CHALLENGE 2: Access Modifiers
==============================

SOLUTION:

class BankAccount {
  private balance: number = 0;

  public deposit(amount: number): void {
    if (amount > 0) {
      this.balance += amount;
      console.log(`Deposited $${amount}. New balance: $${this.balance}`);
    } else {
      console.log("Deposit amount must be positive");
    }
  }

  public withdraw(amount: number): void {
    if (amount > 0 && amount <= this.balance) {
      this.balance -= amount;
      console.log(`Withdrew $${amount}. New balance: $${this.balance}`);
    } else {
      console.log("Insufficient funds or invalid amount");
    }
  }

  public getBalance(): number {
    return this.balance;
  }
}

// Using the bank account
const account = new BankAccount();
account.deposit(100);      // Deposited $100. New balance: $100
account.deposit(50);       // Deposited $50. New balance: $150
account.withdraw(30);      // Withdrew $30. New balance: $120
account.withdraw(200);     // Insufficient funds or invalid amount
console.log(account.getBalance());  // Output: 120

// This would cause an error (balance is private):
// account.balance = 999999;  // ❌ Error! Property 'balance' is private

EXPLANATION:
- "private balance: number = 0" — hidden from outside; only accessible inside the class
- "public deposit(...)" — anyone can call this
- "public getBalance()" — anyone can call this
- Business logic is enforced: withdraw() checks for sufficient funds
- Users can't cheat by directly setting balance

WHY PRIVATE IS IMPORTANT:
Without private, this would be possible (bad!):
  const account = new BankAccount();
  account.balance = 1000000;  // Cheating! No business logic applied

With private, this is impossible:
  account.balance = 1000000;  // ❌ Error! balance is private

EXTENSION: Add a withdraw(amount) return value
If you want to know if withdrawal succeeded:

class BankAccount {
  private balance: number = 0;

  public withdraw(amount: number): boolean {
    if (amount > 0 && amount <= this.balance) {
      this.balance -= amount;
      return true;
    }
    return false;
  }
}

const success = account.withdraw(30);
if (success) {
  console.log("Withdrawal successful");
} else {
  console.log("Withdrawal failed");
}

KEY INSIGHT:
Private properties protect data integrity. They force users to go through methods,
which can validate and enforce business rules.