use super::plumbing::*;

use super::*;

/// `Take` is an iterator that iterates over the first `n` elements.

/// This struct is created by the [`take()`] method on [`IndexedParallelIterator`]

///

/// [`take()`]: IndexedParallelIterator::take()

#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]

#[derive(Debug, Clone)]

pub struct Take<I> {

    base: I,

    n: usize,

}

impl<I> Take<I>

where

    I: IndexedParallelIterator,

{

    /// Creates a new `Take` iterator.

    pub(super) fn new(base: I, n: usize) -> Self {

        let n = Ord::min(base.len(), n);

        Take { base, n }

    }

}

impl<I> ParallelIterator for Take<I>

where

    I: IndexedParallelIterator,

{

    type Item = I::Item;

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

    where

        C: UnindexedConsumer<Self::Item>,

    {

        bridge(self, consumer)

    }

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

        Some(self.len())

    }

}

impl<I> IndexedParallelIterator for Take<I>

where

    I: IndexedParallelIterator,

{

    fn len(&self) -> usize {

        self.n

    }

    fn drive<C: Consumer<Self::Item>>(self, consumer: C) -> C::Result {

        bridge(self, consumer)

    }

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

    where

        CB: ProducerCallback<Self::Item>,

    {

        return self.base.with_producer(Callback {

            callback,

            n: self.n,

        });

        struct Callback<CB> {

            callback: CB,

            n: usize,

        }

        impl<T, CB> ProducerCallback<T> for Callback<CB>

        where

            CB: ProducerCallback<T>,

        {

            type Output = CB::Output;

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

            where

                P: Producer<Item = T>,

            {

                let (producer, _) = base.split_at(self.n);

                self.callback.callback(producer)

            }

        }

    }

}