2 files changed, 56 insertions, 20 deletions

diff --git a/helix-core/src/commands.rs b/helix-core/src/commands.rs
index fdb3fab6..860ec1cb 100644
--- a/helix-core/src/commands.rs
+++ b/helix-core/src/commands.rs
@@ -1,4 +1,4 @@
-use crate::graphemes::next_grapheme_boundary;
+use crate::graphemes;
 use crate::selection::Range;
 use crate::state::{Direction, Granularity, Mode, State};
 use crate::transaction::{ChangeSet, Transaction};
@@ -53,7 +53,10 @@ pub fn append_mode(state: &mut State, _count: usize) {
     let text = &state.doc.slice(..);
     state.selection = state.selection.transform(|range| {
         // TODO: to() + next char
-        Range::new(range.from(), next_grapheme_boundary(text, range.to()))
+        Range::new(
+            range.from(),
+            graphemes::next_grapheme_boundary(text, range.to()),
+        )
     })
 }
 
@@ -75,3 +78,30 @@ pub fn insert_char(state: &mut State, c: char) {
     transaction.apply(state);
     // TODO: need to store into history if successful
 }
+
+// TODO: handle indent-aware delete
+pub fn delete_char_backward(state: &mut State, count: usize) {
+    let text = &state.doc.slice(..);
+    let transaction = Transaction::change_by_selection(state, |range| {
+        (
+            graphemes::nth_prev_grapheme_boundary(text, range.head, count),
+            range.head,
+            None,
+        )
+    });
+    transaction.apply(state);
+    // TODO: need to store into history if successful
+}
+
+pub fn delete_char_forward(state: &mut State, count: usize) {
+    let text = &state.doc.slice(..);
+    let transaction = Transaction::change_by_selection(state, |range| {
+        (
+            graphemes::nth_next_grapheme_boundary(text, range.head, count),
+            range.head,
+            None,
+        )
+    });
+    transaction.apply(state);
+    // TODO: need to store into history if successful
+}
diff --git a/helix-core/src/transaction.rs b/helix-core/src/transaction.rs
index 2f40be76..130f77b8 100644
--- a/helix-core/src/transaction.rs
+++ b/helix-core/src/transaction.rs
@@ -342,31 +342,37 @@ impl Transaction {
         true
     }
 
-    pub fn insert(state: &State, text: Tendril) -> Self {
+    pub fn change_by_selection<F>(state: &State, f: F) -> Self
+    where
+        F: Fn(&SelectionRange) -> (usize, usize, Option<Tendril>),
+    {
         let len = state.doc.len_chars();
         let ranges = state.selection.ranges();
-        let mut changes = Vec::with_capacity(2 * ranges.len() + 1);
-        let mut last = 0;
+        let mut acc = Vec::with_capacity(2 * ranges.len() + 1);
+
+        let changes = ranges.iter().map(f);
+
+        // TODO: verify ranges are ordered and not overlapping.
 
-        for range in state.selection.ranges() {
-            let cur = range.head;
-            changes.push(Change::Retain(cur));
-            changes.push(Change::Insert(text.clone()));
-            last = cur;
+        let mut last = 0;
+        for (from, to, tendril) in changes {
+            // TODO: need to fill the in-between ranges too
+            // Retain from last "to" to current "from"
+            acc.push(Change::Retain(from - last));
+            match tendril {
+                Some(text) => acc.push(Change::Insert(text)),
+                None => acc.push(Change::Delete(to - from)),
+            }
+            last = to;
         }
-        changes.push(Change::Retain(len - last));
+        acc.push(Change::Retain(len - last));
 
-        Self::from(ChangeSet { changes, len })
+        Self::from(ChangeSet { changes: acc, len })
     }
 
-    pub fn change_selection<F>(selection: Selection, f: F) -> Self
-    where
-        F: Fn(SelectionRange) -> ChangeSet,
-    {
-        selection.ranges().iter().map(|range| true);
-        // TODO: most idiomatic would be to return a
-        // Change { from: x, to: y, insert: "str" }
-        unimplemented!()
+    /// Insert text at each selection head.
+    pub fn insert(state: &State, text: Tendril) -> Self {
+        Self::change_by_selection(state, |range| (range.head, range.head, Some(text.clone())))
     }
 }