Contents

module AssetCloud
  class BucketChain < Bucket
    # returns a new Bucket class which writes to each given Bucket
    # but only uses the first one for reading
    def self.chain(*klasses)
      Class.new(self) do
        attr_reader :chained_buckets
        define_method 'initialize' do |cloud, name|
          super(cloud, name)
          @chained_buckets = klasses.map {|klass| klass.new(cloud,name)}
        end
      end
    end

    def ls(key=nil)
      first_possible_bucket {|b| b.ls(key)}
    end
    def read(key)
      first_possible_bucket {|b| b.read(key)}
    end
    def stat(key=nil)
      first_possible_bucket {|b| b.stat(key)}
    end
    def read_version(key, version)
      first_possible_bucket {|b| b.read_version(key, version)}
    end
    def versions(key)
      first_possible_bucket {|b| b.versions(key)}
    end

    def write(key, data)
      every_bucket_with_transaction_on_key(key) {|b| b.write(key, data)}
    end
    def delete(key)
      every_bucket_with_transaction_on_key(key) {|b| b.delete(key)}
    end

    def respond_to?(sym)
      @chained_buckets.any? {|b| b.respond_to?(sym)}
    end
    def method_missing(sym, *args)
      first_possible_bucket {|b| b.send(sym, *args)}
    end

    private

    def first_possible_bucket(&block)
      @chained_buckets.each do |bucket|
        begin
          return yield(bucket)
        rescue NoMethodError, NotImplementedError => e
          nil
        end
      end
    end

    def every_bucket_with_transaction_on_key(key, i=0, &block)
      return unless bucket = @chained_buckets[i]

      old_value = begin
        bucket.read(key)
      rescue AssetCloud::AssetNotFoundError
        nil
      end
      result = yield(bucket)

      begin
        every_bucket_with_transaction_on_key(key, i+1, &block)
        return result
      rescue StandardError => e
        if old_value
          bucket.write(key, old_value)
        else
          bucket.delete(key)
        end
        raise e
      end
    end

  end

end

Version data entries

21 entries across 21 versions & 1 rubygems

Version	Path
asset_cloud-2.1.0	lib/asset_cloud/buckets/bucket_chain.rb