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<?php
/**
 * Outputs the html aria-checked attribute.
 *
 * Compares the first two arguments and if identical marks as checked
 *
 * @since 2016-02-08
 * @see   checked()
 *
 * @param mixed $checked One of the values to compare.
 * @param mixed $current Optional. The other value to compare if not just true. Default true.
 * @param bool  $echo    Optional. Whether to echo or just return the string. Default true.
 * @return string HTML ARIA attribute with appropriate value.
 */
function aria_checked( $checked, $current = true, $echo = true ) {
	return __aria_checked_selected_helper( $checked, $current, $echo, 'checked' );
}

/**
 * Outputs the html aria-selected attribute.
 *
 * Compares the first two arguments and if identical marks as checked
 *
 * @since 2016-02-08
 * @see   selected()
 *
 * @param mixed $checked One of the values to compare.
 * @param mixed $current Optional. The other value to compare if not just true. Default true.
 * @param bool  $echo    Optional. Whether to echo or just return the string. Default true.
 * @return string HTML ARIA attribute with appropriate value.
 */
function aria_selected( $checked, $current = true, $echo = true ) {
	return __aria_checked_selected_helper( $checked, $current, $echo, 'selected' );
}

/**
 * Outputs the html aria-disabled attribute.
 *
 * Compares the first two arguments and if identical marks as checked
 *
 * @since 2016-02-08
 * @see   disabled()
 *
 * @param mixed $checked One of the values to compare.
 * @param mixed $current Optional. The other value to compare if not just true. Default true.
 * @param bool  $echo    Optional. Whether to echo or just return the string. Default true.
 * @return string HTML ARIA attribute with appropriate value.
 */
function aria_disabled( $checked, $current = true, $echo = true ) {
	return __aria_checked_selected_helper( $checked, $current, $echo, 'disabled' );
}

/**
 * Private helper function for checked, selected, and disabled.
 *
 * Compares the first two arguments and if identical marks as 'true'.
 * This provides basic support for checked/selected true/false, but not
 * 'undefined' or 'mixed'.
 *
 * @since  2016-02-08
 * @access private
 * @see    __checked_selected_helper()
 *
 * @param mixed  $helper  One of the values to compare.
 * @param mixed  $current The other value to compare if not just true. Default true.
 * @param bool   $echo    Whether to echo or just return the string.
 * @param string $type    The type of checked|selected|disabled we are doing.
 * @return string HTML ARIA attribute with appropriate value, or empty string if invalid type.
 */

function __aria_checked_selected_helper( $helper, $current, $echo, $type ) {
	//Whitelist the types to check.
	$types = array( 'checked', 'selected', 'disabled' );

	/**
	 * Filter the types of ARIA attributes that allow true/false values.
	 *
	 * @since 2016-02-08
	 *
	 * @param array $types A list of aria-$type attributes.
	 */
	$aria_bool_attributes = apply_filters( 'aria_bool_attributes', $types );
	
	if ( ! in_array( $type, $aria_bool_attributes, true ) ) {
		return '';
	}
	
	$val    = ( (string) $helper === (string) $current ) ? 'true' : 'false';
	$result = sprintf( ' aria-%1$s="%2$s"', $type, $val );

	if ( $echo ) {
		echo $result; //xss okay (use late-escaping)
	}

	return $result;
}