The Dark Art of Rails Plugins
By James Adam of reevoo.com

= Anatomy of a plugin

A folder in vendor/plugins

lib-folder is the most important folder
- Where you put your Ruby code

Added to $LOAD_PATH alphabetically or using config.plugins

== Init.rb
- Evaluated near the end of rails initialization
- evaluated in order of config.plugins
- Special variables available
	- config, directory, name - see source of Rails::Plugin
	
== Other files

install.rb: Will be run only if you use ./script/plugin
tasks: Any files here that ends in .rake should contain rake-tasks
generators: Automatically available as generated when placed here
test: (doh!)


= Writing plugins

== Sharing code

Common files and rake tasks in lib and tasks

== Sample

module Friendly
	def hello
		"hi from #{self}"
	end
end


= Class methods in modules

Can't do this:

module Friendly
	self.is_friendly?
		true
	end
end

Instead do this:

module Friendly::ClassMethods
	is_friendly?
		true
	end
end

class Person
	extend Friendly::ClassMethods
end

class << Person
	def salutations
		...
	end
end


= Enhancing Rails

We don't want every subclass of ActiveRecord (i.e.) to get our methods included

Ruby class definitions are code - it blows your mind!
- So, has_many is a class method



= Changing behaviour

acts_as_archivable
- when a record is deleted, save a YAML version. Just in case.

Core:

module Archivable
	def archive_to_yaml
		File.open("#{id}.yml", 'w) do |f|
			f.write self.to_yaml
		end
	end
end

Tying it into ActiveRecord: (We can't redefine methods in a class by simply including a module)

def destroy_with_archiving
	...
end
alias_method_chain :destroy, :archiving

super can also be used, as explained here:
http://blog.fallingsnow.net/2008/04/02/super-is-your-friend/



= Tips

#2: Developing plugins
Rails only loads plugin code once
Fix this by adding to config/environments/development.rb:

config.after_initialize do
	Dependencies.load_once_paths.
		delete_if do |path|
			path =~ /vendor\/plugins/
		end
	end
end

#3: Gems as plugins
- Coming in Rails 2.1
- Add rails/init.rb
- require "rubygems" in environment.rb