Handle address provider unsupported currencies when creating a new order

lib/straight/address_providers/base.rb

@@ -23,6 +23,12 @@ def new_address(keychain_id:, **args)
       def takes_fees?
         false
       end
+
+      # Address provider is expected to define SUPPORTED_CURRENCIES as an
+      # Enumerable with valid currency codes. e.g. 'EUR', 'USD'
+      def currency_supported?(currency)
+        SUPPORTED_CURRENCIES.include?(currency)
+      end
     end
   end
 end

lib/straight/exchange_rate_adapters/fiat_adapters/fixer_adapter.rb

@@ -4,8 +4,8 @@ class FixerAdapter < FiatAdapter
       FETCH_URL = "http://api.fixer.io/latest?base=#{CROSS_RATE_CURRENCY}"
 
       def rate_for(currency_code)
-        super
-        rate = get_rate_value_from_hash(@rates, 'rates', currency_code)
+        rate = super
+        rate ||= get_rate_value_from_hash(@rates, 'rates', currency_code)
         rate_to_f(rate)
       end
     end

lib/straight/gateway.rb

@@ -91,6 +91,15 @@ def new_order(args)
           raise OrderAmountInvalid, "amount cannot be nil and should be more than 0"
         end
         # Setting default values
+
+        if address_provider.takes_fees? &&
+            !address_provider.currency_supported?(args[:currency])
+          supported_currency = select_supported_currency_by_address_provider
+          args[:amount] = convert_amount_to_supported_currency(args[:amount],
+            args[:currency], supported_currency)
+          args[:currency] = supported_currency
+        end
+
         args[:currency]         ||= default_currency
         args[:btc_denomination] ||= :satoshi
 
@@ -197,6 +206,18 @@ def address_provider_type
 
       private
 
+        def select_supported_currency_by_address_provider
+          address_provider.class::SUPPORTED_CURRENCIES.first
+        end
+
+        def convert_amount_to_supported_currency(amount, currency, supported_currency)
+          adapter = ExchangeRate::FixerAdapter.instance
+          rate_for_supported_currency = adapter.rate_for(supported_currency)
+          rate_for_currency = adapter.rate_for(currency)
+
+          (amount * rate_for_supported_currency) / rate_for_currency
+        end
+
         # Calls the block with each adapter until one of them does not fail.
         # Fails with the:
         #   - priority_exception, if it is set and was raised at least once

spec/lib/exchange_rate_adapters/fiat_adapters/fixer_adapter_spec.rb

@@ -19,4 +19,8 @@
     expect( -> { @exchange_adapter.rate_for('KZT') }).to raise_error(Straight::ExchangeRate::Adapter::CurrencyNotSupported)
   end
 
+  it "returns 1.0 when the currency is the FiatAdapter::CROSS_RATE_CURRENCY" do
+    expect(@exchange_adapter.
+      rate_for(Straight::ExchangeRate::FiatAdapter::CROSS_RATE_CURRENCY)).to eq(1.0)
+  end
 end

spec/lib/gateway_spec.rb

@@ -74,6 +74,18 @@
     @gateway.order_status_changed(order)
   end
 
+  describe "when the address provider doesn't support the selected currency" do
+    it "converts the currency to one the address provider supports" do
+      @gateway.address_provider = AddressProvider.new(provider: :cashila)
+      allow(@gateway.address_provider).to receive(:new_address_and_amount)
+      allow(@gateway).to receive(:select_supported_currency_by_address_provider).
+        and_return("EUR")
+      expect(@gateway).to receive(:amount_from_exchange_rate).
+        with(0.91996, currency: "EUR", btc_denomination: :satoshi)
+      @gateway.new_order(amount: 1, keychain_id: 1, currency: "USD")
+    end
+  end
+
   describe "exchange rate calculation" do
 
     it "sets order amount in satoshis calculated from another currency" do
@@ -153,3 +165,13 @@
   end
 
 end
+
+AddressProvider = Struct.new(:provider) do
+  def takes_fees?
+    true
+  end
+
+  def currency_supported?(currency)
+    currency == "EUR"
+  end
+end