Recognise certain voucher errors

I considered using the vine error message as the translation key (ie I18n.t(vine_voucher_validator_service.errors.#{message.parameterize.underscore}), but thought it might be more predictable to have keys explicitly defined and whitelisted like this.

These error message are still squashed by the controller, we'll deal with that next.

app/services/vine/voucher_validator_service.rb

@@ -2,6 +2,11 @@
 
 module Vine
   class VoucherValidatorService
+    VINE_ERRORS = {
+      # https://github.com/openfoodfoundation/vine/blob/main/app/Enums/ApiResponse.php
+      "This voucher has expired." => :expired,
+    }.freeze
+
     attr_reader :voucher_code, :errors
 
     def initialize(voucher_code:, enterprise:)
@@ -43,7 +48,9 @@ module Vine
 
     def handle_errors(response)
       if response[:status] == 400
-        errors[:invalid_voucher] = I18n.t("vine_voucher_validator_service.errors.invalid_voucher")
+        message = response[:body] && JSON.parse(response[:body]).dig("meta", "message")
+        key = VINE_ERRORS.fetch(message, :invalid_voucher)
+        errors[:invalid_voucher] = I18n.t("vine_voucher_validator_service.errors.#{key}")
       elsif response[:status] == 404
         errors[:not_found_voucher] =
           I18n.t("vine_voucher_validator_service.errors.not_found_voucher")

config/locales/en.yml

@@ -587,6 +587,7 @@ en:
     errors:
       vine_api: "There was an error communicating with the API, please try again later."
       invalid_voucher: "The voucher is not valid"
+      expired: "The voucher has expired"
       not_found_voucher: "Sorry, we couldn't find that voucher, please check the code."
   vine_voucher_redeemer_service:
     errors:

spec/services/vine/voucher_validator_service_spec.rb

@@ -270,11 +270,12 @@ RSpec.describe Vine::VoucherValidatorService, feature: :connected_apps do
           enterprise: distributor, data: { api_key: "1234568", secret: "my_secret" }
         )
       }
+      # Faraday returns un-parsed json
       let(:data) {
         {
           meta: { responseCode: 400, limit: 50, offset: 0, message: "Invalid merchant team." },
           data: []
-        }.deep_stringify_keys
+        }.to_json
       }
 
       before do
@@ -285,7 +286,7 @@ RSpec.describe Vine::VoucherValidatorService, feature: :connected_apps do
         expect_validate_to_be_nil
       end
 
-      it "adds an error message" do
+      it "adds a general error message" do
         validate_voucher_service.validate
 
         expect(validate_voucher_service.errors).to include(
@@ -293,6 +294,23 @@ RSpec.describe Vine::VoucherValidatorService, feature: :connected_apps do
         )
       end
 
+      context "it is expired" do
+        let(:data) {
+          {
+            meta: { responseCode: 400, limit: 50, offset: 0, message: "This voucher has expired." },
+            data: []
+          }.to_json
+        }
+
+        it "adds a specific error message" do
+          validate_voucher_service.validate
+
+          expect(validate_voucher_service.errors).to include(
+            { invalid_voucher: "The voucher has expired" }
+          )
+        end
+      end
+
       it "doesn't creates a new VINE voucher" do
         expect_voucher_count_not_to_change
       end
@@ -420,6 +438,25 @@ RSpec.describe Vine::VoucherValidatorService, feature: :connected_apps do
           }.not_to change { voucher.reload.amount }
         end
       end
+
+      context "it is expired" do
+        let(:data) {
+          {
+            meta: { responseCode: 400, limit: 50, offset: 0, message: "This voucher has expired." },
+            data: []
+          }.to_json
+        }
+
+        it "adds a specific error message" do
+          mock_api_exception(type: Faraday::BadRequestError, status: 400, body: data)
+
+          validate_voucher_service.validate
+
+          expect(validate_voucher_service.errors).to include(
+            { invalid_voucher: "The voucher has expired" }
+          )
+        end
+      end
     end
   end