Add Base Controller v2

This is the new base controller we'll be transitioning to as part of
the controller redesign (#337). It has been added as a separate module
so that we can transition each controller more easily, one at a time.

Additional features will be added in future PRs (e.g. schema,
messaging).

package.json

@@ -50,6 +50,7 @@
     "ethereumjs-wallet": "^1.0.1",
     "human-standard-collectible-abi": "^1.0.2",
     "human-standard-token-abi": "^2.0.0",
+    "immer": "^8.0.1",
     "isomorphic-fetch": "^3.0.0",
     "jsonschema": "^1.2.4",
     "nanoid": "^3.1.12",

src/BaseControllerV2.test.ts

@@ -0,0 +1,148 @@
+import type { Draft } from 'immer';
+import * as sinon from 'sinon';
+
+import BaseController from './BaseControllerV2';
+
+interface MockControllerState {
+  count: number;
+}
+
+class MockController extends BaseController<MockControllerState> {
+  update(callback: (state: Draft<MockControllerState>) => void | MockControllerState) {
+    super.update(callback);
+  }
+
+  destroy() {
+    super.destroy();
+  }
+}
+
+describe('BaseController', () => {
+  it('should set initial state', () => {
+    const controller = new MockController({ count: 0 });
+
+    expect(controller.state).toEqual({ count: 0 });
+  });
+
+  it('should not allow mutating state directly', () => {
+    const controller = new MockController({ count: 0 });
+
+    expect(() => {
+      controller.state = { count: 1 };
+    }).toThrow();
+  });
+
+  it('should allow updating state by modifying draft', () => {
+    const controller = new MockController({ count: 0 });
+
+    controller.update((draft) => {
+      draft.count += 1;
+    });
+
+    expect(controller.state).toEqual({ count: 1 });
+  });
+
+  it('should allow updating state by return a value', () => {
+    const controller = new MockController({ count: 0 });
+
+    controller.update(() => {
+      return { count: 1 };
+    });
+
+    expect(controller.state).toEqual({ count: 1 });
+  });
+
+  it('should throw an error if update callback modifies draft and returns value', () => {
+    const controller = new MockController({ count: 0 });
+
+    expect(() => {
+      controller.update((draft) => {
+        draft.count += 1;
+        return { count: 10 };
+      });
+    }).toThrow();
+  });
+
+  it('should inform subscribers of state changes', () => {
+    const controller = new MockController({ count: 0 });
+    const listener1 = sinon.stub();
+    const listener2 = sinon.stub();
+
+    controller.subscribe(listener1);
+    controller.subscribe(listener2);
+    controller.update(() => {
+      return { count: 1 };
+    });
+
+    expect(listener1.callCount).toEqual(1);
+    expect(listener1.firstCall.args).toEqual([{ count: 1 }]);
+    expect(listener2.callCount).toEqual(1);
+    expect(listener2.firstCall.args).toEqual([{ count: 1 }]);
+  });
+
+  it('should inform a subscriber of each state change once even after multiple subscriptions', () => {
+    const controller = new MockController({ count: 0 });
+    const listener1 = sinon.stub();
+
+    controller.subscribe(listener1);
+    controller.subscribe(listener1);
+    controller.update(() => {
+      return { count: 1 };
+    });
+
+    expect(listener1.callCount).toEqual(1);
+    expect(listener1.firstCall.args).toEqual([{ count: 1 }]);
+  });
+
+  it('should no longer inform a subscriber about state changes after unsubscribing', () => {
+    const controller = new MockController({ count: 0 });
+    const listener1 = sinon.stub();
+
+    controller.subscribe(listener1);
+    controller.unsubscribe(listener1);
+    controller.update(() => {
+      return { count: 1 };
+    });
+
+    expect(listener1.callCount).toEqual(0);
+  });
+
+  it('should no longer inform a subscriber about state changes after unsubscribing once, even if they subscribed many times', () => {
+    const controller = new MockController({ count: 0 });
+    const listener1 = sinon.stub();
+
+    controller.subscribe(listener1);
+    controller.subscribe(listener1);
+    controller.unsubscribe(listener1);
+    controller.update(() => {
+      return { count: 1 };
+    });
+
+    expect(listener1.callCount).toEqual(0);
+  });
+
+  it('should allow unsubscribing listeners who were never subscribed', () => {
+    const controller = new MockController({ count: 0 });
+    const listener1 = sinon.stub();
+
+    expect(() => {
+      controller.unsubscribe(listener1);
+    }).not.toThrow();
+  });
+
+  it('should no longer update subscribers after being destroyed', () => {
+    const controller = new MockController({ count: 0 });
+    const listener1 = sinon.stub();
+    const listener2 = sinon.stub();
+
+    controller.subscribe(listener1);
+    controller.subscribe(listener2);
+    controller.destroy();
+    controller.update(() => {
+      return { count: 1 };
+    });
+
+    expect(listener1.callCount).toEqual(0);
+    expect(listener2.callCount).toEqual(0);
+  });
+});

src/BaseControllerV2.ts

@@ -0,0 +1,91 @@
+import { produce } from 'immer';
+
+// Imported separately because only the type is used
+// eslint-disable-next-line no-duplicate-imports
+import type { Draft } from 'immer';
+
+/**
+ * State change callbacks
+ */
+export type Listener<T> = (state: T) => void;
+
+/**
+ * Controller class that provides state management and subscriptions
+ */
+export class BaseController<S extends Record<string, any>> {
+  private internalState: S;
+
+  private internalListeners: Set<Listener<S>> = new Set();
+
+  /**
+   * Creates a BaseController instance.
+   *
+   * @param state - Initial controller state
+   */
+  constructor(state: S) {
+    this.internalState = state;
+  }
+
+  /**
+   * Retrieves current controller state
+   *
+   * @returns - Current state
+   */
+  get state() {
+    return this.internalState;
+  }
+
+  set state(_) {
+    throw new Error(`Controller state cannot be directly mutated; use 'update' method instead.`);
+  }
+
+  /**
+   * Adds new listener to be notified of state changes
+   *
+   * @param listener - Callback triggered when state changes
+   */
+  subscribe(listener: Listener<S>) {
+    this.internalListeners.add(listener);
+  }
+
+  /**
+   * Removes existing listener from receiving state changes
+   *
+   * @param listener - Callback to remove
+   */
+  unsubscribe(listener: Listener<S>) {
+    this.internalListeners.delete(listener);
+  }
+
+  /**
+   * Updates controller state. Accepts a callback that is passed a draft copy
+   * of the controller state. If a value is returned, it is set as the new
+   * state. Otherwise, any changes made within that callback to the draft are
+   * applied to the controller state.
+   *
+   * @param callback - Callback for updating state, passed a draft state
+   *   object. Return a new state object or mutate the draft to update state.
+   */
+  protected update(callback: (state: Draft<S>) => void | S) {
+    const nextState = produce(this.internalState, callback) as S;
+    this.internalState = nextState;
+    for (const listener of this.internalListeners) {
+      listener(nextState);
+    }
+  }
+
+  /**
+   * Prepares the controller for garbage collection. This should be extended
+   * by any subclasses to clean up any additional connections or events.
+   *
+   * The only cleanup performed here is to remove listeners. While technically
+   * this is not required to ensure this instance is garbage collected, it at
+   * least ensures this instance won't be responsible for preventing the
+   * listeners from being garbage collected.
+   */
+  protected destroy() {
+    this.internalListeners.clear();
+  }
+}
+
+export default BaseController;

yarn.lock

@@ -3597,6 +3597,11 @@ immediate@^3.2.3:
   resolved "https://registry.yarnpkg.com/immediate/-/immediate-3.2.3.tgz#d140fa8f614659bd6541233097ddaac25cdd991c"
   integrity sha1-0UD6j2FGWb1lQSMwl92qwlzdmRw=
 
+immer@^8.0.1:
+  version "8.0.1"
+  resolved "https://registry.yarnpkg.com/immer/-/immer-8.0.1.tgz#9c73db683e2b3975c424fb0572af5889877ae656"
+  integrity sha512-aqXhGP7//Gui2+UrEtvxZxSquQVXTpZ7KDxfCcKAF3Vysvw0CViVaW9RZ1j1xlIYqaaaipBoqdqeibkc18PNvA==
+
 import-fresh@^3.0.0:
   version "3.2.1"
   resolved "https://registry.yarnpkg.com/import-fresh/-/import-fresh-3.2.1.tgz#633ff618506e793af5ac91bf48b72677e15cbe66"