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function ViewModel(columnsSource) {
    this.nextFileterBinaryConditions = ['AND', 'OR'];
    this.columns = ko.observableArray(columnsSource);
    this.filters = ko.observableArray([new Filter()]);

    this.addFilter = function(filterObj) {
        var invalidFilter = ko.utils.arrayFirst(this.filters(), function (filter) {
            return filter.IsValid() === false;
        });
    
        if (invalidFilter == null) {
            var currentIndex = ko.utils.arrayIndexOf(this.filters(), filterObj);
            this.filters.splice(currentIndex + 1, 0, new Filter());
        }
    };

    this.removeFilter = function(filterObj) {
        this.filters.remove(filterObj);

        if (this.filters().length == 0) {
            this.addFilter();
        }
    };

    this.postFilters = function() {
        var items = ko.toJS(this.filters());
        var mappedItems = ko.utils.arrayMap(items, function(filter) {
            delete filter.ColumnObj;
            delete filter.AvailableConditions;

            return filter;
        });

        alert(ko.toJSON(mappedItems));
    };
};