# Copyright 2016 Shawn Neal <sneal@sneal.net>
#
# 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 "securerandom" unless defined?(SecureRandom)
require_relative "base"
require_relative "../psrp/message_fragmenter"
require_relative "../psrp/receive_response_reader"
require_relative "../wsmv/configuration"
require_relative "../wsmv/create_pipeline"
require_relative "../wsmv/send_data"
require_relative "../wsmv/init_runspace_pool"
require_relative "../wsmv/keep_alive"

module WinRM
  module Shells
    # Proxy to a remote PowerShell instance
    class Powershell < Base
      include WinRM::WSMV::SOAP

      class << self
        def close_shell(connection_opts, transport, shell_id)
          msg = WinRM::WSMV::CloseShell.new(
            connection_opts,
            shell_id: shell_id,
            shell_uri: WinRM::WSMV::Header::RESOURCE_URI_POWERSHELL
          )
          transport.send_request(msg.build)
        end
      end

      # Create a new powershell shell
      # @param connection_opts [ConnectionOpts] The WinRM connection options
      # @param transport [HttpTransport] The WinRM SOAP transport
      # @param logger [Logger] The logger to log diagnostic messages to
      def initialize(connection_opts, transport, logger)
        super
        @shell_uri = WinRM::WSMV::Header::RESOURCE_URI_POWERSHELL
      end

      # Runs the specified command
      # @param command [String] The powershell script to run
      # @param block [&block] The optional callback for any realtime output
      # @yield [Message] PSRP Message in response
      # @yieldreturn [Array<Message>] All messages in response
      def send_pipeline_command(command, &block)
        with_command_shell(command) do |shell, cmd|
          response_reader.read_message(command_output_message(shell, cmd), true, &block)
        end
      end

      # calculate the maimum fragment size so that they will be as large as possible yet
      # no greater than the max_envelope_size_kb on the end point. To calculate this
      # threshold, we:
      # - determine the maximum number of bytes accepted on the endpoint
      # - subtract the non-fragment characters in the SOAP envelope
      # - determine the number of bytes that could be base64 encded to the above length
      # - subtract the fragment header bytes (ids, length, etc)
      def max_fragment_blob_size
        @max_fragment_blob_size ||= begin
          fragment_header_length = 21

          begin
            max_fragment_bytes = (max_envelope_size_kb * 1024) - empty_pipeline_envelope.length
            base64_deflated(max_fragment_bytes) - fragment_header_length
          rescue WinRMWSManFault => e
            # A non administrator user will encounter an access denied
            # error attempting to query winrm configuration.
            # we will assin a small default and adjust to a protocol
            # appropriate max length when that info is available
            raise unless e.fault_code == "5"

            WinRM::PSRP::MessageFragmenter::DEFAULT_BLOB_LENGTH
          rescue WinRMSoapFault
            WinRM::PSRP::MessageFragmenter::DEFAULT_BLOB_LENGTH
          end
        end
      end

      protected

      def response_reader
        @response_reader ||= WinRM::PSRP::ReceiveResponseReader.new(transport, logger)
      end

      def send_command(command, _arguments)
        command_id = SecureRandom.uuid.to_s.upcase
        command += "\r\nif (!$?) { if($LASTEXITCODE) { exit $LASTEXITCODE } else { exit 1 } }"
        message = PSRP::MessageFactory.create_pipeline_message(@runspace_id, command_id, command)
        fragmenter.fragment(message) do |fragment|
          command_args = [connection_opts, shell_id, command_id, fragment]
          if fragment.start_fragment
            resp_doc = transport.send_request(WinRM::WSMV::CreatePipeline.new(*command_args).build)
            command_id = REXML::XPath.first(resp_doc, "//*[local-name() = 'CommandId']").text
          else
            transport.send_request(WinRM::WSMV::SendData.new(*command_args).build)
          end
        end

        logger.debug("[WinRM] Command created for #{command} with id: #{command_id}")
        command_id
      end

      def open_shell
        @runspace_id = SecureRandom.uuid.to_s.upcase
        runspace_msg = WinRM::WSMV::InitRunspacePool.new(
          connection_opts,
          @runspace_id,
          open_shell_payload(@runspace_id)
        )
        resp_doc = transport.send_request(runspace_msg.build)
        shell_id = REXML::XPath.first(resp_doc, "//*[@Name='ShellId']").text
        wait_for_running(shell_id)
        shell_id
      end

      def out_streams
        %w{stdout}
      end

      private

      def base64_deflated(inflated_length)
        inflated_length / 4 * 3
      end

      def empty_pipeline_envelope
        WinRM::WSMV::CreatePipeline.new(
          connection_opts,
          "00000000-0000-0000-0000-000000000000",
          "00000000-0000-0000-0000-000000000000"
        ).build
      end

      def max_envelope_size_kb
        @max_envelope_size_kb ||= begin
          config_msg = WinRM::WSMV::Configuration.new(connection_opts)
          msg = config_msg.build
          resp_doc = transport.send_request(msg)
          REXML::XPath.first(resp_doc, "//*[local-name() = 'MaxEnvelopeSizekb']").text.to_i
                                  rescue REXML::ParseException
                                    logger.debug("[WinRM] Endpoint doesn't support config request for MaxEnvelopeSizekb")
                                    raise
        end
      end

      def open_shell_payload(shell_id)
        [
          WinRM::PSRP::MessageFactory.session_capability_message(shell_id),
          WinRM::PSRP::MessageFactory.init_runspace_pool_message(shell_id),
        ].map do |message|
          fragmenter.fragment(message).bytes
        end.flatten
      end

      def wait_for_running(shell_id)
        state = WinRM::PSRP::MessageData::RunspacepoolState::OPENING
        keepalive_msg = WinRM::WSMV::KeepAlive.new(connection_opts, shell_id)

        # 2 is "openned". if we start issuing commands while in "openning" the runspace
        # seems to hang
        until state == WinRM::PSRP::MessageData::RunspacepoolState::OPENED
          response_reader.read_message(keepalive_msg) do |message|
            logger.debug("[WinRM] polling for pipeline state. message: #{message.inspect}")
            parsed = message.parsed_data
            case parsed
            when WinRM::PSRP::MessageData::RunspacepoolState
              state = parsed.runspace_state
            when WinRM::PSRP::MessageData::SessionCapability
              # if the user lacks admin privileges, we cannot query the MaxEnvelopeSizeKB
              # on the server and will assign to a "best effort" default based on protocol version
              if fragmenter.max_blob_length == WinRM::PSRP::MessageFragmenter::DEFAULT_BLOB_LENGTH
                fragmenter.max_blob_length = default_protocol_envelope_size(parsed.protocol_version)
              end
            end
          end
        end
      end

      # Powershell v2.0 has a protocol version of 2.1
      # which defaults to a 150 MaxEnvelopeSizeKB
      # later versions default to 500
      def default_protocol_envelope_size(protocol_version)
        protocol_version > "2.1" ? 512000 : 153600
      end

      def fragmenter
        @fragmenter ||= WinRM::PSRP::MessageFragmenter.new(max_fragment_blob_size)
      end
    end
  end
end
