Undo/redo (#659)

* immutable crossfilter

* first cut at reducer refactor with cascade model

* add initial redo/undo implementation

* small optimization

* integrate expression with history

* add tests for new reducers and fix a couple of small initialization bugs

* treat tiny lasso selections as a clear

* better function name for clarity

* fix undo for differential expression

* remove logging

* fix regression due to bad merge

* cleanup and comments for clarity

* improve undoable configuration for flexibility

* fix stale comments

* remove debugging code from production build

* rename categoricalSelectionState

* rename file

* improve comments

client/__tests__/reducers/cascade.test.js

@@ -0,0 +1,48 @@
+import cascadeReducers from "../../src/reducers/cascade";
+
+describe("create", () => {
+  test("from Array", () => {
+    expect(cascadeReducers([["foo", () => 0]])).toBeInstanceOf(Function);
+  });
+
+  test("from Map", () => {
+    expect(cascadeReducers(new Map([["foo", () => 0]]))).toBeInstanceOf(
+      Function
+    );
+  });
+});
+
+describe("cascade", () => {
+  test("expected arguments provided & cascade ordering", () => {
+    const topLevelState = {};
+    const topLevelAction = { type: "test" };
+
+    const reducer = cascadeReducers([
+      [
+        "foo",
+        (currentState, action, nextSharedState, prevSharedState) => {
+          expect(currentState).toBeUndefined();
+          expect(action).toEqual(topLevelAction);
+          expect(nextSharedState).toStrictEqual({});
+          expect(prevSharedState).toBe(topLevelState);
+          return 0;
+        }
+      ],
+      [
+        "bar",
+        (currentState, action, nextSharedState, prevSharedState) => {
+          expect(currentState).toBeUndefined();
+          expect(action).toEqual(topLevelAction);
+          expect(nextSharedState).toStrictEqual({ foo: 0 });
+          expect(prevSharedState).toBe(topLevelState);
+          return 99;
+        }
+      ]
+    ]);
+
+    const nextState = reducer(topLevelState, topLevelAction);
+    expect(nextState).toStrictEqual({ foo: 0, bar: 99 });
+    expect(topLevelState).toStrictEqual({});
+    expect(topLevelAction).toStrictEqual({ type: "test" });
+  });
+});

client/__tests__/reducers/undoable.test.js

@@ -0,0 +1,87 @@
+import undoable from "../../src/reducers/undoable";
+
+describe("create", () => {
+  test("no keys", () => {
+    expect(() => undoable(() => {})).toThrow();
+    expect(() => undoable(() => {}, null)).toThrow();
+    expect(() => undoable(() => {}, [])).toThrow();
+    expect(() => undoable(() => {}, [], {})).toThrow();
+  });
+
+  test("simple", () => {
+    expect(undoable(() => {}, ["foo"])).toBeInstanceOf(Function);
+    expect(undoable(() => {}, ["foo"], {})).toBeInstanceOf(Function);
+  });
+
+  test("handles undefined initial state", () => {
+    expect(
+      undoable(() => {}, ["a"])(undefined, { type: "test" })
+    ).toMatchObject({});
+  });
+});
+
+describe("undo", () => {
+  test("expected state modifications", () => {
+    const initialState = { a: 0, b: 1000 };
+    const reducer = state => {
+      return { a: state.a + 1, b: state.b + 1 };
+    };
+    const undoableReducer = undoable(reducer, ["a"]);
+
+    const s1 = undoableReducer(initialState, { type: "test" });
+    expect(s1).toMatchObject({ a: 1, b: 1001 });
+
+    // test that only specified keys are undone
+    const s2 = undoableReducer(s1, { type: "@@undoable/undo" });
+    expect(s2).toMatchObject({ a: 0, b: 1001 });
+
+    // test backstop when no more history
+    const s3 = undoableReducer(s2, { type: "@@undoable/undo" });
+    expect(s3).toMatchObject({ a: 0, b: 1001 });
+  });
+});
+
+describe("redo", () => {
+  const initialState = { a: 0, b: 1000 };
+  const reducer = state => {
+    return { a: state.a + 1, b: state.b + 1 };
+  };
+  let UR;
+
+  beforeEach(() => {
+    UR = undoable(reducer, ["a"]);
+  });
+
+  test("expected state modifications", () => {
+    const s1 = UR(initialState, { type: "test" });
+    expect(s1).toMatchObject({ a: 1, b: 1001 });
+
+    // verify undo->redo reverts state.
+    const s2 = UR(UR(s1, { type: "@@undoable/undo" }), {
+      type: "@@undoable/redo"
+    });
+    expect(s2).toMatchObject({ a: 1, b: 1001 });
+
+    // verify backstop when no redo future
+    const s3 = UR(s2, { type: "@@undoable/redo" });
+    expect(s3).toMatchObject({ a: 1, b: 1001 });
+  });
+
+  test("history cleared", () => {
+    // verify future cleared upon a normal state transition
+    const s1 = UR(initialState, { type: "test" });
+    expect(s1).toMatchObject({ a: 1, b: 1001 });
+    const s2 = UR(s1, { type: "@@undoable/undo" });
+    expect(s2).toMatchObject({ a: 0, b: 1001 });
+    const s3 = UR(s2, { type: "test" });
+    expect(s3).toMatchObject({ a: 1, b: 1002 });
+    const s4 = UR(s3, { type: "@@undoable/redo" });
+    expect(s4).toMatchObject({ a: 1, b: 1002 });
+  });
+});
+
+/*
+TODO:
+- historyLimit is enforced
+- action filters
+*/