PayPal Spec

If a merchant wants to integrate with the PayPal module, these are the steps they would take.

1. Import PayPalPayments at the top of their file
2. Create a PaymentsConfig object using their client Id and return Url
3. Create a PayPalClient object using that configuration
4. Set the delegate of the PayPalClient to an object that should receive messages from the SDK, and handle the events (approval, cancellation, errors, and shipping updates)
5. Start the checkout experience using an orderId (which would have been retrieved by the merchant outside the SDK)

Swift Interface

public protocol PayPalClientDelegate {
    // Invoked when a transaction is approved by the 
    // user and ready for authorization or capture by
    // the merchant
    func paypalDidApprove(client: PayPalClient, data: ApprovalData)
    
    // Invoked when the checkout experience has been canceled
    func paypalDidCancel(client: PayPalClient)
    
    // Invoked when the SDK encounters an unrecoverable error
    func paypalDidError(client: PayPalClient, error: PayPalError)
    
    // Invoked when the user wants to change the shipping or 
    // pickup information. Requires merchant response to 
    // confirm the new selection 
    func paypalShippingChange(client: PayPalClient, ...)
} 

public class PayPalClient {
    public weak var delegate: PayPalClientDelegate?
    
    public init(config: PaymentsConfig) {
        ...
    }
    
    public func checkout(orderId: String) {
        
    }
    
    public func checkout(billingAgreement: String) {
    
    }
}

let config = PaymentsConfig(clientId: "", returnUrl: "")
let client = PayPalClient(config: config)

client.delegate = self
client.checkout(orderId)

Kotlin Interface

interface PayPalClientListener {
    fun onPayPalApprove(data: ApprovalData)
    fun onPayPalCancel()
    fun onPayPalError(error: PayPalError)
    fun onPayPalShippingChange(...)
}

class PayPalClient(val config: PaymentsConfig) {
    
    var listener: PayPalClientListener? = null
    
    fun checkout(orderId: String) {
    
    }
    
    fun checkout(billingAgreement: String) {
        
    }
}

val config = PaymentsConfig(clientId = "", returnUrl = "")
val client = PayPalClient(config = config)

Improvements

• Fetch merchant configuration from a PayPal backend and infer returnUrl to reduce the number of parameters needed when constructing a PayPalClient

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