planning

node_modules/decap-cms-core/src/redux/middleware/waitUntilAction.ts

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+// Based on wait-service by Mozilla:
+// https://github.com/mozilla/gecko-dev/blob/master/devtools/client/shared/redux/middleware/wait-service.js
+
+/**
+ * A middleware that provides the ability for actions to install a
+ * function to be run once when a specific condition is met by an
+ * action coming through the system. Think of it as a thunk that
+ * blocks until the condition is met.
+ */
+import type { Middleware, MiddlewareAPI, Dispatch, AnyAction } from 'redux';
+import type { State } from '../../types/redux';
+
+export const WAIT_UNTIL_ACTION = 'WAIT_UNTIL_ACTION';
+
+export interface WaitActionArgs {
+  predicate: (action: AnyAction) => boolean;
+  run: (dispatch: Dispatch, getState: () => State, action: AnyAction) => void;
+}
+
+interface WaitAction extends WaitActionArgs {
+  type: typeof WAIT_UNTIL_ACTION;
+}
+
+// eslint-disable-next-line func-style
+export const waitUntilAction: Middleware<{}, State, Dispatch> = ({
+  dispatch,
+  getState,
+}: MiddlewareAPI<Dispatch, State>) => {
+  let pending: WaitAction[] = [];
+
+  function checkPending(action: AnyAction): void {
+    const readyRequests = [];
+    const stillPending = [];
+
+    // Find the pending requests whose predicates are satisfied with
+    // this action. Wait to run the requests until after we update the
+    // pending queue because the request handler may synchronously
+    // dispatch again and run this service (that use case is
+    // completely valid).
+    for (const request of pending) {
+      if (request.predicate(action)) {
+        readyRequests.push(request);
+      } else {
+        stillPending.push(request);
+      }
+    }
+
+    pending = stillPending;
+    for (const request of readyRequests) {
+      request.run(dispatch, getState, action);
+    }
+  }
+
+  return (next: Dispatch<AnyAction>) =>
+    (action: AnyAction): null | AnyAction => {
+      if (action.type === WAIT_UNTIL_ACTION) {
+        pending.push(action as WaitAction);
+        return null;
+      }
+      const result = next(action);
+      checkPending(action);
+      return result;
+    };
+};