feat: ✨ add readExternalIdFromOrderMetadata

apps/taxes/graphql/queries/FetchOrderExternalId.graphql

@@ -0,0 +1,5 @@
+query FetchOrderExternalId($orderId: ID!) {
+  order(id: $orderId) {
+    externalId: metafield(key: "externalId")
+  }
+}

apps/taxes/src/modules/app/order-metadata-manager.ts

@@ -1,4 +1,6 @@
 import {
+  FetchOrderExternalIdDocument,
+  FetchOrderExternalIdQuery,
   UpdateMetadataDocument,
   UpdateMetadataMutation,
   UpdateMetadataMutationVariables,
@@ -35,4 +37,16 @@ export class OrderMetadataManager {
 
     return { ok: true };
   }
+
+  async readExternalIdFromOrderMetadata(orderId: string) {
+    const { error, data } = await this.client
+      .query<FetchOrderExternalIdQuery>(FetchOrderExternalIdDocument, { id: orderId })
+      .toPromise();
+
+    if (error) {
+      throw error;
+    }
+
+    return data?.order?.externalId;
+  }
 }