class Middleman::CallbackManager

def add(keys, &block)
  immutable_keys = keys.is_a?(Symbol) ? keys : ::Hamster::Vector.new(keys)
  @callbacks = @callbacks.put(immutable_keys) do |v|
    v.nil? ? ::Hamster::Vector.new([block]) : v.push(block)
  end
end

def callbacks_for(keys)
  immutable_keys = keys.is_a?(Symbol) ? keys : ::Hamster::Vector.new(keys)
  @callbacks.get(immutable_keys) || ::Hamster::Vector.empty
end

def execute(keys, args=[], scope=self)
  callbacks = callbacks_for(keys)
  callbacks_count = callbacks.length + @subscribers.length
  return if callbacks_count < 1
  # ::Middleman::Util.instrument "callbacks.execute", keys: keys, length: callbacks_count do
  callbacks.each { |b| scope.instance_exec(*args, &b) }
  @subscribers.each { |b| scope.instance_exec(keys, args, &b) }
  # end
end

def initialize
  @callbacks = ::Hamster::Hash.empty
  @subscribers = ::Hamster::Vector.empty
end

def install_methods!(install_target, names)
  manager = self
  names.each do |method_name|
    install_target.define_singleton_method(method_name) do |*keys, &b|
      key_set = keys.unshift(method_name)
      manager.add(key_set.length > 1 ? key_set : key_set[0], &b)
    end
  end
  install_target.define_singleton_method(:execute_callbacks) do |*args|
    keys = args.shift
    manager.execute(keys, args[0], self)
  end
  install_target.define_singleton_method(:callbacks_for, &method(:callbacks_for))
  install_target.define_singleton_method(:subscribe_to_callbacks, &method(:subscribe))
end

def subscribe(&block)
  @subscribers = @subscribers.push(block)
end