SWIFT.SOLID.DependencyInversion.Good

gistfile1.txt

protocol VendorType {
    func process(order: Order, success: () -> Void, failure: () -> Void)
}

class Administrator: VendorType {
    func process(order: Order, success: () -> Void, failure: () -> Void) { /* process order */ }
}
class Seller: VendorType {
    func process(order: Order, success: () -> Void, failure: () -> Void) { /* process order */ }
}

class StoreService {
    let seller: VendorType
    
    init(seller: VendorType) {
        self.seller = seller
    }
    
    func fetch(order: Order, from customer: Customer, success: () -> Void, failure: () -> Void) {
        //some bisness logic with order & customer requirements
        
        seller.process(order: order, success: {
            success()
        }, failure: {
            failure()
        })
    }
}
let storeService = StoreService(Administrator())
storeService.fetch(order: Order(), from: Customer(), success: {
    /*order complited*/
}) {
    /*process failure*/
}