public CheckoutEngine(Guards guards, IPaymentMethodInfoProvider paymentMethodInfoProvider, TransitionBuilder transitionBuilder)
{
PaymentMethodInfoProvider = paymentMethodInfoProvider;
Guards = guards;
TransitionBuilder = transitionBuilder;
// This state machine defines the checkout validation workflow. The keys are states
// and the values are arrays of transitions out of that state. Transitions describe
// the preconditions that must be met before we can move to a new state.
// When the checkout engine runs, it looks up the current state (dictionary key) and
// gets the transitions for that key (dictionary value). For each transition, it runs
// the guards. Each guard checks some state and simply returns true or false. The first
// transition for which all guards return true will be taken. If there are any triggers
// on that transition, they will be executed, then the current state will be set to
// the transition's target state. Now we have a new current state and we'll run this
// again.
// We keep looping until we end up in a state with no valid transitions (a "terminal
// state") or we transition back to the same state we started from (basic infinite
// loop protection). In either case, we have a final state that we return to the
// caller.
StateMachine = new Dictionary <CheckoutState, IEnumerable <Transition> >
{
{
CheckoutState.Start,
new Transition[]
{
TransitionBuilder
.Always()
.TransitionTo(CheckoutState.ShoppingCart_Validating),
}
},
{
CheckoutState.ShoppingCart_Validating,
new Transition[]
{
TransitionBuilder
.If(Guards.ShoppingCartIsEmpty)
.TransitionTo(CheckoutState.ShoppingCartIsEmpty),
TransitionBuilder
.If(Guards.SubtotalDoesNotMeetMinimumAmount)
.TransitionTo(CheckoutState.SubtotalDoesNotMeetMinimumAmount),
TransitionBuilder
.If(Guards.CartItemsLessThanMinimumItemCount)
.TransitionTo(CheckoutState.CartItemsLessThanMinimumItemCount),
TransitionBuilder
.If(Guards.CartItemsGreaterThanMaximumItemCount)
.TransitionTo(CheckoutState.CartItemsGreaterThanMaximumItemCount),
TransitionBuilder
.If(Guards.RecurringScheduleMismatchOnItems)
.TransitionTo(CheckoutState.RecurringScheduleMismatchOnItems),
TransitionBuilder
.Always()
.TransitionTo(CheckoutState.Account_Validating),
}
},
{
CheckoutState.Account_Validating,
new Transition[]
{
TransitionBuilder
.If(Guards.CustomerAccountRequired)
.TransitionTo(CheckoutState.CustomerAccountRequired)
.Then(
Triggers.UpdateAccount(CheckoutStageStatusExtensions.UpdateAvailable, false),
Triggers.UpdateAccount(CheckoutStageStatusExtensions.UpdateFulfilled, false)),
TransitionBuilder
.Always()
.TransitionTo(CheckoutState.PaymentMethod_Cleaning)
.Then(
Triggers.UpdateAccount(CheckoutStageStatusExtensions.UpdateAvailable, true),
Triggers.UpdateAccount(CheckoutStageStatusExtensions.UpdateFulfilled, true)),
}
},
{
CheckoutState.PaymentMethod_Cleaning,
new Transition[]
{
// If a payment method is selected but no details are entered, then deselect the payment method
TransitionBuilder
.If(
Guards.PaymentMethodIsCreditCard,
Guards.Not(Guards.PaymentMethodIsOffsite),
Guards.CreditCardDetailsMissing)
.TransitionTo(CheckoutState.PaymentMethod_Validating)
.Then(Triggers.ClearSelectedPaymentMethod),
TransitionBuilder
.If(
Guards.PaymentMethodIsPurchaseOrder,
Guards.PurchaseOrderDetailsMissing)
.TransitionTo(CheckoutState.PaymentMethod_Validating)
.Then(Triggers.ClearSelectedPaymentMethod),
TransitionBuilder
.Always()
.TransitionTo(CheckoutState.PaymentMethod_Validating),
}
},
{
CheckoutState.PaymentMethod_Validating,
new Transition[]
{
TransitionBuilder
.If(Guards.PaymentMethodRequired,
Guards.Not(Guards.PaymentMethodPresent))
.TransitionTo(CheckoutState.PaymentMethodRequired)
.Then(Triggers.UpdatePaymentMethod(CheckoutStageStatusExtensions.UpdateFulfilled, false)),
TransitionBuilder
.If(Guards.PaymentMethodIsOffsite)
.TransitionTo(CheckoutState.PaymentMethod_Valid),
TransitionBuilder
.If(Guards.PaymentMethodIsMicroPay)
.TransitionTo(CheckoutState.PaymentMethod_ValidatingMicropayDetails),
TransitionBuilder
.If(Guards.PaymentMethodIsPayPalExpress)
.TransitionTo(CheckoutState.PaymentMethod_ValidatingPayPalExpressDetails),
TransitionBuilder
.If(Guards.PaymentMethodIsAmazonPayments)
.TransitionTo(CheckoutState.PaymentMethod_ValidatingAmazonPaymentsDetails),
TransitionBuilder
.If(Guards.PaymentMethodIsCreditCard)
.TransitionTo(CheckoutState.PaymentMethod_ValidatingCreditCardDetails),
TransitionBuilder
.If(Guards.PaymentMethodIsPurchaseOrder)
.TransitionTo(CheckoutState.PaymentMethod_ValidatingPurchaseOrderDetails),
TransitionBuilder
.If(Guards.Always)
.TransitionTo(CheckoutState.PaymentMethod_Valid),
}
},
{
CheckoutState.PaymentMethod_ValidatingMicropayDetails,
new Transition[]
{
TransitionBuilder
.If(Guards.MicroPayBalanceIsInsufficient)
.TransitionTo(CheckoutState.MicroPayBalanceIsInsufficient)
.Then(Triggers.UpdatePaymentMethod(CheckoutStageStatusExtensions.UpdateFulfilled, false)),
TransitionBuilder
.If(Guards.Always)
.TransitionTo(CheckoutState.PaymentMethod_Valid),
}
},
{
CheckoutState.PaymentMethod_ValidatingPayPalExpressDetails,
new Transition[]
{
TransitionBuilder
.If(Guards.Always)
.TransitionTo(CheckoutState.PaymentMethod_Valid),
}
},
{
CheckoutState.PaymentMethod_ValidatingAmazonPaymentsDetails,
new Transition[]
{
TransitionBuilder
.If(Guards.AmazonPaymentsDetailsMissing)
.TransitionTo(CheckoutState.AmazonPaymentsDetailsRequired)
.Then(
Triggers.UpdatePaymentMethod(CheckoutStageStatusExtensions.UpdateAvailable, false),
Triggers.UpdatePaymentMethod(CheckoutStageStatusExtensions.UpdateFulfilled, false)),
TransitionBuilder
.If(Guards.Always)
.TransitionTo(CheckoutState.PaymentMethod_Valid),
}
},
{
CheckoutState.PaymentMethod_ValidatingCreditCardDetails,
new Transition[]
{
TransitionBuilder
.If(Guards.CreditCardDetailsMissing)
.TransitionTo(CheckoutState.CreditCardDetailsRequired)
.Then(
Triggers.UpdatePaymentMethod(CheckoutStageStatusExtensions.UpdateAvailable, false),
Triggers.UpdatePaymentMethod(CheckoutStageStatusExtensions.UpdateFulfilled, false)),
TransitionBuilder
.If(Guards.Always)
.TransitionTo(CheckoutState.PaymentMethod_Valid),
}
},
{
CheckoutState.PaymentMethod_ValidatingPurchaseOrderDetails,
new Transition[]
{
TransitionBuilder
.If(Guards.PurchaseOrderDetailsMissing)
.TransitionTo(CheckoutState.PurchaseOrderDetailsRequired)
.Then(
Triggers.UpdatePaymentMethod(CheckoutStageStatusExtensions.UpdateAvailable, false),
Triggers.UpdatePaymentMethod(CheckoutStageStatusExtensions.UpdateFulfilled, false)),
TransitionBuilder
.If(Guards.Always)
.TransitionTo(CheckoutState.PaymentMethod_Valid),
}
},
{
CheckoutState.PaymentMethod_Valid,
new Transition[]
{
TransitionBuilder
.If(Guards.Always)
.TransitionTo(CheckoutState.BillingAddress_Validating)
.Then(Triggers.UpdatePaymentMethod(CheckoutStageStatusExtensions.UpdateFulfilled, true)),
}
},
{
CheckoutState.BillingAddress_Validating,
new Transition[]
{
TransitionBuilder
.If(Guards.BillingAddressDisabled)
.TransitionTo(CheckoutState.BillingAddress_Valid)
.Then(Triggers.UpdateBillingAddress(CheckoutStageStatusExtensions.UpdateDisabled, true)),
TransitionBuilder
.If(Guards.BillingAddressRequired,
Guards.Not(Guards.BillingAddressPresent))
.TransitionTo(CheckoutState.BillingAddressRequired)
.Then(Triggers.UpdateBillingAddress(CheckoutStageStatusExtensions.UpdateFulfilled, false)),
TransitionBuilder
.If(Guards.Always)
.TransitionTo(CheckoutState.BillingAddress_Valid),
}
},
{
CheckoutState.BillingAddress_Valid,
new Transition[]
{
TransitionBuilder
.If(Guards.Always)
.TransitionTo(CheckoutState.ShippingAddress_Validating)
.Then(Triggers.UpdateBillingAddress(CheckoutStageStatusExtensions.UpdateFulfilled, true)),
}
},
{
CheckoutState.ShippingAddress_Validating,
new Transition[]
{
TransitionBuilder
.If(Guards.SkipShippingOnCheckout)
.TransitionTo(CheckoutState.ShippingAddress_Valid)
.Then(Triggers.UpdateShippingAddress(CheckoutStageStatusExtensions.UpdateDisabled, true)),
TransitionBuilder
.If(Guards.Not(Guards.AllowShipToDifferentThanBillTo))
.TransitionTo(CheckoutState.ShippingAddress_Valid)
.Then(Triggers.UpdateShippingAddress(CheckoutStageStatusExtensions.UpdateDisabled, true)),
TransitionBuilder
.If(Guards.ShippingAddressRequired,
Guards.Not(Guards.ShippingAddressPresent))
.TransitionTo(CheckoutState.ShippingAddressRequired)
.Then(Triggers.UpdateShippingAddress(CheckoutStageStatusExtensions.UpdateFulfilled, false)),
TransitionBuilder
.If(Guards.Always)
.TransitionTo(CheckoutState.ShippingAddress_Valid),
}
},
{
CheckoutState.ShippingAddress_Valid,
new Transition[]
{
TransitionBuilder
.If(Guards.Always)
.TransitionTo(CheckoutState.ShippingMethod_Validating)
.Then(Triggers.UpdateShippingAddress(CheckoutStageStatusExtensions.UpdateFulfilled, true)),
}
},
{
CheckoutState.ShippingMethod_Validating,
new Transition[]
{
TransitionBuilder
.If(Guards.SkipShippingOnCheckout)
.TransitionTo(CheckoutState.ShippingMethod_Valid)
.Then(Triggers.UpdateShippingMethod(CheckoutStageStatusExtensions.UpdateDisabled, true)),
TransitionBuilder
.If(Guards.Not(Guards.ShippingMethodRequired))
.TransitionTo(CheckoutState.ShippingMethod_Valid)
.Then(Triggers.UpdateShippingMethod(CheckoutStageStatusExtensions.UpdateRequired, false)),
TransitionBuilder
.If(Guards.ShippingMethodRequired,
Guards.Not(Guards.ShippingMethodPresent))
.TransitionTo(CheckoutState.ShippingMethodRequired)
.Then(Triggers.UpdateShippingMethod(CheckoutStageStatusExtensions.UpdateFulfilled, false)),
TransitionBuilder
.If(Guards.ShippingMethodPresent,
Guards.Not(Guards.ShippingMethodIsValid))
.TransitionTo(CheckoutState.ShippingMethodRequired)
.Then(Triggers.UpdateShippingMethod(CheckoutStageStatusExtensions.UpdateFulfilled, false)),
TransitionBuilder
.Always()
.TransitionTo(CheckoutState.ShippingMethod_Valid),
}
},
{
CheckoutState.ShippingMethod_Valid,
new Transition[]
{
TransitionBuilder
.Always()
.TransitionTo(CheckoutState.GiftCardSetup_Validating)
.Then(Triggers.UpdateShippingMethod(CheckoutStageStatusExtensions.UpdateFulfilled, true)),
}
},
{
CheckoutState.GiftCardSetup_Validating,
new Transition[]
{
TransitionBuilder
.If(Guards.CartContainsGiftCard,
Guards.Not(Guards.GiftCardSetupComplete))
.TransitionTo(CheckoutState.GiftCardRequiresSetup)
.Then(Triggers.UpdateGiftCardSetup(CheckoutStageStatusExtensions.UpdateFulfilled, false)),
TransitionBuilder
.Always()
.TransitionTo(CheckoutState.Checkout_Validating)
.Then(Triggers.UpdateGiftCardSetup(CheckoutStageStatusExtensions.UpdateFulfilled, true)),
}
},
{
CheckoutState.Checkout_Validating,
new Transition[]
{
TransitionBuilder
.If(Guards.ShippingAddressMustMatchBillingAddress,
Guards.ShippingAddressDoesNotMatchBillingAddress)
.TransitionTo(CheckoutState.ShippingAddressDoesNotMatchBillingAddress),
TransitionBuilder
.If(Guards.RequireCustomerOver13,
Guards.CustomerIsNotOver13)
.TransitionTo(CheckoutState.CustomerIsNotOver13),
TransitionBuilder
.If(Guards.TermsAndConditionsRequired,
Guards.TermsAndConditionsNotAccepted)
.TransitionTo(CheckoutState.TermsAndConditionsRequired),
TransitionBuilder
.Always()
.TransitionTo(CheckoutState.Valid),
}
},
{
CheckoutState.Valid,
new Transition[]
{ }
},
};
}