From 45b5a3bbf2634c1acb83fb8caf54697a6cb0a3e5 Mon Sep 17 00:00:00 2001
From: Jerko Steiner <jerko.steiner@gmail.com>
Date: Fri, 15 Nov 2019 20:28:13 -0300
Subject: [PATCH] Add TypedEmitter

---
 src/shared/TypedEmitter.test.ts | 74 +++++++++++++++++++++++++++++++++
 src/shared/TypedEmitter.ts      | 19 +++++++++
 2 files changed, 93 insertions(+)
 create mode 100644 src/shared/TypedEmitter.test.ts
 create mode 100644 src/shared/TypedEmitter.ts

diff --git a/src/shared/TypedEmitter.test.ts b/src/shared/TypedEmitter.test.ts
new file mode 100644
index 0000000..11b93c8
--- /dev/null
+++ b/src/shared/TypedEmitter.test.ts
@@ -0,0 +1,74 @@
+import { TypedEmitter } from './TypedEmitter'
+import { EventEmitter } from 'events'
+
+describe('TypedEmitter', () => {
+
+  let stringMock: jest.Mock<void, [string]>
+  let numberMock: jest.Mock<void, [number]>
+  let valueMock: jest.Mock<void, [Value]>
+
+  beforeEach(() => {
+    stringMock = jest.fn()
+    numberMock = jest.fn()
+    valueMock = jest.fn()
+  })
+
+  const listener1 = (arg: string) => {
+    stringMock(arg)
+  }
+
+  const listener2 = (arg: number) => {
+    numberMock(arg)
+  }
+
+  const listener3 = (arg: Value) => {
+    valueMock(arg)
+  }
+
+  interface Value {
+    a: number
+  }
+
+  interface Events {
+    test1: string
+    test2: number
+    test3: Value
+  }
+
+  let emitter: TypedEmitter<Events>
+  beforeEach(() => {
+    emitter = new EventEmitter()
+    emitter.addListener('test1', listener1)
+    emitter.on('test2', listener2)
+    emitter.once('test3', listener3)
+  })
+
+  describe('addListener & on', () => {
+    it('adds an event emitter', () => {
+      emitter.emit('test1', 'value')
+      emitter.emit('test2', 3)
+      expect(stringMock.mock.calls).toEqual([[ 'value' ]])
+      expect(numberMock.mock.calls).toEqual([[ 3 ]])
+    })
+  })
+
+  describe('once', () => {
+    it('adds an event emitter for one use only', () => {
+      emitter.emit('test3', { a: 1 })
+      emitter.emit('test3', { a: 2 })
+      expect(valueMock.mock.calls).toEqual([[ { a: 1 } ]])
+    })
+  })
+
+  describe('removeListener & off', () => {
+    it('removes an event listener', () => {
+      emitter.removeListener('test1', listener1)
+      emitter.off('test2', listener2)
+      emitter.emit('test1', 'value')
+      emitter.emit('test2', 3)
+      expect(stringMock.mock.calls).toEqual([])
+      expect(numberMock.mock.calls).toEqual([])
+    })
+  })
+
+})
diff --git a/src/shared/TypedEmitter.ts b/src/shared/TypedEmitter.ts
new file mode 100644
index 0000000..6dd7acb
--- /dev/null
+++ b/src/shared/TypedEmitter.ts
@@ -0,0 +1,19 @@
+import  { EventEmitter } from 'events'
+
+type Callback<A> = (a: A) => void
+
+// eslint-disable-next-line
+type Events = Record<string | symbol, any>
+
+export interface TypedEmitter<E extends Events>
+extends EventEmitter {
+  addListener<K extends keyof E>(t: K, callback: Callback<E[K]>): this
+  removeListener<K extends keyof E>(t: K, callback: Callback<E[K]>): this
+
+  on<K extends keyof E>(t: K, callback: Callback<E[K]>): this
+  once<K extends keyof E>(t: K, callback: Callback<E[K]>): this
+
+  off<K extends keyof E>(t: K, callback: Callback<E[K]>): this
+
+  emit<K extends keyof E>(t: K, value: E[K]): boolean
+}