#![allow(non_snake_case)]
#![feature(test)]
extern crate test;


use std::iter::FromIterator;

#[cfg(test)]
use test::Bencher;

#[derive(Copy, Clone, PartialEq, Eq, Debug)]
struct LastOne<T>(Option<T>);

impl<T> FromIterator<T> for LastOne<T> {
    #[inline]
    fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> LastOne<T> {
        LastOne(iter.into_iter().last())
    }
}

type Last<T> = LastOne<T>;
impl<T> Last<T> {
    fn new(x: T) -> Last<T> { LastOne(Some(x)) }
}

fn from_iter_baseline<C, T, E, I>(iter: I) -> Result<C, E>
where I: Iterator<Item = Result<T, E>>,
      C: FromIterator<T>,
{
    FromIterator::from_iter(iter)
}

fn from_iter_adapter<C, T, E, I>(iter: I) -> Result<C, E>
where I: Iterator<Item = Result<T, E>>,
      C: FromIterator<T>,
{
    struct Adapter<Iter, E> {
        iter: Iter,
        err: Option<E>,
    }

    impl<T, E, Iter: Iterator<Item=Result<T, E>>> Iterator for Adapter<Iter, E> {
        type Item = T;

        #[inline]
        fn next(&mut self) -> Option<T> {
            match self.iter.next() {
                Some(Ok(value)) => Some(value),
                Some(Err(err)) => {
                    self.err = Some(err);
                    None
                }
                None => None,
            }
        }

        fn size_hint(&self) -> (usize, Option<usize>) {
            let (_min, max) = self.iter.size_hint();
            (0, max)
        }
    }

    let mut adapter = Adapter { iter, err: None };
    let v: C = FromIterator::from_iter(adapter.by_ref());

    match adapter.err {
        Some(err) => Err(err),
        None => Ok(v),
    }
}

fn from_iter_with_scan_with_freevar<C, T, E, I>(iter: I) -> Result<C, E>
where I: Iterator<Item = Result<T, E>>,
      C: FromIterator<T>,
{
    let mut err = None;

    let v = {
        let adapter = iter.scan((), |_, item| {
            match item {
                Ok(x) => Some(x),
                Err(x) => {
                    err = Some(x);
                    None
                },
            }
        });

        FromIterator::from_iter(adapter)
    };

    match err {
        Some(err) => Err(err),
        None => Ok(v),
    }
}

fn from_iter_with_scan_passing_state<C, T, E, I>(iter: I) -> Result<C, E>
where I: Iterator<Item = Result<T, E>>,
      C: FromIterator<T>,
{
    let mut err = None;

    let v = {
        let adapter = iter.scan(&mut err, |err, item| {
            match item {
                Ok(x) => Some(x),
                Err(x) => {
                    **err = Some(x);
                    None
                },
            }
        });

        FromIterator::from_iter(adapter)
    };

    match err {
        Some(err) => Err(err),
        None => Ok(v),
    }
}

fn from_iter_with_filter_map<C, T, E, I>(iter: I) -> Result<C, E>
where I: Iterator<Item = Result<T, E>>,
      C: FromIterator<T>,
{
    let mut err = None;

    let v = {
        let adapter = iter.filter_map(|item| {
            match item {
                Ok(x) => Some(x),
                Err(x) => {
                    err = Some(x);
                    None
                },
            }
        });

        FromIterator::from_iter(adapter)
    };

    match err {
        Some(err) => Err(err),
        None => Ok(v),
    }
}

fn main() {
    let one_a: Result<Last<u8>, _> = from_iter_baseline("1,2,3".split(",").map(|x| x.parse()));
    let one_b: Result<Last<u8>, _> = from_iter_adapter("1,2,3".split(",").map(|x| x.parse()));
    let two_a: Result<Last<u8>, _> = from_iter_with_scan_passing_state("1,2,3".split(",").map(|x| x.parse()));
    let two_b: Result<Last<u8>, _> = from_iter_with_scan_with_freevar("1,2,3".split(",").map(|x| x.parse()));
    let three: Result<Last<u8>, _> = from_iter_with_filter_map("1,2,3".split(",").map(|x| x.parse()));
    println!("{:?}", one_a);
    println!("{:?}", one_b);
    println!("{:?}", two_a);
    println!("{:?}", two_b);
    println!("{:?}", three);

    let one_a: Result<Last<u8>, _> = from_iter_baseline("1,a,3".split(",").map(|x| x.parse()));
    let one_b: Result<Last<u8>, _> = from_iter_adapter("1,a,3".split(",").map(|x| x.parse()));
    let two_a: Result<Last<u8>, _> = from_iter_with_scan_passing_state("1,a,3".split(",").map(|x| x.parse()));
    let two_b: Result<Last<u8>, _> = from_iter_with_scan_with_freevar("1,a,3".split(",").map(|x| x.parse()));
    let three: Result<Last<u8>, _> = from_iter_with_filter_map("1,a,3".split(",").map(|x| x.parse()));
    println!("{:?}", one_a);
    println!("{:?}", one_b);
    println!("{:?}", two_a);
    println!("{:?}", two_b);
    println!("{:?}", three);
}

#[bench]
fn bench__vec_from_iter_using_baseline___(b: &mut Bencher) {
    let expected = vec![1; 1000];
    let v: Vec<Result<isize, String>> = vec![Ok(1); 1000];
    b.iter(|| {
        let result: Result<Vec<isize>, String> = from_iter_baseline(v.iter().cloned());
        assert_eq!(result.unwrap(), expected);
    });
}

#[bench]
fn bench__vec_from_iter_using_adapter____(b: &mut Bencher) {
    let expected = vec![1; 1000];
    let v: Vec<Result<isize, String>> = vec![Ok(1); 1000];
    b.iter(|| {
        let result: Result<Vec<isize>, String> = from_iter_adapter(v.iter().cloned());
        assert_eq!(result.unwrap(), expected);
    });
}

#[bench]
fn bench__vec_from_iter_with_scan_param__(b: &mut Bencher) {
    let expected = vec![1; 1000];
    let v: Vec<Result<isize, String>> = vec![Ok(1); 1000];
    b.iter(|| {
        let result: Result<Vec<isize>, String> = from_iter_with_scan_passing_state(v.iter().cloned());
        assert_eq!(result.unwrap(), expected);
    });
}

#[bench]
fn bench__vec_from_iter_with_scan_freevar(b: &mut Bencher) {
    let expected = vec![1; 1000];
    let v: Vec<Result<isize, String>> = vec![Ok(1); 1000];
    b.iter(|| {
        let result: Result<Vec<isize>, String> = from_iter_with_scan_with_freevar(v.iter().cloned());
        assert_eq!(result.unwrap(), expected);
    });
}

#[bench]
fn bench__vec_from_iter_with_filter_map__(b: &mut Bencher) {
    let expected = vec![1; 1000];
    let v: Vec<Result<isize, String>> = vec![Ok(1); 1000];
    b.iter(|| {
        let result: Result<Vec<isize>, String> = from_iter_with_filter_map(v.iter().cloned());
        assert_eq!(result.unwrap(), expected);
    });
}

#[bench]
fn bench_last_from_iter_using_baseline___(b: &mut Bencher) {
    let expected = Last::new(1);
    let v: Vec<Result<isize, String>> = vec![Ok(1); 3000];
    b.iter(|| {
        let result: Result<Last<isize>, String> = from_iter_baseline(v.iter().cloned());
        assert_eq!(result.unwrap(), expected);
    });
}

#[bench]
fn bench_last_from_iter_using_adapter____(b: &mut Bencher) {
    let expected = Last::new(1);
    let v: Vec<Result<isize, String>> = vec![Ok(1); 3000];
    b.iter(|| {
        let result: Result<Last<isize>, String> = from_iter_adapter(v.iter().cloned());
        assert_eq!(result.unwrap(), expected);
    });
}

#[bench]
fn bench_last_from_iter_with_scan_param__(b: &mut Bencher) {
    let expected = Last::new(1);
    let v: Vec<Result<isize, String>> = vec![Ok(1); 3000];
    b.iter(|| {
        let result: Result<Last<isize>, String> = from_iter_with_scan_passing_state(v.iter().cloned());
        assert_eq!(result.unwrap(), expected);
    });
}

#[bench]
fn bench_last_from_iter_with_scan_freevar(b: &mut Bencher) {
    let expected = Last::new(1);
    let v: Vec<Result<isize, String>> = vec![Ok(1); 3000];
    b.iter(|| {
        let result: Result<Last<isize>, String> = from_iter_with_scan_with_freevar(v.iter().cloned());
        assert_eq!(result.unwrap(), expected);
    });
}

#[bench]
fn bench_last_from_iter_with_filter_map__(b: &mut Bencher) {
    let expected = Last::new(1);
    let v: Vec<Result<isize, String>> = vec![Ok(1); 3000];
    b.iter(|| {
        let result: Result<Last<isize>, String> = from_iter_with_filter_map(v.iter().cloned());
        assert_eq!(result.unwrap(), expected);
    });
}