react/packages/react-devtools-shared/src/devtools/views/Components/NativeStyleEditor/context.js

// @flow

import React, {
  createContext,
  useCallback,
  useContext,
  useEffect,
  useMemo,
  useState,
} from 'react';
import { unstable_batchedUpdates as batchedUpdates } from 'react-dom';
import { createResource } from 'src/devtools/cache';
import { BridgeContext, StoreContext } from 'src/devtools/views/context';
import { TreeStateContext } from '../TreeContext';

import type { StyleAndLayout as StyleAndLayoutBackend } from 'src/backend/NativeStyleEditor/types';
import type { StyleAndLayout as StyleAndLayoutFrontend } from './types';
import type { Element } from 'src/devtools/views/Components/types';
import type { Resource, Thenable } from 'src/devtools/cache';

export type GetStyleAndLayout = (id: number) => StyleAndLayoutFrontend | null;

type Context = {|
  getStyleAndLayout: GetStyleAndLayout,
|};

const NativeStyleContext = createContext<Context>(((null: any): Context));
NativeStyleContext.displayName = 'NativeStyleContext';

type ResolveFn = (styleAndLayout: StyleAndLayoutFrontend) => void;
type InProgressRequest = {|
  promise: Thenable<StyleAndLayoutFrontend>,
  resolveFn: ResolveFn,
|};

const inProgressRequests: WeakMap<Element, InProgressRequest> = new WeakMap();
const resource: Resource<
  Element,
  Element,
  StyleAndLayoutFrontend
> = createResource(
  (element: Element) => {
    let request = inProgressRequests.get(element);
    if (request != null) {
      return request.promise;
    }

    let resolveFn = ((null: any): ResolveFn);
    const promise = new Promise(resolve => {
      resolveFn = resolve;
    });

    inProgressRequests.set(element, { promise, resolveFn });

    return promise;
  },
  (element: Element) => element,
  { useWeakMap: true }
);

type Props = {|
  children: React$Node,
|};

function NativeStyleContextController({ children }: Props) {
  const bridge = useContext(BridgeContext);
  const store = useContext(StoreContext);

  const getStyleAndLayout = useCallback<GetStyleAndLayout>(
    (id: number) => {
      const element = store.getElementByID(id);
      if (element !== null) {
        return resource.read(element);
      } else {
        return null;
      }
    },
    [store]
  );

  // It's very important that this context consumes selectedElementID and not NativeStyleID.
  // Otherwise the effect that sends the "inspect" message across the bridge-
  // would itself be blocked by the same render that suspends (waiting for the data).
  const { selectedElementID } = useContext(TreeStateContext);

  const [
    currentStyleAndLayout,
    setCurrentStyleAndLayout,
  ] = useState<StyleAndLayoutFrontend | null>(null);

  // This effect handler invalidates the suspense cache and schedules rendering updates with React.
  useEffect(() => {
    const onStyleAndLayout = ({ id, layout, style }: StyleAndLayoutBackend) => {
      let element = store.getElementByID(id);
      if (element !== null) {
        const styleAndLayout: StyleAndLayoutFrontend = {
          layout,
          style,
        };
        const request = inProgressRequests.get(element);
        if (request != null) {
          inProgressRequests.delete(element);
          batchedUpdates(() => {
            request.resolveFn(styleAndLayout);
            setCurrentStyleAndLayout(styleAndLayout);
          });
        } else {
          resource.write(element, styleAndLayout);

          // Schedule update with React if the curently-selected element has been invalidated.
          if (id === selectedElementID) {
            setCurrentStyleAndLayout(styleAndLayout);
          }
        }
      }
    };

    bridge.addListener('NativeStyleEditor_styleAndLayout', onStyleAndLayout);
    return () =>
      bridge.removeListener(
        'NativeStyleEditor_styleAndLayout',
        onStyleAndLayout
      );
  }, [bridge, currentStyleAndLayout, selectedElementID, store]);

  // This effect handler polls for updates on the currently selected element.
  useEffect(() => {
    if (selectedElementID === null) {
      return () => {};
    }

    const rendererID = store.getRendererIDForElement(selectedElementID);

    let timeoutID: TimeoutID | null = null;

    const sendRequest = () => {
      timeoutID = null;

      if (rendererID !== null) {
        bridge.send('NativeStyleEditor_measure', {
          id: selectedElementID,
          rendererID,
        });
      }
    };

    // Send the initial measurement request.
    // We'll poll for an update in the response handler below.
    sendRequest();

    const onStyleAndLayout = ({ id }: StyleAndLayoutBackend) => {
      // If this is the element we requested, wait a little bit and then ask for another update.
      if (id === selectedElementID) {
        if (timeoutID !== null) {
          clearTimeout(timeoutID);
        }
        timeoutID = setTimeout(sendRequest, 1000);
      }
    };

    bridge.addListener('NativeStyleEditor_styleAndLayout', onStyleAndLayout);

    return () => {
      bridge.removeListener(
        'NativeStyleEditor_styleAndLayout',
        onStyleAndLayout
      );

      if (timeoutID !== null) {
        clearTimeout(timeoutID);
      }
    };
  }, [bridge, selectedElementID, store]);

  const value = useMemo(
    () => ({ getStyleAndLayout }),
    // NativeStyle is used to invalidate the cache and schedule an update with React.
    // eslint-disable-next-line react-hooks/exhaustive-deps
    [currentStyleAndLayout, getStyleAndLayout]
  );

  return (
    <NativeStyleContext.Provider value={value}>
      {children}
    </NativeStyleContext.Provider>
  );
}

export { NativeStyleContext, NativeStyleContextController };