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/**
* @license
* Copyright 2025 Google LLC
* SPDX-License-Identifier: Apache-2.0
*/
import { useState, useRef, useCallback } from 'react';
import { HistoryItem } from '../types.js';
// Type for the updater function passed to updateHistoryItem
type HistoryItemUpdater = (
prevItem: HistoryItem,
) => Partial<Omit<HistoryItem, 'id'>>;
export interface UseHistoryManagerReturn {
history: HistoryItem[];
addItem: (itemData: Omit<HistoryItem, 'id'>, baseTimestamp: number) => number; // Returns the generated ID
updateItem: (
id: number,
updates: Partial<Omit<HistoryItem, 'id'>> | HistoryItemUpdater,
) => void;
clearItems: () => void;
loadHistory: (newHistory: HistoryItem[]) => 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 useHistory(): 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 => {
messageIdCounterRef.current += 1;
return baseTimestamp + messageIdCounterRef.current;
}, []);
const loadHistory = useCallback((newHistory: HistoryItem[]) => {
setHistory(newHistory);
}, []);
// Adds a new item to the history state with a unique ID.
const addItem = useCallback(
(itemData: Omit<HistoryItem, 'id'>, baseTimestamp: number): number => {
const id = getNextMessageId(baseTimestamp);
const newItem: HistoryItem = { ...itemData, id } as HistoryItem;
setHistory((prevHistory) => {
if (prevHistory.length > 0) {
const lastItem = prevHistory[prevHistory.length - 1];
// Prevent adding duplicate consecutive user messages
if (
lastItem.type === 'user' &&
newItem.type === 'user' &&
lastItem.text === newItem.text
) {
return prevHistory; // Don't add the duplicate
}
}
return [...prevHistory, newItem];
});
return id; // Return the generated ID (even if not added, to keep signature)
},
[getNextMessageId],
);
/**
* Updates an existing history item identified by its ID.
* @deprecated Prefer not to update history item directly as we are currently
* rendering all history items in <Static /> for performance reasons. Only use
* if ABSOLUTELY NECESSARY
*/
//
const updateItem = useCallback(
(
id: number,
updates: Partial<Omit<HistoryItem, 'id'>> | HistoryItemUpdater,
) => {
setHistory((prevHistory) =>
prevHistory.map((item) => {
if (item.id === id) {
// Apply updates based on whether it's an object or a function
const newUpdates =
typeof updates === 'function' ? updates(item) : updates;
return { ...item, ...newUpdates } as HistoryItem;
}
return item;
}),
);
},
[],
);
// Clears the entire history state and resets the ID counter.
const clearItems = useCallback(() => {
setHistory([]);
messageIdCounterRef.current = 0;
}, []);
return {
history,
addItem,
updateItem,
clearItems,
loadHistory,
};
}
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