module Rack
  class Attack
    class Cache

      attr_accessor :prefix

      def initialize
        self.store = ::Rails.cache if defined?(::Rails.cache)
        @prefix = 'rack::attack'
      end

      attr_reader :store
      def store=(store)
        @store = StoreProxy.build(store)
      end

      def count(unprefixed_key, period)
        key, expires_in = key_and_expiry(unprefixed_key, period)
        do_count(key, expires_in)
      end

      def read(unprefixed_key)
        enforce_store_presence!
        enforce_store_method_presence!(:read)

        store.read("#{prefix}:#{unprefixed_key}")
      end

      def write(unprefixed_key, value, expires_in)
        store.write("#{prefix}:#{unprefixed_key}", value, :expires_in => expires_in)
      end

      def reset_count(unprefixed_key, period)
        key, _ = key_and_expiry(unprefixed_key, period)
        store.delete(key)
      end

      def delete(unprefixed_key)
        store.delete("#{prefix}:#{unprefixed_key}")
      end

      private

      def key_and_expiry(unprefixed_key, period)
        epoch_time = Time.now.to_i
        # Add 1 to expires_in to avoid timing error: http://git.io/i1PHXA
        expires_in = (period - (epoch_time % period) + 1).to_i
        ["#{prefix}:#{(epoch_time / period).to_i}:#{unprefixed_key}", expires_in]
      end

      def do_count(key, expires_in)
        enforce_store_presence!
        enforce_store_method_presence!(:increment)

        result = store.increment(key, 1, :expires_in => expires_in)

        # NB: Some stores return nil when incrementing uninitialized values
        if result.nil?
          enforce_store_method_presence!(:write)

          store.write(key, 1, :expires_in => expires_in)
        end
        result || 1
      end

      def enforce_store_presence!
        if store.nil?
          raise Rack::Attack::MissingStoreError
        end
      end

      def enforce_store_method_presence!(method_name)
        if !store.respond_to?(method_name)
          raise Rack::Attack::MisconfiguredStoreError, "Store needs to respond to ##{method_name}"
        end
      end
    end
  end
end