4 files changed, 48 insertions, 4 deletions

diff --git a/helix-core/src/commands.rs b/helix-core/src/commands.rs
index 62e97686..a6b74449 100644
--- a/helix-core/src/commands.rs
+++ b/helix-core/src/commands.rs
@@ -1,4 +1,4 @@
-use crate::state::{Direction, Granularity, State};
+use crate::state::{Direction, Granularity, Mode, State};
 
 /// A command is a function that takes the current state and a count, and does a side-effect on the
 /// state (usually by creating and applying a transaction).
@@ -48,3 +48,23 @@ pub fn move_line_down(state: &mut State, count: usize) {
         count,
     );
 }
+
+pub fn insert_mode(state: &mut State, _count: usize) {
+    state.mode = Mode::Insert;
+}
+
+pub fn normal_mode(state: &mut State, _count: usize) {
+    state.mode = Mode::Normal;
+}
+
+// TODO: insert means add text just before cursor, on exit we should be on the last letter.
+pub fn insert(state: &mut State, c: char) {
+    // TODO: needs to work with multiple cursors
+    use crate::transaction::ChangeSet;
+
+    let pos = state.selection.primary().head;
+    let changes = ChangeSet::insert(&state.doc, pos, c);
+    // TODO: need to store history
+    changes.apply(state.contents_mut());
+    state.selection = state.selection.clone().map(&changes);
+}
diff --git a/helix-core/src/selection.rs b/helix-core/src/selection.rs
index 3e28c9ce..1c0b6b74 100644
--- a/helix-core/src/selection.rs
+++ b/helix-core/src/selection.rs
@@ -63,8 +63,8 @@ impl Range {
     /// Map a range through a set of changes. Returns a new range representing the same position
     /// after the changes are applied.
     pub fn map(self, changes: &ChangeSet) -> Self {
-        let anchor = changes.map_pos(self.anchor, Assoc::Before);
-        let head = changes.map_pos(self.head, Assoc::Before);
+        let anchor = changes.map_pos(self.anchor, Assoc::After);
+        let head = changes.map_pos(self.head, Assoc::After);
 
         // TODO: possibly unnecessary
         if self.anchor == anchor && self.head == head {
diff --git a/helix-core/src/state.rs b/helix-core/src/state.rs
index 9c227a92..8568c3c3 100644
--- a/helix-core/src/state.rs
+++ b/helix-core/src/state.rs
@@ -1,10 +1,16 @@
 use crate::graphemes::{nth_next_grapheme_boundary, nth_prev_grapheme_boundary, RopeGraphemes};
 use crate::{Buffer, Rope, RopeSlice, Selection, SelectionRange};
 
+pub enum Mode {
+    Normal,
+    Insert,
+}
+
 /// A state represents the current editor state of a single buffer.
 pub struct State {
     pub doc: Buffer,
     pub selection: Selection,
+    pub mode: Mode,
 }
 
 #[derive(Copy, Clone, PartialEq, Eq)]
@@ -26,6 +32,7 @@ impl State {
         Self {
             doc,
             selection: Selection::single(0, 0),
+            mode: Mode::Normal,
         }
     }
 
@@ -119,10 +126,15 @@ impl State {
         // TODO: update selection in state via transaction
     }
 
-    pub fn file(&self) -> &Rope {
+    pub fn contents(&self) -> &Rope {
         // used to access file contents for rendering to screen
         &self.doc.contents
     }
+
+    pub fn contents_mut(&mut self) -> &mut Rope {
+        // used to access file contents for rendering to screen
+        &mut self.doc.contents
+    }
 }
 
 /// Coordinates are a 0-indexed line and column pair.
diff --git a/helix-core/src/transaction.rs b/helix-core/src/transaction.rs
index 1619a4db..2d8afc9b 100644
--- a/helix-core/src/transaction.rs
+++ b/helix-core/src/transaction.rs
@@ -47,6 +47,18 @@ impl ChangeSet {
         }
     }
 
+    pub fn insert(buf: &Buffer, pos: usize, c: char) -> Self {
+        let len = buf.contents.len_chars();
+        Self {
+            changes: vec![
+                Change::Retain(pos),
+                Change::Insert(Tendril::from_char(c)),
+                Change::Retain(len - pos),
+            ],
+            len,
+        }
+    }
+
     // TODO: from iter
 
     /// Combine two changesets together.