use super::{
    macros::rb_impl_init,
    utils::{assert_capacity, ranges},
};
#[cfg(feature = "alloc")]
use crate::traits::Split;
use crate::{
    storage::Storage,
    traits::{
        Observer, RingBuffer, SplitRef,
        consumer::{Consumer, impl_consumer_traits},
        producer::{Producer, impl_producer_traits},
    },
    wrap::{CachingCons, CachingProd},
};
use core::{
    mem::{ManuallyDrop, MaybeUninit},
    num::NonZeroUsize,
    ptr,
};
use crossbeam_utils::CachePadded;

#[cfg(not(feature = "portable-atomic"))]
use core::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
#[cfg(feature = "portable-atomic")]
use portable_atomic::{AtomicBool, AtomicUsize, Ordering};
#[cfg(feature = "alloc")]
use {crate::alias::Arc, alloc::boxed::Box};

/// Ring buffer that can be shared between threads.
///
/// Note that there is no explicit requirement of `T: Send`. Instead ring buffer will work just fine even with `T: !Send`
/// until you try to send its producer or consumer to another thread.
#[cfg_attr(
    feature = "std",
    doc = r##"
```
use std::thread;
use ringbuf::{SharedRb, storage::Heap, traits::*};

let rb = SharedRb::<Heap<i32>>::new(256);
let (mut prod, mut cons) = rb.split();
thread::spawn(move || {
    prod.try_push(123).unwrap();
})
.join();
thread::spawn(move || {
    assert_eq!(cons.try_pop().unwrap(), 123);
})
.join();
```
"##
)]
pub struct SharedRb<S: Storage + ?Sized> {
    read_index: CachePadded<AtomicUsize>,
    write_index: CachePadded<AtomicUsize>,
    read_held: AtomicBool,
    write_held: AtomicBool,
    storage: S,
}

impl<S: Storage> SharedRb<S> {
    /// Constructs ring buffer from storage and indices.
    ///
    /// Panics if the storage is empty or its length exceeds `usize::MAX / 2`.
    ///
    /// # Safety
    ///
    /// The items in storage inside `read..write` range must be initialized, items outside this range must be uninitialized.
    /// `read` and `write` positions must be valid (see implementation details).
    pub unsafe fn from_raw_parts(storage: S, read: usize, write: usize) -> Self {
        assert_capacity(storage.len());
        Self {
            storage,
            read_index: CachePadded::new(AtomicUsize::new(read)),
            write_index: CachePadded::new(AtomicUsize::new(write)),
            read_held: AtomicBool::new(false),
            write_held: AtomicBool::new(false),
        }
    }
    /// Destructures ring buffer into underlying storage and `read` and `write` indices.
    ///
    /// # Safety
    ///
    /// Initialized contents of the storage must be properly dropped.
    pub unsafe fn into_raw_parts(self) -> (S, usize, usize) {
        let this = ManuallyDrop::new(self);
        (unsafe { ptr::read(&this.storage) }, this.read_index(), this.write_index())
    }
}

impl<S: Storage + ?Sized> Observer for SharedRb<S> {
    type Item = S::Item;

    #[inline]
    fn capacity(&self) -> NonZeroUsize {
        unsafe { NonZeroUsize::new_unchecked(self.storage.len()) }
    }

    #[inline]
    fn read_index(&self) -> usize {
        self.read_index.load(Ordering::Acquire)
    }
    #[inline]
    fn write_index(&self) -> usize {
        self.write_index.load(Ordering::Acquire)
    }

    unsafe fn unsafe_slices(&self, start: usize, end: usize) -> (&[MaybeUninit<S::Item>], &[MaybeUninit<S::Item>]) {
        let (first, second) = ranges(self.capacity(), start, end);
        unsafe { (self.storage.slice(first), self.storage.slice(second)) }
    }
    unsafe fn unsafe_slices_mut(&self, start: usize, end: usize) -> (&mut [MaybeUninit<S::Item>], &mut [MaybeUninit<S::Item>]) {
        let (first, second) = ranges(self.capacity(), start, end);
        unsafe { (self.storage.slice_mut(first), self.storage.slice_mut(second)) }
    }

    #[inline]
    fn read_is_held(&self) -> bool {
        self.read_held.load(Ordering::Acquire)
    }
    #[inline]
    fn write_is_held(&self) -> bool {
        self.write_held.load(Ordering::Acquire)
    }
}

impl<S: Storage + ?Sized> Producer for SharedRb<S> {
    #[inline]
    unsafe fn set_write_index(&self, value: usize) {
        self.write_index.store(value, Ordering::Release);
    }
}

impl<S: Storage + ?Sized> Consumer for SharedRb<S> {
    #[inline]
    unsafe fn set_read_index(&self, value: usize) {
        self.read_index.store(value, Ordering::Release);
    }
}

impl<S: Storage + ?Sized> RingBuffer for SharedRb<S> {
    #[inline]
    unsafe fn hold_read(&self, flag: bool) -> bool {
        self.read_held.swap(flag, Ordering::AcqRel)
    }
    #[inline]
    unsafe fn hold_write(&self, flag: bool) -> bool {
        self.write_held.swap(flag, Ordering::AcqRel)
    }
}

impl<S: Storage + ?Sized> Drop for SharedRb<S> {
    fn drop(&mut self) {
        self.clear();
    }
}

#[cfg(feature = "alloc")]
impl<S: Storage> Split for SharedRb<S> {
    type Prod = CachingProd<Arc<Self>>;
    type Cons = CachingCons<Arc<Self>>;

    fn split(self) -> (Self::Prod, Self::Cons) {
        Arc::new(self).split()
    }
}
#[cfg(feature = "alloc")]
impl<S: Storage + ?Sized> Split for Arc<SharedRb<S>> {
    type Prod = CachingProd<Self>;
    type Cons = CachingCons<Self>;

    fn split(self) -> (Self::Prod, Self::Cons) {
        (CachingProd::new(self.clone()), CachingCons::new(self))
    }
}
#[cfg(feature = "alloc")]
impl<S: Storage + ?Sized> Split for Box<SharedRb<S>> {
    type Prod = CachingProd<Arc<SharedRb<S>>>;
    type Cons = CachingCons<Arc<SharedRb<S>>>;

    fn split(self) -> (Self::Prod, Self::Cons) {
        Arc::<SharedRb<S>>::from(self).split()
    }
}
impl<S: Storage + ?Sized> SplitRef for SharedRb<S> {
    type RefProd<'a>
        = CachingProd<&'a Self>
    where
        Self: 'a;
    type RefCons<'a>
        = CachingCons<&'a Self>
    where
        Self: 'a;

    fn split_ref(&mut self) -> (Self::RefProd<'_>, Self::RefCons<'_>) {
        (CachingProd::new(self), CachingCons::new(self))
    }
}

rb_impl_init!(SharedRb);

impl_producer_traits!(SharedRb<S: Storage>);
impl_consumer_traits!(SharedRb<S: Storage>);

impl<S: Storage + ?Sized> AsRef<Self> for SharedRb<S> {
    fn as_ref(&self) -> &Self {
        self
    }
}
impl<S: Storage + ?Sized> AsMut<Self> for SharedRb<S> {
    fn as_mut(&mut self) -> &mut Self {
        self
    }
}