module Faraday::MiddlewareRegistry

def load_middleware(key)
  value = registered_middleware[key]
  case value
  when Module
    value
  when Symbol, String
    middleware_mutex do
      @registered_middleware[key] = const_get(value)
    end
  when Proc
    middleware_mutex do
      @registered_middleware[key] = value.call
    end
  end
end

def lookup_middleware(key)
  load_middleware(key) ||
    raise(Faraday::Error, "#{key.inspect} is not registered on #{self}")
end

def middleware_mutex(&block)
  @middleware_mutex ||= Monitor.new
  @middleware_mutex.synchronize(&block)
end

def register_middleware(**mappings)
  middleware_mutex do
    registered_middleware.update(mappings)
  end
end

def registered_middleware
  @registered_middleware ||= {}
end

def unregister_middleware(key)
  registered_middleware.delete(key)
end