feat(contentful): memoizer

packages/botonic-plugin-contentful/src/util/memoizer.ts

@@ -0,0 +1,106 @@
+export class Cache<V> {
+  static readonly NOT_FOUND = Symbol('NOT_FOUND')
+  cache: Record<string, V> = {}
+  set(id: string, val: V): void {
+    this.cache[id] = val
+  }
+  get(id: string): V | typeof Cache.NOT_FOUND {
+    // Cache.has is only checked when undefined to avoid always searching twice in the object
+    const val = this.cache[id]
+    if (val === undefined && !this.has(id)) {
+      return Cache.NOT_FOUND
+    }
+    return val
+  }
+  has(id: string): boolean {
+    return id in this.cache
+  }
+}
+
+export type MemoizerNormalizer = (...args: any) => string
+
+export const jsonNormalizer: MemoizerNormalizer = (...args: any) => {
+  return JSON.stringify(args)
+}
+
+export type MemoizedFunction<Args extends any[], Return> = (
+  ...args: Args
+) => Promise<Return> //& { cache: Cache<Return> }
+
+export type MemoizerStrategy = <Args extends any[], Return>(
+  cache: Cache<Return>,
+  normalizer: typeof jsonNormalizer,
+  func: (...args: Args) => Promise<Return>,
+  ...args: Args
+) => Promise<Return>
+
+export class Memoizer {
+  constructor(
+    private readonly strategy: MemoizerStrategy,
+    private readonly cacheFactory = () => new Cache<any>(),
+    private readonly normalizer = jsonNormalizer
+  ) {}
+
+  memoize<
+    Args extends any[],
+    Return,
+    F extends (...args: Args) => Promise<Return>
+  >(func: F): F {
+    const cache: Cache<Return> = this.cacheFactory()
+    const f = (...args: Args) =>
+      this.strategy<Args, Return>(cache, this.normalizer, func, ...args)
+    // f.cache = cache
+    return f as F
+  }
+}
+
+/***
+ * Only reinvoke if not in cache
+ */
+export const cacheForeverStrategy: MemoizerStrategy = async <
+  Args extends any[],
+  Return
+>(
+  cache: Cache<Return>,
+  normalizer = jsonNormalizer,
+  func: (...args: Args) => Promise<Return>,
+  ...args: Args
+) => {
+  const id = normalizer(...args)
+  let val = cache.get(id)
+  if (val === Cache.NOT_FOUND) {
+    val = await func(...args)
+    cache.set(id, val)
+  }
+  return val
+}
+
+/**
+ * Always invokes the function, but fallbacks to last invocation result if available
+ */
+export function fallbackStrategy(
+  usingFallback: (functName: string, args: any[], error: any) => Promise<void>
+): MemoizerStrategy {
+  return async <Args extends any[], Return>(
+    cache: Cache<Return>,
+    normalizer = jsonNormalizer,
+    func: (...args: Args) => Promise<Return>,
+    ...args: Args
+  ) => {
+    // return func(...args)
+    const id = normalizer(...args)
+    const oldVal = cache.get(id)
+
+    try {
+      const newVal = await func(...args)
+      cache.set(id, newVal)
+      return newVal
+    } catch (e) {
+      if (oldVal !== Cache.NOT_FOUND) {
+        await usingFallback(String(func.name), args, e)
+        return oldVal
+      }
+      throw e
+    }
+  }
+}

packages/botonic-plugin-contentful/tests/util/memoizer.test.ts

@@ -0,0 +1,172 @@
+import {
+  cacheForeverStrategy,
+  fallbackStrategy,
+  Memoizer,
+} from '../../src/util/memoizer'
+
+class MockF {
+  callsFA = 0
+  callsFB = 0
+  error: Error | undefined
+  salt = ''
+
+  fA(a: number, b: string): Promise<string> {
+    this.callsFA++
+    if (this.error) {
+      return Promise.reject(this.error)
+    }
+    return Promise.resolve('A' + String(a) + b + this.salt)
+  }
+
+  fB(a = 1, b = 'b'): Promise<string> {
+    this.callsFB++
+    if (this.error) {
+      return Promise.reject(this.error)
+    }
+    return Promise.resolve('B' + String(a) + b + this.salt)
+  }
+}
+
+describe('Memoizer', () => {
+  it('TEST: cacheForeverStrategy common properties', async () => {
+    await assertCommonStrategyProperties(
+      () => new Memoizer(cacheForeverStrategy),
+      false
+    )
+  })
+  it('TEST: cacheForeverStrategy only fails if last call failed', async () => {
+    const sut = new Memoizer(cacheForeverStrategy)
+    const mock = new MockF()
+    const memoized = sut.memoize(mock.fA.bind(mock))
+
+    // act/assert
+    mock.error = new Error('forced failure')
+    await expect(memoized(2, 'b')).rejects.toThrowError(mock.error)
+    mock.error = undefined
+    await expect(memoized(2, 'b')).resolves.toBe('A2b')
+    expect(mock.callsFA).toBe(2)
+  })
+
+  function usingFallback(funcName: string, args: any[], e: any): Promise<void> {
+    console.error(
+      `Using fallback for ${funcName}(${String(args)}) after error: ${String(
+        e
+      )}`
+    )
+    return Promise.resolve()
+  }
+
+  it('TEST: fallbackStrategy common properties', async () => {
+    await assertCommonStrategyProperties(
+      () => new Memoizer(fallbackStrategy(usingFallback)),
+      true
+    )
+  })
+
+  it('TEST: fallbackStrategy uses last invocation result', async () => {
+    const sut = new Memoizer(fallbackStrategy(usingFallback))
+    const mock = new MockF()
+    const memoized = sut.memoize(mock.fA.bind(mock))
+
+    // act/assert
+    await expect(memoized(2, 'b')).resolves.toBe('A2b')
+    mock.salt = 'pepper'
+    await expect(memoized(2, 'b')).resolves.toBe('A2b' + mock.salt)
+    expect(mock.callsFA).toBe(2)
+  })
+
+  test('TEST: fallbackStrategy returns latest success return if function fails', async () => {
+    const sut = new Memoizer(fallbackStrategy(usingFallback))
+    const mock = new MockF()
+    const memoized = sut.memoize(mock.fA.bind(mock))
+
+    // arrange
+    await memoized(2, 'b')
+    mock.salt = 'pepper'
+    await memoized(2, 'b')
+
+    mock.error = new Error('forced failure')
+    await memoized(2, 'b')
+
+    // act
+    mock.error = undefined
+    await expect(memoized(2, 'b')).resolves.toBe('A2bpepper')
+    expect(mock.callsFA).toBe(4)
+  })
+})
+
+async function assertCommonStrategyProperties(
+  sutFactory: () => Memoizer,
+  expectReinvocation: boolean
+) {
+  await memoizerDoesNotMixUpDifferentFunctionsOrArguments(
+    sutFactory(),
+    expectReinvocation
+  )
+  await memoizerFailsIfAllPreviousInvocationsFailed(sutFactory())
+  await memoizerWorksWithDefaultValueArgs(sutFactory(), expectReinvocation)
+}
+
+async function memoizerFailsIfAllPreviousInvocationsFailed(sut: Memoizer) {
+  const mock = new MockF()
+  const memoized = sut.memoize(mock.fA.bind(mock))
+
+  // act/assert
+  mock.error = new Error('forced failure')
+  await expect(memoized(2, 'b')).rejects.toThrowError(mock.error)
+  await expect(memoized(2, 'b')).rejects.toThrowError(mock.error)
+
+  mock.error = undefined
+  await expect(memoized(2, 'b')).resolves.toBe('A2b')
+}
+
+async function memoizerDoesNotMixUpDifferentFunctionsOrArguments(
+  sut: Memoizer,
+  expectReinvocation: boolean
+) {
+  const mock = new MockF()
+  const memoizedA = sut.memoize(mock.fA.bind(mock))
+  const memoizedB = sut.memoize(mock.fB.bind(mock))
+
+  // act/assert
+  await expect(memoizedA(2, 'b')).resolves.toBe('A2b')
+  //same function, arguments
+  await expect(memoizedA(2, 'b')).resolves.toBe('A2b')
+  expect(mock.callsFA).toBe(expectReinvocation ? 2 : 1)
+
+  //same function, different arguments
+  await expect(memoizedA(2, 'c')).resolves.toBe('A2c')
+  expect(mock.callsFA).toBe(expectReinvocation ? 3 : 2)
+
+  //different function, same arguments
+  await expect(memoizedB(2, 'b')).resolves.toBe('B2b')
+  expect(mock.callsFB).toBe(expectReinvocation ? 1 : 1)
+}
+
+async function memoizerWorksWithDefaultValueArgs(
+  sut: Memoizer,
+  expectReinvocation: boolean
+) {
+  const mock = new MockF()
+  const memoized = sut.memoize(mock.fB.bind(mock))
+
+  // act/assert
+  // All default arguments
+  await expect(memoized()).resolves.toBe('B1b')
+  await expect(memoized()).resolves.toBe('B1b')
+  expect(mock.callsFB).toBe(expectReinvocation ? 2 : 1)
+
+  // explicitly passing the default value
+  await expect(memoized(1, 'b')).resolves.toBe('B1b')
+  await expect(memoized(1, 'b')).resolves.toBe('B1b')
+  expect(mock.callsFB).toBe(expectReinvocation ? 4 : 2)
+
+  // 1 argument by default, 1 explicit
+  await expect(memoized(4)).resolves.toBe('B4b')
+  await expect(memoized(4)).resolves.toBe('B4b')
+  expect(mock.callsFB).toBe(expectReinvocation ? 6 : 3)
+
+  await expect(memoized(4, 'c')).resolves.toBe('B4c')
+  await expect(memoized(4, 'c')).resolves.toBe('B4c')
+  expect(mock.callsFB).toBe(expectReinvocation ? 8 : 4)
+}