const Game = {
  phases: {
    preTurnBegin: [],
    preTurn: [],
    battle: {
      preAction: {
        opponent: [],
        player: [],
      },
      action: {
        opponent: [],
        player: [],
      },
      postAction: {
        opponent: [],
        player: [],
      },
    },
    postTurn: [],
    postTurnEnd: [],
  },

  logMessages: [],

  isLoadingArea: false,
  isProgressingTurn: false,
  playerIsChoosingNextMonster: false,
  doBattleAnimation: true,
  opponentActionTimeout: null,
  isInBattle: false,
  didTechniqueHit: false,

  /* Battle */

  async progressTurn () {
    Game.isProgressingTurn = true;
    Memory.state.turn++;

    // status effects
    await Game.applyStatusEffect(Memory.state.opponent.activeMonster);
    await Game.applyStatusEffect(Memory.state.player.activeMonster);

    Game.logTurn('begin');

    // Phases
    for (const event of Game.phases.preTurn) {
      event();
    }
    Game.phases.preTurn = [];

    for (const phaseKey of Object.keys(Game.phases.battle)) {
      for (const event of Game.phases.battle[phaseKey].player) {
        event();

        await Game.handleDefeatOpponent();
        if (!Game.playerIsChoosingNextMonster) await Game.handleDefeatPlayer();
      }
      Game.phases.battle[phaseKey].player = [];

      Game.doBattleAnimation = false;
      for (const event of Game.phases.battle[phaseKey].opponent) {
        event();

        await Game.handleDefeatOpponent();
        if (!Game.playerIsChoosingNextMonster) await Game.handleDefeatPlayer();
      }
      Game.doBattleAnimation = true;
      Game.phases.battle[phaseKey].opponent = [];
    }

    for (const event of Game.phases.postTurn) {
      event();
    }
    Game.phases.postTurn = [];

    Game.logTurn('end');

    for (const event of Game.phases.postTurnEnd) {
      event();
    }
    Game.phases.postTurnEnd = [];

    UI.progressTurn();
    Game.isProgressingTurn = false;
  },

  async handleDefeatOpponent () {
    if (Memory.state.opponent.activeMonster.hp <= 0) {
      clearTimeout(Game.opponentActionTimeout);
      Game.opponentActionTimeout = null;
      for (const phase of Object.keys(Game.phases.battle)) {
        Game.removeBattlePhaseEvents(phase, 'opponent');
      }
      Game.removeBattlePhaseEvents('action', 'player');

      // money
      const money = calculateAwardedMoney(Memory.state.opponent.activeMonster);
      Memory.state.money += money;
      Game.addPhaseEvent('postTurn', () => {
        Game.log(`Got ${money} money!`);
      });

      // exp
      Memory.state.player.activeMonster.exp += calculateAwardedExperience(Memory.state.opponent.activeMonster, [Memory.state.player.activeMonster])[0];

      if (Memory.state.player.activeMonster.canLevelUp()) {
        Memory.state.player.activeMonster.levelUp();
      }
      if (Memory.state.player.activeMonster.canEvolve('standard')) {
        await Game.evolveMonster(Memory.state.player.activeMonster);
      }

      Game.isInBattle = false;

      if (Memory.state.opponent.type === 'monster') {
        Memory.state.currentArea.monsterProgress++;
        await Game.encounterWildMonster();
      } else if (Memory.state.opponent.type === 'trainer') {
        if (Memory.state.opponent.activeMonster === Memory.state.opponent.monsters[Memory.state.opponent.monsters.length - 1]) {
          Memory.state.currentArea.trainerProgress++;
          Memory.state.currentArea.monsterProgress = 0;
          if (Memory.state.currentArea.encounters.length > 0) {
            await Game.encounterWildMonster();
          } else {
            await Game.encounterTrainer();
          }
        } else {
          await Game.encounterNextTrainerMonster();
        }
      }
    }
  },

  async handleDefeatPlayer () {
    if (Memory.state.player.activeMonster.hp <= 0) {
      clearTimeout(Game.opponentActionTimeout);
      Game.opponentActionTimeout = null;
      for (const phase of Object.keys(Game.phases.battle)) {
        Game.removeBattlePhaseEvents(phase, 'player');
      }
      Game.removeBattlePhaseEvents('action', 'opponent');

      Memory.state.player.activeMonster.statusEffect = await fetchStatusEffect('faint');

      // whole party defeated
      if (!Memory.state.player.monsters.some((monster) => monster.hp > 0)) {
        Game.isInBattle = false;
        Memory.state.currentArea.monsterProgress = 0;

        // go to last visited town
        await Game.goToArea(Memory.state.lastVisitedTown);

        // heal all monsters full
        let totalHealingCenterPrice = 0;
        for (const monster of Memory.state.player.monsters) {
          monster.hp = monster.stats.hp;
          monster.statusEffect = null;

          // pay healing center
          const healingCenterPrice = Object.values(Memory.state.currentArea.locations).find((location) => location.type === 'healingCenter').price;
          totalHealingCenterPrice += healingCenterPrice;
        }

        Memory.state.money -= totalHealingCenterPrice;

        Game.addPhaseEvent('postTurnEnd', () => {
          Game.log(`Whited out!`);
          Game.log(`Payed ${formatPrice(totalHealingCenterPrice)} for full recovery at ${Memory.state.currentArea.name}!`);
        });
      }

      // party members still left
      else {
        Game.playerIsChoosingNextMonster = true;
        const monsterSelectionNode = UI.createPlayerDefeatedMonsterSelection();
        UI.openPlayerDefeatedMonsterSelection(monsterSelectionNode);
      }
    }
  },

  /**
   * @param {('preAction' | 'action' | 'postAction')} phase
   * @param {Monster} monster
   * @param {Function} event
   */
  addBattlePhaseEvent (phase, monster, event) {
    if (monster === Memory.state.player.activeMonster) {
      Game.phases.battle[phase].player.push(event);
    } else {
      Game.phases.battle[phase].opponent.push(event);
    }
  },

  /**
   * @param {('preAction' | 'action' | 'postAction')} phase
   * @param {('player' | 'opponent')} type
   */
  removeBattlePhaseEvents (phase, type) {
    Game.phases.battle[phase][type] = [];
  },

  /**
   * @param {('preTurnBegin' | 'preTurn' | 'postTurn' | 'postTurnEnd')} phase
   * @param {Function} event
   */
  addPhaseEvent (phase, event) {
    Game.phases[phase].push(event);
  },

  clearAllPhaseEvents () {
    Game.removeBattlePhaseEvents('preAction', 'player');
    Game.removeBattlePhaseEvents('preAction', 'opponent');
    Game.removeBattlePhaseEvents('action', 'player');
    Game.removeBattlePhaseEvents('action', 'opponent');
    Game.removeBattlePhaseEvents('postAction', 'player');
    Game.removeBattlePhaseEvents('postAction', 'opponent');
  },

  clearCurrentTurn () {
    Game.clearAllPhaseEvents();
    clearTimeout(Game.opponentActionTimeout);
    Game.opponentActionTimeout = null;
  },

  /**
   * @param {Technique} technique
   * @param {Monster} user
   * @param {Monster} target
   */
  async tryUseTechnique (technique, user, target) {
    let canUse = true;

    const log = (message, indentation) => {
      Game.addBattlePhaseEvent('preAction', user, () => {
        Game.log(message, indentation);
      });
    };

    log(`${user.name} attempts to use ${technique.name}!`);

    // recharge
    if (technique.isRecharging()) {
      if (Game.doBattleAnimation) {
        const feedbackNode = UI.createActionFeedback('recharge');
        feedbackNode.classList.add('recharge');
        UI.drawActionFeedback(feedbackNode);
      }

      log('But has to recharge!', 1);

      canUse = false;
    }

    // noddingoff
    if (user.statusEffect && user.statusEffect.slug === StatusEffectType.noddingoff) {
      if (Game.doBattleAnimation) {
        const feedbackNode = UI.createActionFeedback('noddingoff');
        UI.drawActionFeedback(feedbackNode);
      }

      log('But is nodding off!', 1);

      canUse = false;
    }

    if (canUse) {

      // hit?
      const accuracy = Math.random();
      Game.didTechniqueHit = technique.accuracy >= accuracy;
      if (!Game.didTechniqueHit) {
        technique.use();
        Game.doBattleAnimation && UI.drawDamageMiss(UI.createDamageMiss());

        log('But missed!', 1);

        return;
      }

      await Game.useTechnique(technique, user, target);
    }
  },

  /**
   * @param {Technique} technique
   * @param {Monster} user
   * @param {Monster} target
   */
  async useTechnique (technique, user, target) {
    technique.use();

    Game.addBattlePhaseEvent('action', user, () => {
      Game.log(`${user.name} is using ${technique.name}!`);
    });

    for (const techniqueEffectCode of technique.effects) {
      const techniqueEffect = new TechniqueEffect(techniqueEffectCode);
      techniqueEffect.setUser(user);
      techniqueEffect.setTarget(target);

      // damage
      if (['damage', 'splash', 'area'].includes(techniqueEffect.type)) {
        Game.addBattlePhaseEvent('action', user, () => {
          const damage = simpleDamageCalculation(technique, user, target);

          target.hp -= damage;

          if (Game.doBattleAnimation) {
            const damageNode = UI.createDamage(damage);
            UI.applyMultiplierToDamage(damageNode, simpleDamageMultiplier(technique.types, target.types));
            UI.applyTechniqueToDamage(damageNode, technique);
            UI.drawDamage(damageNode);
            UI.drawTechniqueAnimation(technique);
          }

          Game.log(`Deals ${damage} to ${target.name}!`, 1);
        });
      }

      // money
      else if (techniqueEffect.type === 'money') {
        Game.addBattlePhaseEvent('action', user, () => {
          const money = Math.max(1, Math.floor(Math.random() * target.level));
          Memory.state.money += money;

          if (Game.doBattleAnimation) {
            const damageNode = UI.createDamage(`${money} €`);
            UI.applyTechniqueToDamage(damageNode, technique);
            UI.drawDamage(damageNode);
            UI.drawTechniqueAnimation(technique);
          }
        });
      }

      // healing
      else if (techniqueEffect.type === 'healing') {
        for (const recipient of techniqueEffect.recipients) {
          Game.addBattlePhaseEvent('action', user, () => {
            const heal = (user.level + 7) * technique.healingPower;
            recipient.hp += heal;

            Game.log(`Heals ${heal}!`, 1);
          });
        }
      }

      // switch
      else if (techniqueEffect.type === 'switch') {
        techniqueEffect.recipient.types = [techniqueEffect.switchType];
      }

      // enhance
      else if (techniqueEffect.type === 'enhance') {
        Game.doBattleAnimation && UI.drawTechniqueAnimation(technique);
      }

      // status effect
      else if (techniqueEffect.type === 'status') {
        const statusEffect = await fetchStatusEffect(techniqueEffect.statusEffect);

        if (statusEffect.slug === 'lifeleech') {
          statusEffect.issuer = user;
        }

        Game.addBattlePhaseEvent('action', user, () => {
          // add status effect
          const potency = Math.random();
          const success = technique.potency >= potency;

          if (success) {
            for (const recipient of techniqueEffect.recipients) {
              // TODO: check replace
              if (recipient.statusEffect) continue;

              recipient.statusEffect = statusEffect;

              Game.log(`${techniqueEffect.recipients.map((recipient) => recipient.name).join(', ')} ${techniqueEffect.recipients.length > 1 ? 'are' : 'is'} now ${statusEffect.name}!`, 1);
            }
          }
        });

        Game.doBattleAnimation && UI.drawTechniqueAnimation(technique);
      }
    }
  },

  /**
   * @param {Monster} monster
   */
  async applyStatusEffect (monster) {
    if (!monster.statusEffect) {
      return;
    }

    if (monster.statusEffect.turnsLeft === 0) {
      Game.addBattlePhaseEvent('preAction', monster, () => {
        monster.statusEffect.onRemove && monster.statusEffect.onRemove();

        // if still 0 turns left after remove action
        if (monster.statusEffect.turnsLeft === 0) {
          Game.log(`${monster.name} is not ${monster.statusEffect.name} anymore!`);

          monster.statusEffect = null;
        } else {
          Game.applyStatusEffect(monster);
        }
      });

      return;
    }

    const logStatusIs = () => {
      Game.log(`${monster.name} is ${monster.statusEffect.name}!`);
    }

    // poison / burn
    if (monster.statusEffect.slug === 'poison' || monster.statusEffect.slug === 'burn') {
      const statusEffectDamage = Math.floor(monster.stats.hp / 8);

      Game.addBattlePhaseEvent('postAction', monster, () => {
        monster.hp -= statusEffectDamage;

        if (Game.doBattleAnimation) {
          const damageNode = UI.createDamage(statusEffectDamage);
          UI.applyStatusEffectToDamage(damageNode, monster.statusEffect);
          UI.drawDamage(damageNode);
        }

        logStatusIs();
      });
    }

    // lifeleech
    else if (monster.statusEffect.slug === 'lifeleech') {
      const statusEffectLeech = Math.floor(monster.stats.hp / 16);

      Game.addBattlePhaseEvent('postAction', monster, () => {
        // if issuer is defeated => don't
        if (monster.statusEffect.issuer.hp <= 0) {
          return;
        }

        monster.hp -= statusEffectLeech;
        monster.statusEffect.issuer.hp += statusEffectLeech;

        if (Game.doBattleAnimation) {
          const damageNode = UI.createDamage(statusEffectLeech);
          UI.applyStatusEffectToDamage(damageNode, monster.statusEffect);
          UI.drawDamage(damageNode);
        }

        logStatusIs();
      });
    }

    // recover
    else if (monster.statusEffect.slug === 'recover') {
      const statusEffectHeal = Math.floor(monster.stats.hp / 16);

      Game.addBattlePhaseEvent('postAction', monster, () => {
        monster.hp += statusEffectHeal;

        if (Game.doBattleAnimation) {
          const feedbackNode = UI.createActionFeedback(statusEffectHeal);
          UI.applyStatusEffectToDamage(feedbackNode, monster.statusEffect);
          UI.drawActionFeedback(feedbackNode);
        }

        logStatusIs();
      });
    }

    // confused
    else if (monster.statusEffect.slug === 'confused') {
      Game.addBattlePhaseEvent('preAction', monster, () => {
        // TODO
        logStatusIs();
      });
    }

    // stuck
    else if (monster.statusEffect.slug === 'stuck') {
      for (const technique of monster.activeTechniques) {
        if ([TechniqueRange.melee, TechniqueRange.touch].includes(technique.range)) {
          Game.addBattlePhaseEvent('preAction', monster, () => {
            technique.potency = technique.stats.potency * 0.5;
            technique.power = technique.stats.power * 0.5;

            logStatusIs();
          });

          monster.statusEffect.onRemove = () => {
            technique.resetStats();
          };
        }
      }
    }

    // grabbed
    else if (monster.statusEffect.slug === 'grabbed') {
      for (const technique of monster.activeTechniques) {
        if ([TechniqueRange.ranged, TechniqueRange.reach].includes(technique.range)) {
          Game.addBattlePhaseEvent('preAction', monster, () => {
            technique.potency = technique.stats.potency * 0.5;
            technique.power = technique.stats.power * 0.5;

            logStatusIs();
          });

          monster.statusEffect.onRemove = () => {
            technique.resetStats();
          };
        }
      }
    }

    // charging
    else if (monster.statusEffect.slug === 'charging') {
      const nextStatusEffect = await fetchStatusEffect('chargedup');

      Game.addBattlePhaseEvent('preAction', monster, () => {
        logStatusIs();
      });

      monster.statusEffect.onRemove = () => {
        monster.statusEffect = nextStatusEffect;
      };
    }

    // statchange
    else if (monster.statusEffect.effects.includes('statchange')) {
      monster.resetStatModifiers();

      for (const statType in monster.statusEffect.stats) {
        const statChange = monster.statusEffect.stats[statType];
        const modifiedValue = Math.floor(eval(`${monster.stats[statType]} ${statChange.operation} ${statChange.value}`));

        Game.addBattlePhaseEvent('preAction', monster, () => {
          monster.setStatModifier(statType, modifiedValue);

          logStatusIs();
        });
      }

      monster.statusEffect.onRemove = () => {
        monster.resetStatModifiers();
      };
    }

    Game.addBattlePhaseEvent('postAction', monster, () => {
      monster.statusEffect.turnsLeft--;
    });
  },

  async opponentTryUseTechnique () {
    if (!Game.opponentActionTimeout) {
      let speedDifference = Memory.state.opponent.activeMonster.stats.speed - Memory.state.player.activeMonster.stats.speed;
      if (speedDifference > 0) speedDifference = speedDifference / 2;
      else if (speedDifference < 0 && speedDifference > -100) speedDifference = speedDifference * 2;
      let levelDifference = Memory.state.opponent.activeMonster.level - Memory.state.player.activeMonster.level;
      if (levelDifference >= 5) levelDifference = levelDifference * 2;
      else if (levelDifference < 0 && levelDifference > -10) levelDifference = 0;
      else if (levelDifference <= -10) levelDifference = levelDifference / 10;

      const opponentActiveMonster = Memory.state.opponent.activeMonster;
      Game.opponentActionTimeout = setTimeout(async () => {
        if (opponentActiveMonster.hp <= 0) {
          Game.opponentActionTimeout = null;
          return;
        }

        // technique
        Game.doBattleAnimation = false;
        await Game.tryUseTechnique(
          await fetchTechnique(Memory.state.opponent.activeMonster.getLearnableTechniques()[Math.floor(Math.random() * Memory.state.opponent.activeMonster.getLearnableTechniques().length)].technique),
          Memory.state.opponent.activeMonster,
          Memory.state.player.activeMonster
        );
        Game.doBattleAnimation = true;

        await Game.progressTurn();

        // item
        if (Memory.state.opponent.inventory.length > 0) {
        }

        Game.opponentActionTimeout = null;
      }, Math.max(levelDifference < 10 ? 500 : 50, Math.min(2000 - (speedDifference * 10) - (levelDifference * 100), 3000)));
      console.log(
        'Opponent Attack Timeout',
        Memory.state.opponent.activeMonster.stats.speed, Memory.state.player.activeMonster.stats.speed,
        2000 - (speedDifference * 10) - (levelDifference * 100)
      );
    }
  },

  /**
   * @param {MouseEvent} event
   */
  async battleClick (event) {
    if (Game.isLoadingArea || Game.isProgressingTurn) {
      return;
    }

    Game.isInBattle = true;
    UI.battleClickEvent = event;

    // player
    await Game.tryUseTechnique(Memory.state.activeTechnique, Memory.state.player.activeMonster, Memory.state.opponent.activeMonster);

    // opponent
    await Game.opponentTryUseTechnique();

    await Game.progressTurn();
  },

  /**
   * @param {MouseEvent} event
   */
  techniqueClick (event) {
    if (event.target === UI.elements.techniques) {
      return;
    }

    let target = event.target;
    while (target.dataset.gameElementType !== 'menuBattleTechniquesTechnique') {
      target = target.parentNode;
    }

    const idx = [...UI.elements.techniques.children].indexOf(target);
    Memory.state.activeTechnique = Memory.state.player.activeMonster.activeTechniques[idx];

    // trigger battle click
    const rect = UI.elements.battleOpponent.getBoundingClientRect();
    const xMin = rect.left + 64;
    const xMax = rect.right - 64;
    const yMin = rect.top + 32;
    const yMax = rect.bottom - 32;
    UI.elements.battleOpponent.dispatchEvent(new MouseEvent('click', {
      clientX: Math.random() * (xMax - xMin) + xMin,
      clientY: Math.random() * (yMax - yMin) + yMin,
    }));
  },

  /**
   * @param {string} message
   * @param {number} indentation
   * @param {string} style
   */
  log (message, indentation = 0, style) {
    Game.logMessages.push({
      message: message,
      indentation: indentation,
      style: style,
    });
    UI.drawLog();
  },

  /**
   * @param {('begin' | 'end')}
   */
  logTurn (state) {
    Game.log(
      '- '.repeat(8) + `Turn ${Memory.state.turn} &middot; ${slugToName(state)}` + ' -'.repeat(8),
      0,
      {
        textAlign: 'center',
      }
    );
  },


  /* Progression */

  async encounterWildMonster () {
    const randomMonster = Memory.state.currentArea.encounters[Math.floor(Math.random() * Memory.state.currentArea.encounters.length)];
    const randomLevel = Math.floor(Math.random() * (randomMonster.level_range[1] - randomMonster.level_range[0]) + randomMonster.level_range[0]);

    const monster = await fetchMonster(randomMonster.monster);
    monster.level = randomLevel;

    const wildMonster = new Trainer({ monsters: [monster] });
    wildMonster.type = 'monster';
    await wildMonster.initialize();
    Memory.state.opponent = wildMonster;

    UI.drawOpponentMonster();
  },

  async encounterTrainer () {
    Game.clearCurrentTurn();

    let nextTrainerIdx = Memory.state.currentArea.trainerProgress;
    while (nextTrainerIdx > Memory.state.currentArea.trainers.length - 1) {
      nextTrainerIdx -= Memory.state.currentArea.trainers.length;
    }

    const nextTrainer = Memory.state.currentArea.trainers[nextTrainerIdx];
    if (nextTrainer.name.startsWith('Rival')) {
      for (const idx in nextTrainer.monsters) {
        if (nextTrainer.monsters[idx].slug === 'STARTER') {
          nextTrainer.monsters[idx].slug = Memory.state.rivalMonster;
        }
      }
    }

    const trainer = new Trainer(nextTrainer);
    await trainer.initialize()
    Memory.state.opponent = trainer;

    UI.drawOpponentMonster();
    UI.drawStatus();
  },

  async encounterNextTrainerMonster () {
    const activeMonsterIdx = Memory.state.opponent.monsters.indexOf(Memory.state.opponent.activeMonster);
    Memory.state.opponent.activeMonster = Memory.state.opponent.monsters[activeMonsterIdx + 1];

    UI.drawOpponentMonster();
  },

  /**
   * @param {string} areaSlug
   */
  async goToArea (areaSlug) {
    Game.isLoadingArea = true;
    Game.clearCurrentTurn();

    if (Memory.state.currentArea) {
      Memory.state.areaProgress[Memory.state.currentArea.slug] = Memory.state.currentArea;
    }

    Memory.state.currentArea = await fetchArea(areaSlug);

    if (Game.isTown(Memory.state.currentArea)) {
      if (Object.values(Memory.state.currentArea.locations).some((location) => location.type === 'healingCenter')) {
        Memory.state.lastVisitedTown = areaSlug;
      }
    } else {
      if (Memory.state.currentArea.encounters.length > 0) {
        await Game.encounterWildMonster();
      } else if (Memory.state.currentArea.trainers.length > 0) {
        await Game.encounterTrainer();
      }
    }

    UI.drawArea();

    Game.isLoadingArea = false;
  },


  /* Menu - Inventory */

  /**
   * @param {InventoryItem} item
   * @param {Monster} monster
   *
   * @returns {boolean}
   */
  canUseItem (item, monster = null) {
    let isApplicable = true;

    for (const itemConditionCode of item.conditions) {
      const itemCondition = new ItemCondition(itemConditionCode);
      let conditionIsApplicable = true;

      if (itemCondition.what === 'current_hp') {
        const value = parseInt(itemCondition.value) * monster.stats.hp;
        conditionIsApplicable = eval(`${monster.hp} ${itemCondition.comparator} ${value}`);
      }

      else if (itemCondition.what === 'status') {
        conditionIsApplicable = monster.statusEffect && monster.statusEffect.slug === itemCondition.value.replace('status_', '');
      }

      else if (itemCondition.what === 'wild_monster') {
        conditionIsApplicable = Game.isBattleType('monster');
      }

      else if (itemCondition.what === 'threat') {
        conditionIsApplicable = Memory.state.opponent.activeMonster.category === 'threat';
      }

      else {
        conditionIsApplicable = false;
      }

      if (itemCondition.is === 'not') {
        conditionIsApplicable = !conditionIsApplicable;
      }

      isApplicable = isApplicable && conditionIsApplicable;
    }

    return isApplicable;
  },

  /**
   * @param {InventoryItem}
   * @param {Monster}
   */
  async useItem (item, monster) {
    for (const itemEffectCode of item.effects) {
      const itemEffect = new ItemEffect(itemEffectCode);

      if (itemEffect.type === 'heal') {
        monster.hp += itemEffect.amount;
        item.quantity--;
        UI.drawActiveMonster();
      }

      if (itemEffect.type === 'revive') {
        monster.hp = itemEffect.amount;
        monster.statusEffect = null;
        item.quantity--;
        UI.drawActiveMonster();
      }

      else if (itemEffect.type === 'capture') {
        Memory.state.activeBall = item;
        UI.drawActiveBall();
      }

      else if (itemEffect.type === 'evolve') {
        const evolution = Memory.state.player.activeMonster.getPossibleEvolutions('item')[0];
        if (evolution) {
          await fetchMonster(evolution.monster_slug);
          Memory.state.player.activeMonster.evolve(evolution);
          UI.drawActiveMonster();

          item.quantity--;
        }
      }
    }
  },

  /**
   * @param {Array} inventory
   * @param {InventoryItem} item
   */
  removeItemFromInventory (inventory, item) {
    inventory.splice(inventory.indexOf(item), 1);
  },


  /* Menu - Catch */

  /**
   * @returns {boolean}
   */
  canCatchMonster () {
    return !Game.isTown(Memory.state.currentArea) && Game.isBattleType('monster') && Memory.state.activeBall;
  },

  async catchMonster () {
    if (!Game.canCatchMonster()) {
      return;
    }

    const playerMonster = Memory.state.player.activeMonster;
    const opposingMonster = Memory.state.opponent.activeMonster;
    const activeBall = Memory.state.activeBall;

    // remove ball
    activeBall.quantity--;
    if (activeBall.quantity === 0) {
      Game.removeItemFromInventory(Memory.state.player.inventory, Memory.state.activeBall);
      Memory.state.activeBall = null;
      UI.drawActiveBall();
    }

    // attempt capture
    Game.log('Attempting capture!');
    let success = true;
    let attempts = 1;
    const maxAttempts = 4;
    while (success && attempts <= maxAttempts) {
      success = checkCapture(playerMonster, opposingMonster, activeBall);

      if (!success) {
        Game.log(`Escape attempt ${attempts}: succeeded!`);
        Game.log(`${opposingMonster.name} broke free!`);

        Game.opponentTryUseTechnique();
        return; // can't catch
      }

      Game.log(`Escape attempt ${attempts}: failed!`);

      attempts++;
    }

    Game.clearCurrentTurn();

    const caughtMonster = new Monster(Memory.state.opponent.activeMonster.slug);
    caughtMonster.initialize();
    caughtMonster.level = Memory.state.opponent.activeMonster.level;
    caughtMonster.hp = Memory.state.opponent.activeMonster.hp;

    Memory.state.player.monsters.push(caughtMonster);

    Game.log(`Caught ${caughtMonster.name}!`);

    await Game.encounterWildMonster();
  },


  /* Helper */

  /**
   * @param {Monster} monster
   */
  setActivePlayerMonster (monster) {
    Memory.state.player.activeMonster = monster;
    Memory.state.activeTechnique = Memory.state.player.activeMonster.activeTechniques[0];

    UI.drawActiveMonster();
    UI.drawActiveTechniques();
  },

  /**
   * @param {Monster} monster
   */
  async evolveMonster (monster) {
    await fetchMonster(monster.evolutions[0].monster_slug);
    monster.evolve(monster.evolutions[0]);
  },

  /**
   * @param {string} type
   *
   * @returns {boolean}
   */
  isBattleType (type) {
    return Memory.state.opponent.type === type;
  },

  /**
   * @param {Area} area
   */
  isTown (area) {
    return area.encounters.length === 0 && area.trainers.length === 0;
  },

  getStageOfDaySimple () {
    const hours = (new Date()).getHours();
    if (hours >= 6 && hours < 18) {
      return 'day';
    } else {
      return 'night';
    }
  },
};

// Game click bindings
UI.elements.nextTrainer.addEventListener('click', UI.createEventListener(Game.encounterTrainer));
UI.elements.battleOpponent.addEventListener('click', UI.createEventListener(Game.battleClick));
UI.elements.techniques.addEventListener('click', UI.createEventListener(Game.techniqueClick));
UI.elements.menuCatch.addEventListener('click', UI.createEventListener(Game.catchMonster));