RouteWayCostCalculator: Don't update `costs` if response errors

If there's an API error, we shouldn't update the route's `costs` field.
Let's say we've already calculated some costs for a route A. We then edit
and re-save A, which triggers a recalculation of the costs. Now the
TomTom API responds with an error. We don't want to overwrite our
existing costs with an empty array because they could still be useful.
In this case, we should instead keep the existing costs we already had.

To achieve this, move the `RemoteError` rescue into
`RouteWayCostCalculator`, leaving the error unhandled in
`TomTom.matrix`.

Refs #6884

3 files changed, 31 insertions, 4 deletions

diff --git a/app/services/route_way_cost_calculator.rb b/app/services/route_way_cost_calculator.rb
index d41a2e59a..58f9ad1d0 100644
--- a/app/services/route_way_cost_calculator.rb
+++ b/app/services/route_way_cost_calculator.rb
@@ -8,5 +8,7 @@ class RouteWayCostCalculator
     way_costs = TomTom.matrix(way_costs)
     way_costs = WayCostCollectionJSONSerializer.dump(way_costs)
     @route.update(costs: way_costs)
+  rescue TomTom::Matrix::RemoteError => e
+    Rails.logger.error "TomTom::Matrix server error: #{e}"
   end
 end
diff --git a/lib/tom_tom/matrix.rb b/lib/tom_tom/matrix.rb
index b57495f3f..75c2cc02b 100644
--- a/lib/tom_tom/matrix.rb
+++ b/lib/tom_tom/matrix.rb
@@ -4,6 +4,10 @@ module TomTom
       @connection = connection
     end
 
+    # Exceptions:
+    #
+    # * This raises a `TomTom::Matrix::RemoteError` when the API responds with
+    #   an error.
     def matrix(way_costs)
       points_with_ids = points_from_way_costs(way_costs)
       points = points_as_params(points_with_ids)
@@ -29,10 +33,6 @@ module TomTom
         points_with_ids,
         matrix_json
       )
-    rescue RemoteError => e
-      Rails.logger.error "TomTom::Matrix server error: #{e}"
-
-      []
     end
 
     def points_from_way_costs(way_costs)
diff --git a/spec/services/route_way_cost_calculator_spec.rb b/spec/services/route_way_cost_calculator_spec.rb
index 79b81e34d..593ba29ef 100644
--- a/spec/services/route_way_cost_calculator_spec.rb
+++ b/spec/services/route_way_cost_calculator_spec.rb
@@ -29,5 +29,30 @@ RSpec.describe RouteWayCostCalculator do
       expect(route.costs).not_to be_nil
       expect { JSON.parse(JSON.dump(route.costs)) }.not_to raise_error
     end
+
+    it "doesn't update route costs when there is a server error" do
+      route = create(:route)
+
+      stub_request(
+        :post,
+        "https://api.tomtom.com/routing/1/matrix/json?key&routeType=shortest&travelMode=bus"
+      )
+        .with(
+          headers: {
+            'Accept'=>'*/*',
+            'Accept-Encoding'=>'gzip;q=1.0,deflate;q=0.6,identity;q=0.3',
+            'Content-Type'=>'application/json',
+            'User-Agent'=>'Faraday v0.9.2'
+          })
+        .to_return(
+          status: 200,
+          body: "{\"formatVersion\":\"0.0.1\",\"error\":{\"description\":\"Outputformat:csvisunsupported.\"}}",
+          headers: {}
+        )
+
+      RouteWayCostCalculator.new(route).calculate!
+
+      expect(route.costs).to be_nil
+    end
   end
 end