split off repr

src/repr/misc.rs

@@ -0,0 +1,95 @@
+use either::Either;
+use std::{iter::Rev, ops::RangeInclusive};
+
+pub fn split_from<T>(range: RangeInclusive<T>, x: T) -> [impl Iterator<Item = T> + Clone; 2]
+where
+    T: num::Integer + Copy,
+    RangeInclusive<T>: Iterator<Item = T> + DoubleEndedIterator,
+    Rev<RangeInclusive<T>>: Iterator<Item = T>,
+{
+    let in_range = range.contains(&x);
+    let (start, end) = (*range.start(), *range.end());
+
+    // RangeInclusive (1..=0), has 0 elements
+    let base = Either::Right(T::one()..=T::zero());
+    [
+        if in_range && x > start + T::one() {
+            Either::Left((start..=(x - T::one())).rev())
+        } else {
+            base.clone()
+        },
+        if in_range && x + T::one() < end {
+            Either::Right((x + T::one())..=end)
+        } else {
+            base
+        },
+    ]
+}
+
+pub fn diag_raw<T>(
+    i_chains: [impl Iterator<Item = T> + Clone; 2],
+    j_chains: [impl Iterator<Item = T> + Clone; 2],
+) -> [impl Iterator<Item = (T, T)> + Clone; 4]
+where
+    T: num::Integer + Copy,
+    RangeInclusive<T>: Iterator<Item = T> + DoubleEndedIterator,
+    Rev<RangeInclusive<T>>: Iterator<Item = T>,
+{
+    [(0, 0), (1, 1), (1, 0), (0, 1)].map(move |(a, b)| i_chains[a].clone().zip(j_chains[b].clone()))
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    fn diag_test_helper<T>(
+        i: T,
+        j: T,
+        range_i: RangeInclusive<T>,
+        range_j: RangeInclusive<T>,
+    ) -> [impl Iterator<Item = (T, T)> + Clone; 4]
+    where
+        T: num::Integer + Copy,
+        RangeInclusive<T>: Iterator<Item = T> + DoubleEndedIterator,
+        Rev<RangeInclusive<T>>: Iterator<Item = T>,
+    {
+        diag_raw(split_from(range_i, i), split_from(range_j, j))
+    }
+
+    #[test]
+    fn split_test() {
+        assert_eq!(
+            split_from(0..=6, 2).map(Iterator::collect::<Vec<usize>>),
+            [vec![1, 0], vec![3, 4, 5, 6]]
+        );
+
+        assert_eq!(
+            split_from(0..=6, 0).map(Iterator::collect::<Vec<usize>>),
+            [vec![], vec![1, 2, 3, 4, 5, 6]]
+        );
+
+        assert_eq!(
+            split_from(0..=6, 6).map(Iterator::collect::<Vec<usize>>),
+            [vec![5, 4, 3, 2, 1, 0], vec![]]
+        );
+
+        // test out-of-bounds and also generics
+        assert_eq!(
+            split_from::<i16>(-1i16..=4i16, 10i16).map(Iterator::collect::<Vec<i16>>),
+            [const { Vec::new() }; 2]
+        );
+    }
+
+    #[test]
+    fn diag_test() {
+        assert_eq!(
+            diag_test_helper(2, 3, 0..=7, 0..=7).map(Iterator::collect::<Vec<(usize, usize)>>),
+            [
+                vec![(1, 2), (0, 1)],
+                vec![(3, 4), (4, 5), (5, 6), (6, 7)],
+                vec![(3, 2), (4, 1), (5, 0)],
+                vec![(1, 4), (0, 5)]
+            ]
+        );
+    }
+}