Implement hidden abilities and ability charm

src/modifier/modifier-type.ts

@@ -669,6 +669,7 @@ export const modifierTypes = {
     (type, args) => new Modifiers.SwitchEffectTransferModifier(type, (args[0] as Pokemon).id), 'stick'),
 
   SHINY_CHARM: () => new ModifierType('Shiny Charm', 'Dramatically increases the chance of a wild Pokémon being shiny', (type, _args) => new Modifiers.ShinyRateBoosterModifier(type)),
+  ABILITY_CHARM: () => new ModifierType('Ability Charm', 'Dramatically increases the chance of a wild Pokémon having a hidden ability', (type, _args) => new Modifiers.HiddenAbilityRateBoosterModifier(type)),
 
   MINI_BLACK_HOLE: () => new TurnHeldItemTransferModifierType('Mini Black Hole'),
   
@@ -770,6 +771,7 @@ const modifierPool = {
     new WeightedModifierType(modifierTypes.BERRY_POUCH, 3),
     new WeightedModifierType(modifierTypes.EXP_CHARM, 4),
     new WeightedModifierType(modifierTypes.OVAL_CHARM, 2),
+    new WeightedModifierType(modifierTypes.ABILITY_CHARM, 2),
     new WeightedModifierType(modifierTypes.EXP_BALANCE, 1),
   ].map(m => { m.setTier(ModifierTier.ULTRA); return m; }),
   [ModifierTier.MASTER]: [

src/modifier/modifier.ts

@@ -1050,6 +1050,30 @@ export class ExpBalanceModifier extends PersistentModifier {
   }
 }
 
+export class HiddenAbilityRateBoosterModifier extends PersistentModifier {
+  constructor(type: ModifierType, stackCount?: integer) {
+    super(type, stackCount);
+  }
+
+  match(modifier: Modifier): boolean {
+    return modifier instanceof HiddenAbilityRateBoosterModifier;
+  }
+
+  clone(): HiddenAbilityRateBoosterModifier {
+    return new HiddenAbilityRateBoosterModifier(this.type, this.stackCount);
+  }
+
+  apply(args: any[]): boolean {
+    (args[0] as Utils.IntegerHolder).value *= Math.pow(2, -1 - this.getStackCount());
+
+    return true;
+  }
+
+  getMaxStackCount(): integer {
+    return 4;
+  }
+}
+
 export class ShinyRateBoosterModifier extends PersistentModifier {
   constructor(type: ModifierType, stackCount?: integer) {
     super(type, stackCount);