WP_Query( $query );
			$post_ids  = array_merge( $post_ids, $get_posts->posts );
		}

		return $post_ids;
	}
}