[Init] Initial commit - NetMesh terminal manager

application/state/terminalKeyboardFocus.ts

@@ -0,0 +1,98 @@
+const TERMINAL_KEYBOARD_TARGET_SELECTOR =
+  ".xterm, .xterm-helper-textarea, .xterm-screen, .xterm-viewport";
+
+type FocusDocument = Pick<Document, "activeElement" | "addEventListener" | "removeEventListener">;
+type FocusWindow = Pick<Window, "addEventListener" | "removeEventListener">;
+
+export const isTerminalKeyboardTarget = (target: EventTarget | null): boolean => {
+  const element = target as (Element & {
+    closest?: (selector: string) => Element | null;
+  }) | null;
+  return Boolean(element?.closest?.(TERMINAL_KEYBOARD_TARGET_SELECTOR));
+};
+
+export function installTerminalKeyboardFocusTracking(
+  documentRef: FocusDocument,
+  windowRef: FocusWindow,
+  onFocusChange: (focused: boolean) => void,
+): () => void {
+  let pendingPointerTarget: EventTarget | null | undefined;
+  let pendingPointerClearTimer: ReturnType<typeof setTimeout> | undefined;
+  let isTracking = true;
+  let windowFocused = true;
+
+  const clearPendingPointerTarget = () => {
+    if (pendingPointerClearTimer !== undefined) {
+      clearTimeout(pendingPointerClearTimer);
+      pendingPointerClearTimer = undefined;
+    }
+    pendingPointerTarget = undefined;
+  };
+
+  const publishForTarget = (target: EventTarget | null) => {
+    if (!isTracking) return;
+    onFocusChange(windowFocused && isTerminalKeyboardTarget(target));
+  };
+
+  const handlePointerDown = (event: Event) => {
+    clearPendingPointerTarget();
+    pendingPointerTarget = event.target;
+    pendingPointerClearTimer = setTimeout(() => {
+      const pointerTarget = pendingPointerTarget;
+      clearPendingPointerTarget();
+      if (pointerTarget !== undefined) {
+        publishForTarget(documentRef.activeElement);
+      }
+    }, 0);
+  };
+
+  const handleFocusIn = (event: Event) => {
+    clearPendingPointerTarget();
+    publishForTarget(event.target);
+  };
+
+  const handleFocusOut = () => {
+    queueMicrotask(() => {
+      if (!isTracking) return;
+      const pointerTarget = pendingPointerTarget;
+      clearPendingPointerTarget();
+      if (!windowFocused) {
+        onFocusChange(false);
+        return;
+      }
+      if (pointerTarget !== undefined) {
+        publishForTarget(documentRef.activeElement);
+        return;
+      }
+      publishForTarget(documentRef.activeElement);
+    });
+  };
+
+  const handleWindowBlur = () => {
+    windowFocused = false;
+    clearPendingPointerTarget();
+    onFocusChange(false);
+  };
+
+  const handleWindowFocus = () => {
+    windowFocused = true;
+    publishForTarget(documentRef.activeElement);
+  };
+
+  publishForTarget(documentRef.activeElement);
+  documentRef.addEventListener("pointerdown", handlePointerDown, true);
+  documentRef.addEventListener("focusin", handleFocusIn, true);
+  documentRef.addEventListener("focusout", handleFocusOut, true);
+  windowRef.addEventListener("blur", handleWindowBlur);
+  windowRef.addEventListener("focus", handleWindowFocus);
+
+  return () => {
+    isTracking = false;
+    documentRef.removeEventListener("pointerdown", handlePointerDown, true);
+    documentRef.removeEventListener("focusin", handleFocusIn, true);
+    documentRef.removeEventListener("focusout", handleFocusOut, true);
+    windowRef.removeEventListener("blur", handleWindowBlur);
+    windowRef.removeEventListener("focus", handleWindowFocus);
+    clearPendingPointerTarget();
+  };
+}