connection.rb

module Scada
  class Connection
    attr_accessor :environment
    private :environment, :environment=

    def self.open(&block)
      env = new
      env.connect
      block.call(env)
    ensure
      env.disconnect
    end

    def initialize
      self.environment = Scada.NdaGetEnv
    end

    def connect
      Scada.NdaConnect(environment, host_string, buffer_size = 1024)
    end

    def disconnect
      Scada.NdaDisconnect(environment)
    end

    def get_point_from_name(point_name)
      result_size = 1

      global_error_code = FFI::MemoryPointer.new(:ulong, size = 1)
      ids = FFI::MemoryPointer.new(:ulong, result_size)
      errors = FFI::MemoryPointer.new(:ulong, result_size)
      type_codes = FFI::MemoryPointer.new(:ulong, result_size)
      point_name_ptrs = FFI::MemoryPointer.new(:pointer, result_size)

      point_name_ptrs.write_array_of_pointer([FFI::MemoryPointer.from_string(point_name)])

      Scada.NdaGetipn(environment, result_size, point_name_ptrs, global_error_code, ids, errors, type_codes)

      analog_point_value_function_code = 41
      get_global_error_code = FFI::MemoryPointer.new(:ulong, size = 1)
      values = FFI::MemoryPointer.new(:double, result_size)
      conditions = FFI::MemoryPointer.new(:uchar, result_size)
      get_errors = FFI::MemoryPointer.new(:ulong, result_size)

      Scada.NdaGet(environment, result_size, analog_point_value_function_code, get_global_error_code, ids, values, conditions, errors).to_s(16)

      values.read_array_of_double(result_size)
    end

    private
    def host_string
      "host_a;host_b"
    end
  end
end