Golang状态模式状态机设计与实现示例

type OrderState interface {
    Pay(order *OrderContext)
    Ship(order *OrderContext)
    Complete(order *OrderContext)
}

type OrderContext struct {
    State OrderState
}

func (o *OrderContext) Pay() {
    o.State.Pay(o)
}

func (o *OrderContext) Ship() {
    o.State.Ship(o)
}

func (o *OrderContext) Complete() {
    o.State.Complete(o)
}

type PendingState struct{}

func (s *PendingState) Pay(order *OrderContext) {
    fmt.Println("订单已支付")
    order.State = &PaidState{}
}

func (s *PendingState) Ship(order *OrderContext) {
    fmt.Println("无法发货：订单尚未支付")
}

func (s *PendingState) Complete(order *OrderContext) {
    fmt.Println("无法完成：订单尚未发货")
}

type PaidState struct{}

func (s *PaidState) Pay(order *OrderContext) {
    fmt.Println("订单已支付，无需重复支付")
}

func (s *PaidState) Ship(order *OrderContext) {
    fmt.Println("订单已发货")
    order.State = &ShippedState{}
}

func (s *PaidState) Complete(order *OrderContext) {
    fmt.Println("无法完成：尚未发货")
}

type ShippedState struct{}

func (s *ShippedState) Pay(order *OrderContext) {
    fmt.Println("无法支付：订单已发货")
}

func (s *ShippedState) Ship(order *OrderContext) {
    fmt.Println("无法重复发货")
}

func (s *ShippedState) Complete(order *OrderContext) {
    fmt.Println("订单已完成")
    order.State = &CompletedState{}
}

type CompletedState struct{}

func (s *CompletedState) Pay(order *OrderContext) {
    fmt.Println("订单已完成，无法再次支付")
}

func (s *CompletedState) Ship(order *OrderContext) {
    fmt.Println("订单已完成，无法再次发货")
}

func (s *CompletedState) Complete(order *OrderContext) {
    fmt.Println("订单已完成，无需重复操作")
}

func main() {
    order := &OrderContext{
        State: &PendingState{},
    }

    order.Pay()     // 输出：订单已支付
    order.Ship()    // 输出：订单已发货
    order.Complete()// 输出：订单已完成
    order.Pay()     // 输出：订单已完成，无法再次支付
}

订单已支付
订单已发货
订单已完成
订单已完成，无法再次支付