gameEvent: Implement Throw Card Event

Adds the throw card event handler.

Fixes #44

Signed-off-by: Sagnik Mandal <[email protected]>

ARCHITECTURE.md

@@ -31,13 +31,12 @@ format of the message is:
 
 ```json
 {
-	"type": "DRAW_CARD",
-	"player": "player1",
-	"data": {
-		"cardID": "red-5"
-	}
+	"type": "THROW_CARD",
+	"playerId": "1",
+	"cardId": "card-number-red-5",
 }
 ```
+Other possible values for `type` are `DRAW_CARD`, `ANNOUNCE_UNO`, etc.
 
 When such a request reaches the server, the server updates the game state and sends the message to all clients (through the polling mechanism). The clients update their game state accordingly, and make the necessary changes to their UI and game state.
 

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

@@ -1,7 +1,7 @@
 import { getShuffledCardDeck, shuffle } from './deck';
 import { handleEvent } from './gameEvents';
 
-const NUM_CARDS_PER_PLAYER = 7;
+export const NUM_CARDS_PER_PLAYER = 7;
 
 export class GameEngine {
     cardDeck: UNOCard[];
@@ -47,9 +47,9 @@ export class GameEngine {
         this.currentPlayerIndex =
             (this.currentPlayerIndex + this.direction) % this.players.length;
     }
-    drawCardFromDeck(player: Player): EventResult {
+    drawCardFromDeck(player: Player, numCards = 1): EventResult {
         try {
-            if (this.cardDeck.length === 0) {
+            if (this.cardDeck.length < numCards) {
                 this.cardDeck = [...this.thrownCards];
                 this.thrownCards = [];
                 shuffle(this.cardDeck);
@@ -58,15 +58,18 @@ export class GameEngine {
                 (p: Player) => p.id === player.id
             );
             if (currentPlayer && this.cardDeck) {
-                const card = this.cardDeck.pop();
-                if (card) {
-                    currentPlayer.cards.push(card);
+                const cards = this.cardDeck.splice(-numCards, numCards);
+                if (cards.length > 0) {
+                    currentPlayer.cards.push(...cards);
                     return {
                         type: 'SUCCESS',
-                        message: 'Card drawn successfully',
+                        message: `${numCards} card(s) drawn successfully`,
                     };
                 } else
-                    return { type: 'ERROR', message: 'Unable to draw a card' };
+                    return {
+                        type: 'ERROR',
+                        message: `Unable to draw ${numCards} card(s)`,
+                    };
             } else {
                 return {
                     type: 'ERROR',

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

@@ -0,0 +1,97 @@
+import { registerEventHandler } from '../gameEvents';
+import { GameEngine } from '../engine';
+
+function findPlayer(game: GameEngine, playerId: string) {
+    return game.players.find((p) => p.id === playerId);
+}
+
+function findCard(player, cardId: string) {
+    return player.cards.find((c) => c.id === cardId);
+}
+
+function canThrowCard(game: GameEngine, player, card): EventResult {
+    const { currentPlayerIndex, players } = game;
+    const currentPlayer = players[currentPlayerIndex];
+
+    // check if the player is the current player
+    if (currentPlayer.id !== player.id) {
+        return { type: 'ERROR', message: 'It is not your turn' };
+    }
+
+    // check if the player actually possesses the card
+    if (!player.cards.some((c) => c.id === card.id)) {
+        return { type: 'ERROR', message: 'Player does not possess the card' };
+    }
+
+    // check if the card can be thrown
+    if (
+        game.lastThrownCard &&
+        !(
+            game.lastThrownCard.color === card.color ||
+            game.lastThrownCard.value === card.value ||
+            card.color === 'wild'
+        )
+    ) {
+        return { type: 'ERROR', message: 'Cannot throw this card' };
+    }
+
+    return { type: 'SUCCESS', message: 'Can throw card' };
+}
+
+export function throwCard(game: GameEngine, event: GameEvent): EventResult {
+    const player = findPlayer(game, event.playerId);
+    if (!player) {
+        return { type: 'ERROR', message: 'Player not found' };
+    }
+
+    const card = findCard(player, event.data.card.id);
+    if (!card) {
+        return { type: 'ERROR', message: 'Card not found' };
+    }
+
+    const canThrow = canThrowCard(game, player, card);
+    if (canThrow.type === 'ERROR') {
+        return canThrow;
+    }
+
+    player.cards = player.cards.filter((c) => c.id !== card.id);
+
+    game.thrownCards.push(card);
+    game.lastThrownCard = card;
+
+    game.nextPlayer();
+
+    // handle special cards
+    if (card.type === 'special') {
+        handleSpecialCard(game, card);
+    }
+
+    return { type: 'SUCCESS', message: 'Card thrown successfully' };
+}
+
+function handleSpecialCard(game: GameEngine, card: UNOCard) {
+    switch (card.value) {
+        case 'skip':
+            game.nextPlayer();
+            break;
+        case 'reverse':
+            game.direction *= -1;
+            break;
+        case 'draw2':
+            {
+                const nextPlayer = game.players[game.currentPlayerIndex];
+                game.drawCardFromDeck(nextPlayer, 2);
+            }
+            break;
+        case 'draw4':
+            {
+                const currentPlayer = game.players[game.currentPlayerIndex];
+                game.drawCardFromDeck(currentPlayer, 4);
+            }
+            break;
+        default:
+            break;
+    }
+}
+
+registerEventHandler('THROW_CARD', throwCard);

backend/tests/engine.test.ts

@@ -1,8 +1,24 @@
-import { GameEngine } from '../src/uno-game-engine/engine';
+import {
+    GameEngine,
+    NUM_CARDS_PER_PLAYER,
+} from '../src/uno-game-engine/engine';
+
+function generateMockPlayers(numPlayers: number) {
+    const players: Player[] = [];
+    for (let i = 0; i < numPlayers; i++) {
+        players.push({ id: i.toString(), cards: [] });
+    }
+    return players;
+}
+
+describe('GameEngine', () => {
+    let game: GameEngine;
+
+    beforeEach(() => {
+        game = new GameEngine();
+    });
 
-describe('testing drawCardFromDeck()', () => {
     test('draws a card when deck is empty but thrownCards is not', () => {
-        const game = new GameEngine();
         game.addPlayer({ id: '1', cards: [] });
         game.cardDeck = [];
         game.thrownCards = [
@@ -18,4 +34,59 @@ describe('testing drawCardFromDeck()', () => {
         expect(player.cards.length).toBe(1);
         expect(status.type).toBe('SUCCESS');
     });
+
+    test('allotCards() throws an error when there are not enough cards to distribute', () => {
+        const MAX_CARDS = 108;
+        const MAXIMUM_PLAYERS = Math.ceil(MAX_CARDS / NUM_CARDS_PER_PLAYER) + 1;
+        game.players = generateMockPlayers(MAXIMUM_PLAYERS);
+        expect(() => game.allotCards()).toThrow(
+            'Not enough cards to distribute'
+        );
+    });
+
+    test('addPlayer() adds a player to the game', () => {
+        game.addPlayer({ id: '1', cards: [] });
+        expect(game.players.length).toBe(1);
+    });
+
+    test('startGame() throws an error when there are not enough players', () => {
+        expect(() => game.startGame()).toThrow(
+            'Not enough players to start the game'
+        );
+    });
+
+    test('startGame() changes the status to STARTED when there are enough players', () => {
+        game.players = generateMockPlayers(2);
+        game.startGame();
+        expect(game.status).toBe('STARTED');
+    });
+
+    test('nextPlayer() changes the current player index', () => {
+        game.players = generateMockPlayers(2);
+
+        // Initial player index is 0, so next player should be 1
+        game.nextPlayer();
+        expect(game.currentPlayerIndex).toBe(1);
+
+        // As only 2 players are there, next player should loop back to 0
+        game.nextPlayer();
+        expect(game.currentPlayerIndex).toBe(0);
+    });
+
+    test('drawCardFromDeck() draws a card from the deck', () => {
+        game.players = generateMockPlayers(2);
+        const player = game.players[0];
+        const status = game.drawCardFromDeck(player);
+        expect(game.cardDeck.length).toBe(107);
+        expect(player.cards.length).toBe(1);
+        expect(status.type).toBe('SUCCESS');
+
+        expect(game.cardDeck).not.toContain(player.cards[0]);
+    });
+
+    test('drawCardFromDeck() returns an error when the player is not found', () => {
+        const status = game.drawCardFromDeck({ id: '1', cards: [] });
+        expect(status.type).toBe('ERROR');
+        expect(status.message).toBe('Player not found or cardDeck is empty');
+    });
 });