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use super::*;
use super::internal::*;
use std::cmp::min;
use std::iter;

pub struct ZipIter<A: IndexedParallelIterator, B: IndexedParallelIterator> {
    a: A,
    b: B,
}

impl<A: IndexedParallelIterator, B: IndexedParallelIterator> ZipIter<A, B> {
    pub fn new(a: A, b: B) -> ZipIter<A, B> {
        ZipIter { a: a, b: b }
    }
}

impl<A, B> ParallelIterator for ZipIter<A, B>
    where A: IndexedParallelIterator, B: IndexedParallelIterator
{
    type Item = (A::Item, B::Item);

    fn drive_unindexed<C>(self, consumer: C) -> C::Result
        where C: UnindexedConsumer<Self::Item>
    {
        bridge(self, consumer)
    }
}

impl<A,B> BoundedParallelIterator for ZipIter<A,B>
    where A: IndexedParallelIterator, B: IndexedParallelIterator
{
    fn upper_bound(&mut self) -> usize {
        self.len()
    }

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

impl<A,B> ExactParallelIterator for ZipIter<A,B>
    where A: IndexedParallelIterator, B: IndexedParallelIterator
{
    fn len(&mut self) -> usize {
        min(self.a.len(), self.b.len())
    }
}

impl<A,B> IndexedParallelIterator for ZipIter<A,B>
    where A: IndexedParallelIterator, B: IndexedParallelIterator
{
    fn with_producer<CB>(self, callback: CB) -> CB::Output
        where CB: ProducerCallback<Self::Item>
    {
        return self.a.with_producer(CallbackA {
            callback: callback,
            b: self.b,
        });

        struct CallbackA<CB, B> {
            callback: CB,
            b: B
        }

        impl<CB, A_ITEM, B> ProducerCallback<A_ITEM> for CallbackA<CB, B>
            where B: IndexedParallelIterator,
                  CB: ProducerCallback<(A_ITEM, B::Item)>,
        {
            type Output = CB::Output;

            fn callback<A>(self, a_producer: A) -> Self::Output
                where A: Producer<Item=A_ITEM>
            {
                return self.b.with_producer(CallbackB {
                    a_producer: a_producer,
                    callback: self.callback,
                });
            }
        }

        struct CallbackB<CB, A> {
            a_producer: A,
            callback: CB
        }

        impl<CB, A, B_ITEM> ProducerCallback<B_ITEM> for CallbackB<CB, A>
            where A: Producer,
                  CB: ProducerCallback<(A::Item, B_ITEM)>,
        {
            type Output = CB::Output;

            fn callback<B>(self, b_producer: B) -> Self::Output
                where B: Producer<Item=B_ITEM>
            {
                self.callback.callback(ZipProducer { a: self.a_producer, b: b_producer })
            }
        }

    }
}

///////////////////////////////////////////////////////////////////////////

pub struct ZipProducer<A: Producer, B: Producer> {
    a: A,
    b: B,
}

impl<A: Producer, B: Producer> Producer for ZipProducer<A, B> {
    fn weighted(&self) -> bool {
        self.a.weighted() || self.b.weighted()
    }

    fn cost(&mut self, len: usize) -> f64 {
        // Rather unclear that this should be `+`. It might be that max is better?
        self.a.cost(len) + self.b.cost(len)
    }

    fn split_at(self, index: usize) -> (Self, Self) {
        let (a_left, a_right) = self.a.split_at(index);
        let (b_left, b_right) = self.b.split_at(index);
        (ZipProducer { a: a_left, b: b_left },
         ZipProducer { a: a_right, b: b_right, })
    }
}

impl<A: Producer, B: Producer> IntoIterator for ZipProducer<A, B> {
    type Item = (A::Item, B::Item);
    type IntoIter = iter::Zip<A::IntoIter, B::IntoIter>;

    fn into_iter(self) -> Self::IntoIter {
        self.a.into_iter().zip(self.b)
    }
}