/**
 * Makes "skip to content" link work correctly in IE9, Chrome, and Opera
 * for better accessibility.
 *
 * @link http://www.nczonline.net/blog/2013/01/15/fixing-skip-to-content-links/
 */

( function() {
    var isWebkit = navigator.userAgent.toLowerCase().indexOf( 'webkit' ) > -1,
        isOpera  = navigator.userAgent.toLowerCase().indexOf( 'opera' )  > -1,
        isIE     = navigator.userAgent.toLowerCase().indexOf( 'msie' )   > -1;

    if ( ( isWebkit || isOpera || isIE ) && document.getElementById && window.addEventListener ) {
        window.addEventListener( 'hashchange', function() {
            var id = location.hash.substring( 1 ),
                element;

            if ( ! ( /^[A-z0-9_-]+$/.test( id ) ) ) {
                return;
            }

            element = document.getElementById( id );

            if ( element ) {
                if ( ! ( /^(?:a|select|input|button|textarea)$/i.test( element.tagName ) ) ) {
                    element.tabIndex = -1;
                }

                element.focus();

                // Repositions the window on jump-to-anchor to account for admin bar and border height.
                window.scrollBy( 0, -53 );
            }
        }, false );
    }
} )();
