From 9c33b5340ac057a8e2dbe6028b52385346594f3d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bla=C5=BE=20Hrastnik?= <blaz@mxxn.io>
Date: Thu, 4 Feb 2021 19:49:29 +0900
Subject: [PATCH] A dumb "next view" implementation that works.

---
 helix-term/src/commands.rs |  5 +++
 helix-term/src/keymap.rs   |  4 +++
 helix-view/src/tree.rs     | 66 ++++++++++++++++++++++++++++++++++++--
 3 files changed, 72 insertions(+), 3 deletions(-)

diff --git a/helix-term/src/commands.rs b/helix-term/src/commands.rs
index be43159d4..9bd6bb8f5 100644
--- a/helix-term/src/commands.rs
+++ b/helix-term/src/commands.rs
@@ -951,3 +951,8 @@ pub fn completion(cx: &mut Context) {
         // language server client needs to be accessible via a registry of some sort
     }
 }
+
+// view movements
+pub fn next_view(cx: &mut Context) {
+    cx.editor.tree.focus_next()
+}
diff --git a/helix-term/src/keymap.rs b/helix-term/src/keymap.rs
index a27abf09c..efc72b60e 100644
--- a/helix-term/src/keymap.rs
+++ b/helix-term/src/keymap.rs
@@ -190,6 +190,10 @@ pub fn default() -> Keymaps {
 
                 vec![ctrl!('p')] => commands::file_picker,
                 vec![ctrl!('b')] => commands::buffer_picker,
+                vec![Key {
+                    code: KeyCode::Tab,
+                    modifiers: Modifiers::NONE
+                }] => commands::next_view,
             ),
             Mode::Insert => hashmap!(
                 vec![Key {
diff --git a/helix-view/src/tree.rs b/helix-view/src/tree.rs
index 5c583cbd5..a866d6600 100644
--- a/helix-view/src/tree.rs
+++ b/helix-view/src/tree.rs
@@ -95,7 +95,7 @@ impl Tree {
         self.focus = node;
 
         // recalculate all the sizes
-        self.traverse();
+        self.recalculate();
 
         node
     }
@@ -126,10 +126,10 @@ impl Tree {
 
     pub fn resize(&mut self, area: Rect) {
         self.area = area;
-        self.traverse();
+        self.recalculate();
     }
 
-    pub fn traverse(&mut self) {
+    pub fn recalculate(&mut self) {
         self.stack.push((self.root, self.area));
 
         // take the area
@@ -170,4 +170,64 @@ impl Tree {
             }
         }
     }
+
+    pub fn traverse(&self) -> Traverse {
+        Traverse::new(self)
+    }
+
+    pub fn focus_next(&mut self) {
+        // This function is very dumb, but that's because we don't store any parent links.
+        // (we'd be able to go parent.next_sibling() recursively until we find something)
+        // For now that's okay though, since it's unlikely you'll be able to open a large enough
+        // number of splits to notice.
+
+        let iter = self.traverse();
+
+        let mut iter = iter.skip_while(|&(key, _view)| key != self.focus);
+        iter.next(); // take the focused value
+
+        match iter.next() {
+            Some((key, _)) => {
+                self.focus = key;
+            }
+            None => {
+                // extremely crude, take the first item again
+                let (key, _) = self.traverse().next().unwrap();
+                self.focus = key;
+            }
+        }
+    }
+}
+
+pub struct Traverse<'a> {
+    tree: &'a Tree,
+    stack: Vec<Key>, // TODO: reuse the one we use on update
+}
+
+impl<'a> Traverse<'a> {
+    fn new(tree: &'a Tree) -> Self {
+        Self {
+            tree,
+            stack: vec![tree.root],
+        }
+    }
+}
+
+impl<'a> Iterator for Traverse<'a> {
+    type Item = (Key, &'a View);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        loop {
+            let key = self.stack.pop()?;
+
+            let node = &self.tree.nodes[key];
+
+            match node {
+                Node::View(view) => return Some((key, view)),
+                Node::Container(container) => {
+                    self.stack.extend(container.children.iter().rev());
+                }
+            }
+        }
+    }
 }