Question

For example, I have several different merchant clients who I handle transactions for. They want different metrics for determining fraud, many of which are common. I’d like to have something to the effect of:

class Fraud
{

}

class InvalidCheckFraud extends Fraud
{

}

class NotAMemberFRaud extends Fraud
{

}

class CustomerLooksFunnyFraud extends Fraud
{

}

etc…

I’d like to just be able to run zero to many extended Fraud classes using a command like:

$fraudCheck = new Fraud();
$fraudCheck->checkMerchant($merchId);

I don’t mind solving this in a completely home grown fashion, but if it’s already been figured out, I’d like to go that route.

I’m coding in PHP, but am fine with a reference using any other language.

Answer 1

Looks like you’re looking for something like the Strategy pattern.

You should define an interface for your Fraud classes that accept a $merchId:

interface Fraud {
    public function check($merchId);
}

Then implement each subclass:

class InvalidCheckFraud implements Fraud {
    public function check($merchId) {
        // do something and return
        return true;
    }
}

class NotAMemberFraud implements Fraud
{
    public function check($merchId) {
        // do something and return
        return false;
    }
}

Then, create a context class that checks for each one:

class FraudContext implements Fraud {
    protected $_frauds = array();    

    public function addFraud(Fraud $fraud) {
        $this->_frauds[] = $fraud;
    }

    public function check($merchId) {
        foreach ($this->_frauds as $fraud) {
            if (!$fraud->check($merchId)) {
                throw new LogicException(
                  "{$merchId} has failed the check for ".get_class($fraud)
                );
            }
        }
        return true;
    }
}

$merchId = 42;
$context = new FraudContext;
$context->addFraud(new InvalidCheckFraud);
$context->addFraud(new NotAMemberFRaud);
$context->check($merchId);