Class DragDropMonitor

packages/dnd-core/src/DragDropMonitor.js:8–184

import { areDirty } from './reducers/dirtyHandlerIds';

export default class DragDropMonitor {
  constructor(store) {
    this.store = store;
    this.registry = new HandlerRegistry(store);
  }

  subscribeToStateChange(listener, options = {}) {
    const { handlerIds } = options;
    invariant(
      typeof listener === 'function',
      'listener must be a function.',
    );
    invariant(
      typeof handlerIds === 'undefined' || isArray(handlerIds),
      'handlerIds, when specified, must be an array of strings.',
    );

    let prevStateId = this.store.getState().stateId;
    const handleChange = () => {
      const state = this.store.getState();
      const currentStateId = state.stateId;
      try {
        const canSkipListener = currentStateId === prevStateId || (
          currentStateId === prevStateId + 1 &&
          !areDirty(state.dirtyHandlerIds, handlerIds)
        );

        if (!canSkipListener) {
          listener();
        }
      } finally {
        prevStateId = currentStateId;
      }
    };

    return this.store.subscribe(handleChange);
  }

  subscribeToOffsetChange(listener) {
    invariant(
      typeof listener === 'function',
      'listener must be a function.',
    );

    let previousState = this.store.getState().dragOffset;
    const handleChange = () => {
      const nextState = this.store.getState().dragOffset;
      if (nextState === previousState) {
        return;
      }

      previousState = nextState;
      listener();
    };

    return this.store.subscribe(handleChange);
  }