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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<O, E>>` to filter one kind of result (and leaving the other as is)
pub trait Filter<O, E>: Sized {
    /// Filter `Ok` items while keeping `Err`
    ///
    /// ```
    /// use resiter::filter::Filter;
    /// use std::str::FromStr;
    ///
    /// let mapped: Vec<_> = ["1", "2", "a", "4", "5"]
    ///     .iter()
    ///     .map(|txt| usize::from_str(txt))
    ///     .filter_ok(|i| i % 2 == 0)
    ///     .collect();
    /// assert_eq!(mapped.len(), 3);
    /// assert_eq!(mapped[0], Ok(2));
    /// assert!(mapped[1].is_err());
    /// assert_eq!(mapped[2], Ok(4))
    /// ```
    fn filter_ok<F>(self, _: F) -> FilterOk<Self, F>
    where
        F: FnMut(&O) -> bool;

    /// Filter `Err` values while keeping `Ok`
    ///
    /// ```
    /// use resiter::filter::Filter;
    /// use std::str::FromStr;
    ///
    /// let mapped: Vec<_> = ["1", "2", "a", "4", "5"]
    ///     .iter()
    ///     .map(|txt| usize::from_str(txt))
    ///     .filter_err(|_| false)
    ///     .collect();
    ///
    /// assert_eq!(mapped, vec![Ok(1), Ok(2), Ok(4), Ok(5)]);
    /// ```
    fn filter_err<F>(self, _: F) -> FilterErr<Self, F>
    where
        F: FnMut(&E) -> bool;
}

impl<I, O, E> Filter<O, E> for I
where
    I: Iterator<Item = Result<O, E>> + Sized,
{
    #[inline]
    fn filter_ok<F>(self, f: F) -> FilterOk<Self, F>
    where
        F: FnMut(&O) -> bool,
    {
        FilterOk { iter: self, f }
    }

    #[inline]
    fn filter_err<F>(self, f: F) -> FilterErr<Self, F>
    where
        F: FnMut(&E) -> bool,
    {
        FilterErr { iter: self, f }
    }
}

#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct FilterOk<I, F> {
    iter: I,
    f: F,
}

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

    fn next(&mut self) -> Option<Self::Item> {
        loop {
            match self.iter.next() {
                Some(Ok(x)) => {
                    if (self.f)(&x) {
                        return Some(Ok(x));
                    }
                }
                other => {
                    return other;
                }
            }
        }
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        let hint_sup = self.iter.size_hint().1;
        (0, hint_sup)
    }
}

#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct FilterErr<I, F> {
    iter: I,
    f: F,
}

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

    fn next(&mut self) -> Option<Self::Item> {
        loop {
            match self.iter.next() {
                Some(Err(x)) => {
                    if (self.f)(&x) {
                        return Some(Err(x));
                    }
                }
                other => {
                    return other;
                }
            }
        }
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        let hint_sup = self.iter.size_hint().1;
        (0, hint_sup)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_filter_ok_hint() {
        use std::str::FromStr;

        let hint = ["1", "2", "a", "4", "5"]
            .iter()
            .map(|txt| usize::from_str(txt))
            .filter_ok(|i| i % 2 == 0)
            .size_hint();

        assert_eq!(hint, (0, Some(5)));
    }

    #[test]
    fn test_filter_err_hint() {
        use std::str::FromStr;

        let hint = ["1", "2", "a", "4", "5"]
            .iter()
            .map(|txt| usize::from_str(txt))
            .filter_err(|_| false)
            .size_hint();

        assert_eq!(hint, (0, Some(5)));
    }
}