var layout = function () {
    var needed_slots;

    var scale;
    var feature_height = 20;
    var callback = function (){};

    var feature_layout = function (new_features) {
        var track = this;
        scale = track.display().scale();

        needed_slots = collition_detector(new_features);
        track.height(needed_slots * feature_height);
        callback();

        return new_features;
    };

    function collition_detector (features) {
        var allocated = [];
        var remaining = features;
        var needed_slots = 0;

        for (var i=0; i<remaining.length; i++) {
            var features_by_slot = sort_features_by_slot(allocated);
            var current = remaining[i];
            var slot = 0;
            OUTER: while (true) {
                if (slot_has_space(current, features_by_slot[slot])) {
                    current.slot = slot;
                    allocated.push(current);
                    if (slot > needed_slots) {
                        needed_slots = slot;
                    }
                    break;
                }
                slot++;
            }
        }
        return needed_slots + 1;
    }

    function slot_has_space (feature, features_in_slot) {
        if (!features_in_slot) {
            return true;
        }
        for (var i=0; i<features_in_slot.length; i++) {
            var subject = features_in_slot[i];
            var y1 = scale(subject.start);
            var y2 = scale(subject.end);
            var x1 = scale(feature.start);
            var x2 = scale(feature.end);

            if ( ((x1 <= y1) && (x2 >= y1)) ||
            ((x1 >= y1) && (x1 <= y2)) ) {
                return false;
            }
        }
        return true;
    }

    function sort_features_by_slot (features) {
        var slots = [];
        for (var i=0; i<features.length; i++) {
            var feature = features[i];
            if (!slots[feature.slot]) {
                slots[feature.slot] = [];
            }
            slots[feature.slot].push(feature);
        }
        return slots;
    }

    feature_layout.elements = function () {};
    feature_layout.slots = function () {
        return needed_slots;
    };
    feature_layout.on_run = function(cbak) {
        callback = cbak;
        return this;
    };

    return feature_layout;
};