module ElasticAPM::Injectors

def self.const_defined?(const_name)
  const = Util::Inflector.constantize(const_name)
  !!const
rescue NameError
  false
end

def self.hook_into(name)
  return unless (registration = require_hooks[name])
  return unless const_defined?(registration.const_name)
  installed[registration.const_name] = registration
  registration.install
  registration.require_paths.each do |path|
    require_hooks.delete path
  end
end

def self.installed
  @installed ||= {}
end

def self.register(*args)
  registration = Registration.new(*args)
  if const_defined?(registration.const_name)
    installed[registration.const_name] = registration
    registration.install
  else
    register_require_hook registration
  end
end

def self.register_require_hook(registration)
  registration.require_paths.each do |path|
    require_hooks[path] = registration
  end
end

def self.require_hooks
  @require_hooks ||= {}
end