1 files changed, 81 insertions, 0 deletions
diff --git a/helix-core/src/movement.rs b/helix-core/src/movement.rs
index 57abc498..88d6df0a 100644
--- a/helix-core/src/movement.rs
+++ b/helix-core/src/movement.rs
@@ -1,6 +1,66 @@
 use crate::graphemes::{nth_next_grapheme_boundary, nth_prev_grapheme_boundary, RopeGraphemes};
 use crate::{coords_at_pos, pos_at_coords, ChangeSet, Position, Range, Rope, RopeSlice, Selection};
 
+#[derive(Copy, Clone, PartialEq, Eq)]
+pub enum Direction {
+    Forward,
+    Backward,
+}
+
+pub fn move_horizontally(
+    text: RopeSlice,
+    range: Range,
+    dir: Direction,
+    count: usize,
+    extend: bool,
+) -> Range {
+    let pos = range.head;
+    let line = text.char_to_line(pos);
+    // TODO: we can optimize clamping by passing in RopeSlice limited to current line. that way
+    // we stop calculating past start/end of line.
+    let pos = match dir {
+        Direction::Backward => {
+            let start = text.line_to_char(line);
+            nth_prev_grapheme_boundary(text, pos, count).max(start)
+        }
+        Direction::Forward => {
+            // Line end is pos at the start of next line - 1
+            // subtract another 1 because the line ends with \n
+            let end = text.line_to_char(line + 1).saturating_sub(2);
+            nth_next_grapheme_boundary(text, pos, count).min(end)
+        }
+    };
+    Range::new(if extend { range.anchor } else { pos }, pos)
+}
+
+pub fn move_vertically(
+    text: RopeSlice,
+    range: Range,
+    dir: Direction,
+    count: usize,
+    extend: bool,
+) -> Range {
+    let Position { row, col } = coords_at_pos(text, range.head);
+
+    let horiz = range.horiz.unwrap_or(col as u32);
+
+    let new_line = match dir {
+        Direction::Backward => row.saturating_sub(count),
+        Direction::Forward => std::cmp::min(row.saturating_add(count), text.len_lines() - 1),
+    };
+
+    // convert to 0-indexed, subtract another 1 because len_chars() counts \n
+    let new_line_len = text.line(new_line).len_chars().saturating_sub(2);
+
+    let new_col = std::cmp::min(horiz as usize, new_line_len);
+
+    let pos = pos_at_coords(text, Position::new(new_line, new_col));
+
+    let mut range = Range::new(if extend { range.anchor } else { pos }, pos);
+    range.horiz = Some(horiz);
+    range
+}
+
 pub fn move_next_word_start(slice: RopeSlice, mut pos: usize, count: usize) -> usize {
     for _ in 0..count {
         if pos + 1 == slice.len_chars() {
@@ -155,3 +215,24 @@ where
         *pos = pos.saturating_sub(1);
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_vertical_move() {
+        let text = Rope::from("abcd\nefg\nwrs");
+        let slice = text.slice(..);
+        let pos = pos_at_coords(slice, (0, 4).into());
+
+        let range = Range::new(pos, pos);
+        assert_eq!(
+            coords_at_pos(
+                slice,
+                move_vertically(slice, range, Direction::Forward, 1, false).head
+            ),
+            (1, 2).into()
+        );
+    }
+}