1 files changed, 74 insertions, 0 deletions

diff --git a/helix-core/src/position.rs b/helix-core/src/position.rs
index 5e5f902b..346779b0 100644
--- a/helix-core/src/position.rs
+++ b/helix-core/src/position.rs
@@ -1,3 +1,8 @@
+use crate::{
+    graphemes::{nth_next_grapheme_boundary, RopeGraphemes},
+    Rope, RopeSlice,
+};
+
 /// Represents a single point in a text buffer. Zero indexed.
 #[derive(Debug, Default, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
 pub struct Position {
@@ -44,6 +49,21 @@ impl From<Position> for tree_sitter::Point {
         Self::new(pos.row, pos.col)
     }
 }
+/// Convert a character index to (line, column) coordinates.
+pub fn coords_at_pos(text: RopeSlice, pos: usize) -> Position {
+    let line = text.char_to_line(pos);
+    let line_start = text.line_to_char(line);
+    let col = RopeGraphemes::new(text.slice(line_start..pos)).count();
+    Position::new(line, col)
+}
+
+/// Convert (line, column) coordinates to a character index.
+pub fn pos_at_coords(text: RopeSlice, coords: Position) -> usize {
+    let Position { row, col } = coords;
+    let line_start = text.line_to_char(row);
+    // line_start + col
+    nth_next_grapheme_boundary(text, line_start, col)
+}
 
 #[cfg(test)]
 mod test {
@@ -54,4 +74,58 @@ mod test {
         // (0, 5) is less than (1, 0)
         assert!(Position::new(0, 5) < Position::new(1, 0));
     }
+
+    #[test]
+    fn test_coords_at_pos() {
+        let text = Rope::from("ḧëḷḷö\nẅöṛḷḋ");
+        let slice = text.slice(..);
+        // assert_eq!(coords_at_pos(slice, 0), (0, 0).into());
+        // assert_eq!(coords_at_pos(slice, 5), (0, 5).into()); // position on \n
+        // assert_eq!(coords_at_pos(slice, 6), (1, 0).into()); // position on w
+        // assert_eq!(coords_at_pos(slice, 7), (1, 1).into()); // position on o
+        // assert_eq!(coords_at_pos(slice, 10), (1, 4).into()); // position on d
+
+        // test with grapheme clusters
+        let text = Rope::from("a̐éö̲\r\n");
+        let slice = text.slice(..);
+        assert_eq!(coords_at_pos(slice, 0), (0, 0).into());
+        assert_eq!(coords_at_pos(slice, 2), (0, 1).into());
+        assert_eq!(coords_at_pos(slice, 4), (0, 2).into());
+        assert_eq!(coords_at_pos(slice, 7), (0, 3).into());
+
+        let text = Rope::from("किमपि");
+        let slice = text.slice(..);
+        assert_eq!(coords_at_pos(slice, 0), (0, 0).into());
+        assert_eq!(coords_at_pos(slice, 2), (0, 1).into());
+        assert_eq!(coords_at_pos(slice, 3), (0, 2).into());
+        assert_eq!(coords_at_pos(slice, 5), (0, 3).into());
+    }
+
+    #[test]
+    fn test_pos_at_coords() {
+        let text = Rope::from("ḧëḷḷö\nẅöṛḷḋ");
+        let slice = text.slice(..);
+        assert_eq!(pos_at_coords(slice, (0, 0).into()), 0);
+        assert_eq!(pos_at_coords(slice, (0, 5).into()), 5); // position on \n
+        assert_eq!(pos_at_coords(slice, (1, 0).into()), 6); // position on w
+        assert_eq!(pos_at_coords(slice, (1, 1).into()), 7); // position on o
+        assert_eq!(pos_at_coords(slice, (1, 4).into()), 10); // position on d
+
+        // test with grapheme clusters
+        let text = Rope::from("a̐éö̲\r\n");
+        let slice = text.slice(..);
+        assert_eq!(pos_at_coords(slice, (0, 0).into()), 0);
+        assert_eq!(pos_at_coords(slice, (0, 1).into()), 2);
+        assert_eq!(pos_at_coords(slice, (0, 2).into()), 4);
+        assert_eq!(pos_at_coords(slice, (0, 3).into()), 7); // \r\n is one char here
+        assert_eq!(pos_at_coords(slice, (0, 4).into()), 9);
+        let text = Rope::from("किमपि");
+        // 2 - 1 - 2 codepoints
+        // TODO: delete handling as per https://news.ycombinator.com/item?id=20058454
+        let slice = text.slice(..);
+        assert_eq!(pos_at_coords(slice, (0, 0).into()), 0);
+        assert_eq!(pos_at_coords(slice, (0, 1).into()), 2);
+        assert_eq!(pos_at_coords(slice, (0, 2).into()), 3);
+        assert_eq!(pos_at_coords(slice, (0, 3).into()), 5); // eol
+    }
 }