// in concurrency: task1 write | task2 write | task3 write | task4 write
//                      \_____________\_____________\_____________\
//             task4 read depends on task 1-4 write  \___________
//                                                               \
// in concurrency:              | task2 read  | task3 read  | task4 read

use par_iter_sync::IntoParallelIteratorSync;
use std::sync::{Arc, Mutex};
use std::collections::HashSet;

// there are 100 tasks
let tasks = 0..100;

// an in-memory cache for integers
let cache: Arc<Mutex<HashSet<i32>>> = Arc::new(Mutex::new(HashSet::new()));
let cache_clone = cache.clone();

// iterate through tasks
tasks.into_par_iter_sync(move |task_number| {

    // writes cache (write the integer in cache), in parallel
    cache.lock().unwrap().insert(task_number);
    // return the task number to the next iterator
    Ok(task_number)

}).into_par_iter_sync(move |task_number| { // <- synced to sequential order

    // reads
    assert!(cache_clone.lock().unwrap().contains(&task_number));
    Ok(())

// append a for each to actually run the whole chain
}).for_each(|_| ());

use par_iter_sync::IntoParallelIteratorSync;

(0..100).into_par_iter_sync(|i| {
    Ok(i)                     // <~ async execution
}).into_par_iter_sync(|i| { // <- sync order
    Ok(i)                     // <~async execution
}).into_par_iter_sync(|i| { // <- sync order
    Ok(i)                     // <~async execution
});                           // <- sync order

use par_iter_sync::IntoParallelIteratorSync;

let mut count = 0;

// for loop
for i in (0..100).into_par_iter_sync(|i| Ok(i)) {
    assert_eq!(i, count);
    count += 1;
}

// sum
let sum: i32 = (1..=100).into_par_iter_sync(|i| Ok(i)).sum();

// take and collect
let results: Vec<i32> = (0..10).into_par_iter_sync(|i| Ok(i)).take(5).collect();

assert_eq!(sum, 5050);
assert_eq!(results, vec![0, 1, 2, 3, 4])

use par_iter_sync::IntoParallelIteratorSync;
use std::sync::Arc;

// use `Arc` to save RAM
let resource_captured = Arc::new(vec![3, 1, 4, 1, 5, 9, 2, 6, 5, 3]);
let len = resource_captured.len();

let result_iter = (0..len).into_par_iter_sync(move |i| {
    // `resource_captured` is moved into the closure
    // and cloned to worker threads.
    let read_from_resource = resource_captured.get(i).unwrap();
    Ok(*read_from_resource)
});

// the result is produced in sequential order
let collected: Vec<i32> = result_iter.collect();
assert_eq!(collected, vec![3, 1, 4, 1, 5, 9, 2, 6, 5, 3])

use par_iter_sync::IntoParallelIteratorSync;
use std::sync::Arc;
use log::warn;

/// this function returns `Err` when it reads 1000
fn error_at_1000(n: i32) -> Result<i32, ()> {
    if n == 1000 {
        // you may log this error
        warn!("Some Error Occurs");
        Err(())
    } else {
        Ok(n)
    }
}

let results: Vec<i32> = (0..10000).into_par_iter_sync(move |a| {
    Ok(a)
}).into_par_iter_sync(move |a| {
    // error at 1000
    error_at_1000(a)
}).into_par_iter_sync(move |a| {
    Ok(a)
}).collect();

let expected: Vec<i32> = (0..1000).collect();
assert_eq!(results, expected)

use par_iter_sync::IntoParallelIteratorSync;
use std::sync::Arc;

let results: Vec<Result<i32, ()>> = (0..5).into_par_iter_sync(move |n| {
    // error at 3, but skip
    if n == 3 {
        Ok(Err(()))
    } else {
        Ok(Ok(n))
    }
}).collect();

assert_eq!(results, vec![Ok(0), Ok(1), Ok(2), Err(()), Ok(4)])