/*!
* jQuery Column cell selector v0.13
*
* Licensed under the new BSD License.
* Copyright 2009, Bram Stein
* All rights reserved.
*/
/*global jQuery*/
(function($) {
    var equationRegExp = /([\+\-]?\d*)[nN]([\+\-]?\d*)/,
		cache, equation;

    function parseEquation(str) {
        var tmp = [],
			result = {
			    multiplier: 0,
			    offset: 0
			};

        if (str === 'even') {
            str = '2n';
        } else if (str === 'odd') {
            str = '2n+1';
        } else if (/^\d*$/.test(str)) {
            str = '0n+' + str;
        }

        tmp = equationRegExp.exec(str);

        if (tmp !== null) {
            result.multiplier = tmp[1] - 0;
            result.offset = tmp[2] - 0;
        }
        return result;
    }

    function generateCache(cells, equation) {
        var currentRow, currentSection, matrix = [], first = 0, lookup = [];

        $.each(cells, function(k, cell) {
            var i = 0, j = 0,
				rowSpan = cell.rowSpan || 1,
				colSpan = cell.colSpan || 1;

            if (cell.parentNode !== currentRow) {
                currentRow = cell.parentNode;

                if (currentRow.parentNode !== currentSection) {
                    currentSection = currentRow.parentNode;
                    matrix = [];
                }

                first = 0;

                if (matrix[currentRow.rowIndex] === undefined) {
                    matrix[currentRow.rowIndex] = [];
                }

            }

            for (i = 0; i < matrix[currentRow.rowIndex].length + 1; i += 1) {
                if (matrix[currentRow.rowIndex][i] === undefined) {
                    first = i;
                    break;
                }
            }

            lookup[k] = first;

            for (i = currentRow.rowIndex; i < currentRow.rowIndex + rowSpan; i += 1) {
                if (matrix[i] === undefined) {
                    matrix[i] = [];
                }

                for (j = first; j < first + colSpan; j += 1) {
                    matrix[i][j] = true;
                }
            }
        });
        return lookup;
    }

    function nthCol(element, match, index) {
        var difference = cache[index] - (equation.offset - 1);
        if (equation.multiplier === 0) {
            return difference === 0;
        } else {
            return (difference % equation.multiplier === 0 && difference / equation.multiplier >= 0);
        }
    }

    $.extend(jQuery.fn, {
        nthCol: function(e) {
            equation = parseEquation(e);
            cache = generateCache(this);
            return $(this).filter(function(i) {
                return nthCol(this, undefined, i);
            });
        }
    });

    $.extend(jQuery.expr.match, {
        COLUMN: /:nth-col\((even|odd|[\dnN\+\-]*)\)/
    });

    $.extend(jQuery.expr.preFilter, {
        COLUMN: function(match, items) {
            equation = parseEquation(match[1]);
            cache = generateCache(items);
            return match;
        }
    });

    $.extend(jQuery.expr.filter, {
        COLUMN: nthCol
    });
})(jQuery);