(function() {

db.generator = function generator() {

    var that = this,
        myQuery = null;
        default_offset = 0,
        limit = 5;

    // text parameter for queries
    function _generator(text) {

        var db = that;

        var R = [],
            offset = default_offset,
            last = limit,
            done = false;

        // see what next() would return
        function peek() {
            console.log("peek");
            if(done)
                return Promise.resolve({done: true});
            else if(R.length)
                return Promise.resolve({value: R[0], done: false});
            else 
                return fetch().then(peek);
        }

        // returns a Promise that resolves to {value, done}
        function next() {
            console.log("next");
            if(done)
                return Promise.resolve({done: true});
            else if(R.length)
                return Promise.resolve({value: R.shift(), done: false});
            else 
                return fetch().then(next);
        }

        // returns Promise after fetching more results and setting internal
        // buffer to contain the <limit> results, starting at <offset>
        function fetch() {
            console.log("fetch");
            return myQuery(text, limit, offset).then(function(rows){
                if(rows.length) {
                    R = rows;
                    offset += rows.length;
                    last = rows.length;
                }
                else {
                    done = true;
                }
            });
        }

        return {
            next: next,
            peek: peek
        }
    }

    // modify type of generator
    _generator.query = function(q) {
        if (!arguments.length) return myQuery;
        myQuery = q;
        return _generator;
    };

    // set or get size of internal buffer
    _generator.limit = function(_) {
        if (!arguments.length) return limit;
        limit = _;
        return _generator;
    };

    // set or get offset
    _generator.offset = function(_) {
        if (!arguments.length) return offset;
        offset = _;
        return _generator;
    };

    return _generator;
}
})();