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use super::ParallelIterator;
use super::len::ParallelLen;
use super::state::ParallelIteratorState;
use std::marker::PhantomData;

pub struct Map<M, MAP_OP> {
    base: M,
    map_op: MAP_OP,
}

impl<M, MAP_OP> Map<M, MAP_OP> {
    pub fn new(base: M, map_op: MAP_OP) -> Map<M, MAP_OP> {
        Map { base: base, map_op: map_op }
    }
}

impl<M, MAP_OP, R> ParallelIterator for Map<M, MAP_OP>
    where M: ParallelIterator,
          MAP_OP: Fn(M::Item) -> R + Sync,
          R: Send,
{
    type Item = R;
    type Shared = MapShared<M, MAP_OP>;
    type State = MapState<M, MAP_OP>;

    fn state(self) -> (Self::Shared, Self::State) {
        let (base_shared, base_state) = self.base.state();
        (MapShared { base: base_shared, map_op: self.map_op },
         MapState { base: base_state, map_op: PhantomMapOp::new() })
    }
}

pub struct MapShared<M, MAP_OP>
    where M: ParallelIterator,
{
    base: M::Shared,
    map_op: MAP_OP,
}

pub struct MapState<M, MAP_OP>
    where M: ParallelIterator,
{
    base: M::State,
    map_op: PhantomMapOp<MAP_OP>,
}

// Wrapper for `PhantomData` to allow `MapState` to impl `Send`
struct PhantomMapOp<MAP_OP>(PhantomData<*const MAP_OP>);

impl<MAP_OP> PhantomMapOp<MAP_OP> {
    fn new() -> PhantomMapOp<MAP_OP> {
        PhantomMapOp(PhantomData)
    }
}

unsafe impl<MAP_OP: Sync> Send for PhantomMapOp<MAP_OP> { }

unsafe impl<M, MAP_OP, R> ParallelIteratorState for MapState<M, MAP_OP>
    where M: ParallelIterator,
          MAP_OP: Fn(M::Item) -> R + Sync,
{
    type Item = R;
    type Shared = MapShared<M, MAP_OP>;

    fn len(&mut self, shared: &Self::Shared) -> ParallelLen {
        self.base.len(&shared.base)
    }

    fn split_at(self, index: usize) -> (Self, Self) {
        let (left, right) = self.base.split_at(index);
        (MapState { base: left, map_op: PhantomMapOp::new() },
         MapState { base: right, map_op: PhantomMapOp::new() })
    }

    fn next(&mut self, shared: &Self::Shared) -> Option<Self::Item> {
        self.base.next(&shared.base)
                 .map(|base| (shared.map_op)(base))
    }
}