2 files changed, 59 insertions, 0 deletions
diff --git a/helix-core/src/lib.rs b/helix-core/src/lib.rs
index f697bc7f..7d51f88c 100644
--- a/helix-core/src/lib.rs
+++ b/helix-core/src/lib.rs
@@ -16,6 +16,7 @@ pub mod register;
 pub mod search;
 pub mod selection;
 mod state;
+pub mod surround;
 pub mod syntax;
 mod transaction;
 
diff --git a/helix-core/src/surround.rs b/helix-core/src/surround.rs
new file mode 100644
index 00000000..a629d2d3
--- /dev/null
+++ b/helix-core/src/surround.rs
@@ -0,0 +1,58 @@
+use crate::{search, Selection};
+use ropey::RopeSlice;
+
+pub const PAIRS: &[(char, char)] = &[('(', ')'), ('[', ']'), ('{', '}'), ('<', '>')];
+
+/// Given any char in [PAIRS], return the open and closing chars. If not found in
+/// [PAIRS] return (ch, ch).
+pub fn get_pair(ch: char) -> (char, char) {
+    PAIRS
+        .iter()
+        .find(|(open, close)| *open == ch || *close == ch)
+        .copied()
+        .unwrap_or((ch, ch))
+}
+
+/// Find the position of surround pairs of `ch` which can be either a closing
+/// or opening pair. `n` will skip n - 1 pairs (eg. n=2 will discard (only)
+/// the first pair found and keep looking)
+pub fn find_nth_pairs_pos(
+    text: RopeSlice,
+    ch: char,
+    pos: usize,
+    n: usize,
+) -> Option<(usize, usize)> {
+    let (open, close) = get_pair(ch);
+    let open_pos = search::find_nth_prev(text, open, pos, n, true)?;
+    let close_pos = search::find_nth_next(text, close, pos, n, true)?;
+
+    Some((open_pos, close_pos))
+}
+
+/// Find position of surround characters around every cursor. Returns None
+/// if any positions overlap. Note that the positions are in a flat Vec.
+/// Use get_surround_pos().chunks(2) to get matching pairs of surround positions.
+/// `ch` can be either closing or opening pair.
+pub fn get_surround_pos(
+    text: RopeSlice,
+    selection: &Selection,
+    ch: char,
+    skip: usize,
+) -> Option<Vec<usize>> {
+    let mut change_pos = Vec::new();
+
+    for range in selection {
+        let head = range.head;
+
+        match find_nth_pairs_pos(text, ch, head, skip) {
+            Some((open_pos, close_pos)) => {
+                if change_pos.contains(&open_pos) || change_pos.contains(&close_pos) {
+                    return None;
+                }
+                change_pos.extend_from_slice(&[open_pos, close_pos]);
+            }
+            None => return None,
+        }
+    }
+    Some(change_pos)
+}