Added Money::Bank::Coinbase class to use Coinbase rates with the Mone…

…y gem

README.md

@@ -282,6 +282,39 @@ r.oauth.access_token
 => "93865b9cae83706ae59220c013bc0afd93865b9cae83706ae59220c013bc0afd"
 ```
 
+## Exchange rates
+
+This gem also extends Money::Bank::VariableExchange with Money::Bank::Coinbase to give you access to Coinbase exchange rates.
+
+### Usage
+
+``` ruby
+cb_bank = Money::Bank::Coinbase.new
+
+# Call this before calculating exchange rates
+# This will download the rates from CB
+cb_bank.fetch_rates!
+
+# Exchange 100 USD to BTC
+# API is the same as the money gem
+cb_bank.exchange_with(Money.new(10000, :USD), :BTC) # '0.15210000'.to_money(:BTC)
+
+# Set as default bank to do arithmetic and comparisons on Money objects
+Money.default_bank = cb_bank
+money1 = Money.new(10)
+money1.bank # cb_bank
+
+Money.us_dollar(10000).exchange_to(:BTC) # '0.15210000'.to_money(:BTC)
+'1'.to_money(:BTC) > '1'.to_money(:USD) # true
+
+# Expire rates after some number of seconds (by default, rates are only updated when you call fetch_rates!)
+cb_bank.ttl_in_seconds = 3600 # Cache rates for one hour
+
+# After an hour, different rates
+cb_bank.exchange_with(Money.new(10000, :USD), :BTC) # '0.15310000'.to_money(:BTC)
+
+```
+
 ## Adding new methods
 
 You can see a [list of method calls here](https://github.com/coinbase/coinbase-ruby/blob/master/lib/coinbase/client.rb) and how they are implemented.  They are a wrapper around the [Coinbase JSON API](https://coinbase.com/api/doc).

lib/coinbase.rb

@@ -3,3 +3,4 @@
 require "coinbase/version"
 require "coinbase/client"
 require "coinbase/oauth_client"
+require "coinbase/rates"

lib/coinbase/client.rb

@@ -12,7 +12,7 @@ class Client
 
     BASE_URI = 'https://coinbase.com/api/v1'
 
-    def initialize(api_key, api_secret, options={})
+    def initialize(api_key='', api_secret='', options={})
       @api_key = api_key
       @api_secret = api_secret
 
@@ -165,6 +165,10 @@ def spot_price currency='USD'
       r['amount'].to_money(r['currency'])
     end
 
+    def exchange_rates
+      get('/currencies/exchange_rates')
+    end
+
     # Buys
 
     def buy! qty

lib/coinbase/rates.rb

@@ -0,0 +1,84 @@
+class Money
+  module Bank
+    class Coinbase < VariableExchange
+
+      def initialize(coinbase=nil)
+        @coinbase = coinbase || ::Coinbase::Client.new
+        super()
+      end
+
+      # @return [Integer] Returns the Time To Live (TTL) in seconds.
+      attr_reader :ttl_in_seconds
+
+      # @return [Time] Returns the time when the rates expire.
+      attr_reader :rates_expiration
+
+      ##
+      # Set the Time To Live (TTL) in seconds.
+      #
+      # @param [Integer] the seconds between an expiration and another.
+      def ttl_in_seconds=(value)
+        @ttl_in_seconds = value
+        refresh_rates_expiration! if ttl_in_seconds
+      end
+
+      ##
+      # Fetch fresh rates from Coinbase
+      def fetch_rates!(opts={})
+        fn = lambda do
+          @rates = @coinbase.exchange_rates
+          refresh_rates_expiration!
+        end
+
+        if opts[:without_mutex]
+          fn.call
+        else
+          @mutex.synchronize { fn.call }
+        end
+      end
+
+      # Refreshes all the rates if they are expired.
+      #
+      # @return [Boolean]
+      def expire_rates
+        if @ttl_in_seconds && @rates_expiration <= Time.now
+          fetch_rates!
+          true
+        else
+          false
+        end
+      end
+
+      def get_rate(from, to, opts = {})
+        expire_rates
+        super
+      end
+
+    private
+
+      ##
+      # Set the rates expiration TTL seconds from the current time.
+      #
+      # @return [Time] The next expiration.
+      def refresh_rates_expiration!
+        if @ttl_in_seconds
+          @rates_expiration = Time.now + @ttl_in_seconds 
+        end
+      end
+
+      # Return the rate hashkey for the given currencies.
+      #
+      # @param [Currency, String, Symbol] from The currency to exchange from.
+      # @param [Currency, String, Symbol] to The currency to exchange to.
+      #
+      # @return [String]
+      #
+      # @example
+      #   rate_key_for("USD", "CAD") #=> "usd_to_cad"
+      def rate_key_for(from, to)
+        "#{::Money::Currency.wrap(from).iso_code}_to_#{::Money::Currency.wrap(to).iso_code}".downcase
+      end
+
+    end
+  end
+end