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use std::sync::atomic::Ordering;

use crate::rw_lock_cycler::RwLockCycler;
use crate::traits::{CyclerReader, EnsureSend, EnsureSync, ReadAccess};
use parking_lot::{RwLock, RwLockReadGuard};
use std::mem::swap;

#[cfg(feature = "unsafe_cleanup")]
use crate::static_ref_holder::StaticRefHolder;
#[cfg(feature = "unsafe_cleanup")]
use std::sync::Arc;

/// The reader for a data distributor
#[derive(Debug)]
pub struct RwLockCyclerReader<T>
where
    T: 'static,
{
    pub(super) cycler: &'static RwLockCycler<T>,
    pub(super) reader: Option<RwLockReadGuard<'static, T>>,
    #[allow(dead_code)]
    #[cfg(feature = "unsafe_cleanup")]
    pub(super) ref_holder: Arc<StaticRefHolder<RwLockCycler<T>>>,
}
impl<T> EnsureSend for RwLockCyclerReader<T> where T: Send + Sync {}
impl<T> EnsureSync for RwLockCyclerReader<T> where T: Send + Sync {}
impl<T> ReadAccess for RwLockCyclerReader<T>
where
    T: ReadAccess,
{
    type Read = T::Read;

    #[inline]
    fn read_data(&self) -> &Self::Read {
        // Reader should never be None except inside of read_latest
        self.reader.as_ref().unwrap().read_data()
    }
}
impl<T> CyclerReader<T> for RwLockCyclerReader<T>
where
    T: ReadAccess,
{
    fn read_latest(&mut self) {
        let mut old_reader = None;
        swap(&mut self.reader, &mut old_reader);
        drop(old_reader);
        let mut most_up_to_date = self.cycler.most_up_to_date.load(Ordering::Relaxed);
        loop {
            if let Some(reader) =
                RwLock::try_read(&self.cycler.data_slots[most_up_to_date as usize])
            {
                self.reader = Some(reader);
                return;
            } else {
                most_up_to_date = self.cycler.most_up_to_date.load(Ordering::Relaxed);
            }
        }
    }
}