use futures_util::task::ArcWake;

use super::SchedulerMsg;
use crate::innerlude::{push_future, remove_future, Runtime};
use crate::ScopeId;
use std::cell::RefCell;
use std::future::Future;
use std::pin::Pin;
use std::sync::Arc;
use std::task::Waker;

/// A task's unique identifier.
///
/// `TaskId` is a `usize` that is unique across the entire VirtualDOM and across time. TaskIDs will never be reused
/// once a Task has been completed.
#[cfg_attr(feature = "serialize", derive(serde::Serialize, serde::Deserialize))]
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
pub struct Task(pub(crate) usize);

impl Task {
    /// Start a new future on the same thread as the rest of the VirtualDom.
    ///
    /// This future will not contribute to suspense resolving, so you should primarily use this for reacting to changes
    /// and long running tasks.
    ///
    /// Whenever the component that owns this future is dropped, the future will be dropped as well.
    ///
    /// Spawning a future onto the root scope will cause it to be dropped when the root component is dropped - which
    /// will only occur when the VirtualDom itself has been dropped.
    pub fn new(task: impl Future<Output = ()> + 'static) -> Self {
        push_future(task).expect("to be in a dioxus runtime")
    }

    /// Drop the task immediately.
    ///
    /// This does not abort the task, so you'll want to wrap it in an abort handle if that's important to you
    pub fn stop(self) {
        remove_future(self);
    }
}

/// the task itself is the waker
pub(crate) struct LocalTask {
    pub scope: ScopeId,
    pub parent: Option<Task>,
    pub task: RefCell<Pin<Box<dyn Future<Output = ()> + 'static>>>,
    pub waker: Waker,
}

impl Runtime {
    /// Start a new future on the same thread as the rest of the VirtualDom.
    ///
    /// This future will not contribute to suspense resolving, so you should primarily use this for reacting to changes
    /// and long running tasks.
    ///
    /// Whenever the component that owns this future is dropped, the future will be dropped as well.
    ///
    /// Spawning a future onto the root scope will cause it to be dropped when the root component is dropped - which
    /// will only occur when the VirtualDom itself has been dropped.
    pub fn spawn(&self, scope: ScopeId, task: impl Future<Output = ()> + 'static) -> Task {
        let mut tasks = self.tasks.borrow_mut();

        let entry = tasks.vacant_entry();
        let task_id = Task(entry.key());

        let task = LocalTask {
            parent: self.current_task(),
            task: RefCell::new(Box::pin(task)),
            scope,
            waker: futures_util::task::waker(Arc::new(LocalTaskHandle {
                id: task_id,
                tx: self.sender.clone(),
            })),
        };

        let mut cx = std::task::Context::from_waker(&task.waker);

        if !task.task.borrow_mut().as_mut().poll(&mut cx).is_ready() {
            self.sender
                .unbounded_send(SchedulerMsg::TaskNotified(task_id))
                .expect("Scheduler should exist");
        }

        entry.insert(task);

        task_id
    }

    /// Drop the future with the given TaskId
    ///
    /// This does not abort the task, so you'll want to wrap it in an abort handle if that's important to you
    pub(crate) fn remove_task(&self, id: Task) -> Option<LocalTask> {
        self.tasks.borrow_mut().try_remove(id.0)
    }

    /// Get the currently running task
    pub fn current_task(&self) -> Option<Task> {
        self.current_task.get()
    }
}

pub struct LocalTaskHandle {
    id: Task,
    tx: futures_channel::mpsc::UnboundedSender<SchedulerMsg>,
}

impl ArcWake for LocalTaskHandle {
    fn wake_by_ref(arc_self: &Arc<Self>) {
        // This can fail if the scheduler has been dropped while the application is shutting down
        let _ = arc_self
            .tx
            .unbounded_send(SchedulerMsg::TaskNotified(arc_self.id));
    }
}