module Mattermost
  class NoSessionError < StandardError; end
  # This class' prime objective is to obtain a session token on a Mattermost
  # instance with SSO configured where this GitLab instance is the provider.
  #
  # The process depends on OAuth, but skips a step in the authentication cycle.
  # For example, usually a user would click the 'login in GitLab' button on
  # Mattermost, which would yield a 302 status code and redirects you to GitLab
  # to approve the use of your account on Mattermost. Which would trigger a
  # callback so Mattermost knows this request is approved and gets the required
  # data to create the user account etc.
  #
  # This class however skips the button click, and also the approval phase to
  # speed up the process and keep it without manual action and get a session
  # going.
  class Session
    include Doorkeeper::Helpers::Controller
    include HTTParty

    attr_accessor :current_resource_owner

    def initialize(uri, current_user)
      # Sets the base uri for HTTParty, so we can use paths
      self.class.base_uri(uri)

      @current_resource_owner = current_user
    end

    def with_session
      raise NoSessionError unless create

      begin
        yield
      ensure
        destroy
      end
    end

    # Next methods are needed for Doorkeeper
    def pre_auth
      @pre_auth ||= Doorkeeper::OAuth::PreAuthorization.new(
        Doorkeeper.configuration, server.client_via_uid, params)
    end

    def authorization
      @authorization ||= strategy.request
    end

    def strategy
      @strategy ||= server.authorization_request(pre_auth.response_type)
    end

    def request
      @request ||= OpenStruct.new(parameters: params)
    end

    def params
      Rack::Utils.parse_query(@oauth_uri.query).symbolize_keys
    end

    private

    def create
      return unless oauth_uri
      return unless token_uri

      self.class.headers("Cookie" => "MMAUTHTOKEN=#{request_token}")

      request_token
    end

    def destroy
      post('/api/v3/users/logout')
    end

    def oauth_uri
      response = get("/api/v3/oauth/gitlab/login", follow_redirects: false)
      return unless 300 <= response.code && response.code < 400

      redirect_uri = response.headers['location']
      return unless redirect_uri

      @oauth_uri ||= URI.parse(redirect_uri)
    end

    def token_uri
      @token_uri ||= if @oauth_uri
                       authorization.authorize.redirect_uri if pre_auth.authorizable?
                     end
    end

    def request_token
      @request_token ||= begin
                           response = get(@token_uri, follow_redirects: false)
                           response.headers['token'] if 200 <= response.code && response.code < 400
                         end
    end

    def get(path, options = {})
      self.class.get(path, options)
    end

    def post(path, options = {})
      self.class.post(path, options)
    end
  end
end