feat(cli): add useHistoryManager hook for chat history (#234)

Co-authored-by: Brandon Keiji <brandonkeiji@google.com>

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

@@ -0,0 +1,70 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { useState, useRef, useCallback } from 'react';
+import { HistoryItem } from '../types.js';
+
+export interface UseHistoryManagerReturn {
+  history: HistoryItem[];
+  addItemToHistory: (
+    itemData: Omit<HistoryItem, 'id'>,
+    baseTimestamp: number,
+  ) => number; // Return the ID of the added item
+  updateHistoryItem: (
+    id: number,
+    updates: Partial<Omit<HistoryItem, 'id'>>,
+  ) => void;
+  clearHistory: () => void;
+}
+
+/**
+ * Custom hook to manage the chat history state.
+ *
+ * Encapsulates the history array, message ID generation, adding items,
+ * updating items, and clearing the history.
+ */
+export function useHistoryManager(): UseHistoryManagerReturn {
+  const [history, setHistory] = useState<HistoryItem[]>([]);
+  const messageIdCounterRef = useRef(0);
+
+  // Generates a unique message ID based on a timestamp and a counter.
+  const getNextMessageId = useCallback((baseTimestamp: number): number => {
+    // Increment *before* adding to ensure uniqueness against the base timestamp
+    messageIdCounterRef.current += 1;
+    return baseTimestamp + messageIdCounterRef.current;
+  }, []);
+
+  // Adds a new item to the history state with a unique ID and returns the ID.
+  const addItemToHistory = useCallback(
+    (itemData: Omit<HistoryItem, 'id'>, baseTimestamp: number): number => {
+      const id = getNextMessageId(baseTimestamp);
+      const newItem: HistoryItem = { ...itemData, id } as HistoryItem;
+      setHistory((prevHistory) => [...prevHistory, newItem]);
+      return id; // Return the generated ID
+    },
+    [getNextMessageId],
+  );
+
+  // Updates an existing history item identified by its ID.
+  const updateHistoryItem = useCallback(
+    (id: number, updates: Partial<Omit<HistoryItem, 'id'>>) => {
+      setHistory((prevHistory) =>
+        prevHistory.map((item) =>
+          item.id === id ? ({ ...item, ...updates } as HistoryItem) : item,
+        ),
+      );
+    },
+    [],
+  );
+
+  // Clears the entire history state.
+  const clearHistory = useCallback(() => {
+    setHistory([]);
+    messageIdCounterRef.current = 0; // Reset counter when history is cleared
+  }, []);
+
+  return { history, addItemToHistory, updateHistoryItem, clearHistory };
+}