1 files changed, 155 insertions, 0 deletions
diff --git a/helix-term/src/compositor.rs b/helix-term/src/compositor.rs
new file mode 100644
index 00000000..2e65f02a
--- /dev/null
+++ b/helix-term/src/compositor.rs
@@ -0,0 +1,155 @@
+// Features:
+// Tracks currently focused component which receives all input
+// Event loop is external as opposed to cursive-rs
+// Calls render on the component and translates screen coords to local component coords
+//
+// TODO:
+// Q: where is the Application state stored? do we store it into an external static var?
+// A: probably makes sense to initialize the editor into a `static Lazy<>` global var.
+//
+// Q: how do we composit nested structures? There should be sub-components/views
+//
+// Each component declares it's own size constraints and gets fitted based on it's parent.
+// Q: how does this work with popups?
+// cursive does compositor.screen_mut().add_layer_at(pos::absolute(x, y), <component>)
+
+use crossterm::event::Event;
+use helix_core::Position;
+use smol::Executor;
+use tui::buffer::Buffer as Surface;
+use tui::layout::Rect;
+
+pub type Callback = Box<dyn Fn(&mut Compositor)>;
+
+// --> EventResult should have a callback that takes a context with methods like .popup(),
+// .prompt() etc. That way we can abstract it from the renderer.
+// Q: How does this interact with popups where we need to be able to specify the rendering of the
+// popup?
+// A: It could just take a textarea.
+//
+// If Compositor was specified in the callback that's then problematic because of
+
+// Cursive-inspired
+pub enum EventResult {
+    Ignored,
+    Consumed(Option<Callback>),
+}
+
+use helix_view::{Editor, View};
+// shared with commands.rs
+pub struct Context<'a> {
+    pub editor: &'a mut Editor,
+    pub executor: &'static smol::Executor<'static>,
+}
+
+pub trait Component {
+    /// Process input events, return true if handled.
+    fn handle_event(&mut self, event: Event, ctx: &mut Context) -> EventResult;
+    // , args: ()
+
+    /// Should redraw? Useful for saving redraw cycles if we know component didn't change.
+    fn should_update(&self) -> bool {
+        true
+    }
+
+    fn render(&self, area: Rect, frame: &mut Surface, ctx: &mut Context);
+
+    fn cursor_position(&self, area: Rect, ctx: &mut Context) -> Option<Position> {
+        None
+    }
+}
+
+// struct Editor { };
+
+// For v1:
+// Child views are something each view needs to handle on it's own for now, positioning and sizing
+// options, focus tracking. In practice this is simple: we only will need special solving for
+// splits etc
+
+// impl Editor {
+//     fn render(&mut self, surface: &mut Surface, args: ()) {
+//         // compute x, y, w, h rects for sub-views!
+//         // get surface area
+//         // get constraints for textarea, statusbar
+//         // -> cassowary-rs
+
+//         // first render textarea
+//         // then render statusbar
+//     }
+// }
+
+// usecases to consider:
+// - a single view with subviews (textarea + statusbar)
+// - a popup panel / dialog with it's own interactions
+// - an autocomplete popup that doesn't change focus
+
+//fn main() {
+//    let root = Editor::new();
+//    let compositor = Compositor::new();
+
+//    compositor.push(root);
+
+//    // pos: clip to bottom of screen
+//    compositor.push_at(pos, Prompt::new(
+//        ":",
+//        (),
+//        |input: &str| match input {}
+//    )); // TODO: this Prompt needs to somehow call compositor.pop() on close, but it can't refer to parent
+//    // Cursive solves this by allowing to return a special result on process_event
+//    // that's either Ignore | Consumed(Opt<C>) where C: fn (Compositor) -> ()
+
+//    // TODO: solve popup focus: we want to push autocomplete popups on top of the current layer
+//    // but retain the focus where it was. The popup will also need to update as we type into the
+//    // textarea. It should also capture certain input, such as tab presses etc
+//    //
+//    // 1) This could be faked by the top layer pushing down edits into the previous layer.
+//    // 2) Alternatively,
+//}
+
+pub struct Compositor {
+    layers: Vec<Box<dyn Component>>,
+}
+
+impl Compositor {
+    pub fn new() -> Self {
+        Self { layers: Vec::new() }
+    }
+
+    pub fn push(&mut self, layer: Box<dyn Component>) {
+        self.layers.push(layer);
+    }
+
+    pub fn pop(&mut self) {
+        self.layers.pop();
+    }
+
+    pub fn handle_event(&mut self, event: Event, cx: &mut Context) -> bool {
+        // TODO: custom focus
+        if let Some(layer) = self.layers.last_mut() {
+            return match layer.handle_event(event, cx) {
+                EventResult::Consumed(Some(callback)) => {
+                    callback(self);
+                    true
+                }
+                EventResult::Consumed(None) => true,
+                EventResult::Ignored => false,
+            };
+        }
+        false
+    }
+
+    pub fn render(&self, area: Rect, surface: &mut Surface, cx: &mut Context) {
+        for layer in &self.layers {
+            layer.render(area, surface, cx)
+        }
+    }
+
+    pub fn cursor_position(&self, area: Rect, cx: &mut Context) -> Position {
+        for layer in self.layers.iter().rev() {
+            if let Some(pos) = layer.cursor_position(area, cx) {
+                return pos;
+            }
+        }
+        panic!("No layer returned a position!");
+    }
+}