/*! Copyright (c) 2010 Brandon Aaron (http://brandonaaron.net)
 * Licensed under the MIT License (LICENSE.txt).
 *
 * Version 1.0
 *
 * Contributions by:
 *   - Karl Swedberg
 */

(function($) {

$.fn.extend({
    expandable: function(givenOptions) {
        var options = $.extend({
            duration: 'normal',
            interval: 750,
            within: 1,
            by: 2,
            init: false 
        }, givenOptions);
        
        return this.filter('textarea').each(function() {
            var $this = $(this).css({ display: 'block', overflow: 'hidden' }),
                minHeight = $this.height(),
                heightDiff = this.offsetHeight - minHeight,
                rowSize = ( parseInt($this.css('lineHeight'), 10) || parseInt($this.css('fontSize'), 10) ),
                // $mirror is used for determining the height of the text within the textarea
                // it isn't perfect but is pretty close
                // white-space rules from: http://petesbloggerama.blogspot.com/2007/02/firefox-ie-word-wrap-word-break-tables.html
                $mirror = $('<div style="position:absolute;top:-999px;left:-999px;border-color:#000;border-style:solid;overflow-x:hidden;visibility:hidden;z-index:0;white-space: pre-wrap;white-space:-moz-pre-wrap;white-space:-pre-wrap;white-space:-o-pre-wrap;word-wrap:break-word;" />').appendTo('body'),
                interval;
            
            // copy styles from textarea to mirror to mirror the textarea as best possible
            $.each('borderTopWidth borderRightWidth borderBottomWidth borderLeftWidth paddingTop paddingRight paddingBottom paddingLeft fontSize fontFamily fontWeight fontStyle fontStretch fontVariant wordSpacing lineHeight width'.split(' '), function(i,prop) {
                $mirror.css(prop, $this.css(prop));
            });
            
            // setup events
            $this
                .bind('keypress', function(event) { if ( event.keyCode == '13' ) check(); })
                .bind('focus blur', function(event) {
                    if ( event.type == 'blur' ) clearInterval( interval );
                    if ( event.type == 'focus' ) interval = setInterval(check, options.interval);
                });

            function check() {
                var text = $this.val(), newHeight, height, usedHeight, usedRows, availableRows;
                // copy textarea value to the $mirror
                // encode any html passed in and replace new lines with a <br>
                // the &nbsp; is to try and normalize browser behavior
                $mirror.html( encodeHTML(text).replace(/\n/g, '&nbsp;<br>') );
                
                height = $this[0].offsetHeight - heightDiff;
                usedHeight = $mirror[0].offsetHeight - heightDiff;
                usedRows = Math.floor(usedHeight / rowSize);
                availableRows = Math.floor((height / rowSize) - usedRows);
                
                // adjust height if needed by either growing or shrinking the text area to within the specified bounds
                if ( availableRows <= options.within ) {
                    newHeight = rowSize * (usedRows + Math.max(availableRows, 0) + options.by);
                    $this.stop().animate({ height: newHeight }, options.duration);
                } else if ( availableRows > options.by + options.within ) {
                    newHeight = Math.max( height - (rowSize * (availableRows - (options.by + options.within))), minHeight );
                    $this.stop().animate({ height: newHeight }, options.duration);
                }
            };
            if ( options.init ) check();
        }).end();
    }
});
    
function encodeHTML(text) {
    var characters = {
        '<' : '&lt;',
        '>' : '&gt;',
        '&' : '&amp;',
        '"' : '&quot;',
        '\'': '&#x27;',
        '/' : '&#x2F;'
    };
    return (text + '').replace(/[<>&"'\/]/g, function(c) {
        return characters[c];
    });
}

})(jQuery);