import _ from 'lodash';
import moment from 'moment';
import common from '../../common';
import * as Tasks from '../models/task';
import Bluebird from 'bluebird';
import { model as Group } from '../models/group';
import { model as User } from '../models/user';
import { recoverCron, cron } from '../libs/cron';
import { v4 as uuid } from 'uuid';

const daysSince = common.daysSince;

async function cronAsync (req, res) {
  let user = res.locals.user;
  if (!user) return null; // User might not be available when authentication is not mandatory

  let analytics = res.analytics;
  let now = new Date();

  try {
    // If the user's timezone has changed (due to travel or daylight savings),
    // cron can be triggered twice in one day, so we check for that and use
    // both timezones to work out if cron should run.
    // CDS = Custom Day Start time.
    let timezoneOffsetFromUserPrefs = user.preferences.timezoneOffset;
    let timezoneOffsetAtLastCron = _.isFinite(user.preferences.timezoneOffsetAtLastCron) ? user.preferences.timezoneOffsetAtLastCron : timezoneOffsetFromUserPrefs;
    let timezoneOffsetFromBrowser = Number(req.header('x-user-timezoneoffset'));
    timezoneOffsetFromBrowser = _.isFinite(timezoneOffsetFromBrowser) ? timezoneOffsetFromBrowser : timezoneOffsetFromUserPrefs;
    // NB: All timezone offsets can be 0, so can't use `... || ...` to apply non-zero defaults

    if (timezoneOffsetFromBrowser !== timezoneOffsetFromUserPrefs) {
      // The user's browser has just told Habitica that the user's timezone has
      // changed so store and use the new zone.
      user.preferences.timezoneOffset = timezoneOffsetFromBrowser;
      timezoneOffsetFromUserPrefs = timezoneOffsetFromBrowser;
    }

    // How many days have we missed using the user's current timezone:
    let daysMissed = daysSince(user.lastCron, _.defaults({now}, user.preferences));

    if (timezoneOffsetAtLastCron !== timezoneOffsetFromUserPrefs) {
      // Since cron last ran, the user's timezone has changed.
      // How many days have we missed using the old timezone:
      let daysMissedNewZone = daysMissed;
      let daysMissedOldZone = daysSince(user.lastCron, _.defaults({
        now,
        timezoneOffsetOverride: timezoneOffsetAtLastCron,
      }, user.preferences));

      if (timezoneOffsetAtLastCron < timezoneOffsetFromUserPrefs) {
        // The timezone change was in the unsafe direction.
        // E.g., timezone changes from UTC+1 (offset -60) to UTC+0 (offset 0).
        //    or timezone changes from UTC-4 (offset 240) to UTC-5 (offset 300).
        // Local time changed from, for example, 03:00 to 02:00.

        if (daysMissedOldZone > 0 && daysMissedNewZone > 0) {
          // Both old and new timezones indicate that we SHOULD run cron, so
          // it is safe to do so immediately.
          daysMissed = Math.min(daysMissedOldZone, daysMissedNewZone);
          // use minimum value to be nice to user
        } else if (daysMissedOldZone > 0) {
          // The old timezone says that cron should run; the new timezone does not.
          // This should be impossible for this direction of timezone change, but
          // just in case I'm wrong...
          // TODO
          // console.log("zone has changed - old zone says run cron, NEW zone says no - stop cron now only -- SHOULD NOT HAVE GOT TO HERE", timezoneOffsetAtLastCron, timezoneOffsetFromUserPrefs, now); // used in production for confirming this never happens
        } else if (daysMissedNewZone > 0) {
          // The old timezone says that cron should NOT run -- i.e., cron has
          // already run today, from the old timezone's point of view.
          // The new timezone says that cron SHOULD run, but this is almost
          // certainly incorrect.
          // This happens when cron occurred at a time soon after the CDS. When
          // you reinterpret that time in the new timezone, it looks like it
          // was before the CDS, because local time has stepped backwards.
          // To fix this, rewrite the cron time to a time that the new
          // timezone interprets as being in today.

          daysMissed = 0; // prevent cron running now
          let timezoneOffsetDiff = timezoneOffsetAtLastCron - timezoneOffsetFromUserPrefs;
          // e.g., for dangerous zone change: 240 - 300 = -60 or  -660 - -600 = -60

          user.lastCron = moment(user.lastCron).subtract(timezoneOffsetDiff, 'minutes');
          // NB: We don't change user.auth.timestamps.loggedin so that will still record the time that the previous cron actually ran.
          // From now on we can ignore the old timezone:
          user.preferences.timezoneOffsetAtLastCron = timezoneOffsetFromUserPrefs;
        } else {
          // Both old and new timezones indicate that cron should
          // NOT run.
          daysMissed = 0; // prevent cron running now
        }
      } else if (timezoneOffsetAtLastCron > timezoneOffsetFromUserPrefs) {
        daysMissed = daysMissedNewZone;
        // TODO: Either confirm that there is nothing that could possibly go wrong here and remove the need for this else branch, or fix stuff.
        // There are probably situations where the Dailies do not reset early enough for a user who was expecting the zone change and wants to use all their Dailies immediately in the new zone;
        // if so, we should provide an option for easy reset of Dailies (can't be automatic because there will be other situations where the user was not prepared).
      }
    }

    if (daysMissed <= 0) {
      if (user.isModified()) await user.save();
      return null;
    }

    let _cronSignature = uuid();

    // To avoid double cron we first set _cronSignature and then check that it's not changed while processing
    let userUpdateResult = await User.update({
      _id: user._id,
      _cronSignature: 'NOT_RUNNING', // Check that in the meantime another cron has not started
    }, {
      $set: {
        _cronSignature,
        lastCron: now, // setting lastCron now so we don't risk re-running parts of cron if it fails
        'auth.timestamps.loggedin': now,
      },
    }).exec();

    // If the cron signature is already set, cron is running in another request
    // throw an error and recover later,
    if (userUpdateResult.nMatched === 0 || userUpdateResult.nModified === 0) {
      throw new Error('CRON_ALREADY_RUNNING');
    }

    let tasks = await Tasks.Task.find({
      userId: user._id,
      $or: [ // Exclude completed todos
        {type: 'todo', completed: false},
        {type: {$in: ['habit', 'daily', 'reward']}},
      ],
    }).exec();

    let tasksByType = {habits: [], dailys: [], todos: [], rewards: []};
    tasks.forEach(task => tasksByType[`${task.type}s`].push(task));

    // Run cron
    let progress = cron({user, tasksByType, now, daysMissed, analytics, timezoneOffsetFromUserPrefs, headers: req.headers});

    // Clear old completed todos - 30 days for free users, 90 for subscribers
    // Do not delete challenges completed todos TODO unless the task is broken?
    Tasks.Task.remove({
      userId: user._id,
      type: 'todo',
      completed: true,
      dateCompleted: {
        $lt: moment(now).subtract(user.isSubscribed() ? 90 : 30, 'days').toDate(),
      },
      'challenge.id': {$exists: false},
    }).exec();

    res.locals.wasModified = true; // TODO remove after v2 is retired

    // Group.tavernBoss(user, progress);

    // Save user and tasks
    let toSave = [user.save()];
    tasks.forEach(task => {
      if (task.isModified()) toSave.push(task.save());
    });
    await Bluebird.all(toSave);

    await Group.processQuestProgress(user, progress);

    // Set _cronSignature, lastCron and auth.timestamps.loggedin to signal end of cron
    await User.update({
      _id: user._id,
    }, {
      $set: {
        _cronSignature: 'NOT_RUNNING',
      },
    }).exec();

    // Reload user
    res.locals.user = await User.findOne({_id: user._id}).exec();
    return null;
  } catch (err) {
    // If cron was aborted for a race condition try to recover from it
    if (err.message === 'CRON_ALREADY_RUNNING') {
      // Recovering after abort, wait 300ms and reload user
      // do it for max 5 times then reset _cronSignature so that it doesn't prevent cron from running
      // at the next request
      let recoveryStatus = {
        times: 0,
      };

      await recoverCron(recoveryStatus, res.locals);
    } else {
      // For any other error make sure to reset _cronSignature so that it doesn't prevent cron from running
      // at the next request
      await User.update({
        _id: user._id,
      }, {
        _cronSignature: 'NOT_RUNNING',
      }).exec();

      throw err; // re-throw the original error
    }
  }
}

module.exports = function cronMiddleware (req, res, next) {
  cronAsync(req, res)
    .then(() => {
      next();
    })
    .catch(next);
};