Add ConditionStore

Author: notwillk

src/ConditionStore.ts

@@ -1 +1,40 @@
-export default ConditionStore {}
+export type UnsubscribeFunction = () => void;
+
+export default class ConditionStore {
+  value: boolean;
+  listeners: Array<() => void> = [];
+
+  constructor(initialValue?: boolean) {
+    this.value = Boolean(initialValue);
+  }
+
+  set() {
+    if(this.value !== true) {
+      this.value = true;
+      this.notify();
+    }
+  }
+
+  clear() {
+    if(this.value !== false) {
+      this.value = false;
+      this.notify();
+    }
+  }
+
+  getSnapshot() {
+    return this.value;
+  }
+
+  subscribe(listener: () => void): UnsubscribeFunction {
+    this.listeners = [...this.listeners, listener];
+
+    return () => {
+      this.listeners = this.listeners.filter(l => l !== listener);
+    }
+  }
+
+  private notify() {
+    this.listeners.forEach(listener => listener());
+  }
+}

src/__tests__/ConditionStore.test.ts

@@ -1,4 +1,82 @@
+import ConditionStore from "ConditionStore";
+
 describe('#ConditionStore', () => {
-    it('xxx', () => {
-    });
+  it('stores initial values', () => {
+    const store1 = new ConditionStore(false);
+    expect(store1.getSnapshot()).toBe(false);
+
+    const store2 = new ConditionStore(true);
+    expect(store2.getSnapshot()).toBe(true);
   });
+
+  it('updates value on `set`', () => {
+    const store = new ConditionStore(false);
+    store.set();
+    expect(store.getSnapshot()).toBe(true);
+  });
+
+  it('updates value on `clear`', () => {
+    const store = new ConditionStore(true);
+    store.clear();
+    expect(store.getSnapshot()).toBe(false);
+  });
+
+  it('notifies listeners on `set` or `clear`', () => {
+    const listener = jest.fn();
+
+    const store = new ConditionStore(false);
+    store.subscribe(listener);
+    expect(listener.mock.calls.length).toBe(0);
+
+    store.set();
+    expect(listener.mock.calls.length).toBe(1);
+
+    store.clear();
+    expect(listener.mock.calls.length).toBe(2);
+  });
+
+  it('does not notify listeners that have been unsubscribed', () => {
+    const listener1 = jest.fn();
+    const listener2 = jest.fn();
+
+    const store = new ConditionStore(false);
+    const unsubscribeListener1 = store.subscribe(listener1);
+    const unsubscribeListener2 = store.subscribe(listener2);
+    expect(listener1.mock.calls.length).toBe(0);
+    expect(listener2.mock.calls.length).toBe(0);
+
+    store.set();
+    expect(listener1.mock.calls.length).toBe(1);
+    expect(listener2.mock.calls.length).toBe(1);
+
+    unsubscribeListener2();
+
+    store.clear();
+    expect(listener1.mock.calls.length).toBe(2);
+    expect(listener2.mock.calls.length).toBe(1);
+
+    unsubscribeListener1();
+
+    store.set();
+    expect(listener1.mock.calls.length).toBe(2);
+    expect(listener2.mock.calls.length).toBe(1);
+  });
+
+  it('notifies listeners on `set` or `clear` only if value changes', () => {
+    const listener = jest.fn();
+
+    const store = new ConditionStore(false);
+    store.subscribe(listener);
+    expect(listener.mock.calls.length).toBe(0);
+
+    store.set();
+    expect(listener.mock.calls.length).toBe(1);
+    store.set();
+    expect(listener.mock.calls.length).toBe(1);
+
+    store.clear();
+    expect(listener.mock.calls.length).toBe(2);
+    store.clear();
+    expect(listener.mock.calls.length).toBe(2);
+  });
+});

src/__tests__/index.test.tsx

@@ -3,6 +3,6 @@
 // import { PropsWithChildren } from 'react';
 
 describe('#react-conditional-fallback', () => {
-  it('xxx', async () => {
+  xit('xxx', async () => {
   });
 });