From 7c752dff4f6ec20f91ddeef8abf6879471612f4d Mon Sep 17 00:00:00 2001
From: etienne-k <2804556+etienne-k@users.noreply.github.com>
Date: Fri, 31 Mar 2023 19:17:20 +0200
Subject: [PATCH] feat(commands): avoid selections in the normal/insert mode

---
 helix-term/src/commands.rs      | 45 ++++++++++++++---------
 helix-term/src/commands/evil.rs | 64 +++++++++++++++++++++++++++++++++
 2 files changed, 93 insertions(+), 16 deletions(-)

diff --git a/helix-term/src/commands.rs b/helix-term/src/commands.rs
index 6a2d6a78b..153f8d34d 100644
--- a/helix-term/src/commands.rs
+++ b/helix-term/src/commands.rs
@@ -4,8 +4,8 @@ pub(crate) mod lsp;
 pub(crate) mod typed;
 
 pub use dap::*;
-use helix_vcs::Hunk;
 pub use evil::*;
+use helix_vcs::Hunk;
 pub use lsp::*;
 use tokio::sync::oneshot;
 use tui::widgets::Row;
@@ -2449,6 +2449,11 @@ fn ensure_selections_forward(cx: &mut Context) {
 }
 
 pub fn enter_insert_mode(cx: &mut Context) {
+    if EvilCommands::is_enabled() {
+        // In evil mode, selections are possible in the selection/visual mode only.
+        EvilCommands::collapse_selections(cx, CollapseMode::Backward);
+    }
+
     cx.editor.mode = Mode::Insert;
 }
 
@@ -2501,6 +2506,12 @@ fn append_mode(cx: &mut Context) {
         )
     });
     doc.set_selection(view.id, selection);
+
+    // We already collapsed selections in `enter_insert_mode()`, but this function creates selections again,
+    // and we want to leave the cursor(s) at the end of the range(s).
+    if EvilCommands::is_enabled() {
+        EvilCommands::collapse_selections(cx, CollapseMode::Forward);
+    }
 }
 
 fn file_picker(cx: &mut Context) {
@@ -3110,6 +3121,11 @@ pub fn select_mode(cx: &mut Context) {
 }
 
 pub fn exit_select_mode(cx: &mut Context) {
+    if EvilCommands::is_enabled() {
+        // In evil mode, selections are possible in the selection/visual mode only.
+        EvilCommands::collapse_selections(cx, CollapseMode::ToHead);
+    }
+
     if cx.editor.mode == Mode::Select {
         cx.editor.mode = Mode::Normal;
     }
@@ -5605,22 +5621,19 @@ where
     let (view, doc) = current!(cx.editor);
     let text = doc.text().slice(..);
 
-    let selection = doc
-        .selection(view.id)
-        .clone()
-        .transform(|range| {
-            let old_anchor = range.anchor;
-            let mut new_range = move_fn(text, range, count);
-
-            new_range.anchor = match cx.editor.mode {
-                // In select mode, use a sticky anchor and move the head only
-                Mode::Select => old_anchor,
-                // When not in select mode, just move the cursor and do not select
-                _ => new_range.head
-            };
+    let selection = doc.selection(view.id).clone().transform(|range| {
+        let old_anchor = range.anchor;
+        let mut new_range = move_fn(text, range, count);
+
+        new_range.anchor = match cx.editor.mode {
+            // In select mode, use a sticky anchor and move the head only
+            Mode::Select => old_anchor,
+            // When not in select mode, just move the cursor and do not select
+            _ => new_range.head,
+        };
 
-            return new_range;
-        });
+        return new_range;
+    });
 
     doc.set_selection(view.id, selection);
 }
diff --git a/helix-term/src/commands/evil.rs b/helix-term/src/commands/evil.rs
index f199c4282..d899c0c86 100644
--- a/helix-term/src/commands/evil.rs
+++ b/helix-term/src/commands/evil.rs
@@ -51,6 +51,14 @@ enum Motion {
     LineEnd,
 }
 
+#[derive(Debug)]
+pub enum CollapseMode {
+    Forward,
+    Backward,
+    ToAnchor,
+    ToHead,
+}
+
 impl TryFrom<char> for Motion {
     type Error = ();
 
@@ -104,6 +112,62 @@ impl EvilCommands {
         true
     }
 
+    /// Collapse selections such that the selections cover one character per cursor only.
+    pub fn collapse_selections(cx: &mut Context, collapse_mode: CollapseMode) {
+        let (view, doc) = current!(cx.editor);
+
+        doc.set_selection(
+            view.id,
+            doc.selection(view.id).clone().transform(|mut range| {
+                log::warn!(
+                    "Adjusting range (mode: {:?}): {} -> {}",
+                    collapse_mode,
+                    range.anchor,
+                    range.head
+                );
+
+                // TODO: when exiting insert mode after appending, we end up on the character _after_ the curson,
+                // while vim returns to the character _before_ the cursor.
+
+                match collapse_mode {
+                    CollapseMode::Forward => {
+                        let end = range.anchor.max(range.head);
+                        range.anchor = 0.max(end - 1);
+                        range.head = end;
+                    }
+                    CollapseMode::Backward => {
+                        let start = range.anchor.min(range.head);
+                        range.anchor = start;
+                        range.head = start + 1;
+                    }
+                    CollapseMode::ToAnchor => {
+                        if range.head > range.anchor {
+                            range.head = range.anchor + 1;
+                        } else {
+                            range.head = 0.max(range.anchor - 1);
+                        }
+                    }
+                    CollapseMode::ToHead => {
+                        if range.head > range.anchor {
+                            range.anchor = 0.max(range.head - 1);
+                        } else {
+                            range.anchor = range.head + 1;
+                        }
+                    }
+                }
+
+                log::warn!(
+                    "- Adjusted range (mode: {:?}): {} -> {}",
+                    collapse_mode,
+                    range.anchor,
+                    range.head
+                );
+
+                return range;
+            }),
+        );
+    }
+
     fn context() -> RwLockReadGuard<'static, EvilContext> {
         return CONTEXT.read().unwrap();
     }