/**
 * Copyright (c) 2017-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @flow
 * @format
 */

import type {LRUCache} from 'lru-cache';
import type {NuclideUri} from './nuclideUri';

import LRU from 'lru-cache';
import fsPromise from './fsPromise';

export type SearchStrategy = 'nearest' | 'furthest' | 'priority';

export class ConfigCache {
  _configFileNames: Array<string>;
  _searchStrategy: SearchStrategy;
  _configCache: LRUCache<NuclideUri, Promise<?NuclideUri>>;

  constructor(
    configFileNames: Array<string>,
    searchStrategy?: SearchStrategy = 'nearest',
  ) {
    this._configFileNames = configFileNames;
    this._searchStrategy = searchStrategy;
    this._configCache = LRU({
      max: 200, // Want this to exceed the maximum expected number of open files + dirs.
      maxAge: 1000 * 30, // 30 seconds
    });
  }

  getConfigDir(path: NuclideUri): Promise<?NuclideUri> {
    let result = this._configCache.get(path);
    if (result == null) {
      result = this._findConfigDir(path);
      this._configCache.set(path, result);
    }
    return result;
  }

  async _findConfigDir(path: NuclideUri): Promise<?NuclideUri> {
    const configDirs = await Promise.all(
      this._configFileNames.map(configFile => {
        if (this._searchStrategy === 'furthest') {
          return fsPromise.findFurthestFile(configFile, path);
        } else {
          return fsPromise.findNearestFile(configFile, path);
        }
      }),
    );

    if (this._searchStrategy === 'nearest') {
      // Find the result with the greatest length (the closest match).
      return configDirs.filter(Boolean).reduce((previous, configDir) => {
        if (previous == null || configDir.length > previous.length) {
          return configDir;
        }
        return previous;
      }, null);
    } else if (this._searchStrategy === 'furthest') {
      return configDirs.filter(Boolean).reduce((previous, configDir) => {
        if (previous == null || configDir.length < previous.length) {
          return configDir;
        }
        return previous;
      }, null);
    } else {
      // Find the first match.
      return configDirs.find(Boolean);
    }
  }

  dispose(): void {
    this._configCache.reset();
  }
}