/*
 * Copyright (C)  2022 Kristóf Marussy <kristof@marussy.com>
 *
 * This file is part of Sophie.
 *
 * Sophie is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, version 3.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 *
 * SPDX-License-Identifier: AGPL-3.0-only
 */

import type {
  BackendModule,
  InitOptions,
  ReadCallback,
  Services,
} from 'i18next';
import { debounce } from 'lodash-es';

import getLogger from '../utils/getLogger.js';

import type LocatlizationRepository from './LocalizationRepository.js';

const MISSING_ENTRIES_DEBOUNCE_TIME_MS = 1000;

const log = getLogger('RepositoryBasedI18nBackend');

/**
 * I18next backend for loading translations from a file.
 *
 * Loosely based on [i18next-fs-backend](https://github.com/i18next/i18next-fs-backend),
 * but we shrink bundle size by omitting JSON5 or YAML translation handling.
 * Direct file IO is replaced by the `LocalizationRepository`,
 * which handles platform-specific concerns.
 */
export default class RepositoryBasedI18nBackend
  implements BackendModule<unknown>
{
  type = 'backend' as const;

  private writeQueue: Map<string, Map<string, Map<string, string>>> = new Map();

  private keySeparator: string | false = '.';

  private readonly flushWriteQueueImmediately = () => {
    const savedWriteQueue = this.writeQueue;
    this.writeQueue = new Map();
    savedWriteQueue.forEach((languagesMap, namespace) => {
      languagesMap.forEach((keysMap, language) => {
        this.flushChanges(language, namespace, keysMap).catch((error) => {
          log.error(
            'Cannot write missing',
            language,
            'translations for namespace',
            namespace,
            error,
          );
        });
      });
    });
  };

  private readonly flushWriteQueue = debounce(
    this.flushWriteQueueImmediately,
    MISSING_ENTRIES_DEBOUNCE_TIME_MS,
  );

  constructor(
    private readonly repository: LocatlizationRepository,
    private readonly devMode = false,
  ) {}

  init(
    _services: Services,
    _backendOptions: unknown,
    { keySeparator }: InitOptions,
  ) {
    if (keySeparator !== undefined) {
      this.keySeparator = keySeparator;
    }
  }

  read(language: string, namespace: string, callback: ReadCallback): void {
    const readAsync = async () => {
      const translations = await this.repository.getResourceContents(
        language,
        namespace,
      );
      // eslint-disable-next-line unicorn/no-null -- `i18next` API requires `null`.
      setImmediate(() => callback(null, translations));
    };

    readAsync().catch((error) => {
      log.error(
        'Error while loading',
        language,
        'translations for namespace',
        namespace,
        error,
      );
      const callbackError =
        error instanceof Error
          ? error
          : new Error(`Unknown error: ${JSON.stringify(error)}`);
      /*
        eslint-disable-next-line promise/no-callback-in-promise, unicorn/no-null --
        Converting from promise based API to a callback. `i18next` API requires `null`.
      */
      setImmediate(() => callback(callbackError, null));
    });
  }

  create(
    languages: string[],
    namespace: string,
    key: string,
    fallbackValue: string,
  ): void {
    if (!this.devMode) {
      throw new Error(
        'Refusing to write missing translations in production mode',
      );
    }
    let languagesMapOrUndefined = this.writeQueue.get(namespace);
    if (languagesMapOrUndefined === undefined) {
      languagesMapOrUndefined = new Map();
      this.writeQueue.set(namespace, languagesMapOrUndefined);
    }
    const languagesMap = languagesMapOrUndefined;
    languages.forEach((language) => {
      let keysMap = languagesMap.get(language);
      if (keysMap === undefined) {
        keysMap = new Map();
        languagesMap.set(language, keysMap);
      }
      keysMap.set(key, fallbackValue);
    });
    this.flushWriteQueue();
  }

  /**
   * Flushes new translations to the missing translations file.
   *
   * Will always fails if `devMode` is `false`.
   * If no changes are made to the translations, the file won't be rewritten.
   *
   * @param language The language to add translations for.
   * @param namespace The namespace to add translations for.
   * @param entries The translations to add.
   * @returns A promise that resolves when changes were flushed successfully.
   */
  private async flushChanges(
    language: string,
    namespace: string,
    entries: Map<string, string>,
  ): Promise<void> {
    if (!this.devMode) {
      throw new Error(
        'Refusing to write missing translations in production mode',
      );
    }
    const resourceContents = await this.repository.getMissingResourceContents(
      language,
      namespace,
    );
    const translations =
      typeof resourceContents === 'object' ? resourceContents : {};
    let changed = false;
    entries.forEach((value, key) => {
      const splitKey = this.keySeparator ? key.split(this.keySeparator) : [key];
      let obj = translations;
      /*
        eslint-disable @typescript-eslint/no-unsafe-assignment,
        security/detect-object-injection --
        We need to modify raw objects, because this is the storage format for i18next.
        To mitigate the prototype injection security risk,
        we make sure to only ever run this in development mode.
      */
      for (let i = 0; i < splitKey.length - 1; i += 1) {
        let nextObj = obj[splitKey[i]];
        if (typeof nextObj !== 'object') {
          nextObj = {};
          obj[splitKey[i]] = nextObj;
        }
        obj = nextObj;
      }
      const lastKey = splitKey[splitKey.length - 1];
      if (obj[lastKey] !== value) {
        obj[lastKey] = value;
        changed = true;
      }
      /*
        eslint-enable @typescript-eslint/no-unsafe-assignment,
        security/detect-object-injection
      */
    });
    if (!changed) {
      return;
    }
    await this.repository.setMissingResourceContents(
      language,
      namespace,
      translations,
    );
    log.debug(
      'Wrote',
      entries.size,
      'missing',
      language,
      'translations for namespace',
      namespace,
    );
  }
}