# Copyright (C) 2017 MongoDB, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#   http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

require 'mongo/session/session_pool'
require 'mongo/session/server_session'

module Mongo

  # A logical client session representing a set of sequential operations executed
  #   by an application that are related in some way.
  #
  # @since 2.5.0
  class Session
    extend Forwardable

    # Get the options for this session.
    #
    # @since 2.5.0
    attr_reader :options

    # Get the client through which this session was created.
    #
    # @since 2.5.0
    attr_reader :client

    def_delegators :@server_session, :session_id

    # Error message describing that the session was attempted to be used by a client different from the
    # one it was originally associated with.
    #
    # @since 2.5.0
    MISTMATCHED_CLUSTER_ERROR_MSG = 'The client used to create this session does not match that of client ' +
        'initiating this operation. Please only use this session for operations through its parent client.'.freeze

    # Error message describing that the session cannot be used because it has already been ended.
    #
    # @since 2.5.0
    SESSION_ENDED_ERROR_MSG = 'This session has ended and cannot be used. Please create a new one.'.freeze

    # Error message describing that sessions are not supported by the server version.
    #
    # @since 2.5.0
    SESSIONS_NOT_SUPPORTED = 'Sessions are not supported by the connected servers.'.freeze

    # Initialize a Session.
    #
    # @example
    #   Session.new(server_session, client, options)
    #
    # @param [ ServerSession ] server_session The server session this client session is associated with.
    # @param [ Client ] client The client through which this session is created.
    # @param [ Hash ] options The options for this session.
    #
    # @since 2.5.0
    def initialize(server_session, client, options = {})
      @server_session = server_session
      @client = client
      @options = options
    end

    # End this session.
    #
    # @example
    #   session.end_session
    #
    # @return [ nil ] Always nil.
    #
    # @since 2.5.0
    def end_session
      if !ended? && @client
        @client.instance_variable_get(:@session_pool).checkin(@server_session)
        nil
      end
    ensure
      @server_session = nil
    end

    # End this session if it's an implicit session.
    #
    # @example
    #   session.end_implicit_session
    #
    # @return [ nil ] Always nil.
    #
    # @since 2.5.0
    def end_implicit_session
      end_session if implicit_session?
    end

    # Whether this session has ended.
    #
    # @example
    #   session.ended?
    #
    # @return [ true, false ] Whether the session has ended.
    #
    # @since 2.5.0
    def ended?
      @server_session.nil?
    end

    # Add this session's id to a command document.
    #
    # @example
    #   session.add_id!(cmd)
    #
    # @return [ Hash, BSON::Document ] The command document.
    #
    # @since 2.5.0
    def add_id!(command)
      command.merge!(lsid: session_id)
    end

    # Validate the session.
    #
    # @example
    #   session.validate!(client)
    #
    # @param [ Client ] client The client the session is attempted to be used with.
    #
    # @return [ nil ] nil if the session is valid.
    #
    # @raise [ Mongo::Error::InvalidSession ] Raise error if the session is not valid.
    #
    # @since 2.5.0
    def validate!(client)
      check_matching_client!(client)
      check_if_ended!
    end

    # Process a response from the server that used this session.
    #
    # @example Process a response from the server.
    #   session.process(result)
    #
    # @param [ Operation::Result ] The result from the operation.
    #
    # @return [ Operation::Result ] The result.
    #
    # @since 2.5.0
    def process(result)
      set_operation_time(result)
      @server_session.set_last_use!
      result
    end

    private

    def implicit_session?
      @implicit_session ||= !!(@options.key?(:implicit) && @options[:implicit] == true)
    end

    def set_operation_time(result)
      if result && result.operation_time
        @operation_time = result.operation_time
      end
    end

    def check_if_ended!
      raise Mongo::Error::InvalidSession.new(SESSION_ENDED_ERROR_MSG) if ended?
    end

    def check_matching_client!(client)
      if @client != client
        raise Mongo::Error::InvalidSession.new(MISTMATCHED_CLUSTER_ERROR_MSG)
      end
    end
  end
end