module Google::Auth::BaseClient

def apply a_hash, opts = {}
  a_copy = a_hash.clone
  apply! a_copy, opts
  a_copy
end

def apply! a_hash, opts = {}
  # fetch the access token there is currently not one, or if the client
  # has expired
  fetch_access_token! opts if needs_access_token?
  a_hash[AUTH_METADATA_KEY] = "Bearer #{send token_type}"
end

def expires_within?
  raise NotImplementedError
end

def fetch_access_token!
  raise NotImplementedError
end

def needs_access_token?
  send(token_type).nil? || expires_within?(60)
end

def notify_refresh_listeners
  listeners = defined?(@refresh_listeners) ? @refresh_listeners : []
  listeners.each do |block|
    block.call self
  end
end

def on_refresh &block
  @refresh_listeners = [] unless defined? @refresh_listeners
  @refresh_listeners << block
end

def token_type
  raise NotImplementedError
end

def updater_proc
  proc { |a_hash, opts = {}| apply a_hash, opts }
end