Fix duplicate currencies causing negative balance in hasCurrencies/pa…

packages/ludiek/src/plugins/currency/CurrencyPlugin.ts

@@ -99,14 +99,13 @@ export class CurrencyPlugin extends LudiekPlugin {
   /**
    * Try to spend the specified amount of currencies if you have it.
    * @return true if it was spent
-   *
-   * @todo(#61) Each currency is checked individually, meaning that if there are duplicate Ids it could lead to negative balance.
    */
   public payCurrencies(currencies: Currency[]): boolean {
-    if (!this.hasCurrencies(currencies)) {
+    const simplified = this.simplifyCurrencyList(currencies);
+    if (!this.hasCurrencies(simplified)) {
       return false;
     }
-    this.loseCurrencies(currencies);
+    this.loseCurrencies(simplified);
     return true;
   }
 
@@ -120,13 +119,9 @@ export class CurrencyPlugin extends LudiekPlugin {
 
   /**
    * Whether we have a list of currencies
-   *
-   * @todo(#61) Each currency is checked individually, meaning that if there are duplicate Ids the answer could be misleading.
    */
   public hasCurrencies(currencies: Currency[]): boolean {
-    return currencies.every((c) => {
-      return this.hasCurrency(c);
-    });
+    return this.simplifyCurrencyList(currencies).every((c) => this.hasCurrency(c));
   }
 
   /**
@@ -167,6 +162,14 @@ export class CurrencyPlugin extends LudiekPlugin {
     return id in this._state.balances;
   }
 
+  private simplifyCurrencyList(currencies: Currency[]): Currency[] {
+    const merged: Record<string, number> = {};
+    for (const c of currencies) {
+      merged[c.id] = (merged[c.id] ?? 0) + c.amount;
+    }
+    return Object.entries(merged).map(([id, amount]) => ({ id, amount }));
+  }
+
   private validate(currency: Currency, action: string): void {
     if (!this.supportsCurrency(currency.id)) {
       throw new InvalidCurrencyError(`Cannot ${action} '${currency.amount}' of '${currency.id}'. Unknown currency`);

packages/ludiek/tests/plugins/currency/currency-plugin-multiples.spec.ts

@@ -92,4 +92,48 @@ describe('Multiple currencies', () => {
     // Assert
     expect(isPaid).toBe(false);
   });
+
+  it('does not pay duplicate currencies when combined amount exceeds balance', () => {
+    // Arrange
+    currency.gainCurrency({ id: '/currency/money', amount: 1 });
+
+    // Act — paying 1+1=2 money with only 1 in balance should fail
+    const isPaid = currency.payCurrencies([
+      { id: '/currency/money', amount: 1 },
+      { id: '/currency/money', amount: 1 },
+    ]);
+
+    // Assert
+    expect(isPaid).toBe(false);
+    expect(currency.getBalance('/currency/money')).toBe(1);
+  });
+
+  it('pays duplicate currencies when combined amount is within balance', () => {
+    // Arrange
+    currency.gainCurrency({ id: '/currency/money', amount: 3 });
+
+    // Act — paying 1+1=2 money with 3 in balance should succeed
+    const isPaid = currency.payCurrencies([
+      { id: '/currency/money', amount: 1 },
+      { id: '/currency/money', amount: 1 },
+    ]);
+
+    // Assert
+    expect(isPaid).toBe(true);
+    expect(currency.getBalance('/currency/money')).toBe(1);
+  });
+
+  it('hasCurrencies returns false for duplicate currencies exceeding balance', () => {
+    // Arrange
+    currency.gainCurrency({ id: '/currency/money', amount: 1 });
+
+    // Act
+    const has = currency.hasCurrencies([
+      { id: '/currency/money', amount: 1 },
+      { id: '/currency/money', amount: 1 },
+    ]);
+
+    // Assert
+    expect(has).toBe(false);
+  });
 });