kata-business-rules

To solve this one I had used Java (which is not as sexy as Ruby or JS, though it got the job done:) as the language and TestNG as the testing framework and FEST Assertions to ease the pain of writing test methods.

Usage

Processes can be defined ad hoc (though there is BusinessProcessHelper class which defines all the ones described in the problem statement, using syntax like the one below:

BusinessProcess fourthProcess = new BusinessProcess()
  .withConditions(
    new IsType("Membership"),
    new HasState(new State("ACTIVE")),
    new PaymentHasReason(Reason.UPGRADE))
  .withResults(
    new ChangeState(new State("UPGRADED")));

which when applied to a Payment:

Payment payment = new Payment(
  new Product().withProperties(
    new Type("Membership"),
    new State("ACTIVE")), Reason.UPGRADE);

would change the State property of that product to new State("UPGRADED").

Overview of solution

Considering the fact, that each business rule can (and will) be something arbitrary, I had came with a simple solution and created a poor man's component system. There are 3 main groups of componentes

• Properties (which can be applied to a product)
• Conditions (which the process is checking before applying the results)
• Results (which will be produced by a process).

Condition is defined as an interface:

public interface Condition {

    public boolean validate(Product product);
    public boolean validate(Property property);
}

as is Result:

public interface Result {

    public void on(Product product);
}

Property is an abstract class:

public abstract class Property {
    private Product parentProduct;

    public Product getParentProduct() {
        return parentProduct;
    }

    public void setParentProduct(Product parentProduct) {
        this.parentProduct = parentProduct;
    }
}

Code has PaymentProcessor class defined, which can gather different BusinessProcesses and then apply each one to each of the Payments passed to it. Each Payment has both a Product for which it's done and a Reason for the payment (generic payment, upgrade, commision, etc.)

Test Log Output.

Just for the reference, this is log.debug() output from running BusinessProcessTest tests (tests for rules defined in problem description were run in more or less random order):

i.business.processes.BusinessProcess - using conditions = [{IsType -> expecting [Video]}, {HasName -> expecting [Learning To Ski]}]
i.business.processes.BusinessProcess - starting to process [{type = 'Video'}, {name = 'Learning To Ski'}, {physical = 'true'}, {Payment: reason = 'PAYMENT'}]
i.business.processes.BusinessProcess - producing results = [{AddProduct -> new product [[{type = 'Video'}, {name = 'First Aid'}, null]]}] if conditions are fulfilled
i.business.processes.BusinessProcess - produced results: [{AddProduct -> new product [[{type = 'Video'}, {name = 'First Aid'}, null]]}]

i.business.processes.BusinessProcess - using conditions = [{IsType -> expecting [book]}]
i.business.processes.BusinessProcess - starting to process [{type = 'book'}, {Payment: reason = 'null'}]
i.business.processes.BusinessProcess - producing results = [{PackingSlip -> [department = 'Royalty Department']}] if conditions are fulfilled
i.business.processes.BusinessProcess - produced results: [{PackingSlip -> [department = 'Royalty Department']}]

i.business.processes.BusinessProcess - using conditions = [{IsType -> expecting [book]}, {PaymentHasReason -> expecting [PAYMENT]}]
i.business.processes.BusinessProcess - starting to process [{type = 'book'}, {Payment: reason = 'PAYMENT'}]
i.business.processes.BusinessProcess - producing results = [{GenerateExtraPayment -> [receiver = Agent, paymentReason = COMMISSION]}] if conditions are fulfilled
i.business.processes.BusinessProcess - produced results: [{GenerateExtraPayment -> [receiver = Agent, paymentReason = COMMISSION]}]

i.business.processes.BusinessProcess - using conditions = [{IsType -> expecting [Membership]}, {PaymentHasReason -> expecting [PAYMENT]}]
i.business.processes.BusinessProcess - starting to process [{type = 'Membership'}, {Payment: reason = 'PAYMENT'}]
i.business.processes.BusinessProcess - producing results = [{ChangeState -> to [{state = 'ACTIVE'}]}] if conditions are fulfilled
i.business.processes.BusinessProcess - produced results: [{ChangeState -> to [{state = 'ACTIVE'}]}]

i.business.processes.BusinessProcess - using conditions = [{IsType -> expecting [Membership]}, {HasState -> expecting [{state = 'INACTIVE'}]}, {PaymentHasReason -> expecting [P] DEBUG i.business.processes.BusinessProcess - starting to process [{type = 'Membership'}, {state = 'INACTIVE'}, {Payment: reason = 'PAYMENT'}]
i.business.processes.BusinessProcess - producing results = [{ChangeState -> to [{state = 'ACTIVE'}]}, {Email -> message [Membership activated.]}] if conditions are fulfilled
i.business.processes.BusinessProcess - produced results: [{ChangeState -> to [{state = 'ACTIVE'}]}, {Email -> message [Membership activated.]}]

i.business.processes.BusinessProcess - using conditions = [{IsType -> expecting [Membership]}, {HasState -> expecting [{state = 'ACTIVE'}]}, {PaymentHasReason -> expecting [UPG] DEBUG i.business.processes.BusinessProcess - starting to process [{type = 'Membership'}, {state = 'ACTIVE'}, {Payment: reason = 'UPGRADE'}]
i.business.processes.BusinessProcess - producing results = [{ChangeState -> to [{state = 'UPGRADED'}]}, {Email -> message [Membership upgraded.]}] if conditions are fulfilled
i.business.processes.BusinessProcess - produced results: [{ChangeState -> to [{state = 'UPGRADED'}]}, {Email -> message [Membership upgraded.]}]

i.business.processes.BusinessProcess - using conditions = [{IsPhysical -> expecting [true]}, {PaymentHasReason -> expecting [PAYMENT]}]
i.business.processes.BusinessProcess - starting to process [{physical = 'true'}, {Payment: reason = 'PAYMENT'}]
i.business.processes.BusinessProcess - producing results = [{GenerateExtraPayment -> [receiver = Agent, paymentReason = COMMISSION]}] if conditions are fulfilled
i.business.processes.BusinessProcess - produced results: [{GenerateExtraPayment -> [receiver = Agent, paymentReason = COMMISSION]}]

i.business.processes.BusinessProcess - using conditions = [{IsType -> expecting [Membership]}, {HasState -> expecting [{state = 'ACTIVE'}]}, {PaymentHasReason -> expecting [UPG] DEBUG i.business.processes.BusinessProcess - starting to process [{type = 'Membership'}, {state = 'ACTIVE'}, {Payment: reason = 'UPGRADE'}]
i.business.processes.BusinessProcess - producing results = [{ChangeState -> to [{state = 'UPGRADED'}]}] if conditions are fulfilled
i.business.processes.BusinessProcess - produced results: [{ChangeState -> to [{state = 'UPGRADED'}]}]

i.business.processes.BusinessProcess - using conditions = [{IsPhysical -> expecting [true]}]
i.business.processes.BusinessProcess - starting to process [{physical = 'true'}, {Payment: reason = 'null'}]
i.business.processes.BusinessProcess - producing results = [{PackingSlip -> [department = '']}] if conditions are fulfilled
i.business.processes.BusinessProcess - produced results: [{PackingSlip -> [department = '']}]