Add timestamp class to convert from PDU format to DateTime

lib/biju/pdu.rb

@@ -4,6 +4,7 @@ require 'biju/pdu/encoding/ucs2'
 require 'biju/pdu/user_data'
 require 'biju/pdu/data_coding_scheme'
 
+require 'biju/pdu/timestamp'
 require 'biju/pdu/phone_number'
 require 'biju/pdu/type_of_address'
 
@@ -38,9 +39,7 @@ module Biju
 
         protocol_identifier: string[34..35],
         data_coding_scheme: string[36..37],
-        timestamp: DateTime.strptime(
-          "#{string[38..49].reverse}+#{string[50..51].reverse}",
-          '%S%M%H%d%m%y%Z'),
+        timestamp: Timestamp.new(string[38, 14]).to_datetime,
         user_data_length: string[52..53],
       }
       res[:sender_number] = PhoneNumber.new(

lib/biju/pdu/timestamp.rb

@@ -0,0 +1,26 @@
+module Biju
+  module PDU
+    class Timestamp
+      attr_reader :timestamp
+
+      def initialize(timestamp)
+        @timestamp = timestamp
+      end
+
+      def timezone
+        timezone = timestamp[-2, 2].reverse.hex
+
+        sign = (timezone >> 7 == 0 ? '+' : '-')
+        tens_digit = ((timezone & 0b01110000) >> 4)
+        units_digit = (timezone & 0b00001111)
+
+         sign << '%02d' % ((tens_digit * 10 + units_digit) / 4)
+      end
+
+      def to_datetime
+        DateTime.strptime(
+          "#{timestamp[0..-3].reverse}#{timezone}", '%S%M%H%d%m%y%Z')
+      end
+    end
+  end
+end

spec/biju/pdu/timestamp_spec.rb

@@ -0,0 +1,9 @@
+require 'spec_helper'
+require 'biju/pdu'
+
+describe Biju::PDU::Timestamp do
+  subject { Biju::PDU::Timestamp.new('31900141039580') }
+
+  its(:timezone) { should eq('+02') }
+  its(:to_datetime) { should eq(DateTime.new(2013, 9, 10, 14, 30, 59, '+02')) }
+end

spec/biju/sms_spec.rb

@@ -6,7 +6,7 @@ describe Biju::Sms do
     Biju::Sms.new(
       id: 1,
       phone_number: "144",
-      datetime: "11/07/28,15:34:08-12",
+      datetime: DateTime.new(2011, 7, 28, 15, 34, 8, '-12'),
       message: "Some text here")
   end
 
@@ -21,7 +21,7 @@ describe Biju::Sms do
         '07913396050066F3040B913366666666F600003190509095928004D4F29C0E')
     end
 
-    its(:datetime) { should eq(DateTime.new(2013, 9, 5, 9, 59, 29, '+08')) }
+    its(:datetime) { should eq(DateTime.new(2013, 9, 5, 9, 59, 29, '+02')) }
     its(:message) { should eq('Test') }
     its(:phone_number) { should eq('33666666666') }
     its(:type_of_address) { should eq(:international) }