/*
 * 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 { watch } from 'fs';
import { readFile, stat, writeFile } from 'fs/promises';
import JSON5 from 'json5';
import { throttle } from 'lodash';
import { IDisposer } from 'mobx-state-tree';
import { join } from 'path';

import type { ConfigSnapshotOut } from  '../stores/Config';

export type ReadConfigResult = { found: true; data: unknown; } | { found: false; };

export class ConfigPersistenceService {
  readonly #userDataDir: string;

  readonly #configFileName: string;

  readonly #configFilePath: string;

  constructor(
    userDataDir: string,
    configFileName: string,
  ) {
    this.#userDataDir = userDataDir;
    this.#configFileName = configFileName;
    this.#configFilePath = join(this.#userDataDir, this.#configFileName);
  }

  async readConfig(): Promise<ReadConfigResult> {
    let configStr;
    try {
      configStr = await readFile(this.#configFilePath, 'utf8');
    } catch (err) {
      if ((err as NodeJS.ErrnoException).code === 'ENOENT') {
        return { found: false };
      }
      throw err;
    }
    return {
      found: true,
      data: JSON5.parse(configStr),
    };
  }

  async writeConfig(configSnapshot: ConfigSnapshotOut): Promise<Date> {
    const configJson = JSON5.stringify(configSnapshot, {
      space: 2,
    });
    await writeFile(this.#configFilePath, configJson, 'utf8');
    const { mtime } = await stat(this.#configFilePath);
    return mtime;
  }

  watchConfig(callback: (mtime: Date) => Promise<void>, throttleMs: number): IDisposer {
    const configChanged = throttle(async () => {
      let mtime: Date;
      try {
        const stats = await stat(this.#configFilePath);
        mtime = stats.mtime;
      } catch (err) {
        if ((err as NodeJS.ErrnoException).code === 'ENOENT') {
          return;
        }
        throw err;
      }
      return callback(mtime);
    }, throttleMs);

    const watcher = watch(this.#userDataDir, {
      persistent: false,
    });

    watcher.on('change', (eventType, filename) => {
      if (eventType === 'change'
        && (filename === this.#configFileName || filename === null)) {
        configChanged()?.catch((err) => {
          console.log('Unhandled error while listening for config changes', err);
        });
      }
    });

    return () => watcher.close();
  }
}