Implement the event stream IPC

3 files changed, 301 insertions, 3 deletions

diff --git a/niri-ipc/src/lib.rs b/niri-ipc/src/lib.rs
index ecf202f2..e6058ca1 100644
--- a/niri-ipc/src/lib.rs
+++ b/niri-ipc/src/lib.rs
@@ -9,6 +9,8 @@ use serde::{Deserialize, Serialize};
 mod socket;
 pub use socket::{Socket, SOCKET_PATH_ENV};
 
+pub mod state;
+
 /// Request from client to niri.
 #[derive(Debug, Serialize, Deserialize, Clone)]
 #[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
@@ -38,6 +40,11 @@ pub enum Request {
     FocusedOutput,
     /// Request information about the keyboard layout.
     KeyboardLayouts,
+    /// Start continuously receiving events from the compositor.
+    ///
+    /// The compositor should reply with `Reply::Ok(Response::Handled)`, then continuously send
+    /// [`Event`]s, one per line.
+    EventStream,
     /// Respond with an error (for testing error handling).
     ReturnError,
 }
@@ -536,10 +543,18 @@ pub enum Transform {
 #[derive(Serialize, Deserialize, Debug, Clone)]
 #[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 pub struct Window {
+    /// Unique id of this window.
+    pub id: u64,
     /// Title, if set.
     pub title: Option<String>,
     /// Application ID, if set.
     pub app_id: Option<String>,
+    /// Id of the workspace this window is on, if any.
+    pub workspace_id: Option<u64>,
+    /// Whether this window is currently focused.
+    ///
+    /// There can be either one focused window or zero (e.g. when a layer-shell surface has focus).
+    pub is_focused: bool,
 }
 
 /// Output configuration change result.
@@ -556,6 +571,10 @@ pub enum OutputConfigChanged {
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq)]
 #[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
 pub struct Workspace {
+    /// Unique id of this workspace.
+    ///
+    /// This id remains constant regardless of the workspace moving around and across monitors.
+    pub id: u64,
     /// Index of the workspace on its monitor.
     ///
     /// This is the same index you can use for requests like `niri msg action focus-workspace`.
@@ -567,7 +586,15 @@ pub struct Workspace {
     /// Can be `None` if no outputs are currently connected.
     pub output: Option<String>,
     /// Whether the workspace is currently active on its output.
+    ///
+    /// Every output has one active workspace, the one that is currently visible on that output.
     pub is_active: bool,
+    /// Whether the workspace is currently focused.
+    ///
+    /// There's only one focused workspace across all outputs.
+    pub is_focused: bool,
+    /// Id of the active window on this workspace, if any.
+    pub active_window_id: Option<u64>,
 }
 
 /// Configured keyboard layouts.
@@ -580,6 +607,77 @@ pub struct KeyboardLayouts {
     pub current_idx: u8,
 }
 
+/// A compositor event.
+#[derive(Serialize, Deserialize, Debug, Clone)]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
+pub enum Event {
+    /// The workspace configuration has changed.
+    WorkspacesChanged {
+        /// The new workspace configuration.
+        ///
+        /// This configuration completely replaces the previous configuration. I.e. if any
+        /// workspaces are missing from here, then they were deleted.
+        workspaces: Vec<Workspace>,
+    },
+    /// A workspace was activated on an output.
+    ///
+    /// This doesn't always mean the workspace became focused, just that it's now the active
+    /// workspace on its output. All other workspaces on the same output become inactive.
+    WorkspaceActivated {
+        /// Id of the newly active workspace.
+        id: u64,
+        /// Whether this workspace also became focused.
+        ///
+        /// If `true`, this is now the single focused workspace. All other workspaces are no longer
+        /// focused, but they may remain active on their respective outputs.
+        focused: bool,
+    },
+    /// An active window changed on a workspace.
+    WorkspaceActiveWindowChanged {
+        /// Id of the workspace on which the active window changed.
+        workspace_id: u64,
+        /// Id of the new active window, if any.
+        active_window_id: Option<u64>,
+    },
+    /// The window configuration has changed.
+    WindowsChanged {
+        /// The new window configuration.
+        ///
+        /// This configuration completely replaces the previous configuration. I.e. if any windows
+        /// are missing from here, then they were closed.
+        windows: Vec<Window>,
+    },
+    /// A new toplevel window was opened, or an existing toplevel window changed.
+    WindowOpenedOrChanged {
+        /// The new or updated window.
+        ///
+        /// If the window is focused, all other windows are no longer focused.
+        window: Window,
+    },
+    /// A toplevel window was closed.
+    WindowClosed {
+        /// Id of the removed window.
+        id: u64,
+    },
+    /// Window focus changed.
+    ///
+    /// All other windows are no longer focused.
+    WindowFocusChanged {
+        /// Id of the newly focused window, or `None` if no window is now focused.
+        id: Option<u64>,
+    },
+    /// The configured keyboard layouts have changed.
+    KeyboardLayoutsChanged {
+        /// The new keyboard layout configuration.
+        keyboard_layouts: KeyboardLayouts,
+    },
+    /// The keyboard layout switched.
+    KeyboardLayoutSwitched {
+        /// Index of the newly active layout.
+        idx: u8,
+    },
+}
+
 impl FromStr for WorkspaceReferenceArg {
     type Err = &'static str;
 
diff --git a/niri-ipc/src/socket.rs b/niri-ipc/src/socket.rs
index 3964f000..d629f1a4 100644
--- a/niri-ipc/src/socket.rs
+++ b/niri-ipc/src/socket.rs
@@ -6,7 +6,7 @@ use std::net::Shutdown;
 use std::os::unix::net::UnixStream;
 use std::path::Path;
 
-use crate::{Reply, Request};
+use crate::{Event, Reply, Request};
 
 /// Name of the environment variable containing the niri IPC socket path.
 pub const SOCKET_PATH_ENV: &str = "NIRI_SOCKET";
@@ -47,7 +47,11 @@ impl Socket {
     /// * `Ok(Ok(response))`: successful [`Response`](crate::Response) from niri
     /// * `Ok(Err(message))`: error message from niri
     /// * `Err(error)`: error communicating with niri
-    pub fn send(self, request: Request) -> io::Result<Reply> {
+    ///
+    /// This method also returns a blocking function that you can call to keep reading [`Event`]s
+    /// after requesting an [`EventStream`][Request::EventStream]. This function is not useful
+    /// otherwise.
+    pub fn send(self, request: Request) -> io::Result<(Reply, impl FnMut() -> io::Result<Event>)> {
         let Self { mut stream } = self;
 
         let mut buf = serde_json::to_string(&request).unwrap();
@@ -60,6 +64,14 @@ impl Socket {
         reader.read_line(&mut buf)?;
 
         let reply = serde_json::from_str(&buf)?;
-        Ok(reply)
+
+        let events = move || {
+            buf.clear();
+            reader.read_line(&mut buf)?;
+            let event = serde_json::from_str(&buf)?;
+            Ok(event)
+        };
+
+        Ok((reply, events))
     }
 }
diff --git a/niri-ipc/src/state.rs b/niri-ipc/src/state.rs
new file mode 100644
index 00000000..8d2d1744
--- /dev/null
+++ b/niri-ipc/src/state.rs
@@ -0,0 +1,188 @@
+//! Helpers for keeping track of the event stream state.
+
+use std::collections::hash_map::Entry;
+use std::collections::HashMap;
+
+use crate::{Event, KeyboardLayouts, Window, Workspace};
+
+/// Part of the state communicated via the event stream.
+pub trait EventStreamStatePart {
+    /// Returns a sequence of events that replicates this state from default initialization.
+    fn replicate(&self) -> Vec<Event>;
+
+    /// Applies the event to this state.
+    ///
+    /// Returns `None` after applying the event, and `Some(event)` if the event is ignored by this
+    /// part of the state.
+    fn apply(&mut self, event: Event) -> Option<Event>;
+}
+
+/// The full state communicated over the event stream.
+///
+/// Different parts of the state are not guaranteed to be consistent across every single event
+/// sent by niri. For example, you may receive the first [`Event::WindowOpenedOrChanged`] for a
+/// just-opened window *after* an [`Event::WorkspaceActiveWindowChanged`] for that window. Between
+/// these two events, the workspace active window id refers to a window that does not yet exist in
+/// the windows state part.
+#[derive(Debug, Default)]
+pub struct EventStreamState {
+    /// State of workspaces.
+    pub workspaces: WorkspacesState,
+
+    /// State of workspaces.
+    pub windows: WindowsState,
+
+    /// State of the keyboard layouts.
+    pub keyboard_layouts: KeyboardLayoutsState,
+}
+
+/// The workspaces state communicated over the event stream.
+#[derive(Debug, Default)]
+pub struct WorkspacesState {
+    /// Map from a workspace id to the workspace.
+    pub workspaces: HashMap<u64, Workspace>,
+}
+
+/// The windows state communicated over the event stream.
+#[derive(Debug, Default)]
+pub struct WindowsState {
+    /// Map from a window id to the window.
+    pub windows: HashMap<u64, Window>,
+}
+
+/// The keyboard layout state communicated over the event stream.
+#[derive(Debug, Default)]
+pub struct KeyboardLayoutsState {
+    /// Configured keyboard layouts.
+    pub keyboard_layouts: Option<KeyboardLayouts>,
+}
+
+impl EventStreamStatePart for EventStreamState {
+    fn replicate(&self) -> Vec<Event> {
+        let mut events = Vec::new();
+        events.extend(self.workspaces.replicate());
+        events.extend(self.windows.replicate());
+        events.extend(self.keyboard_layouts.replicate());
+        events
+    }
+
+    fn apply(&mut self, event: Event) -> Option<Event> {
+        let event = self.workspaces.apply(event)?;
+        let event = self.windows.apply(event)?;
+        let event = self.keyboard_layouts.apply(event)?;
+        Some(event)
+    }
+}
+
+impl EventStreamStatePart for WorkspacesState {
+    fn replicate(&self) -> Vec<Event> {
+        let workspaces = self.workspaces.values().cloned().collect();
+        vec![Event::WorkspacesChanged { workspaces }]
+    }
+
+    fn apply(&mut self, event: Event) -> Option<Event> {
+        match event {
+            Event::WorkspacesChanged { workspaces } => {
+                self.workspaces = workspaces.into_iter().map(|ws| (ws.id, ws)).collect();
+            }
+            Event::WorkspaceActivated { id, focused } => {
+                let ws = self.workspaces.get(&id);
+                let ws = ws.expect("activated workspace was missing from the map");
+                let output = ws.output.clone();
+
+                for ws in self.workspaces.values_mut() {
+                    let got_activated = ws.id == id;
+                    if ws.output == output {
+                        ws.is_active = got_activated;
+                    }
+
+                    if focused {
+                        ws.is_focused = got_activated;
+                    }
+                }
+            }
+            Event::WorkspaceActiveWindowChanged {
+                workspace_id,
+                active_window_id,
+            } => {
+                let ws = self.workspaces.get_mut(&workspace_id);
+                let ws = ws.expect("changed workspace was missing from the map");
+                ws.active_window_id = active_window_id;
+            }
+            event => return Some(event),
+        }
+        None
+    }
+}
+
+impl EventStreamStatePart for WindowsState {
+    fn replicate(&self) -> Vec<Event> {
+        let windows = self.windows.values().cloned().collect();
+        vec![Event::WindowsChanged { windows }]
+    }
+
+    fn apply(&mut self, event: Event) -> Option<Event> {
+        match event {
+            Event::WindowsChanged { windows } => {
+                self.windows = windows.into_iter().map(|win| (win.id, win)).collect();
+            }
+            Event::WindowOpenedOrChanged { window } => {
+                let (id, is_focused) = match self.windows.entry(window.id) {
+                    Entry::Occupied(mut entry) => {
+                        let entry = entry.get_mut();
+                        *entry = window;
+                        (entry.id, entry.is_focused)
+                    }
+                    Entry::Vacant(entry) => {
+                        let entry = entry.insert(window);
+                        (entry.id, entry.is_focused)
+                    }
+                };
+
+                if is_focused {
+                    for win in self.windows.values_mut() {
+                        if win.id != id {
+                            win.is_focused = false;
+                        }
+                    }
+                }
+            }
+            Event::WindowClosed { id } => {
+                let win = self.windows.remove(&id);
+                win.expect("closed window was missing from the map");
+            }
+            Event::WindowFocusChanged { id } => {
+                for win in self.windows.values_mut() {
+                    win.is_focused = Some(win.id) == id;
+                }
+            }
+            event => return Some(event),
+        }
+        None
+    }
+}
+
+impl EventStreamStatePart for KeyboardLayoutsState {
+    fn replicate(&self) -> Vec<Event> {
+        if let Some(keyboard_layouts) = self.keyboard_layouts.clone() {
+            vec![Event::KeyboardLayoutsChanged { keyboard_layouts }]
+        } else {
+            vec![]
+        }
+    }
+
+    fn apply(&mut self, event: Event) -> Option<Event> {
+        match event {
+            Event::KeyboardLayoutsChanged { keyboard_layouts } => {
+                self.keyboard_layouts = Some(keyboard_layouts);
+            }
+            Event::KeyboardLayoutSwitched { idx } => {
+                let kb = self.keyboard_layouts.as_mut();
+                let kb = kb.expect("keyboard layouts must be set before a layout can be switched");
+                kb.current_idx = idx;
+            }
+            event => return Some(event),
+        }
+        None
+    }
+}