Design: dynamic palette

Design notes for #322

Currently, the palette of nodes is loaded when the runtime starts and does not change.

The runtime needs to allow nodes to be added/removed dynamically.

Some points that need to be considered:

• nodes can be added by dropping files into the node path, or by npm. Both of these mechanisms should be supported by this feature
  • adding by file will expect the file to have already been copied into node path
  • adding by npm will trigger an npm install of the module
  • future support for importing a zip or files themselves?
• removing a node cannot 'unload' the module - care must be taken if the node creates any 'static' resources
• removing a node in the editor must allow it to remove any artefacts added to the page (eg, debug node's tab)
• a node file or module can contain multiple nodes. Making a request to remove a single node type may trigger the removal of multiple node types.
• what to do if the node is being used in the current flow? Safest option is to reject the removal.
• removing a node, without also removing the files, will mean it returns to the palette on the next restart. That would be unexpected.

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See Definitions for a description of node/node set/node module/node pack.

Add/Remove vs Enable/Disable

The Add/Remove api is for getting new nodes installed into the runtime as well as removing them. It operates at either the js/html level, or the node module level.

The Enable/Disable api is used with node sets. This is how a user can install a node module using the Add/Remove API, then elect to disable one or more of the node sets it contains so they don't appear in the palette.

Adding a node set/module

To add a new node to the palette:

1. a request is POSTed to {admin root}/nodes to trigger the add. Its Content-Type must be application/json. The post body is a JSON structure that identifies where the node information comes from, either a local file (file) or an npm module (module).

    {
        file: "path to local node .js file or package.json",
        module: "npm module name"
    }
   

2. The response to this request is the corresponding node information object. This is a json object containing the node set id, a list of the specific types in the set and a boolean flag to show if it is enabled or not. If not enabled, it may also list an error message describing why it is not enabled - unless if has been disabled by the user.

3. An event is fired over the comms link telling any connected editors that nodes have been added. This triggers a HTTP Get back to {admin root}/nodes/{node-set-id} to load the node definition/help/edit template.

Remove node set/module

To remove a node from the palette:

1. a DELETE http request is sent to {admin root}/nodes/{node-set-id} to trigger the removal.
2. If the any of the corresponding nodes are in use, the request is rejected
3. The runtime registry removes the corresponding nodes.
4. An event is fired over the comms link telling any connected editors that the nodes have been removed.

Enable/Disable a node set

1. a PUT http request is sent to {admin root}/nodes/{node-set-id}. Its Content-Type must be application/json.The PUT body is a JSON structure that identifies the desired state of the node set's enabled property.

    {
        enabled: true | false
    }
   

2. if the request succeeds, it returns the updated node information object.

3. the request will fail if the request is to disable a node that is currently in use.

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ToDo

• Create UI for enabling/disabling nodes
• Create UI for uninstalling nodes
• Editor registry of types that is populated with the node list
• Update registry in response to node/enabled/node/disabled events
• Remove node from palette on node/disabled event
• Add node back to palette on node/enabled event - definition should already be loaded