feat: Implement background shell commands (#14849)

packages/cli/src/ui/hooks/useBackgroundShellManager.ts

@@ -0,0 +1,91 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { useState, useEffect, useMemo } from 'react';
+import { type BackgroundShell } from './shellCommandProcessor.js';
+
+export interface BackgroundShellManagerProps {
+  backgroundShells: Map<number, BackgroundShell>;
+  backgroundShellCount: number;
+  isBackgroundShellVisible: boolean;
+  activePtyId: number | null | undefined;
+  embeddedShellFocused: boolean;
+  setEmbeddedShellFocused: (focused: boolean) => void;
+  terminalHeight: number;
+}
+
+export function useBackgroundShellManager({
+  backgroundShells,
+  backgroundShellCount,
+  isBackgroundShellVisible,
+  activePtyId,
+  embeddedShellFocused,
+  setEmbeddedShellFocused,
+  terminalHeight,
+}: BackgroundShellManagerProps) {
+  const [isBackgroundShellListOpen, setIsBackgroundShellListOpen] =
+    useState(false);
+  const [activeBackgroundShellPid, setActiveBackgroundShellPid] = useState<
+    number | null
+  >(null);
+
+  useEffect(() => {
+    if (backgroundShells.size === 0) {
+      if (activeBackgroundShellPid !== null) {
+        setActiveBackgroundShellPid(null);
+      }
+      if (isBackgroundShellListOpen) {
+        setIsBackgroundShellListOpen(false);
+      }
+    } else if (
+      activeBackgroundShellPid === null ||
+      !backgroundShells.has(activeBackgroundShellPid)
+    ) {
+      // If active shell is closed or none selected, select the first one (last added usually, or just first in iteration)
+      setActiveBackgroundShellPid(backgroundShells.keys().next().value ?? null);
+    }
+  }, [
+    backgroundShells,
+    activeBackgroundShellPid,
+    backgroundShellCount,
+    isBackgroundShellListOpen,
+  ]);
+
+  useEffect(() => {
+    if (embeddedShellFocused) {
+      const hasActiveForegroundShell = !!activePtyId;
+      const hasVisibleBackgroundShell =
+        isBackgroundShellVisible && backgroundShells.size > 0;
+
+      if (!hasActiveForegroundShell && !hasVisibleBackgroundShell) {
+        setEmbeddedShellFocused(false);
+      }
+    }
+  }, [
+    isBackgroundShellVisible,
+    backgroundShells,
+    embeddedShellFocused,
+    backgroundShellCount,
+    activePtyId,
+    setEmbeddedShellFocused,
+  ]);
+
+  const backgroundShellHeight = useMemo(
+    () =>
+      isBackgroundShellVisible && backgroundShells.size > 0
+        ? Math.max(Math.floor(terminalHeight * 0.3), 5)
+        : 0,
+    [isBackgroundShellVisible, backgroundShells.size, terminalHeight],
+  );
+
+  return {
+    isBackgroundShellListOpen,
+    setIsBackgroundShellListOpen,
+    activeBackgroundShellPid,
+    setActiveBackgroundShellPid,
+    backgroundShellHeight,
+  };
+}