feat: Bank Sync Connector Architecture (#75)

app/src/lib/connectors.ts

@@ -0,0 +1,38 @@
+export interface Transaction {
+  date: string;
+  amount: number;
+  description: string;
+  category?: string;
+}
+
+export interface BankConnector {
+  authenticate(credentials: Record<string, any>): Promise<boolean>;
+  fetchTransactions(startDate: string, endDate: string): Promise<Transaction[]>;
+  fetchBalance(): Promise<number>;
+}
+
+export class MockBankConnector implements BankConnector {
+  private isAuthenticated = false;
+
+  async authenticate(credentials: Record<string, any>): Promise<boolean> {
+    if (credentials.username === 'test_user') {
+      this.isAuthenticated = true;
+      return true;
+    }
+    return false;
+  }
+
+  async fetchTransactions(startDate: string, endDate: string): Promise<Transaction[]> {
+    if (!this.isAuthenticated) throw new Error('Not authenticated');
+    return [
+      { date: startDate, amount: -15.50, description: 'Coffee Shop', category: 'Food' },
+      { date: startDate, amount: -100.00, description: 'Grocery Store', category: 'Groceries' },
+      { date: endDate, amount: 2000.00, description: 'Payroll Deposit', category: 'Income' }
+    ];
+  }
+
+  async fetchBalance(): Promise<number> {
+    if (!this.isAuthenticated) throw new Error('Not authenticated');
+    return 1884.50;
+  }
+}