use rayon::prelude::*;

#[cfg(not(has_std))]
use alloc::collections::LinkedList;

#[cfg(has_std)]
use std::collections::LinkedList;

use crate::vec::Vec;

// generate `ParallelIterator` methods by just forwarding to the underlying
// self.entries and mapping its elements.
macro_rules! parallel_iterator_methods {
    // $map_elt is the mapping function from the underlying iterator's element
    ($map_elt:expr) => {
        fn drive_unindexed<C>(self, consumer: C) -> C::Result
        where
            C: UnindexedConsumer<Self::Item>,
        {
            self.entries
                .into_par_iter()
                .map($map_elt)
                .drive_unindexed(consumer)
        }

        // NB: This allows indexed collection, e.g. directly into a `Vec`, but the
        // underlying iterator must really be indexed.  We should remove this if we
        // start having tombstones that must be filtered out.
        fn opt_len(&self) -> Option<usize> {
            Some(self.entries.len())
        }
    };
}

// generate `IndexedParallelIterator` methods by just forwarding to the underlying
// self.entries and mapping its elements.
macro_rules! indexed_parallel_iterator_methods {
    // $map_elt is the mapping function from the underlying iterator's element
    ($map_elt:expr) => {
        fn drive<C>(self, consumer: C) -> C::Result
        where
            C: Consumer<Self::Item>,
        {
            self.entries.into_par_iter().map($map_elt).drive(consumer)
        }

        fn len(&self) -> usize {
            self.entries.len()
        }

        fn with_producer<CB>(self, callback: CB) -> CB::Output
        where
            CB: ProducerCallback<Self::Item>,
        {
            self.entries
                .into_par_iter()
                .map($map_elt)
                .with_producer(callback)
        }
    };
}

pub mod map;
pub mod set;

// This form of intermediate collection is also how Rayon collects `HashMap`.
// Note that the order will also be preserved!
fn collect<I: IntoParallelIterator>(iter: I) -> LinkedList<Vec<I::Item>> {
    iter.into_par_iter()
        .fold(Vec::new, |mut vec, elem| {
            vec.push(elem);
            vec
        })
        .map(|vec| {
            let mut list = LinkedList::new();
            list.push_back(vec);
            list
        })
        .reduce(LinkedList::new, |mut list1, mut list2| {
            list1.append(&mut list2);
            list1
        })
}