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use std::{
    io,
    sync::{Arc, Weak},
};

use mio::Token;

use crate::{InterestHandler, InterestType, InterestWakerMap, Selector};

#[derive(Debug)]
#[must_use = "Leaking token guards will break the IO subsystem"]
pub struct InterestGuard {
    selector: Weak<Selector>,
    pub(crate) token: Token,
}
impl Drop for InterestGuard {
    fn drop(&mut self) {
        self.drop_internal();
    }
}
impl InterestGuard {
    pub fn new(
        selector: &Arc<Selector>,
        handler: Box<dyn InterestHandler + Send + Sync>,
        source: &mut dyn mio::event::Source,
        interest: mio::Interest,
    ) -> io::Result<InterestGuard> {
        let token = selector.add(handler, source, interest)?;
        Ok(Self {
            selector: Arc::downgrade(selector),
            token,
        })
    }

    pub fn unregister(&mut self, source: &mut dyn mio::event::Source) -> io::Result<()> {
        if let Some(selector) = self.selector.upgrade() {
            selector.remove(self.token, Some(source))?;
        }
        Ok(())
    }

    pub fn replace_handler(
        &mut self,
        handler: Box<dyn InterestHandler + Send + Sync>,
    ) -> Result<(), Box<dyn InterestHandler + Send + Sync>> {
        if let Some(selector) = self.selector.upgrade() {
            selector.replace(self.token, handler);
            Ok(())
        } else {
            Err(handler)
        }
    }

    pub fn interest(&mut self, interest: InterestType) {
        if let Some(selector) = self.selector.upgrade() {
            selector.handle(self.token, |h| h.push_interest(interest));
        }
    }

    fn drop_internal(&mut self) {
        if let Some(selector) = self.selector.upgrade() {
            selector.remove(self.token, None).ok();
        }
    }
}

#[derive(Debug)]
pub enum HandlerGuardState {
    None,
    ExternalHandler(InterestGuard),
    WakerMap(InterestGuard, InterestWakerMap),
}

pub fn state_as_waker_map<'a>(
    state: &'a mut HandlerGuardState,
    selector: &'_ Arc<Selector>,
    source: &'_ mut dyn mio::event::Source,
) -> io::Result<&'a mut InterestWakerMap> {
    if !matches!(state, HandlerGuardState::WakerMap(_, _)) {
        let waker_map = InterestWakerMap::default();
        *state = HandlerGuardState::WakerMap(
            InterestGuard::new(
                selector,
                Box::new(waker_map.clone()),
                source,
                mio::Interest::READABLE | mio::Interest::WRITABLE,
            )?,
            waker_map,
        );
    }
    Ok(match state {
        HandlerGuardState::WakerMap(_, map) => map,
        _ => unreachable!(),
    })
}