Improve Weight Handling (#535)

- All weight modification code is moved to `src/mechanics/util.ts`
- Heavy/Light Metal and Float Stone can now stack.
- Heavy Metal, Light Metal, and Float are now shown in the description when applicable
- Weight modification is now done in Hectograms, though it still returns Kilograms after truncating fractional hectograms (Showdown implementation uses truncation, not rounding).
- It is now impossible to get a weight lower than 0.1kg.
- Tests have been written for weight handling that mirror Showdown's.

calc/src/mechanics/gen56.ts

@@ -31,7 +31,7 @@ import {
   getModifiedStat,
   getMoveEffectiveness,
   getStabMod,
-  getWeightFactor,
+  getWeight,
   handleFixedDamageMoves,
   isGrounded,
   OF16, OF32,
@@ -461,7 +461,7 @@ export function calculateBasePowerBWXY(
     break;
   case 'Low Kick':
   case 'Grass Knot':
-    const w = defender.weightkg * getWeightFactor(defender);
+    const w = getWeight(defender, desc, 'defender');
     basePower = w >= 200 ? 120 : w >= 100 ? 100 : w >= 50 ? 80 : w >= 25 ? 60 : w >= 10 ? 40 : 20;
     desc.moveBP = basePower;
     break;
@@ -472,8 +472,8 @@ export function calculateBasePowerBWXY(
   case 'Heavy Slam':
   case 'Heat Crash':
     const wr =
-        (attacker.weightkg * getWeightFactor(attacker)) /
-        (defender.weightkg * getWeightFactor(defender));
+        getWeight(attacker, desc, 'attacker') /
+        getWeight(defender, desc, 'defender');
     basePower = wr >= 5 ? 120 : wr >= 4 ? 100 : wr >= 3 ? 80 : wr >= 2 ? 60 : 40;
     desc.moveBP = basePower;
     break;

calc/src/mechanics/gen789.ts

@@ -38,7 +38,7 @@ import {
   getQPBoostedStat,
   getMoveEffectiveness,
   getShellSideArmCategory,
-  getWeightFactor,
+  getWeight,
   handleFixedDamageMoves,
   isGrounded,
   OF16, OF32,
@@ -716,7 +716,7 @@ export function calculateBasePowerSMSSSV(
     break;
   case 'Low Kick':
   case 'Grass Knot':
-    const w = defender.weightkg * getWeightFactor(defender);
+    const w = getWeight(defender, desc, 'defender');
     basePower = w >= 200 ? 120 : w >= 100 ? 100 : w >= 50 ? 80 : w >= 25 ? 60 : w >= 10 ? 40 : 20;
     desc.moveBP = basePower;
     break;
@@ -733,8 +733,8 @@ export function calculateBasePowerSMSSSV(
   case 'Heavy Slam':
   case 'Heat Crash':
     const wr =
-        (attacker.weightkg * getWeightFactor(attacker)) /
-        (defender.weightkg * getWeightFactor(defender));
+        getWeight(attacker, desc, 'attacker') /
+        getWeight(defender, desc, 'defender');
     basePower = wr >= 5 ? 120 : wr >= 4 ? 100 : wr >= 3 ? 80 : wr >= 2 ? 60 : 40;
     desc.moveBP = basePower;
     break;

calc/src/mechanics/util.ts

@@ -552,9 +552,23 @@ export function getShellSideArmCategory(source: Pokemon, target: Pokemon): MoveC
   return physicalDamage > specialDamage ? 'Physical' : 'Special';
 }
 
-export function getWeightFactor(pokemon: Pokemon) {
-  return pokemon.hasAbility('Heavy Metal') ? 2
-    : (pokemon.hasAbility('Light Metal') || pokemon.hasItem('Float Stone')) ? 0.5 : 1;
+export function getWeight(pokemon: Pokemon, desc: RawDesc, role: 'defender' | 'attacker') {
+  let weightHG = pokemon.weightkg * 10;
+  const abilityFactor = pokemon.hasAbility('Heavy Metal') ? 2
+    : pokemon.hasAbility('Light Metal') ? 0.5
+    : 1;
+  if (abilityFactor !== 1) {
+    weightHG = Math.max(Math.trunc(weightHG * abilityFactor), 1);
+    desc[`${role}Ability`] = pokemon.ability;
+  }
+
+  if (pokemon.hasItem('Float Stone')) {
+    weightHG = Math.max(Math.trunc(weightHG * 0.5), 1);
+    desc[`${role}Item`] = pokemon.item;
+  }
+
+  // convert back to kg
+  return weightHG / 10;
 }
 
 export function getStabMod(pokemon: Pokemon, move: Move, desc: RawDesc) {

calc/src/test/calc.test.ts

@@ -264,6 +264,41 @@ describe('calc', () => {
           '0 Atk Abomasnow Ice Shard vs. 0 HP / 0 Def Multiscale Dragonite: 84-102 (26 - 31.5%) -- guaranteed 4HKO'
         );
       });
+      describe('Weight', function () {
+        describe('Heavy Metal', () => {
+          function testBP(ability: string) {
+            return calculate(
+              Pokemon('Simisage', {ability}),
+              Pokemon('Simisear', {ability: 'Heavy Metal'}),
+              Move('Grass Knot')
+            ).rawDesc.moveBP;
+          }
+          it('should double the weight of a Pokemon', () => expect(testBP('Gluttony')).toBe(80));
+          it('should be negated by Mold Breaker', () => expect(testBP('Mold Breaker')).toBe(60));
+        });
+        describe('Light Metal', () => {
+          function testBP(ability: string) {
+            return calculate(
+              Pokemon('Simisage', {ability}),
+              Pokemon('Registeel', {ability: 'Light Metal'}),
+              Move('Grass Knot')
+            ).rawDesc.moveBP;
+          }
+          it('should halve the weight of a Pokemon', () => expect(testBP('Gluttony')).toBe(100));
+          it('should be negated by Mold Breaker', () => expect(testBP('Mold Breaker')).toBe(120));
+        });
+        describe('Float Stone', () => {
+          function testBP(ability?: string) {
+            return calculate(
+              Pokemon('Simisage', {ability: 'Gluttony'}),
+              Pokemon('Registeel', {ability, item: 'Float Stone'}),
+              Move('Grass Knot')
+            ).rawDesc.moveBP;
+          }
+          it('should halve the weight of a Pokemon', () => expect(testBP()).toBe(100));
+          it('should stack with Light Metal', () => expect(testBP('Light Metal')).toBe(80));
+        });
+      });
     });
 
     inGen(8, ({gen, Pokemon}) => {