From 646fca7ca671599eb25cb87acf53ddf8468696d1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E2=80=9Cchrisshank=E2=80=9D?= <chris.shank.23@gmail.com>
Date: Thu, 12 Aug 2021 18:07:41 -0700
Subject: [PATCH] feat(use-selectors): add useSelectors composable

---
 src/index.ts                  |  1 +
 src/useSelector.ts            | 19 ++------
 src/useSelectors.ts           | 91 +++++++++++++++++++++++++++++++++++
 test/UseSelectors.vue         | 59 +++++++++++++++++++++++
 test/UseSelectorsCustomFn.vue | 48 ++++++++++++++++++
 test/useSelectors.test.ts     | 49 +++++++++++++++++++
 6 files changed, 253 insertions(+), 14 deletions(-)
 create mode 100644 src/useSelectors.ts
 create mode 100644 test/UseSelectors.vue
 create mode 100644 test/UseSelectorsCustomFn.vue
 create mode 100644 test/useSelectors.test.ts

diff --git a/src/index.ts b/src/index.ts
index 7b4748e..25dc469 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -3,4 +3,5 @@ export { useService } from './useService';
 export { useActor } from './useActor';
 export { useInterpret } from './useInterpret';
 export { useSelector } from './useSelector';
+export { useSelectors } from './useSelectors';
 export { useSpawn } from './useSpawn';
diff --git a/src/useSelector.ts b/src/useSelector.ts
index fd80d96..1109ddc 100644
--- a/src/useSelector.ts
+++ b/src/useSelector.ts
@@ -1,8 +1,8 @@
-import { onMounted, onBeforeUnmount, shallowRef } from '@vue/composition-api';
+import { onBeforeUnmount, shallowRef } from '@vue/composition-api';
 import { ActorRef, Subscribable } from 'xstate';
 import { defaultGetSnapshot } from './useActor';
 
-const defaultCompare = (a, b) => a === b;
+export const defaultCompare = (a, b) => a === b;
 
 export function useSelector<
   TActor extends ActorRef<any, any>,
@@ -16,24 +16,15 @@ export function useSelector<
 ) {
   const selected = shallowRef(selector(getSnapshot(actor)));
 
-  const updateSelectedIfChanged = (nextSelected: T) => {
+  let sub = actor.subscribe((emitted) => {
+    const nextSelected = selector(emitted);
     if (!compare(selected.value, nextSelected)) {
       selected.value = nextSelected;
     }
-  };
-
-  let sub;
-  onMounted(() => {
-    const initialSelected = selector(getSnapshot(actor));
-    updateSelectedIfChanged(initialSelected);
-    sub = actor.subscribe((emitted) => {
-      const nextSelected = selector(emitted);
-      updateSelectedIfChanged(nextSelected);
-    });
   });
 
   onBeforeUnmount(() => {
-    sub?.unsubscribe();
+    sub.unsubscribe();
   });
 
   return selected;
diff --git a/src/useSelectors.ts b/src/useSelectors.ts
new file mode 100644
index 0000000..a59003b
--- /dev/null
+++ b/src/useSelectors.ts
@@ -0,0 +1,91 @@
+import { onBeforeUnmount, shallowRef, Ref } from '@vue/composition-api';
+import { ActorRef, Subscribable } from 'xstate';
+import { defaultGetSnapshot } from './useActor';
+import { defaultCompare } from './useSelector';
+
+type SelectorFunction<
+  TActor extends ActorRef<any, any>,
+  T = any,
+  TEmitted = TActor extends Subscribable<infer Emitted> ? Emitted : never
+> = (emitted: TEmitted) => T;
+
+type SelectorObject<
+  TActor extends ActorRef<any, any>,
+  T = any,
+  TEmitted = TActor extends Subscribable<infer Emitted> ? Emitted : never
+> = {
+  selector: SelectorFunction<TActor, T, TEmitted>;
+  compare?: (a: T, b: T) => boolean;
+  getSnapshot?: (a: TActor) => TEmitted;
+};
+
+type Selector<
+  TActor extends ActorRef<any, any>,
+  T = any,
+  TEmitted = TActor extends Subscribable<infer Emitted> ? Emitted : never
+> = SelectorFunction<TActor, T, TEmitted> | SelectorObject<TActor, T, TEmitted>;
+
+type ExtractSelectorsToRefs<
+  TActor extends ActorRef<any, any>,
+  TSelectors extends Record<string, Selector<TActor>>
+> = {
+  [Key in keyof TSelectors]: TSelectors[Key] extends Selector<TActor, infer T>
+    ? Ref<T>
+    : never;
+};
+
+function isSelectorObject<TActor extends ActorRef<any, any>>(
+  selector: Selector<TActor>
+): selector is SelectorObject<TActor> {
+  return typeof selector === 'object';
+}
+
+function normalizeSelectors<TActor extends ActorRef<any, any>>(
+  selectors: Record<string, Selector<TActor>>
+) {
+  return Object.entries(selectors).reduce((acc, [name, selector]) => {
+    const selectorObject: SelectorObject<TActor> = isSelectorObject(selector)
+      ? selector
+      : { selector };
+
+    acc[name] = {
+      compare: defaultCompare,
+      getSnapshot: defaultGetSnapshot,
+      ...selectorObject
+    };
+
+    return acc;
+  }, {} as Record<string, Required<SelectorObject<TActor>>>);
+}
+
+export function useSelectors<
+  TActor extends ActorRef<any, any>,
+  TSelectors extends Record<string, Selector<TActor>>
+>(actor: TActor, selectors: TSelectors) {
+  const normalizedSelectors = normalizeSelectors(selectors);
+
+  const selected = Object.entries(normalizedSelectors).reduce(
+    (acc, [name, { selector, getSnapshot }]) => {
+      acc[name as keyof TSelectors] = shallowRef(selector(getSnapshot(actor)));
+      return acc;
+    },
+    {} as ExtractSelectorsToRefs<TActor, TSelectors>
+  );
+
+  let sub = actor.subscribe((emitted) => {
+    Object.entries(normalizedSelectors).forEach(
+      ([name, { selector, compare }]) => {
+        const nextSelected = selector(emitted);
+        if (!compare(selected[name].value, nextSelected)) {
+          selected[name].value = nextSelected;
+        }
+      }
+    );
+  });
+
+  onBeforeUnmount(() => {
+    sub?.unsubscribe();
+  });
+
+  return selected;
+}
diff --git a/test/UseSelectors.vue b/test/UseSelectors.vue
new file mode 100644
index 0000000..819c7f8
--- /dev/null
+++ b/test/UseSelectors.vue
@@ -0,0 +1,59 @@
+<template>
+  <div>
+    <div data-testid="count">{{ count }}</div>
+    <button data-testid="other" @click="service.send('OTHER')">Other</button>
+    <button data-testid="increment" @click="service.send('INCREMENT')">
+      Increment
+    </button>
+  </div>
+</template>
+
+<script lang="ts">
+import { defineComponent, onMounted, onUpdated } from '@vue/composition-api';
+import { assign, createMachine } from 'xstate';
+import { useInterpret, useSelectors } from '../src';
+
+const machine = createMachine<{ count: number; other: number }>({
+  initial: 'active',
+  context: {
+    other: 0,
+    count: 0
+  },
+  states: {
+    active: {}
+  },
+  on: {
+    OTHER: {
+      actions: assign({ other: (ctx) => ctx.other + 1 })
+    },
+    INCREMENT: {
+      actions: assign({ count: (ctx) => ctx.count + 1 })
+    }
+  }
+});
+
+// Shim Vue 3 debugging function
+function onRenderTracked(callback: () => void) {
+  onMounted(callback);
+  onUpdated(callback);
+}
+
+export default defineComponent({
+  emits: ['rerender'],
+  setup(props, { emit }) {
+    const service = useInterpret(machine);
+    const { count } = useSelectors(service, {
+      count: (state) => state.context.count
+    });
+
+    let rerenders = 0;
+
+    onRenderTracked(() => {
+      rerenders++;
+      emit('rerender', rerenders);
+    });
+
+    return { service, count };
+  }
+});
+</script>
diff --git a/test/UseSelectorsCustomFn.vue b/test/UseSelectorsCustomFn.vue
new file mode 100644
index 0000000..5b22f94
--- /dev/null
+++ b/test/UseSelectorsCustomFn.vue
@@ -0,0 +1,48 @@
+<template>
+  <div>
+    <div data-testid="name">{{ name }}</div>
+    <button
+      data-testid="sendUpper"
+      @click="service.send({ type: 'CHANGE', value: 'DAVID' })"
+    ></button>
+    <button
+      data-testid="sendOther"
+      @click="service.send({ type: 'CHANGE', value: 'other' })"
+    ></button>
+  </div>
+</template>
+
+<script lang="ts">
+import { defineComponent } from '@vue/composition-api';
+import { assign, createMachine } from 'xstate';
+import { useInterpret, useSelectors } from '../src';
+
+const machine = createMachine<{ name: string }>({
+  initial: 'active',
+  context: {
+    name: 'david'
+  },
+  states: {
+    active: {}
+  },
+  on: {
+    CHANGE: {
+      actions: assign({ name: (_, e) => e.value })
+    }
+  }
+});
+
+export default defineComponent({
+  setup() {
+    const service = useInterpret(machine);
+    const { name } = useSelectors(service, {
+      name: {
+        selector: (state) => state.context.name,
+        compare: (a, b) => a.toUpperCase() === b.toUpperCase()
+      }
+    });
+
+    return { service, name };
+  }
+});
+</script>
diff --git a/test/useSelectors.test.ts b/test/useSelectors.test.ts
new file mode 100644
index 0000000..5063393
--- /dev/null
+++ b/test/useSelectors.test.ts
@@ -0,0 +1,49 @@
+import { render, fireEvent } from '@testing-library/vue';
+import UseSelectors from './UseSelectors.vue';
+import useSelectorsCustomFn from './UseSelectorsCustomFn.vue';
+
+describe('useSelector', () => {
+  it('only rerenders for selected values', async () => {
+    const { getByTestId, emitted } = render(UseSelectors);
+
+    const countButton = getByTestId('count');
+    const otherButton = getByTestId('other');
+    const incrementEl = getByTestId('increment');
+
+    await fireEvent.click(incrementEl);
+    expect(countButton.textContent).toBe('1');
+
+    await fireEvent.click(otherButton);
+    await fireEvent.click(otherButton);
+    await fireEvent.click(otherButton);
+    await fireEvent.click(otherButton);
+
+    await fireEvent.click(incrementEl);
+    expect(countButton.textContent).toBe('2');
+
+    expect(emitted()['rerender'].length).toBe(3);
+  });
+
+  it('should work with a custom comparison function', async () => {
+    const { getByTestId } = render(useSelectorsCustomFn);
+
+    const nameEl = getByTestId('name');
+    const sendUpperButton = getByTestId('sendUpper');
+    const sendOtherButton = getByTestId('sendOther');
+
+    expect(nameEl.textContent).toEqual('david');
+
+    await fireEvent.click(sendUpperButton);
+
+    // unchanged due to comparison function
+    expect(nameEl.textContent).toEqual('david');
+
+    await fireEvent.click(sendOtherButton);
+
+    expect(nameEl.textContent).toEqual('other');
+
+    await fireEvent.click(sendUpperButton);
+
+    expect(nameEl.textContent).toEqual('DAVID');
+  });
+});