class ActiveModelSerializers::Adapter::JsonApi::Relationship

def as_json
  hash = {}
  hash[:data] = data_for(association) if association.include_data?
  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)
  if association.collection?
    data_for_many(association)
  else
    data_for_one(association)
  end
end

def data_for_many(association)
  # TODO(BF): Process relationship without evaluating lazy_association
  collection_serializer = association.lazy_association.serializer
  if collection_serializer.respond_to?(:each)
    collection_serializer.map do |serializer|
      ResourceIdentifier.new(serializer, serializable_resource_options).as_json
    end
  elsif (virtual_value = association.virtual_value)
    virtual_value
  else
    []
  end
end

def data_for_one(association)
  if association.belongs_to? &&
      parent_serializer.object.respond_to?(association.reflection.foreign_key)
    id = parent_serializer.object.send(association.reflection.foreign_key)
    type = association.reflection.type.to_s
    ResourceIdentifier.for_type_with_id(type, id, serializable_resource_options)
  else
    # TODO(BF): Process relationship without evaluating lazy_association
    serializer = association.lazy_association.serializer
    if (virtual_value = association.virtual_value)
      virtual_value
    elsif serializer && association.object
      ResourceIdentifier.new(serializer, serializable_resource_options).as_json
    else
      nil
    end
  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