readest/apps/readest-app/src/pages/api/deepl/translate.ts

import crypto from 'crypto';
import { NextApiRequest, NextApiResponse } from 'next';
import { corsAllMethods, runMiddleware } from '@/utils/cors';
import { getCloudflareContext } from '@opennextjs/cloudflare';
import { getDailyTranslationPlanData, getUserPlan, validateUserAndToken } from '@/utils/access';
import { ErrorCodes } from '@/services/translators';

const DEFAULT_DEEPL_FREE_API = 'https://api-free.deepl.com/v2/translate';
const DEFAULT_DEEPL_PRO_API = 'https://api.deepl.com/v2/translate';

interface KVNamespace {
  get(key: string): Promise<string | null>;
  put(key: string, value: string, options?: { expirationTtl?: number }): Promise<void>;
  delete(key: string): Promise<void>;
}

interface CloudflareEnv {
  TRANSLATIONS_KV?: KVNamespace;
}

const LANG_V2_V1_MAP: Record<string, string> = {
  'ZH-HANS': 'ZH',
  'ZH-HANT': 'ZH-TW',
};

const getDeepLAPIKey = (keys: string | undefined) => {
  const keyArray = keys?.split(',') ?? [];
  return keyArray.length ? keyArray[Math.floor(Math.random() * keyArray.length)]! : '';
};

const generateCacheKey = (text: string, sourceLang: string, targetLang: string): string => {
  const inputString = `${sourceLang}:${targetLang}:${text}`;
  const hash = crypto.createHash('sha1').update(inputString).digest('hex');
  return `tr:${hash}`;
};

const getDailyUsageKey = (userId?: string, token?: string) => {
  let dailyUsageKey = '';
  if (userId && token) {
    const currentDate = new Date().toISOString().split('T')[0]!;
    dailyUsageKey = `daily_usage:${currentDate}:${userId}`;
  }
  return dailyUsageKey;
};

const checkDailyUsage = async (
  userId: string,
  token: string,
  chars: number,
  translationsKV?: KVNamespace,
) => {
  const usageKey = getDailyUsageKey(userId, token);
  const dailyUsage = (await translationsKV?.get(usageKey)) || '0';
  const { quota: dailyQuota } = getDailyTranslationPlanData(token);
  const dailyUsageChars = parseInt(dailyUsage);
  if (dailyQuota <= dailyUsageChars + chars) {
    throw new Error(ErrorCodes.DAILY_QUOTA_EXCEEDED);
  }
  return dailyUsageChars;
};

const updateDailyUsage = async (
  userId: string | undefined,
  token: string | undefined,
  newUsage: number,
  translationsKV?: KVNamespace,
) => {
  const usageKey = getDailyUsageKey(userId, token);
  if (!usageKey) return 0;

  try {
    const dailyUsage = (await translationsKV?.get(usageKey)) || '0';
    const newDailyUsage = parseInt(dailyUsage) + newUsage;
    await translationsKV?.put(usageKey, newDailyUsage.toString(), {
      expirationTtl: 86400 * 30,
    });
    return newDailyUsage;
  } catch (cacheError) {
    console.error('Update daily usage error:', cacheError);
  }

  return 0;
};

const handler = async (req: NextApiRequest, res: NextApiResponse) => {
  await runMiddleware(req, res, corsAllMethods);

  if (req.method !== 'POST') {
    return res.status(405).json({ error: 'Method not allowed' });
  }

  const env = (getCloudflareContext().env || {}) as CloudflareEnv;
  const hasKVCache = !!env['TRANSLATIONS_KV'];

  const { user, token } = await validateUserAndToken(req.headers['authorization']);
  const { DEEPL_PRO_API, DEEPL_FREE_API } = process.env;
  const deepFreeApiUrl = DEEPL_FREE_API || DEFAULT_DEEPL_FREE_API;
  const deeplProApiUrl = DEEPL_PRO_API || DEFAULT_DEEPL_PRO_API;

  let deeplApiUrl = deepFreeApiUrl;
  let userPlan = 'free';
  if (user && token) {
    userPlan = getUserPlan(token);
    if (userPlan === 'pro') deeplApiUrl = deeplProApiUrl;
  }
  const deeplAuthKey =
    deeplApiUrl === deeplProApiUrl
      ? getDeepLAPIKey(process.env['DEEPL_PRO_API_KEYS'])
      : getDeepLAPIKey(process.env['DEEPL_FREE_API_KEYS']);

  const {
    text,
    source_lang: sourceLang = 'AUTO',
    target_lang: targetLang = 'EN',
    use_cache: useCache = false,
  }: { text: string[]; source_lang: string; target_lang: string; use_cache: boolean } = req.body;

  try {
    const translations = await Promise.all(
      text.map(async (singleText) => {
        if (!singleText?.trim()) {
          return { text: '', daily_usage: 0 };
        }
        if (useCache && hasKVCache) {
          try {
            const cacheKey = generateCacheKey(singleText, sourceLang, targetLang);
            const cachedTranslation = await env['TRANSLATIONS_KV']!.get(cacheKey);

            if (cachedTranslation) {
              return {
                text: cachedTranslation,
                daily_usage: 0,
                detected_source_language: sourceLang,
              };
            }
          } catch (cacheError) {
            console.error('Cache retrieval error:', cacheError);
          }
        }

        if (!user || !token) return res.status(401).json({ error: ErrorCodes.UNAUTHORIZED });
        await checkDailyUsage(user?.id, token, singleText.length, env['TRANSLATIONS_KV']);

        return await callDeepLAPI(
          singleText,
          sourceLang,
          targetLang,
          deeplApiUrl,
          deeplAuthKey,
          env['TRANSLATIONS_KV'],
          useCache,
        );
      }),
    );
    const originalCharsCount = text.reduce((a, b) => a + b.length, 0);
    const translatedCharsCount = translations.reduce((a, b) => a + (b?.text.length || 0), 0);
    const newDailyUsage = await updateDailyUsage(
      user?.id,
      token,
      originalCharsCount + translatedCharsCount,
      env['TRANSLATIONS_KV'],
    );
    translations.forEach((translation) => {
      if (translation && translation.text) {
        translation.daily_usage = newDailyUsage;
      }
    });
    return res.status(200).json({ translations });
  } catch (error) {
    console.error('Error proxying DeepL request:', error);
    if (error instanceof Error && error.message.includes(ErrorCodes.DAILY_QUOTA_EXCEEDED)) {
      return res.status(429).json({ error: ErrorCodes.DAILY_QUOTA_EXCEEDED });
    }
    return res.status(500).json({ error: ErrorCodes.INTERNAL_SERVER_ERROR });
  }
};

async function callDeepLAPI(
  text: string,
  sourceLang: string,
  targetLang: string,
  apiUrl: string,
  authKey: string,
  translationsKV: KVNamespace | undefined,
  useCache: boolean,
) {
  const isV2Api = apiUrl.endsWith('/v2/translate');

  // TODO: this should be processed in the client, but for now, we need to do it here
  // please remove this when most clients are updated
  const input = text.replaceAll('\n', '').trim();
  const requestBody = {
    text: isV2Api ? [input] : input,
    source_lang: isV2Api ? sourceLang : (LANG_V2_V1_MAP[sourceLang] ?? sourceLang),
    target_lang: isV2Api ? targetLang : (LANG_V2_V1_MAP[targetLang] ?? targetLang),
  };

  const response = await fetch(apiUrl, {
    method: 'POST',
    headers: {
      Authorization: `DeepL-Auth-Key ${authKey}`,
      'x-fingerprint': process.env['DEEPL_X_FINGERPRINT'] || '',
      'Content-Type': 'application/json',
    },
    body: JSON.stringify(requestBody),
  });

  if (!response.ok) {
    const errorText = await response.text();
    throw new Error(`DeepL API error (${response.status}): ${errorText}`);
  }

  const data = (await response.json()) as {
    translations?: { text: string; detected_source_language?: string }[];
    data?: string;
  };

  let translatedText = '';
  let detectedSourceLanguage = '';

  if (data.translations && data.translations.length > 0) {
    translatedText = data.translations[0]!.text;
    detectedSourceLanguage = data.translations[0]!.detected_source_language || '';
  } else if (data.data) {
    translatedText = data.data;
  }

  if (useCache && translationsKV && translatedText) {
    try {
      const cacheKey = generateCacheKey(text, sourceLang, targetLang);
      await translationsKV.put(cacheKey, translatedText, { expirationTtl: 86400 * 90 });
    } catch (cacheError) {
      console.error('Cache storage error:', cacheError);
    }
  }

  return {
    text: translatedText,
    daily_usage: 0,
    detected_source_language: detectedSourceLanguage,
  };
}

export default handler;