Order and Payment

payment/payment-worker/src/main/java/demo/function/PaymentFunction.java

@@ -0,0 +1,51 @@
+package demo.function;
+
+import demo.payment.Payment;
+import demo.payment.PaymentStatus;
+import demo.event.PaymentEvent;
+import demo.event.PaymentEventType;
+import org.apache.log4j.Logger;
+import org.springframework.statemachine.StateContext;
+
+import java.util.function.Function;
+
+/**
+ * The {@link PaymentFunction} is an abstraction used to map actions that are triggered by
+ * state transitions on a {@link demo.payment.Payment} resource on to a function. Mapped functions
+ * can take multiple forms and reside either remotely or locally on the classpath of this application.
+ *
+ * @author kbastani
+ */
+public abstract class PaymentFunction {
+
+    final private Logger log = Logger.getLogger(PaymentFunction.class);
+    final protected StateContext<PaymentStatus, PaymentEventType> context;
+    final protected Function<PaymentEvent, Payment> lambda;
+
+    /**
+     * Create a new instance of a class that extends {@link PaymentFunction}, supplying
+     * a state context and a lambda function used to apply {@link PaymentEvent} to a provided
+     * action.
+     *
+     * @param context is the {@link StateContext} for a replicated state machine
+     * @param lambda  is the lambda function describing an action that consumes an {@link PaymentEvent}
+     */
+    public PaymentFunction(StateContext<PaymentStatus, PaymentEventType> context,
+                           Function<PaymentEvent, Payment> lambda) {
+        this.context = context;
+        this.lambda = lambda;
+    }
+
+    /**
+     * Apply an {@link PaymentEvent} to the lambda function that was provided through the
+     * constructor of this {@link PaymentFunction}.
+     *
+     * @param event is the {@link PaymentEvent} to apply to the lambda function
+     */
+    public Payment apply(PaymentEvent event) {
+        // Execute the lambda function
+        Payment result = lambda.apply(event);
+        context.getExtendedState().getVariables().put("payment", result);
+        return result;
+    }
+}