sdset 0.4.0

use std::cmp;
use crate::set::{Set, vec_sets_into_slices};
use crate::{SetOperation, Collection, exponential_offset_ge};

/// Represent the _difference_ set operation that will be applied to the slices.
///
/// Note that the difference is all the elements
/// that are in the first slice but not in all the others.
///
/// # Examples
/// ```
/// # use sdset::Error;
/// # fn try_main() -> Result<(), Error> {
/// use sdset::multi::OpBuilder;
/// use sdset::{SetOperation, Set, SetBuf};
///
/// let a = Set::new(&[1, 2, 4])?;
/// let b = Set::new(&[2, 3, 5, 7])?;
/// let c = Set::new(&[4, 6, 7])?;
///
/// let op = OpBuilder::from_vec(vec![a, b, c]).difference();
///
/// let res: SetBuf<i32> = op.into_set_buf();
/// assert_eq!(&res[..], &[1]);
/// # Ok(()) }
/// # try_main().unwrap();
/// ```
#[derive(Clone)]
pub struct Difference<'a, T: 'a> {
    slices: Vec<&'a [T]>,
}

impl<'a, T> Difference<'a, T> {
    /// Construct one with slices checked to be sorted and deduplicated.
    pub fn new(slices: Vec<&'a Set<T>>) -> Self {
        Self {
            slices: vec_sets_into_slices(slices),
        }
    }
}

impl<'a, T: Ord> Difference<'a, T> {
    #[inline]
    fn extend_collection<C, U, F>(mut self, output: &mut C, extend: F)
    where C: Collection<U>,
          F: Fn(&mut C, &'a [T])
    {
        let (base, others) = match self.slices.split_first_mut() {
            Some(split) => split,
            None => return,
        };

        while let Some(first) = base.first() {
            let mut minimum = None;
            for slice in others.iter_mut() {
                *slice = exponential_offset_ge(slice, first);
                minimum = match (minimum, slice.first()) {
                    (Some(min), Some(first)) => Some(cmp::min(min, first)),
                    (None, Some(first)) => Some(first),
                    (min, _) => min,
                };
            }

            match minimum {
                Some(min) if min == first => *base = exponential_offset_ge(&base[1..], min),
                Some(min) => {
                    let off = base.iter().take_while(|&x| x < min).count();
                    extend(output, &base[..off]);

                    *base = &base[off..];
                },
                None => {
                    extend(output, base);
                    break;
                },
            }
        }
    }
}

impl<'a, T: Ord + Clone> SetOperation<T> for Difference<'a, T> {
    fn extend_collection<C>(self, output: &mut C) where C: Collection<T> {
        self.extend_collection(output, Collection::extend_from_slice);
    }
}

impl<'a, T: Ord> SetOperation<&'a T> for Difference<'a, T> {
    fn extend_collection<C>(self, output: &mut C) where C: Collection<&'a T> {
        self.extend_collection(output, Collection::extend);
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::set::{sort_dedup_vec, SetBuf};

    #[test]
    fn no_slice() {
        let difference_: SetBuf<i32> = Difference { slices: vec![] }.into_set_buf();
        assert_eq!(&difference_[..], &[]);
    }

    #[test]
    fn one_empty_slice() {
        let a: &[i32] = &[];

        let difference_: SetBuf<i32> = Difference { slices: vec![a] }.into_set_buf();
        assert_eq!(&difference_[..], &[]);
    }

    #[test]
    fn one_slice() {
        let a = &[1, 2, 3];

        let difference_: SetBuf<i32> = Difference { slices: vec![a] }.into_set_buf();
        assert_eq!(&difference_[..], &[1, 2, 3]);
    }

    #[test]
    fn two_slices() {
        let a = &[1, 2, 3];
        let b = &[2, 4];

        let difference_: SetBuf<i32> = Difference { slices: vec![a, b] }.into_set_buf();
        assert_eq!(&difference_[..], &[1, 3]);
    }

    #[test]
    fn two_slices_special_case() {
        let a = &[1, 2, 3];
        let b = &[3];

        let difference_: SetBuf<i32> = Difference { slices: vec![a, b] }.into_set_buf();
        assert_eq!(&difference_[..], &[1, 2]);
    }

    #[test]
    fn three_slices() {
        let a = &[1, 2, 3, 6, 7];
        let b = &[2, 3, 4];
        let c = &[3, 4, 5, 7];

        let difference_: SetBuf<i32> = Difference { slices: vec![a, b, c] }.into_set_buf();
        assert_eq!(&difference_[..], &[1, 6]);
    }

    quickcheck! {
        fn qc_difference(xss: Vec<Vec<i32>>) -> bool {
            use std::collections::BTreeSet;
            use std::iter::FromIterator;

            // FIXME temporary hack (can have mutable parameters!)
            let mut xss = xss;

            for xs in &mut xss {
                sort_dedup_vec(xs);
            }

            let x: SetBuf<i32> = {
                let xss = xss.iter().map(|xs| xs.as_slice()).collect();
                Difference { slices: xss }.into_set_buf()
            };

            let mut xss = xss.into_iter();
            let mut y = match xss.next() {
                Some(xs) => BTreeSet::from_iter(xs),
                None => BTreeSet::new(),
            };

            for v in xss {
                let x = BTreeSet::from_iter(v.iter().cloned());
                y = y.difference(&x).cloned().collect();
            }
            let y: Vec<_> = y.into_iter().collect();

            x.as_slice() == y.as_slice()
        }
    }
}

#[cfg(all(feature = "unstable", test))]
mod bench {
    extern crate test;
    use super::*;
    use self::test::Bencher;
    use crate::set::SetBuf;

    #[bench]
    fn two_slices_big(bench: &mut Bencher) {
        let a: Vec<_> = (0..100).collect();
        let b: Vec<_> = (1..101).collect();

        bench.iter(|| {
            let difference_: SetBuf<i32> = Difference { slices: vec![&a, &b] }.into_set_buf();
            test::black_box(|| difference_);
        });
    }

    #[bench]
    fn two_slices_big2(bench: &mut Bencher) {
        let a: Vec<_> = (0..100).collect();
        let b: Vec<_> = (51..151).collect();

        bench.iter(|| {
            let difference_: SetBuf<i32> = Difference { slices: vec![&a, &b] }.into_set_buf();
            test::black_box(|| difference_);
        });
    }

    #[bench]
    fn two_slices_big3(bench: &mut Bencher) {
        let a: Vec<_> = (0..100).collect();
        let b: Vec<_> = (100..200).collect();

        bench.iter(|| {
            let difference_: SetBuf<i32> = Difference { slices: vec![&a, &b] }.into_set_buf();
            test::black_box(|| difference_);
        });
    }

    #[bench]
    fn three_slices_big(bench: &mut Bencher) {
        let a: Vec<_> = (0..100).collect();
        let b: Vec<_> = (1..101).collect();
        let c: Vec<_> = (2..102).collect();

        bench.iter(|| {
            let difference_: SetBuf<i32> = Difference { slices: vec![&a, &b, &c] }.into_set_buf();
            test::black_box(|| difference_);
        });
    }

    #[bench]
    fn three_slices_big2(bench: &mut Bencher) {
        let a: Vec<_> = (0..100).collect();
        let b: Vec<_> = (34..134).collect();
        let c: Vec<_> = (66..167).collect();

        bench.iter(|| {
            let difference_: SetBuf<i32> = Difference { slices: vec![&a, &b, &c] }.into_set_buf();
            test::black_box(|| difference_);
        });
    }

    #[bench]
    fn three_slices_big3(bench: &mut Bencher) {
        let a: Vec<_> = (0..100).collect();
        let b: Vec<_> = (100..200).collect();
        let c: Vec<_> = (200..300).collect();

        bench.iter(|| {
            let difference_: SetBuf<i32> = Difference { slices: vec![&a, &b, &c] }.into_set_buf();
            test::black_box(|| difference_);
        });
    }
}