Create ShippingInformationValidator and ShippingMethodsFactory interf…

…ace (#1847)

stripe/src/main/java/com/stripe/android/PaymentSessionConfig.kt

@@ -2,11 +2,14 @@ package com.stripe.android
 
 import android.os.Parcelable
 import androidx.annotation.LayoutRes
+import androidx.annotation.WorkerThread
 import com.stripe.android.model.PaymentMethod
 import com.stripe.android.model.ShippingInformation
+import com.stripe.android.model.ShippingMethod
 import com.stripe.android.view.SelectShippingMethodWidget
 import com.stripe.android.view.ShippingInfoWidget
 import com.stripe.android.view.ShippingInfoWidget.CustomizableShippingField
+import java.io.Serializable
 import java.util.Locale
 import kotlinx.android.parcel.Parcelize
 
@@ -40,6 +43,33 @@ data class PaymentSessionConfig internal constructor(
         }
     }
 
+    private interface ShippingInformationValidator : Serializable {
+        /**
+         * @return whether the customer's [ShippingInformation] is valid. Will run on
+         * a background thread.
+         */
+        @WorkerThread
+        fun isValid(shippingInformation: ShippingInformation): Boolean
+
+        /**
+         * @return the error message to show if [isValid] returns `false`. Will run on
+         * a background thread.
+         */
+        @WorkerThread
+        fun getErrorMessage(shippingInformation: ShippingInformation): String
+    }
+
+    private interface ShippingMethodsFactory : Serializable {
+        /**
+         * @return a list of [ShippingMethod] options to present to the customer. Will run on
+         * a background thread.
+         */
+        @WorkerThread
+        fun create(
+            shippingInformation: ShippingInformation
+        ): List<ShippingMethod>
+    }
+
     class Builder : ObjectBuilder<PaymentSessionConfig> {
         private var shippingInfoRequired = true
         private var shippingMethodsRequired = true