key_registry.cr

require "json"

class Object
  macro def_find_by_name
    {{:macro.id}} def self.find_by_name(name) : {{@type.name.id}}.class
      case name
        \{% for subclass in {{@type.name.id}}.all_subclasses %}
          when \{{subclass.name}}
            \{{subclass.name.id}}
        \{% end %}
      else
        raise "Can't find {{@type.name.id}} by this name: #{name}"
      end
    end
  end
end

class JSON::KeyRegistry(T)
  def self.new(pull : JSON::PullParser)
    plugins = [] of T
    pull.read_object do |key|
      plugins << T.find_by_name(key).new(pull)
    end
    plugins
  end
end

abstract class Plugin
  def_find_by_name
end

class PluginOne < Plugin
  json_mapping({one: String})
end

class PluginTwo < Plugin
  json_mapping({two: String})
end

class Config
  json_mapping({plugins: JSON::KeyRegistry(Plugin)})
end

json = %(
  {
    "plugins": {
      "PluginOne": {
        "one": "HOLA"
      },
      "PluginTwo": {
        "two": "CHAU"
      }
    }
  }
)

config = Config.from_json(json)
pp config