Refactor useGeminiStream to pull slash commands and passthrough comma… (#215)

* Refactor useGeminiStream to pull slash commands and passthrough commands into their own processors.

* whitespace lint errors.

* Add sugestions from code review.

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

@@ -0,0 +1,110 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { useCallback } from 'react';
+import { type PartListUnion } from '@google/genai';
+import { HistoryItem } from '../types.js';
+import { isSlashCommand } from '../utils/commandUtils.js';
+
+interface SlashCommand {
+  name: string; // slash command
+  description: string; // flavor text in UI
+  action: (value: PartListUnion) => void;
+}
+
+const addHistoryItem = (
+  setHistory: React.Dispatch<React.SetStateAction<HistoryItem[]>>,
+  itemData: Omit<HistoryItem, 'id'>,
+  id: number,
+) => {
+  setHistory((prevHistory) => [
+    ...prevHistory,
+    { ...itemData, id } as HistoryItem,
+  ]);
+};
+
+export const useSlashCommandProcessor = (
+  setHistory: React.Dispatch<React.SetStateAction<HistoryItem[]>>,
+  setDebugMessage: React.Dispatch<React.SetStateAction<string>>,
+  getNextMessageId: (baseTimestamp: number) => number,
+) => {
+  const slashCommands: SlashCommand[] = [
+    {
+      name: 'clear',
+      description: 'clear the screen',
+      action: (_value: PartListUnion) => {
+        // This just clears the *UI* history, not the model history.
+        setDebugMessage('Clearing terminal.');
+        setHistory((_) => []);
+      },
+    },
+    {
+      name: 'exit',
+      description: 'Exit gemini-code',
+      action: (_value: PartListUnion) => {
+        setDebugMessage('Exiting. Good-bye.');
+        const timestamp = getNextMessageId(Date.now());
+        addHistoryItem(
+          setHistory,
+          { type: 'info', text: 'good-bye!' },
+          timestamp,
+        );
+        process.exit(0);
+      },
+    },
+    {
+      // TODO: dedup with exit by adding altName or cmdRegex.
+      name: 'quit',
+      description: 'Quit gemini-code',
+      action: (_value: PartListUnion) => {
+        setDebugMessage('Quitting. Good-bye.');
+        const timestamp = getNextMessageId(Date.now());
+        addHistoryItem(
+          setHistory,
+          { type: 'info', text: 'good-bye!' },
+          timestamp,
+        );
+        process.exit(0);
+      },
+    },
+    // Removed /theme command, handled in App.tsx
+  ];
+
+  // Checks if the query is a slash command and executes it if it is.
+  const handleSlashCommand = useCallback(
+    (rawQuery: PartListUnion): boolean => {
+      if (typeof rawQuery !== 'string') {
+        return false;
+      }
+
+      const trimmedQuery = rawQuery.trim();
+      if (!isSlashCommand(trimmedQuery)) {
+        return false; // Not a slash command
+      }
+
+      const commandName = trimmedQuery.slice(1).split(/\s+/)[0]; // Get command name after '/'
+
+      for (const cmd of slashCommands) {
+        if (commandName === cmd.name) {
+          // Add user message *before* execution
+          const userMessageTimestamp = Date.now();
+          addHistoryItem(
+            setHistory,
+            { type: 'user', text: trimmedQuery },
+            userMessageTimestamp,
+          );
+          cmd.action(trimmedQuery);
+          return true; // Command was handled
+        }
+      }
+
+      return false; // Not a recognized slash command
+    },
+    [setDebugMessage, setHistory, getNextMessageId, slashCommands],
+  );
+
+  return { handleSlashCommand };
+};