Create an Agnostic Vendor Infrastructure in Ruby

Depending how the code was written adding new services to it can be difficult.
For instance, let's say we are building a rails application that gets integrated to cloud storage vendors.
A naive implementation would be to directly integrate to a cloud storage specific APIs.
In this case when new cloud storage vendors are added it is very probable that several nasty case... when ... end statements would be inserted in code.

	def list_folder(cloud_storage,folder)
	case cloud_storage
	when "dropbox"
	list_dropbox_folder(folder)
	when "box"
	list_box_folder(folder)
	when "google-drive"
	list_googledrive_folder(folder)
	else
	raise InvalidCloudStorageService(cloud_storage)
	end
	end

view raw naive_ruby_implementation_for_vendors.rb hosted with ❤ by GitHub

When a new cloud storage service is added the developer must remember all places where those growing case-like statements are inserted. This makes the system more susceptible to errors due to  changes in several parts of the code. This problem is explained in detail by the shotgun surgery anti-pattern (http://en.wikipedia.org/wiki/Shotgun_surgery)

The rest of the system shouldn't be aware that a new cloudstorage service was added. That is where a combination of design patterns come in handy:

• a facade to provide a simple interface for cloud storage operations 
• a service locator to find the right cloud storage adapter
• a cloud storage adapters that make each vendor API compliant to a single defined interface that can be understood by the facade

1) Cloud Storage Facade

	class CloudStorageFacade
	def initialize
	@cloud_storage_adapter_locator = CloudStorageAdapterLocator.instance
	end
	def find_adapter(cloud_storage)
	@cloud_storage_adapter_locator.find(cloud_storage)
	end
	def list_folder(cloud_storage,folder)
	adapter = find_adapter(cloud_storage)
	adapter.list_folder(folder)
	end
	# other cloud storage operations are declared here
	end

view raw cloud_storage_facade.rb hosted with ❤ by GitHub

2) Cloud Storage Adapter Locator

	class CloudStorageAdapterLocator
	def initialize
	@adapters = {}
	end
	def self.instance
	@@instance ||= CloudStorageAdapterLocator.new
	@@instance
	end
	def find(cloud_storage)
	@adapters[cloud_storage]
	end
	def register(cloud_storage,cloud_storage_adapter)
	@adapters[cloud_storage] = cloud_storage_adapter
	end
	end

view raw cloud_storage_adapter_locator.rb hosted with ❤ by GitHub

3) Cloud Storage Adapters

	class DropboxStorageAdapter # which implements Cloud Storage Adapter protocol
	def list(folder)
	# specific dropbox API code goes here
	# note that the output must be translated to
	# a format that is known by the facade
	end
	# other cloud storage operations declared here
	end
	# register the adapter right after and keep everything in one file
	DropBoxAdapterLocator.instance.register(DropboxStorageAdapter.new)

view raw dropbox_storage_adapter.rb hosted with ❤ by GitHub

Note that this combination of patterns can be used to abstract many other types of services. Cloud storage service was just an example used here.