feat(await): add await class

Author: tusharmath

src/main/Await.ts

@@ -0,0 +1,63 @@
+import {LinkedList} from 'dbl-linked-list-ds'
+import {CB} from '../internals/CB'
+import {FIO, IO, UIO} from './FIO'
+
+export class Await<E, A> {
+  private readonly Q = new LinkedList<[CB<E>, CB<A>]>()
+  private result: A | undefined
+  private flag = false
+  private resolved = false
+
+  public static of<E = never, A = never>(): UIO<Await<E, A>> {
+    return FIO.uio(() => new Await())
+  }
+
+  public set(io: IO<E, A>): UIO<boolean> {
+    return this.isSet().chain(flag =>
+      flag
+        ? FIO.of(false)
+        : this.setFlag(true)
+            .and(io.chain(result => this.update(result)))
+            .const(true)
+    )
+  }
+
+  public isSet(): UIO<boolean> {
+    return FIO.uio(() => this.flag)
+  }
+
+  public get(): IO<E, A | undefined> {
+    return this.isResolved().chain(resolved =>
+      resolved ? FIO.of(this.result) : this.addListener()
+    )
+  }
+
+  private addListener(): FIO<unknown, E, A> {
+    return FIO.asyncIO((rej, res) => {
+      const id = this.Q.add([rej, res])
+
+      return {cancel: () => this.Q.remove(id)}
+    })
+  }
+
+  private setFlag(value: boolean): UIO<void> {
+    return FIO.uio(() => void (this.flag = value))
+  }
+
+  private isResolved(): UIO<boolean> {
+    return FIO.uio(() => this.resolved)
+  }
+
+  private update(result: A): UIO<void> {
+    return FIO.uio(() => {
+      this.result = result
+      this.resolved = true
+      if (this.result !== undefined) {
+        while (this.Q.length > 0) {
+          const cb = this.Q.shift() as [CB<E>, CB<A>]
+          cb[1](this.result)
+        }
+      }
+    })
+  }
+}

test/Await.test.ts

@@ -0,0 +1,106 @@
+import {assert} from 'chai'
+import {Await} from '../src/main/Await'
+import {FIO} from '../src/main/FIO'
+import {testRuntime} from '../src/runtimes/TestRuntime'
+
+describe('Await', () => {
+  describe('of', () => {
+    it('should create an instance of Await', () => {
+      const actual = testRuntime({color: 'red'}).executeSync(Await.of())
+      assert.instanceOf(actual, Await)
+    })
+  })
+
+  describe('set', () => {
+    it('should return true', () => {
+      const actual = testRuntime({color: 'red'}).executeSync(
+        Await.of<never, string>().chain(await => await.set(FIO.of('Hi')))
+      )
+      assert.ok(actual)
+    })
+  })
+
+  describe('set', () => {
+    it('should return true', () => {
+      const actual = testRuntime({color: 'red'}).executeSync(
+        Await.of<never, string>().chain(await => await.set(FIO.of('Hi')))
+      )
+      assert.ok(actual)
+    })
+    it('should set only once', () => {
+      const runtime = testRuntime({color: 'red'})
+      const actual = runtime.executeSync(
+        Await.of<never, string>().chain(await =>
+          await
+            .set(FIO.of('Hi'))
+            .and(await.set(FIO.of('Bye')))
+            .and(await.get())
+        )
+      )
+      assert.strictEqual(actual, 'Hi')
+    })
+
+    it('should return false if its not set', () => {
+      const runtime = testRuntime({color: 'red'})
+      const actual = runtime.executeSync(
+        Await.of<never, string>().chain(await =>
+          await.set(FIO.of('Hi')).and(await.set(FIO.of('Bye')))
+        )
+      )
+      assert.notOk(actual)
+    })
+  })
+
+  describe('get', () => {
+    it('should return the IO value', () => {
+      const actual = testRuntime({color: 'red'}).executeSync(
+        Await.of<never, string>().chain(await =>
+          await.set(FIO.of('Hi')).and(await.get())
+        )
+      )
+      assert.strictEqual(actual, 'Hi')
+    })
+
+    it('should not resolve unless set', () => {
+      const actual = testRuntime({color: 'red'}).executeSync(
+        Await.of<never, string>().chain(await => await.get())
+      )
+      assert.isUndefined(actual)
+    })
+
+    it('should not return', () => {
+      const runtime = testRuntime({color: 'red'})
+      const await = runtime.executeSync(Await.of<never, string>()) as Await<
+        never,
+        string
+      >
+      let actual: string | undefined
+      runtime.execute(await.get(), r => (actual = r))
+      runtime.execute(await.set(FIO.timeout('Hey', 1000)))
+
+      assert.isUndefined(actual)
+      runtime.scheduler.run()
+      assert.strictEqual(actual, 'Hey')
+    })
+  })
+
+  describe('isSet()', () => {
+    it('should return false initially', () => {
+      const actual = testRuntime({color: 'red'}).executeSync(
+        Await.of<never, string>().chain(await => await.isSet())
+      )
+
+      assert.notOk(actual)
+    })
+
+    it('should return true after setting', () => {
+      const actual = testRuntime({color: 'red'}).executeSync(
+        Await.of<never, number>().chain(await =>
+          await.set(FIO.of(100)).and(await.isSet())
+        )
+      )
+
+      assert.ok(actual)
+    })
+  })
+})