Fetch exchange rates in bulk from synth (#1069)

* Fetch exchnage rates in bulk

* Handle paginated response

* Rename method and improve tests

* Change argument names

* Use standard date format

test/models/exchange_rate_test.rb

@@ -62,8 +62,16 @@ class ExchangeRateTest < ActiveSupport::TestCase
   end
 
   test "finds multiple rates from provider and caches to DB" do
-    @provider.expects(:fetch_exchange_rate).with(from: "EUR", to: "USD", date: 1.day.ago.to_date).returns(OpenStruct.new(success?: true, rate: 1.1)).once
-    @provider.expects(:fetch_exchange_rate).with(from: "EUR", to: "USD", date: Date.current).returns(OpenStruct.new(success?: true, rate: 1.2)).once
+    @provider.expects(:fetch_exchange_rates).with(from: "EUR", to: "USD", start_date: 1.day.ago.to_date, end_date: Date.current)
+      .returns(
+        OpenStruct.new(
+          rates: [
+            OpenStruct.new(date: 1.day.ago.to_date, rate: 1.1),
+            OpenStruct.new(date: Date.current, rate: 1.2)
+          ],
+          success?: true
+        )
+      ).once
 
     fetched_rates = ExchangeRate.find_rates(from: "EUR", to: "USD", start_date: 1.day.ago.to_date, cache: true)
     refetched_rates = ExchangeRate.find_rates(from: "EUR", to: "USD", start_date: 1.day.ago.to_date)
@@ -73,7 +81,15 @@ class ExchangeRateTest < ActiveSupport::TestCase
   end
 
   test "finds missing db rates from provider and appends to results" do
-    @provider.expects(:fetch_exchange_rate).with(from: "EUR", to: "GBP", date: 2.days.ago.to_date).returns(OpenStruct.new(success?: true, rate: 1.1)).once
+    @provider.expects(:fetch_exchange_rates).with(from: "EUR", to: "GBP", start_date: 2.days.ago.to_date, end_date: 2.days.ago.to_date)
+      .returns(
+        OpenStruct.new(
+          rates: [
+            OpenStruct.new(date: 2.day.ago.to_date, rate: 1.1)
+          ],
+          success?: true
+        )
+      ).once
 
     rate1 = exchange_rates(:one) # EUR -> GBP, today
     rate2 = exchange_rates(:two) # EUR -> GBP, yesterday

test/models/provider/synth_test.rb

@@ -16,6 +16,17 @@ class Provider::SynthTest < ActiveSupport::TestCase
     end
   end
 
+  test "fetches paginated exchange_rate historical data" do
+    VCR.use_cassette("synth/exchange_rate_historical") do
+      response = @synth.fetch_exchange_rates(
+        from: "USD", to: "GBP", start_date: Date.parse("01.01.2024"), end_date: Date.parse("31.07.2024")
+      )
+
+      assert 213, response.rates.size # 213 days between 01.01.2024 and 31.07.2024
+      assert_equal [ :date, :rate ], response.rates.first.keys
+    end
+  end
+
   test "retries then provides failed response" do
     @client = mock
     Faraday.stubs(:new).returns(@client)