#Facade

#Overview

Provide a simplified interface to a complex subsystem.

#When to use

• You want a clean API for a complex set of classes.
• You want to decouple clients from subsystem details.

#Java example

class PaymentFacade {
    private final FraudCheck fraud = new FraudCheck();
    private final PaymentGateway gateway = new PaymentGateway();

    public boolean pay(String userId, int amount) {
        if (!fraud.isAllowed(userId, amount)) {
            return false;
        }
        return gateway.charge(userId, amount);
    }
}

#TypeScript example

class PaymentFacade {
  private fraud = new FraudCheck();
  private gateway = new PaymentGateway();

  pay(userId: string, amount: number): boolean {
    if (!this.fraud.isAllowed(userId, amount)) {
      return false;
    }
    return this.gateway.charge(userId, amount);
  }
}

#Pros and cons

Pros:

• Simplifies client usage.
• Reduces coupling.

Cons:

• Can become a god object.
• May hide important capabilities.

#Common pitfalls

• Putting business logic into the facade.
• Growing the facade instead of creating focused APIs.

#Related patterns

• Adapter
• Singleton