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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/.

//! Filter pipes.

use std::ops::BitOr;

use signalo_traits::{Filter, Finalize, Sink, Source};

/// A `Pipe` is a simple container joining a pair of `Filter`/`Source`/`Sink`/`Finalize` impls.
#[derive(Default, Clone, Debug)]
pub struct Pipe<T, U> {
    lhs: T,
    rhs: U,
}

impl<T, U> Pipe<T, U> {
    /// Creates a new pipe connecting `lhs` and `rhs`.
    #[inline]
    pub fn new(lhs: T, rhs: U) -> Self {
        Self { lhs, rhs }
    }
}

impl<T, U, Rhs> BitOr<Rhs> for Pipe<T, U> {
    type Output = Pipe<Self, Rhs>;

    #[inline]
    fn bitor(self, rhs: Rhs) -> Self::Output {
        Pipe::new(self, rhs)
    }
}

impl<T, U, I> Filter<I> for Pipe<T, U>
where
    T: Filter<I>,
    U: Filter<T::Output>,
{
    type Output = U::Output;

    #[inline]
    fn filter(&mut self, input: I) -> Self::Output {
        self.rhs.filter(self.lhs.filter(input))
    }
}

impl<T, U> Source for Pipe<T, U>
where
    T: Source,
    U: Filter<T::Output>,
{
    type Output = U::Output;

    #[inline]
    fn source(&mut self) -> Option<Self::Output> {
        self.lhs.source().map(|input| self.rhs.filter(input))
    }
}

impl<T, U, I> Sink<I> for Pipe<T, U>
where
    T: Filter<I>,
    U: Sink<T::Output>,
{
    #[inline]
    fn sink(&mut self, input: I) {
        self.rhs.sink(self.lhs.filter(input))
    }
}

impl<T, U> Finalize for Pipe<T, U>
where
    U: Finalize,
{
    type Output = U::Output;

    #[inline]
    fn finalize(self) -> Self::Output {
        self.rhs.finalize()
    }
}

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

    type Value = usize;

    struct DummyFilterAdd;

    impl Filter<Value> for DummyFilterAdd {
        type Output = Value;

        #[inline]
        fn filter(&mut self, input: Value) -> Self::Output {
            input + 1
        }
    }

    struct DummyFilterMul;

    impl Filter<Value> for DummyFilterMul {
        type Output = Value;

        #[inline]
        fn filter(&mut self, input: Value) -> Self::Output {
            input * 2
        }
    }

    #[test]
    fn test() {
        let input = vec![
            0, 1, 7, 2, 5, 8, 16, 3, 19, 6, 14, 9, 9, 17, 17, 4, 12, 20, 20, 7,
        ];
        let filter_add = DummyFilterAdd;
        let filter_mul = DummyFilterMul;
        let pipe = Pipe::new(filter_add, filter_mul);
        let subject: Vec<_> = input
            .iter()
            .scan(pipe, |pipe, &input| Some(pipe.filter(input)))
            .collect();
        let expected = vec![
            2, 4, 16, 6, 12, 18, 34, 8, 40, 14, 30, 20, 20, 36, 36, 10, 26, 42, 42, 16,
        ];
        assert_eq!(subject, expected);
    }
}