From d1810272257f597ddba4fd3496dbdde8cda59638 Mon Sep 17 00:00:00 2001
From: Blaž Hrastnik
Date: Mon, 21 Dec 2020 13:42:47 +0900
Subject: fix: undo/redo selection handling.

---
 helix-term/src/commands.rs | 24 ++++++++++++++++++++----
 helix-view/src/document.rs | 10 ++++++++--
 2 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/helix-term/src/commands.rs b/helix-term/src/commands.rs
index 5f8f63f1..a8aea914 100644
--- a/helix-term/src/commands.rs
+++ b/helix-term/src/commands.rs
@@ -322,17 +322,23 @@ pub fn select_line(cx: &mut Context) {
     cx.view.doc.set_selection(Selection::single(start, end));
 }
 
-pub fn delete_selection(cx: &mut Context) {
+// heuristic: append changes to history after each command, unless we're in insert mode
+
+fn _delete_selection(cx: &mut Context) {
     let transaction = Transaction::change_by_selection(&cx.view.doc.state, |range| {
         (range.from(), range.to() + 1, None)
     });
     cx.view.doc.apply(&transaction);
+}
+
+pub fn delete_selection(cx: &mut Context) {
+    _delete_selection(cx);
 
     append_changes_to_history(cx);
 }
 
 pub fn change_selection(cx: &mut Context) {
-    delete_selection(cx);
+    _delete_selection(cx);
     insert_mode(cx);
 }
 
@@ -359,8 +365,9 @@ pub fn flip_selections(cx: &mut Context) {
 fn enter_insert_mode(cx: &mut Context) {
     cx.view.doc.mode = Mode::Insert;
 
-    append_changes_to_history(cx);
+    // TODO: store selection for undo
 }
+
 // inserts at the start of each selection
 pub fn insert_mode(cx: &mut Context) {
     enter_insert_mode(cx);
@@ -535,6 +542,8 @@ fn append_changes_to_history(cx: &mut Context) {
         return;
     }
 
+    // TODO: change -> change -> undo -> change -> change fails, probably old_state needs reset
+
     let new_changeset = ChangeSet::new(cx.view.doc.text());
     let changes = std::mem::replace(&mut cx.view.doc.changes, new_changeset);
     // Instead of doing this messy merge we could always commit, and based on transaction
@@ -548,7 +557,13 @@ fn append_changes_to_history(cx: &mut Context) {
     // TODO: trigger lsp/documentDidChange with changes
 
     // HAXX: we need to reconstruct the state as it was before the changes..
-    let old_state = std::mem::replace(&mut cx.view.doc.old_state, cx.view.doc.state.clone());
+    let old_state = cx
+        .view
+        .doc
+        .old_state
+        .take()
+        .expect("no old_state available");
+
     // TODO: take transaction by value?
     cx.view
         .doc
@@ -649,6 +664,7 @@ pub fn undo(cx: &mut Context) {
     if let Some(revert) = cx.view.doc.history.undo() {
         cx.view.doc.version += 1;
         cx.view.doc.apply(&revert);
+        // TODO: undo/redo needs to avoid storing in self.changes/self.old_state
     }
 
     // TODO: each command could simply return a Option<transaction>, then the higher level handles storing it?
diff --git a/helix-view/src/document.rs b/helix-view/src/document.rs
index 323c7bff..0dc40c5a 100644
--- a/helix-view/src/document.rs
+++ b/helix-view/src/document.rs
@@ -30,7 +30,7 @@ pub struct Document {
 
     /// Pending changes since last history commit.
     pub changes: ChangeSet,
-    pub old_state: State,
+    pub old_state: Option<State>,
     pub history: History,
     pub version: i32, // should be usize?
 
@@ -58,7 +58,7 @@ use url::Url;
 impl Document {
     fn new(state: State) -> Self {
         let changes = ChangeSet::new(&state.doc);
-        let old_state = state.clone();
+        let old_state = None;
 
         Self {
             path: None,
@@ -156,6 +156,12 @@ impl Document {
     pub fn apply(&mut self, transaction: &Transaction) -> bool {
         let old_doc = self.text().clone();
 
+        // store the state just before any changes are made. This allows us to undo to the
+        // state just before a transaction was applied.
+        if self.changes.is_empty() && !transaction.changes().is_empty() {
+            self.old_state = Some(self.state.clone());
+        }
+
         let success = transaction.apply(&mut self.state);
 
         if !transaction.changes().is_empty() {
-- 
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