class ActiveStorage::Attached::Changes::CreateOne

def attachment
  @attachment ||= find_or_build_attachment
end

def blob
  @blob ||= find_or_build_blob
end

def build_attachment
  ActiveStorage::Attachment.new(record: record, name: name, blob: blob)
end

def find_attachment
  if record.public_send("#{name}_blob") == blob
    record.public_send("#{name}_attachment")
  end
end

def find_or_build_attachment
  find_attachment || build_attachment
end

def find_or_build_blob
  case attachable
  when ActiveStorage::Blob
    attachable
  when ActionDispatch::Http::UploadedFile, Rack::Test::UploadedFile
    ActiveStorage::Blob.build_after_unfurling \
      io: attachable.open,
      filename: attachable.original_filename,
      content_type: attachable.content_type
  when Hash
    ActiveStorage::Blob.build_after_unfurling(attachable)
  when String
    ActiveStorage::Blob.find_signed(attachable)
  else
    raise ArgumentError, "Could not find or build blob: expected attachable, got #{attachable.inspect}"
  end
end

def initialize(name, record, attachable)
  @name, @record, @attachable = name, record, attachable
end

def save
  record.public_send("#{name}_attachment=", attachment)
  record.public_send("#{name}_blob=", blob)
end

def upload
  case attachable
  when ActionDispatch::Http::UploadedFile, Rack::Test::UploadedFile
    blob.upload_without_unfurling(attachable.open)
  when Hash
    blob.upload_without_unfurling(attachable.fetch(:io))
  end
end