/*
 * Copyright (C)  2021-2022 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 deepEqual from 'deep-equal';
import { debounce } from 'lodash-es';
import { reaction } from 'mobx';
import ms from 'ms';

import type ConfigPersistence from '../infrastructure/ConfigPersistence';
import { Config, SharedStore } from '../stores/SharedStore';
import type Disposer from '../utils/Disposer';
import { getLogger } from '../utils/log';

const DEFAULT_CONFIG_DEBOUNCE_TIME = ms('1s');

const log = getLogger('config');

export default async function initConfig(
  sharedStore: SharedStore,
  persistenceService: ConfigPersistence,
  debounceTime: number = DEFAULT_CONFIG_DEBOUNCE_TIME,
): Promise<Disposer> {
  log.trace('Initializing config controller');

  let lastConfigOnDisk: Config | undefined;

  async function writeConfig(): Promise<void> {
    const { config } = sharedStore;
    await persistenceService.writeConfig(config);
    lastConfigOnDisk = config;
  }

  async function readConfig(): Promise<boolean> {
    const result = await persistenceService.readConfig();
    if (result.found) {
      try {
        // This cast is unsound if the config file is invalid,
        // but we'll throw an error in the end anyways.
        sharedStore.loadConfig(result.data as Config);
      } catch (error) {
        log.error('Failed to apply config snapshot', result.data, error);
        return true;
      }
      lastConfigOnDisk = sharedStore.config;
      if (!deepEqual(result.data, lastConfigOnDisk, { strict: true })) {
        await writeConfig();
      }
    }
    return result.found;
  }

  if (!(await readConfig())) {
    log.info('Config file was not found');
    await writeConfig();
    log.info('Created config file');
  }

  const disposeReaction = reaction(
    () => sharedStore.config,
    debounce((config) => {
      // We can compare snapshots by reference, since it is only recreated on store changes.
      if (lastConfigOnDisk !== config) {
        writeConfig().catch((error) => {
          log.error('Failed to write config on config change', error);
        });
      }
    }, debounceTime),
  );

  const disposeWatcher = persistenceService.watchConfig(async () => {
    try {
      await readConfig();
    } catch (error) {
      log.error('Failed to read config', error);
    }
  }, debounceTime);

  return () => {
    log.trace('Disposing config controller');
    disposeWatcher();
    disposeReaction();
  };
}