gameEvents: created CHALLENGE_UNO event.

- Created `challengeUno.ts`.
- Checked if a player can be challenged.
- Player can be challenged only if `vulnerableToUNO` is equal to that player.
- If the challenge is successful, the player must draw two cards from the deck.
- Created tests for the challenge_uno event and its corner cases.

fixes: #145

backend/src/types.ts

@@ -63,6 +63,7 @@ export enum GameEventTypes {
     JOIN_GAME = 'JOIN_GAME',
     LEAVE_GAME = 'LEAVE_GAME',
     ANNOUNCE_UNO = 'ANNOUNCE_UNO',
+    CHALLENGE_UNO = 'CHALLENGE_UNO',
     STATE_SYNC = 'STATE_SYNC',
     START_GAME = 'START_GAME',
 }
@@ -97,6 +98,13 @@ export type GameEvent =
           playerId: string;
           data?: null;
       }
+    | {
+          type: GameEventTypes.CHALLENGE_UNO;
+          playerId: string;
+          data: {
+              challengedPlayerId: string;
+          };
+      }
     | {
           type: GameEventTypes.STATE_SYNC;
           data: {

backend/src/uno-game-engine/events/challengeUno.ts

@@ -0,0 +1,40 @@
+import assert from 'assert';
+import { EventResult, GameEvent, GamePlayer } from '../../types';
+import { GameEngine } from '../engine';
+import { getPlayer } from './eventHandlerUtils';
+
+export function canChallengeUNO(
+    game: GameEngine,
+    player: GamePlayer
+): EventResult {
+    if (game.runningEvents.vulnerableToUNO !== player) {
+        return {
+            type: 'ERROR',
+            message: 'Cannot challenge this player',
+        };
+    }
+
+    return { type: 'SUCCESS', message: 'Can challenge UNO' };
+}
+
+export function challengeUNO(game: GameEngine, event: GameEvent): EventResult {
+    assert(event.type === 'CHALLENGE_UNO', 'Invalid event type');
+    const player = getPlayer(game, event.data.challengedPlayerId);
+    if (!player) {
+        return { type: 'ERROR', message: 'Player not found' };
+    }
+
+    const canChallenge = canChallengeUNO(game, player);
+    if (canChallenge.type === 'ERROR') {
+        return canChallenge;
+    }
+
+    // draw two cards as penalty
+    // drawCardFromDeck() will set vulnerableToUNO to null
+    const drawPenaltyCards = game.drawCardFromDeck(player, 2);
+    if (drawPenaltyCards.type === 'ERROR') {
+        return drawPenaltyCards;
+    }
+
+    return { type: 'SUCCESS', message: 'UNO challenged successfully' };
+}

backend/src/uno-game-engine/gameEvents.ts

@@ -3,6 +3,7 @@
 import { EventResult, GameEvent, GameEventTypes } from '../types';
 import { type GameEngine } from './engine';
 import { announceUNO } from './events/announceUno';
+import { challengeUNO } from './events/challengeUno';
 import { drawCard } from './events/drawCard';
 import { joinGame } from './events/joinGame';
 import { leaveGame } from './events/leaveGame';
@@ -33,4 +34,5 @@ registerEventHandler(GameEventTypes.LEAVE_GAME, leaveGame);
 registerEventHandler(GameEventTypes.DRAW_CARD, drawCard);
 registerEventHandler(GameEventTypes.THROW_CARD, throwCard);
 registerEventHandler(GameEventTypes.ANNOUNCE_UNO, announceUNO);
+registerEventHandler(GameEventTypes.CHALLENGE_UNO, challengeUNO);
 registerEventHandler(GameEventTypes.START_GAME, startGame);

backend/tests/events.test.ts

@@ -1,6 +1,7 @@
 import { CardNumber, GameEventTypes } from '../src/types';
 import { GameEngine } from '../src/uno-game-engine/engine';
 import { announceUNO } from '../src/uno-game-engine/events/announceUno';
+import { challengeUNO } from '../src/uno-game-engine/events/challengeUno';
 import { drawCard } from '../src/uno-game-engine/events/drawCard';
 import { getPlayer } from '../src/uno-game-engine/events/eventHandlerUtils';
 import { throwCard } from '../src/uno-game-engine/events/throwCard';
@@ -33,6 +34,7 @@ describe('Events', () => {
         game = new GameEngine('dummyGame');
     });
 
+    // test cases for UNO announcement
     test('Announce UNO when player has only two cards and at least one of them is throwable', () => {
         // when player announces UNO first, then throws a card
         initializeMockGame(game, 3, 2, 1);
@@ -127,4 +129,88 @@ describe('Events', () => {
             getPlayer(game, '1')
         );
     });
+
+    // test cases for challenging UNO
+    test('Player did not announce UNO, and a player challenged him', () => {
+        initializeMockGame(game, 3, 2, 1);
+
+        const player = getPlayer(game, '1');
+        const throwStatus = throwCard(game, {
+            type: GameEventTypes.THROW_CARD,
+            playerId: '1',
+            data: { cardId: 'card-number-yellow-1-1' },
+        });
+        expect(throwStatus.type).toBe('SUCCESS');
+        expect(player?.cards.length).toBe(1);
+        expect(game.runningEvents.hasAnnouncedUNO).toBe(null);
+        expect(game.runningEvents.vulnerableToUNO).toBe(getPlayer(game, '1'));
+
+        challengeUNO(game, {
+            type: GameEventTypes.CHALLENGE_UNO,
+            playerId: '2', // player 2 challenged player 1
+            data: { challengedPlayerId: '1' },
+        });
+
+        expect(game.runningEvents.vulnerableToUNO).toBe(null);
+        expect(player!.cards.length).toBe(3);
+    });
+
+    test('Player announced UNO, and a player challenged him', () => {
+        initializeMockGame(game, 3, 1, 1);
+
+        const player = getPlayer(game, '1');
+        const announceStatus = announceUNO(game, {
+            type: GameEventTypes.ANNOUNCE_UNO,
+            playerId: '1',
+        });
+
+        expect(announceStatus.type).toBe('SUCCESS');
+        expect(game.runningEvents.hasAnnouncedUNO).toBe(player);
+        expect(game.runningEvents.vulnerableToUNO).toBe(null);
+
+        const challengeStatus = challengeUNO(game, {
+            type: GameEventTypes.CHALLENGE_UNO,
+            playerId: '2', // player 2 challenged player 1
+            data: { challengedPlayerId: '1' },
+        });
+
+        expect(challengeStatus.type).toBe('ERROR');
+        expect(player!.cards.length).toBe(1);
+    });
+
+    test('Player did not announce UNO and next player played take his turn without challenging, then another player challenged the previous player', () => {
+        initializeMockGame(game, 3, 2, 1);
+
+        const player1 = getPlayer(game, '1');
+        const player2 = getPlayer(game, '2');
+
+        const throwStatus1 = throwCard(game, {
+            type: GameEventTypes.THROW_CARD,
+            playerId: '1',
+            data: { cardId: 'card-number-yellow-1-1' },
+        });
+
+        expect(throwStatus1.type).toBe('SUCCESS');
+        expect(player1?.cards.length).toBe(1);
+        expect(game.runningEvents.hasAnnouncedUNO).toBe(null);
+        expect(game.runningEvents.vulnerableToUNO).toBe(player1);
+
+        const throwStatus2 = throwCard(game, {
+            type: GameEventTypes.THROW_CARD,
+            playerId: '2',
+            data: { cardId: 'card-number-yellow-2-1' },
+        });
+
+        expect(throwStatus2.type).toBe('SUCCESS');
+        expect(player2?.cards.length).toBe(1);
+
+        const challengeStatus = challengeUNO(game, {
+            type: GameEventTypes.CHALLENGE_UNO,
+            playerId: '2', // player 2 challenged player 1
+            data: { challengedPlayerId: '1' },
+        });
+
+        expect(challengeStatus.type).toBe('ERROR');
+        expect(player1!.cards.length).toBe(1);
+    });
 });