lib/danconia/exchanges/exchange.rb in danconia-0.2.8 vs lib/danconia/exchanges/exchange.rb in danconia-0.2.9

@@ -1,33 +1,47 @@
+require 'danconia/pair'
+
 module Danconia
   module Exchanges
     class Exchange
       attr_reader :store
 
       def initialize store: Stores::InMemory.new
         @store = store
       end
 
       def rate from, to
-        if from == to
-          1.0
-        elsif from == 'USD' and direct_rate = @store.direct_rate(from, to)
-          direct_rate
-        elsif to == 'USD' and inverse_rate = @store.direct_rate(to, from)
-          (1.0 / inverse_rate).round 6
-        elsif from != 'USD' and to != 'USD' and from_in_usd = rate(from, 'USD') and to_per_usd = rate('USD', to)
-          (from_in_usd * to_per_usd).round 6
-        else
-          raise Errors::ExchangeRateNotFound.new(from, to)
-        end
+        return 1.0 if from == to
+
+        pair = Pair.new(from, to)
+        rates = direct_and_inverted_rates()
+        rates[pair] or indirect_rate(pair, rates) or raise Errors::ExchangeRateNotFound.new(from, to)
       end
 
       def rates
         @store.rates
       end
 
       def update_rates!
         @store.save_rates fetch_rates
+      end
+
+      private
+
+      # Returns the original rates plus the inverted ones, to simplify rate finding logic.
+      def direct_and_inverted_rates
+        rates.each_with_object({}) do |(pair_str, rate), rs|
+          pair = Pair.parse(pair_str)
+          rs[pair] = rate
+          rs[pair.invert] ||= 1.0 / rate
+        end
+      end
+
+      def indirect_rate ind_pair, rates
+        if (from_pair = rates.keys.detect { |(pair, rate)| pair.from == ind_pair.from }) &&
+           (to_pair = rates.keys.detect { |(pair, rate)| pair.to == ind_pair.to })
+          rates[from_pair] * rates[to_pair]
+        end
       end
     end
   end
 end