class ActiveModelSerializers::Adapter::JsonApi::Relationship

def as_json
  hash = {}
  if association.options[:include_data]
    hash[:data] = data_for(association)
  end
  links = links_for(association)
  hash[:links] = links if links.any?
  meta = meta_for(association)
  hash[:meta] = meta if meta
  hash[:meta] = {} if hash.empty?
  hash
end

def data_for(association)
  serializer = association.serializer
  if serializer.respond_to?(:each)
    serializer.map { |s| ResourceIdentifier.new(s, serializable_resource_options).as_json }
  elsif (virtual_value = association.options[:virtual_value])
    virtual_value
  elsif serializer && serializer.object
    ResourceIdentifier.new(serializer, serializable_resource_options).as_json
  end
end

def initialize(parent_serializer, serializable_resource_options, association)
  @parent_serializer = parent_serializer
  @association = association
  @serializable_resource_options = serializable_resource_options
end

def links_for(association)
  association.links.each_with_object({}) do |(key, value), hash|
    result = Link.new(parent_serializer, value).as_json
    hash[key] = result if result
  end
end

def meta_for(association)
  meta = association.meta
  meta.respond_to?(:call) ? parent_serializer.instance_eval(&meta) : meta
end