def user(user, options={})
      raise 'Error: Param user is nil!' if user.nil?

      url = if user.is_a?(Resource::User)
              url_for_resource(user)
            elsif user.is_a?(String)
              url_for_path(user_path(user))
            else
              raise 'Error: Invalid parameter!'
            end
      url = append_query_params(url, options)
      client.get(url, options) do |response|
        a_hash = parse(response)
        Resource::User.from_coach a_hash
      end
    end
def user(user, options={})
      raise 'Error: Param user is nil!' if user.nil?

      url = if user.is_a?(Resource::User)
              url_for_resource(user)
            elsif user.is_a?(String)
              url_for_path(user_path(user))
            else
              raise 'Error: Invalid parameter!'
            end
      url = append_query_params(url, options)
      client.get(url, options) do |response|
        a_hash = parse(response)
        Resource::User.from_coach a_hash
      end
    end
Retrieves a user by its username.

 @param [String|User] username | user
 @param [Hash] options
 @return [User]

 ====Examples
 @example
   user = @coach.user a_user
 @example
   user = @coach.user 'arueedlinger'
 @example
   user = @coach.user 'arueedlinger', query: { start: 0, soze: 10 }