habitica/website/common/script/fns/randomDrop.js

import cloneDeepWith from 'lodash/cloneDeepWith';
import isFunction from 'lodash/isFunction';
import min from 'lodash/min';
import reduce from 'lodash/reduce';
import filter from 'lodash/filter';
import pickBy from 'lodash/pickBy';
import size from 'lodash/size';
import moment from 'moment';
import content from '../content/index';
import i18n from '../i18n';
import { daysSince } from '../cron';
import { diminishingReturns } from '../statHelpers';
import randomVal from '../libs/randomVal';
import statsComputed from '../libs/statsComputed';
import firstDrops from './firstDrops';

// TODO This is only used on the server
// move to user model as an instance method?

// Clone a drop object maintaining its functions
// so that we can change it without affecting the original item
function cloneDropItem (drop) {
  return cloneDeepWith(drop, val => (isFunction(val) ? val : undefined));
}

function trueRandom () {
  return Math.random();
}

export default function randomDrop (user, options, req = {}, analytics) {
  let acceptableDrops;
  let drop;
  let dropMultiplier;
  let rarity;

  if (
    size(user.items.eggs) < 1
    && size(user.items.hatchingPotions) < 1
  ) {
    // @TODO why are we using both _tmp.firstDrops and the FIRST_DROPS notification?
    user._tmp.firstDrops = firstDrops(user);
    return;
  }

  const predictableRandom = options.predictableRandom || trueRandom;
  const { task } = options;

  let chance = min([Math.abs(task.value - 21.27), 37.5]) / 150 + 0.02;
  chance *= task.priority // Task priority: +50% for Medium, +100% for Hard
    // start users with +75% drops, diminishing by 5% per level gained
    * (1 + Math.max(0, 80 - (5 * user.stats.lvl)) / 100)
    * (1 + (task.streak / 100 || 0)) // Streak bonus: +1% per streak
    * (1 + statsComputed(user).per / 100) // PERception: +1% per point
    * (1 + (user.contributor.level / 40 || 0)) // Contrib levels: +2.5% per level
    * (1 + (user.achievements.rebirths / 20 || 0)) // Rebirths: +5% per achievement
    * (1 + (user.achievements.streak / 200 || 0)) // Streak achievements: +0.5% per achievement
    // +50% per checklist item complete. TODO: make this into X individual drop chances instead
    * (user._tmp.crit || 1)
    * (1 + 0.5 * (reduce(
      task.checklist,
(m, i) => m + (i.completed ? 1 : 0), // eslint-disable-line indent
      0,
) || 0)); // eslint-disable-line indent
  chance = diminishingReturns(chance, 0.75);

  if (predictableRandom() < chance) {
    user.party.quest.progress.collectedItems = user.party.quest.progress.collectedItems || 0;
    user.party.quest.progress.collectedItems += 1;
    user._tmp.quest = user._tmp.quest || {};
    user._tmp.quest.collection = 1;
    if (user.markModified) user.markModified('party.quest.progress');
  }

  if (user.purchased && user.purchased.plan && user.purchased.plan.customerId) {
    dropMultiplier = 2;
  } else {
    dropMultiplier = 1;
  }

  const maxDropCount = dropMultiplier * (5 + Math.floor(statsComputed(user).per / 25) + (user.contributor.level || 0)); // eslint-disable-line max-len

  if (
    daysSince(user.items.lastDrop.date, user.preferences) === 0
    && user.items.lastDrop.count >= maxDropCount
  ) {
    return;
  }

  const firstFoodDrop = size(user.items.food) < 1;

  if (firstFoodDrop || predictableRandom() < chance) {
    rarity = predictableRandom();

    if (firstFoodDrop || rarity > 0.6) { // food 40% chance
      drop = cloneDropItem(randomVal(filter(content.food, {
        canDrop: true,
      })));

      user.items.food = {
        ...user.items.food,
        [drop.key]: user.items.food[drop.key] || 0,
      };
      user.items.food[drop.key] += 1;
      if (user.markModified) user.markModified('items.food');

      drop.type = 'Food';
      drop.dialog = i18n.t('messageDropFood', {
        dropText: drop.textA(req.language),
        dropNotes: drop.notes(req.language),
      }, req.language);
    } else if (rarity > 0.3) { // eggs 30% chance
      drop = cloneDropItem(randomVal(content.dropEggs));

      user.items.eggs = {
        ...user.items.eggs,
        [drop.key]: user.items.eggs[drop.key] || 0,
      };
      user.items.eggs[drop.key] += 1;
      if (user.markModified) user.markModified('items.eggs');

      drop.type = 'Egg';
      drop.dialog = i18n.t('messageDropEgg', {
        dropText: drop.text(req.language),
        dropNotes: drop.notes(req.language),
      }, req.language);
    } else { // Hatching Potion, 30% chance - break down by rarity.
      if (rarity < 0.02) { // Very Rare: 10% (of 30%)
        acceptableDrops = ['Golden'];
      } else if (rarity < 0.09) { // Rare: 20% of 30%
        acceptableDrops = ['Zombie', 'CottonCandyPink', 'CottonCandyBlue'];
      } else if (rarity < 0.18) { // uncommon: 30% of 30%
        acceptableDrops = ['Red', 'Shade', 'Skeleton'];
      } else { // common, 40% of 30%
        acceptableDrops = ['Base', 'White', 'Desert'];
      }
      drop = cloneDropItem(
        randomVal(pickBy(content.hatchingPotions, (v, k) => acceptableDrops.indexOf(k) >= 0)),
      );

      user.items.hatchingPotions = {
        ...user.items.hatchingPotions,
        [drop.key]: user.items.hatchingPotions[drop.key] || 0,
      };
      user.items.hatchingPotions[drop.key] += 1;

      if (user.markModified) user.markModified('items.hatchingPotions');

      drop.type = 'HatchingPotion';
      drop.dialog = i18n.t('messageDropPotion', {
        dropText: drop.text(req.language),
        dropNotes: drop.notes(req.language),
      }, req.language);
    }

    // @TODO use notifications
    user._tmp.drop = drop;
    user.items.lastDrop.date = Number(new Date());
    user.items.lastDrop.count += 1;

    if (analytics && moment().diff(user.auth.timestamps.created, 'days') < 7) {
      analytics.track('dropped item', {
        user,
        uuid: user._id,
        itemKey: drop.key,
        category: 'behavior',
        headers: req.headers,
      });
    }
  }
}