drawio/lib/versioning/SelectionHandler.js

class SelectionHandler {
  constructor(getUserId, userColors) {
    this.userColors = userColors;
    this.getUserId = getUserId;
    this.map = new Map();
  }

  install(graph, controller) {
    graph.selectionModel.addListener(mxEvent.CHANGE, (source, eventObj) => {
      if (listenerEnabled) {
        const {added, removed} = eventObj.properties;
        controller.addInput(
          "broadcast",
          // "selection_change",
          "in",
          [{
            userId: this.getUserId(),
            addedIds: removed ? removed.map(cell => cell.id) : [],
            removedIds: added ? added.map(cell => cell.id) : [],
          }],
          controller.wallclockToSimtime(),
        );
      }
    });

    controller.addMyOwnOutputListener({
      'add': event => {
        if (event.name === "selection_change") {
          const [{userId, addedIds, removedIds}] = event.parameters;
          const color = this.userColors.getColor(userId);

          for (const cellId of addedIds) {
            const cell = graph.model.cells[cellId];
            const highlight = new mxCellHighlight(graph, color,
              6); // width
            highlight.highlight(graph.view.getState(cell));
            this.map.set(cellId, highlight);
          }

          for (const cellId of removedIds) {
            const cell = graph.model.cells[cellId];
            const highlight = this.map.get(cellId);
            highlight.destroy();
            this.map.delete(cellId);
          }
        }
      }
    })
  }

  clearAll() {
    this.map.forEach(highlight => highlight.destroy());
    this.map.clear();
  }

}