//! Parallel iterator types for [results][std::result]

//!

//! You will rarely need to interact with this module directly unless you need

//! to name one of the iterator types.

//!

//! [std::result]: https://doc.rust-lang.org/stable/std/result/

use crate::iter::plumbing::*;

use crate::iter::*;

use std::sync::Mutex;

use crate::option;

/// Parallel iterator over a result

#[derive(Debug, Clone)]

pub struct IntoIter<T: Send> {

    inner: option::IntoIter<T>,

}

impl<T: Send, E> IntoParallelIterator for Result<T, E> {

    type Item = T;

    type Iter = IntoIter<T>;

    fn into_par_iter(self) -> Self::Iter {

        IntoIter {

            inner: self.ok().into_par_iter(),

        }

    }

}

delegate_indexed_iterator! {

    IntoIter<T> => T,

    impl<T: Send>

}

/// Parallel iterator over an immutable reference to a result

#[derive(Debug)]

pub struct Iter<'a, T: Sync> {

    inner: option::IntoIter<&'a T>,

}

impl<'a, T: Sync> Clone for Iter<'a, T> {

    fn clone(&self) -> Self {

        Iter {

            inner: self.inner.clone(),

        }

    }

}

impl<'a, T: Sync, E> IntoParallelIterator for &'a Result<T, E> {

    type Item = &'a T;

    type Iter = Iter<'a, T>;

    fn into_par_iter(self) -> Self::Iter {

        Iter {

            inner: self.as_ref().ok().into_par_iter(),

        }

    }

}

delegate_indexed_iterator! {

    Iter<'a, T> => &'a T,

    impl<'a, T: Sync + 'a>

}

/// Parallel iterator over a mutable reference to a result

#[derive(Debug)]

pub struct IterMut<'a, T: Send> {

    inner: option::IntoIter<&'a mut T>,

}

impl<'a, T: Send, E> IntoParallelIterator for &'a mut Result<T, E> {

    type Item = &'a mut T;

    type Iter = IterMut<'a, T>;

    fn into_par_iter(self) -> Self::Iter {

        IterMut {

            inner: self.as_mut().ok().into_par_iter(),

        }

    }

}

delegate_indexed_iterator! {

    IterMut<'a, T> => &'a mut T,

    impl<'a, T: Send + 'a>

}

/// Collect an arbitrary `Result`-wrapped collection.

///

/// If any item is `Err`, then all previous `Ok` items collected are

/// discarded, and it returns that error.  If there are multiple errors, the

/// one returned is not deterministic.

impl<C, T, E> FromParallelIterator<Result<T, E>> for Result<C, E>

where

    C: FromParallelIterator<T>,

    T: Send,

    E: Send,

{

    fn from_par_iter<I>(par_iter: I) -> Self

    where

        I: IntoParallelIterator<Item = Result<T, E>>,

    {

        fn ok<T, E>(saved: &Mutex<Option<E>>) -> impl Fn(Result<T, E>) -> Option<T> + '_ {

            move |item| match item {

                Ok(item) => Some(item),

                Err(error) => {

                    // We don't need a blocking `lock()`, as anybody

                    // else holding the lock will also be writing

                    // `Some(error)`, and then ours is irrelevant.

                    if let Ok(mut guard) = saved.try_lock() {

                        if guard.is_none() {

                            *guard = Some(error);

                        }

                    }

                    None

                }

            }

        }

        let saved_error = Mutex::new(None);

        let collection = par_iter

            .into_par_iter()

            .map(ok(&saved_error))

            .while_some()

            .collect();

        match saved_error.into_inner().unwrap() {

            Some(error) => Err(error),

            None => Ok(collection),

        }

    }

}