'use strict';

module.exports = function () {
  const User = require('../model/user'),
    ObjectId = require('mongodb').ObjectId,
    moment = require('moment'),
    { Errors, DEFAULT_LANG } = require('./constants'),
    { AppParamError, AppAuthError } = require('./app_error');

  return {
    _cache: {},

    get: function (key) { 
      return this._cache[key] ? { id: key, ...this._cache[key] } : null;
    },
    set: function (key, val) { this._cache[key] = val; },
    delete: function (key) {
      delete this._cache[key];
    },
    isExpired: function (key, seconds) {
      const userInfo = this._cache[key];
      if (!userInfo) return false;
      return (!userInfo.ts || (moment.utc().unix() - userInfo.ts) >= seconds);
    },
    clear: function () {
      this._cache = {};
    },
    loadUser: async function (uid) {
      try {
        if (!ObjectId.isValid(uid)) throw AppParamError.throw();

        // Project migratedDate to be used in the cache        
        const updatedRes = await User.aggregate([
          { $match: { _id: ObjectId(uid) } },
          { $addFields: { 'parentUser': { $ifNull: ['$parent', '$_id'] } } },
          {
            $lookup: {
              from: 'users',
              let: { parentUser: '$parentUser' },
              pipeline: [{ $match: { $expr: { $eq: ['$_id', '$$parentUser'] } } }],
              as: 'applicator'
            }
          },
          { $unwind: { path: '$applicator', 'preserveNullAndEmptyArrays': true } },
          {
            $project: {
              puid: '$parentUser',
              kind: 1,
              premium: { $ifNull: ['$applicator.premium', 0] },
              membership: '$applicator.membership', // Also load the user's membership info (applicator's) when fetching user data from DB
              markedDelete: 1,
              lang: 1,
              migratedDate: { $ifNull: ['$migratedDate', '$applicator.migratedDate'] }
            }
          }
        ]);

        if (!updatedRes || !updatedRes.length) AppAuthError.throw();
        const userInfo = updatedRes[0];

        this.set(uid,
          {
            kind: userInfo.kind, puid: userInfo.puid.toHexString(), premium: userInfo.premium, membership: userInfo.membership, lang: userInfo.lang || DEFAULT_LANG,
            markedDelete: userInfo.markedDelete || false, ts: moment.utc().unix(),
            migratedDate: userInfo.migratedDate
          }
        );
        return userInfo;
      } catch (err) {
        throw err;
      }
    },

    /**
     * Filter cache entries by parent user and kind
     * @param { string } pUser required
     * @param { number } kind user type
     * @returns [[key, value ]] array of logged in user and session info object
     */
    filterByKind: function (pUser, kind) {
      const all = Object.entries(this._cache) || [];
      if (kind === undefined) {
        return all.filter(it => {
          return Object.values(it).length > 1 && Object.values(it)[1]['puid'] === pUser;
        });
      } else {
        return all.filter(it => Object.values(it).length > 1 && (Object.values(it)[1]['puid'] === pUser && Object.values(it)[1]['type'] === kind));
      }
    }
  }
}();