gistfile1.txt

if (typeof iD === 'undefined') iD = {};

iD.SceneGraph = function () {
    this.ways      = {};
    this.nodes     = {};
    this.relations = {};
};

function mutable(entity) {
    if (entity.isFrozen()) {
        entity = Object.create(entity, {dirty: {value: true}})
    }
    return entity;
}

function immutable(entity) {
    if (!entity.isFrozen()) {
        Object.freeze(entity);
    }
    return entity;
}

function mutate(entity, callback) {
    entity = mutable(entity);
    callback.call(entity, entity);
    return immutable(entity);
}

iD.SceneGraph.prototype.mutate = function () {
    mutate(this, function () {
        var callback = arguments.pop();
        var entities = arguments.map(function (entity) {
            if (entity.entityType === 'node') {
                this.nodes = mutate(this.nodes);
                return this.nodes[entity.id] = mutate(entity);
            } else if (entity.entityType == 'way') {
                this.ways = mutate(this.ways);
                return this.ways[entity.id] = mutate(entity);
            } else if (entity.entityType == 'relation') {
                this.relations = mutate(this.relations);
                return this.relations[entity.id] = mutate(entity);
            }
        });
        entities.shift(this);
        callback.apply(this, entities);
        entities.each(immutable);
    });
};

iD.SceneGraph.prototype.changes = function () {
    return {
        nodes:     // filter by dirty property
        ways:      // etc
        relations: // etc
    }
};

iD.Actions = {};

iD.Actions.AddNodeToWay = function (scenegraph, way, node, index) {
    return scenegraph.mutate(way, function (scenegraph, way) {
        if (index === -1) {
            index = way.nodes.length;
        }

        nodes = way.mutableNodes();
        nodes.splice(index, 0, node.id);
    });
};

iD.Actions.DeleteNode = function (scenegraph, node) {
    return scenegraph.mutate(function (scenegraph) {
        delete scenegraph.nodes[node.id];

        // for ids in node.parent_way_ids
        //   way = scenegraph.ways[id].mutable(scenegraph)
        //   way.nodes.delete(node.id); // TODO: copy nodes first

        // for ids in node.parent_relation_ids
        //   relation = scenegraph.relations[id].mutable(scenegraph)
        //   relation.nodes.delete(node.id); // TODO: copy nodes first
    });
};