TomTom::Matrix: Serialize `BigDecimal` as float

Rails serialises `BigDecimal`s as JSON strings to prevent loss of
precision. The `latitude` and `longitude` columns in `StopArea` are
stored as `BigDecimal`s. The trouble is that TomTom's API requires the
latitude & longitude values to be JSON floats, not strings.

Make a new JSON serialiser that converts the `BigDecimal` coordinates to
float to allow the values to be correctly interpreted by the API.

Refs #6222

4 files changed, 144 insertions, 4 deletions

diff --git a/lib/tom_tom/matrix.rb b/lib/tom_tom/matrix.rb
index 49c000148..71eb6c75d 100644
--- a/lib/tom_tom/matrix.rb
+++ b/lib/tom_tom/matrix.rb
@@ -15,10 +15,7 @@ module TomTom
         req.params[:routeType] = 'shortest'
         req.params[:travelMode] = 'bus'
 
-        req.body = {
-          origins: points,
-          destinations: points
-        }.to_json
+        req.body = build_request_body(points)
       end
 
       extract_costs_to_way_costs!(
@@ -69,6 +66,13 @@ module TomTom
       end
     end
 
+    def build_request_body(points)
+      RequestJSONSerializer.dump({
+        origins: points,
+        destinations: points
+      })
+    end
+
     def extract_costs_to_way_costs!(way_costs, points, matrix_json)
       way_costs = []
 
diff --git a/lib/tom_tom/matrix/request_json_serializer.rb b/lib/tom_tom/matrix/request_json_serializer.rb
new file mode 100644
index 000000000..f4d12e482
--- /dev/null
+++ b/lib/tom_tom/matrix/request_json_serializer.rb
@@ -0,0 +1,25 @@
+module TomTom
+  class Matrix
+    class RequestJSONSerializer
+      def self.dump(hash)
+        hash[:origins].map! do |point|
+          point_to_f(point)
+        end
+        hash[:destinations].map! do |point|
+          point_to_f(point)
+        end
+
+        JSON.dump(hash)
+      end
+
+      private
+
+      def self.point_to_f(point)
+        point[:point][:latitude] = point[:point][:latitude].to_f
+        point[:point][:longitude] = point[:point][:longitude].to_f
+
+        point
+      end
+    end
+  end
+end
diff --git a/spec/lib/tom_tom/matrix/request_json_serializer_spec.rb b/spec/lib/tom_tom/matrix/request_json_serializer_spec.rb
new file mode 100644
index 000000000..1fafad302
--- /dev/null
+++ b/spec/lib/tom_tom/matrix/request_json_serializer_spec.rb
@@ -0,0 +1,39 @@
+RSpec.describe TomTom::Matrix::RequestJSONSerializer do
+  describe ".dump" do
+    it "serializes BigDecimal values to floats" do
+      points = [{
+        point: {
+          latitude: 52.50867.to_d,
+          longitude: 13.42879.to_d
+        },
+      }]
+      data = {
+        origins: points,
+        destinations: points
+      }
+
+      expect(
+        TomTom::Matrix::RequestJSONSerializer.dump(data)
+      ).to eq(<<-JSON.delete(" \n"))
+        {
+          "origins": [
+            {
+              "point": {
+                "latitude": 52.50867,
+                "longitude": 13.42879
+              }
+            }
+          ],
+          "destinations": [
+            {
+              "point": {
+                "latitude": 52.50867,
+                "longitude": 13.42879
+              }
+            }
+          ]
+        }
+      JSON
+    end
+  end
+end
diff --git a/spec/lib/tom_tom/matrix_spec.rb b/spec/lib/tom_tom/matrix_spec.rb
index b63ebc70b..605f1d254 100644
--- a/spec/lib/tom_tom/matrix_spec.rb
+++ b/spec/lib/tom_tom/matrix_spec.rb
@@ -77,6 +77,78 @@ RSpec.describe TomTom::Matrix do
     end
   end
 
+  describe "#build_request_body" do
+    it "serializes BigDecimal coordinates to floats" do
+      points = [
+        {
+          point: {
+            latitude: 48.85086.to_d,
+            longitude: 2.36143.to_d
+          },
+        },
+        {
+          point: {
+            latitude: 47.91231.to_d,
+            longitude: 1.87606.to_d
+          },
+        },
+        {
+          point: {
+            latitude: 52.50867.to_d,
+            longitude: 13.42879.to_d
+          },
+        }
+      ]
+
+      expect(
+        matrix.build_request_body(points)
+      ).to eq(<<-JSON.delete(" \n"))
+        {
+          "origins": [
+            {
+              "point": {
+                "latitude": 48.85086,
+                "longitude": 2.36143
+              }
+            },
+            {
+              "point": {
+                "latitude": 47.91231,
+                "longitude": 1.87606
+              }
+            },
+            {
+              "point": {
+                "latitude": 52.50867,
+                "longitude": 13.42879
+              }
+            }
+          ],
+          "destinations": [
+            {
+              "point": {
+                "latitude": 48.85086,
+                "longitude": 2.36143
+              }
+            },
+            {
+              "point": {
+                "latitude": 47.91231,
+                "longitude": 1.87606
+              }
+            },
+            {
+              "point": {
+                "latitude": 52.50867,
+                "longitude": 13.42879
+              }
+            }
+          ]
+        }
+      JSON
+    end
+  end
+
   describe "#extract_costs_to_way_costs!" do
     it "puts distance & time costs in way_costs" do
       way_costs = [