//! Parallel iterator types for [options]

//!

//! You will rarely need to interact with this module directly unless you need

//! to name one of the iterator types.

//!

//! [options]: std::option

use crate::iter::plumbing::*;

use crate::iter::*;

use std::sync::atomic::{AtomicBool, Ordering};

/// A parallel iterator over the value in [`Some`] variant of an [`Option`].

///

/// The iterator yields one value if the [`Option`] is a [`Some`], otherwise none.

///

/// This `struct` is created by the [`into_par_iter`] function.

///

/// [`into_par_iter`]: IntoParallelIterator::into_par_iter()

#[derive(Debug, Clone)]

pub struct IntoIter<T> {

    opt: Option<T>,

}

impl<T: Send> IntoParallelIterator for Option<T> {

    type Item = T;

    type Iter = IntoIter<T>;

    fn into_par_iter(self) -> Self::Iter {

        IntoIter { opt: self }

    }

}

impl<T: Send> ParallelIterator for IntoIter<T> {

    type Item = T;

    fn drive_unindexed<C>(self, consumer: C) -> C::Result

    where

        C: UnindexedConsumer<Self::Item>,

    {

        self.drive(consumer)

    }

    fn opt_len(&self) -> Option<usize> {

        Some(self.len())

    }

}

impl<T: Send> IndexedParallelIterator for IntoIter<T> {

    fn drive<C>(self, consumer: C) -> C::Result

    where

        C: Consumer<Self::Item>,

    {

        let mut folder = consumer.into_folder();

        if let Some(item) = self.opt {

            folder = folder.consume(item);

        }

        folder.complete()

    }

    fn len(&self) -> usize {

        match self.opt {

            Some(_) => 1,

            None => 0,

        }

    }

    fn with_producer<CB>(self, callback: CB) -> CB::Output

    where

        CB: ProducerCallback<Self::Item>,

    {

        callback.callback(OptionProducer { opt: self.opt })

    }

}

/// A parallel iterator over a reference to the [`Some`] variant of an [`Option`].

///

/// The iterator yields one value if the [`Option`] is a [`Some`], otherwise none.

///

/// This `struct` is created by the [`par_iter`] function.

///

/// [`par_iter`]: IntoParallelRefIterator::par_iter()

#[derive(Debug)]

pub struct Iter<'a, T> {

    inner: IntoIter<&'a T>,

}

impl<T> Clone for Iter<'_, T> {

    fn clone(&self) -> Self {

        Iter {

            inner: self.inner.clone(),

        }

    }

}

impl<'a, T: Sync> IntoParallelIterator for &'a Option<T> {

    type Item = &'a T;

    type Iter = Iter<'a, T>;

    fn into_par_iter(self) -> Self::Iter {

        Iter {

            inner: self.as_ref().into_par_iter(),

        }

    }

}

delegate_indexed_iterator! {

    Iter<'a, T> => &'a T,

    impl<'a, T: Sync>

}

/// A parallel iterator over a mutable reference to the [`Some`] variant of an [`Option`].

///

/// The iterator yields one value if the [`Option`] is a [`Some`], otherwise none.

///

/// This `struct` is created by the [`par_iter_mut`] function.

///

/// [`par_iter_mut`]: IntoParallelRefMutIterator::par_iter_mut()

#[derive(Debug)]

pub struct IterMut<'a, T> {

    inner: IntoIter<&'a mut T>,

}

impl<'a, T: Send> IntoParallelIterator for &'a mut Option<T> {

    type Item = &'a mut T;

    type Iter = IterMut<'a, T>;

    fn into_par_iter(self) -> Self::Iter {

        IterMut {

            inner: self.as_mut().into_par_iter(),

        }

    }

}

delegate_indexed_iterator! {

    IterMut<'a, T> => &'a mut T,

    impl<'a, T: Send>

}

/// Private producer for an option

struct OptionProducer<T: Send> {

    opt: Option<T>,

}

impl<T: Send> Producer for OptionProducer<T> {

    type Item = T;

    type IntoIter = std::option::IntoIter<T>;

    fn into_iter(self) -> Self::IntoIter {

        self.opt.into_iter()

    }

    fn split_at(self, index: usize) -> (Self, Self) {

        debug_assert!(index <= 1);

        let none = OptionProducer { opt: None };

        if index == 0 {

            (none, self)

        } else {

            (self, none)

        }

    }

}

/// Collect an arbitrary `Option`-wrapped collection.

///

/// If any item is `None`, then all previous items collected are discarded,

/// and it returns only `None`.

impl<C, T> FromParallelIterator<Option<T>> for Option<C>

where

    C: FromParallelIterator<T>,

    T: Send,

{

    fn from_par_iter<I>(par_iter: I) -> Self

    where

        I: IntoParallelIterator<Item = Option<T>>,

    {

        fn check<T>(found_none: &AtomicBool) -> impl Fn(&Option<T>) + '_ {

            move |item| {

                if item.is_none() {

                    found_none.store(true, Ordering::Relaxed);

                }

            }

        }

        let found_none = AtomicBool::new(false);

        let collection = par_iter

            .into_par_iter()

            .inspect(check(&found_none))

            .while_some()

            .collect();

        if found_none.load(Ordering::Relaxed) {

            None

        } else {

            Some(collection)

        }

    }

}