Wind Rider gives an attack boost under Tailwind (#609)

When a Pokemon has the ability Wind Rider and has Tailwind on its side of the field, it will gain an Attack boost.

Case: Brambleghast using Power Whip against Brambleghast, with the attacking Brambleghast under Tailwind.

Current:
`0 Atk Brambleghast Power Whip vs. 0 HP / 0 Def Brambleghast: 97-115 (38.6 - 45.8%) -- guaranteed 3HKO`

New:
`+1 0 Atk Brambleghast Power Whip vs. 0 HP / 0 Def Brambleghast: 146-172 (58.1 - 68.5%) -- guaranteed 2HKO`

calc/src/mechanics/gen789.ts

@@ -28,6 +28,7 @@ import {
   checkMultihitBoost,
   checkSeedBoost,
   checkTeraformZero,
+  checkWindRider,
   checkWonderRoom,
   computeFinalStats,
   countBoosts,
@@ -83,6 +84,9 @@ export function calculateSMSSSV(
   checkIntrepidSword(attacker, gen);
   checkIntrepidSword(defender, gen);
 
+  checkWindRider(attacker, field.attackerSide);
+  checkWindRider(defender, field.defenderSide);
+
   if (move.named('Meteor Beam', 'Electro Shot')) {
     attacker.boosts.spa +=
       attacker.hasAbility('Simple') ? 2

calc/src/mechanics/util.ts

@@ -253,6 +253,12 @@ export function checkDauntlessShield(source: Pokemon, gen: Generation) {
   }
 }
 
+export function checkWindRider(source: Pokemon, attackingSide: Side) {
+  if (source.hasAbility('Wind Rider') && attackingSide.isTailwind) {
+    source.boosts.atk = Math.min(6, source.boosts.atk + 1);
+  }
+}
+
 export function checkEmbody(source: Pokemon, gen: Generation) {
   if (gen.num < 9) return;
   switch (source.ability) {

calc/src/test/calc.test.ts

@@ -1222,6 +1222,22 @@ describe('calc', () => {
           "0 Atk Weavile with an ally's Flower Gift Power Spot boosted switching boosted Pursuit (80 BP) vs. 0 HP / 0 Def Vulpix in Sun: 399-469 (183.8 - 216.1%) -- guaranteed OHKO"
         );
       });
+
+      test('Wind Rider should give an Attack boost in Tailwind', () => {
+        const attacker = Pokemon('Brambleghast', {'ability': 'Wind Rider'});
+        const defender = Pokemon('Brambleghast', {'ability': 'Wind Rider'});
+        const field = Field({
+          attackerSide: {
+            isTailwind: true,
+          },
+        });
+
+        const result = calculate(attacker, defender, Move('Power Whip'), field);
+
+        expect(attacker.boosts.atk).toBe(0);
+        expect(result.attacker.boosts.atk).toBe(1);
+      });
+
       describe('Tera Stellar', () => {
         const terastal = Pokemon('Arceus', {teraType: 'Stellar'});
         const control = Pokemon('Arceus');