/* ALAN runs array operations in parallel
  utilizing all the available CPU cores
  if the array is large enough
  and the inner function given to it is pure. */
  fn sumMaybeConcurrent(nums: Array<int>): int {
    return nums.reducePar(fn (accum: int, val: int): int = accum + val);
  }
          

  /* GOLANG
  https://play.golang.org/p/yB7gR3r09ZU
  */
  func sum(nums []int, out chan int) {
    var sum int
    for _, num := range nums {
      sum += num
    }
    out <- sum
  }
  func sumConcurrent(numbers []int) int {
    threads := runtime.NumCPU() - 1
    out := make(chan int)
    stride := len(numbers) / threads
    for i := 0; i < threads; i++ {
      go sum(numbers[i*stride:(i*stride)+stride], out)
    }
    go sum(numbers[threads*stride:len(numbers)], out)
    var s int
    for i := 0; i <= threads; i++ {
      s += <-out
    }
    return s
  }
          

  /* ALAN */
  fn fetchAndSum(urls: Array<string>): int {
    return urls
      .map(fn (url: string): int {
        const website = http.get(url) || http.none;
        return toString(website.body).length();
      })
      .reducePar(fn (accum: int, val: int): int = accum + val);
  }
        

  /* JAVA */
  Integer fetchAndSum(String...urls) {
    var sum = CompletableFuture.completedFuture(0);
    try {
      return Stream
            .of(urls)
            .parallel()
            .map(url -> httpClient
                .sendAsync(request(url), BodyHandlers.ofString())
                .thenApply(HttpResponse::body)
                .thenApply(String::length))
            .reduce(sum, (prev, curr) -> prev
                .thenCombine(curr, (p, c) -> p + c))
            .get();
    } catch(Exception e){
      System.out.println(e.toString());
      return 0;
    }
  }
        

  /* ALAN automatically executes IO concurrently when possible */
  fn getValidUids() {
    const authUids = Auth.getAllUsers().map(fn (u: AuthUser): int = u.id);
    const dbUids = Store.getAllUsers().map(fn (u: User): int = u.uid);
    const crmUids = Crm.getAllUsers().map(fn (u: CrmUser): int = u.uid);
    return authUids.filter(fn (v: int): bool = dbUids.has(v) && crmUids.has(v));
  }
        

  /* NODE.JS equivalent */
  async function getValidUids() {
    const [authUsers, dbUsers, crmUsers] = await Promise.all([
      Auth.getAll(),
      Store.getAllUsers(),
      Crm.getAllUsers()
    ]);
    const authUids = authUsers.map(u => u['id']);
    const dbUids = dbUsers.map(u => u['uid']);
    const crmUids = crmUsers.map(u => u['uid']);
    return authUids.filter(v => dbUids.includes(v) && crmUids.includes(v))
  }