use std::cmp::{max, Ord, Ordering};

use crate::{Driver, Executor, ParallelIterator};

/* Max */

pub struct Max<X> {
    iterator: X,
}

impl<X> Max<X> {
    pub fn new(iterator: X) -> Self {
        Self { iterator }
    }
}

impl<'a, X, T> Driver<'a, Option<T>> for Max<X>
where
    X: ParallelIterator<'a, Item = T>,
    T: Send + Ord + 'a,
{
    fn exec_with<E>(self, executor: E) -> E::Result
    where
        E: Executor<'a, Option<T>>,
    {
        self.iterator.reduce_with(max).exec_with(executor)
    }
}

/* MaxBy */

pub struct MaxBy<X, O> {
    iterator: X,
    operation: O,
}

impl<X, O> MaxBy<X, O> {
    pub fn new(iterator: X, operation: O) -> Self {
        Self {
            iterator,
            operation,
        }
    }
}

impl<'a, X, O, T> Driver<'a, Option<T>> for MaxBy<X, O>
where
    X: ParallelIterator<'a, Item = T>,
    O: Fn(&T, &T) -> Ordering + Clone + Send + Sync + 'a,
    T: Send + Ord + 'a,
{
    fn exec_with<E>(self, executor: E) -> E::Result
    where
        E: Executor<'a, Option<T>>,
    {
        let operation = self.operation;

        self.iterator
            .reduce_with(move |a, b| match operation(&a, &b) {
                Ordering::Greater => b,
                _ => a,
            })
            .exec_with(executor)
    }
}