AddLondisteExtension.rb

class AddLondisteExtension < ActiveRecord::Migration
  def up
    load_postgres_extension("londiste") do
      verify "pgq"
      verify "pgq_node"
      verify "londiste"
    end
  end
  
  def down
    unload_postgres_extension("londiste")
  end
end

## elsewhere in the universe!

class UnableToInstallError < RuntimeError; end

module PostgresExtensionLoader
  
  def load_postgres_extension(extension, &block)
    ext = PostgresExtension.new(extension)
    ext.install or raise UnableToInstallError
    ext.instance_eval(&block)
  end
  
  def unload_postgres_extension(extension)
    PostgresExtension.new(extension).uninstall
  end
  
  class PostgresExtension
    attr_accessor :extension
    
    def initialize(extension)
      @extension = extension
    end
    
    def install
      # when in prod, make sure it's already built or raise.
      # when in dev or test, do this:
      exec("cleanup") &&
      exec("download") &&
      exec("make") &&
      exec("build")
    end
    
    def verify(lib)
      # check that system includes lib
      raise unless lib_installed(lib)
    end
    
    def uninstall
      # remove everything
    end
  end
end