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//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
//

/// Extension trait for `Iterator<Item = Result<T, E>>` to unwrap everything.
///
/// Errors can be unwraped as well. If the closure `F` returns `Some(O)`, that `O` will be inserted
/// instead of the `E` into the resulting iterator.
/// If the closure returns `None`, the error will be dropped (equally to
/// `iter.filter_map(Result::ok)`.
///
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct UnwrapWith<I, O, E, F>(I, F)
where
    I: Iterator<Item = Result<O, E>>,
    F: FnMut(E) -> Option<O>;

impl<I, O, E, F> Iterator for UnwrapWith<I, O, E, F>
where
    I: Iterator<Item = Result<O, E>>,
    F: FnMut(E) -> Option<O>,
{
    type Item = O;

    fn next(&mut self) -> Option<Self::Item> {
        while let Some(o) = self.0.by_ref().next() {
            match o {
                Ok(t) => return Some(t),
                Err(e) => {
                    if let Some(t) = (self.1)(e) {
                        return Some(t);
                    }
                }
            }
        }

        None
    }
}

pub trait UnwrapWithExt<I, O, E, F>
where
    I: Iterator<Item = Result<O, E>>,
    F: FnMut(E) -> Option<O>,
{
    /// Unwraps all results
    ///
    /// Errors can be ignored:
    /// ```
    /// use resiter::unwrap::UnwrapWithExt;
    /// use std::str::FromStr;
    ///
    /// let unwrapped: Vec<usize> = ["1", "2", "a", "b", "5"]
    ///     .iter()
    ///     .map(|e| usize::from_str(e))
    ///     .unwrap_with(|_| None) // ignore errors
    ///     .collect();
    ///
    /// assert_eq!(unwrapped, vec![1, 2, 5],);
    /// ```
    ///
    /// Or simply converted:
    /// ```
    /// use resiter::unwrap::UnwrapWithExt;
    /// use std::str::FromStr;
    ///
    /// let unwrapped: Vec<usize> = ["1", "2", "a", "b", "5"]
    ///     .iter()
    ///     .map(|e| usize::from_str(e))
    ///     .unwrap_with(|_| Some(8)) // convert errors
    ///     .collect();
    ///
    /// assert_eq!(unwrapped, vec![1, 2, 8, 8, 5],);
    /// ```
    fn unwrap_with(self, _: F) -> UnwrapWith<I, O, E, F>;
}

impl<I, O, E, F> UnwrapWithExt<I, O, E, F> for I
where
    I: Iterator<Item = Result<O, E>>,
    F: FnMut(E) -> Option<O>,
{
    #[inline]
    fn unwrap_with(self, f: F) -> UnwrapWith<I, O, E, F> {
        UnwrapWith(self, f)
    }
}