FEATURE: Give option to repurchase products multiple times (#46)

Feature requested here: https://meta.discourse.org/t/subscriptions-allow-users-to-purchase-one-time-products-multiple-times/173732/

There may be cases where a site admin wants to allow the repurchasing of a product. This implements the functionality by adding a repurchaseable toggle in the admin screen when creating a product. This saves an attribute to the Stripe product metadata.

When a user has already purchased an item with this toggle enabled, they will be able to purchase it again when browsing to `/s`.

assets/javascripts/discourse/controllers/s-show.js.es6

@@ -3,6 +3,7 @@ import Subscription from "discourse/plugins/discourse-subscriptions/discourse/mo
 import Transaction from "discourse/plugins/discourse-subscriptions/discourse/models/transaction";
 import I18n from "I18n";
 import { not } from "@ember/object/computed";
+import discourseComputed from "discourse-common/utils/decorators";
 
 export default Controller.extend({
   selectedPlan: null,
@@ -24,6 +25,15 @@ export default Controller.extend({
     bootbox.alert(I18n.t(`discourse_subscriptions.${path}`));
   },
 
+  @discourseComputed("model.product.repurchaseable", "model.product.subscribed")
+  canPurchase(repurchaseable, subscribed) {
+    if (!repurchaseable && subscribed) {
+      return false;
+    }
+
+    return true;
+  },
+
   createSubscription(plan) {
     return this.stripe.createToken(this.get("cardElement")).then((result) => {
       if (result.error) {