// 独立 Tokio 参照只实现本组一层任务工作负载，不调用 Dever 调度器。
// 任务和 worker 分别限流；遇到失败或取消仍领取所有 JoinHandle，已启动阻塞工作不强停。
use std::{sync::Arc, time::Duration};
use tokio::{runtime, sync::Semaphore, task::JoinHandle};
use tokio_util::sync::CancellationToken;

struct NativeTasks {
    runtime: runtime::Runtime,
    workers: Arc<Semaphore>,
    tasks: Arc<Semaphore>,
}

fn task_fault(_: impl std::fmt::Debug) -> Fault {
    &FaultInfo {
        source: "task-reference",
        line: 1,
        column: 1,
        message: "task failure",
    }
}

fn native_total(values: &[i64]) -> Result<i64, Fault> {
    values.iter().try_fold(0i64, |total, value| {
        total
            .checked_add(*value)
            .ok_or_else(|| task_fault("integer overflow"))
    })
}

impl NativeTasks {
    fn new() -> Self {
        Self {
            runtime: runtime::Builder::new_multi_thread()
                .worker_threads(2)
                .max_blocking_threads(2)
                .enable_time()
                .build()
                .unwrap(),
            workers: Arc::new(Semaphore::new(2)),
            tasks: Arc::new(Semaphore::new(8)),
        }
    }

    fn start(
        &self,
        values: Vec<i64>,
        asynchronous: bool,
        cancel: CancellationToken,
    ) -> JoinHandle<Result<i64, Fault>> {
        let admission = self.tasks.clone().try_acquire_owned().unwrap();
        let workers = self.workers.clone();
        tokio::spawn(async move {
            let result = if asynchronous {
                tokio::select! {
                    biased;
                    result = async { native_total(&values) } => result,
                    () = cancel.cancelled() => Err(task_fault("cancelled")),
                }
            } else {
                let worker = tokio::select! {
                    biased;
                    () = cancel.cancelled() => return Err(task_fault("cancelled")),
                    worker = workers.acquire_owned() => worker.unwrap(),
                };
                let result = tokio::task::spawn_blocking(move || native_total(&values))
                    .await
                    .map_err(task_fault)?;
                drop(worker);
                result
            };
            drop(admission);
            result
        })
    }

    fn pair(&self, values: &[i64], asynchronous: bool) -> Result<i64, Fault> {
        self.runtime.block_on(async {
            let cancel = CancellationToken::new();
            let first = self.start(values.to_vec(), asynchronous, cancel.child_token());
            let second = self.start(values.to_vec(), asynchronous, cancel.child_token());
            let first = first.await.map_err(task_fault).and_then(|value| value);
            if first.is_err() {
                cancel.cancel();
            }
            let second = second.await.map_err(task_fault).and_then(|value| value);
            cancel.cancel();
            first?
                .checked_add(second?)
                .ok_or_else(|| task_fault("integer overflow"))
        })
    }

    fn blocking(&self, values: &[i64], sleep: bool) -> Result<i64, Fault> {
        let values = values.to_vec();
        self.runtime.block_on(async {
            let worker = self.workers.clone().acquire_owned().await.unwrap();
            let result = tokio::task::spawn_blocking(move || {
                if sleep {
                    std::time::Instant::now()
                        .checked_add(Duration::ZERO)
                        .ok_or_else(|| task_fault("sleep deadline"))?;
                    std::thread::sleep(Duration::ZERO);
                }
                native_total(&values)
            })
            .await
            .map_err(task_fault)?;
            drop(worker);
            result
        })
    }

    fn cancel(&self) -> Result<i64, Fault> {
        self.runtime.block_on(async {
            let admission = self.tasks.clone().try_acquire_owned().unwrap();
            let cancel = CancellationToken::new();
            let child = cancel.child_token();
            let task = tokio::spawn(async move {
                let deadline = tokio::time::Instant::now()
                    .checked_add(Duration::from_millis(60000))
                    .unwrap();
                tokio::select! {
                    biased;
                    () = tokio::time::sleep_until(deadline) => panic!("cancelled timer completed"),
                    () = child.cancelled() => (),
                }
                drop(admission);
            });
            cancel.cancel();
            task.await.map_err(task_fault)?;
            Ok(1)
        })
    }

    fn timer(&self) -> Result<i64, Fault> {
        self.runtime.block_on(async {
            let deadline = tokio::time::Instant::now()
                .checked_add(Duration::ZERO)
                .ok_or_else(|| task_fault("sleep deadline"))?;
            tokio::time::sleep_until(deadline).await;
            Ok(1)
        })
    }
}