4 files changed, 115 insertions, 13 deletions

diff --git a/glucometerutils/drivers/otultraeasy.py b/glucometerutils/drivers/otultraeasy.py
index 579c07c..0f95e80 100644
--- a/glucometerutils/drivers/otultraeasy.py
+++ b/glucometerutils/drivers/otultraeasy.py
@@ -25,18 +25,13 @@ import logging
 import construct
 
 from glucometerutils import common
+from glucometerutils.support import construct_extras
 from glucometerutils.support import lifescan
 from glucometerutils.support import serial
 
 
 _INVALID_RECORD = 501
 
-_EPOCH = datetime.datetime.utcfromtimestamp(0)
-
-def datetime_to_timestamp(date):
-    delta = date - _EPOCH
-    return int(delta.total_seconds())
-
 
 _PACKET = construct.Struct(
     construct.RawCopy(
@@ -63,10 +58,6 @@ _PACKET = construct.Struct(
 )
 
 _COMMAND_SUCCESS = construct.Const(b'\x05\x06')
-_TIMESTAMP_ADAPTER = construct.ExprAdapter(
-    construct.Int32ul,
-    encoder=lambda obj, ctx: datetime_to_timestamp(obj),
-    decoder=lambda obj, ctx: datetime.datetime.fromtimestamp(obj))
 
 _VERSION_REQUEST = construct.Const(b'\x05\x0d\x02')
 
@@ -86,12 +77,14 @@ _SERIAL_NUMBER_RESPONSE = construct.Struct(
 _DATETIME_REQUEST = construct.Struct(
     construct.Const(b'\x05\x20'),  # 0x20 is the datetime
     'request_type' / construct.Enum(construct.Byte, write=0x01, read=0x02),
-    'timestamp' / construct.Default(_TIMESTAMP_ADAPTER, _EPOCH),
+    'timestamp' / construct.Default(
+        construct_extras.Timestamp(construct.Int32ul),
+        datetime.datetime(1970, 1, 1, 0, 0)),
 )
 
 _DATETIME_RESPONSE = construct.Struct(
     _COMMAND_SUCCESS,
-    'timestamp' / _TIMESTAMP_ADAPTER,
+    'timestamp' / construct_extras.Timestamp(construct.Int32ul),
 )
 
 _GLUCOSE_UNIT_REQUEST = construct.Const(
@@ -123,7 +116,7 @@ _READ_RECORD_REQUEST = construct.Struct(
 
 _READING_RESPONSE = construct.Struct(
     _COMMAND_SUCCESS,
-    'timestamp' / _TIMESTAMP_ADAPTER,
+    'timestamp' / construct_extras.Timestamp(construct.Int32ul),
     'value' / construct.Int32ul,
 )
 
diff --git a/glucometerutils/support/construct_extras.py b/glucometerutils/support/construct_extras.py
new file mode 100644
index 0000000..cb42105
--- /dev/null
+++ b/glucometerutils/support/construct_extras.py
@@ -0,0 +1,33 @@
+# -*- coding: utf-8 -*-
+"""Extra classes for Construct."""
+
+__author__ = 'Diego Elio Pettenò'
+__email__ = 'flameeyes@flameeyes.eu'
+__copyright__ = 'Copyright © 2018, Diego Elio Pettenò'
+__license__ = 'MIT'
+
+import datetime
+
+import construct
+
+class Timestamp(construct.Adapter):
+    """Adapter for converting datetime object into timestamps.
+
+    Take two parameters: the subcon object to output the resulting timestamp as,
+    and an optional epoch offset to the UNIX Epoch.
+
+    """
+    __slots__ = ["epoch"]
+
+    def __init__(self, subcon, epoch=0):
+        super(Timestamp, self).__init__(subcon)
+        self.epoch = epoch
+
+    def _encode(self, obj, context):
+        assert isinstance(obj, datetime.datetime)
+        epoch_date = datetime.datetime.utcfromtimestamp(self.epoch)
+        delta = obj - epoch_date
+        return int(delta.total_seconds())
+
+    def _decode(self, obj, context):
+        return datetime.datetime.utcfromtimestamp(obj + self.epoch)
diff --git a/test-requirements.txt b/test-requirements.txt
index 9f7c85b..29ac573 100644
--- a/test-requirements.txt
+++ b/test-requirements.txt
@@ -1,4 +1,5 @@
 absl-py
+construct
 pytest
 pytest-timeout
 pyserial
diff --git a/test/test_construct_extras.py b/test/test_construct_extras.py
new file mode 100644
index 0000000..faccabf
--- /dev/null
+++ b/test/test_construct_extras.py
@@ -0,0 +1,75 @@
+# -*- coding: utf-8 -*-
+"""Tests for the common routines."""
+
+__author__ = 'Diego Elio Pettenò'
+__email__ = 'flameeyes@flameeyes.eu'
+__copyright__ = 'Copyright © 2018, Diego Elio Pettenò'
+__license__ = 'MIT'
+
+import datetime
+import os
+import sys
+import unittest
+
+import construct
+
+sys.path.append(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from glucometerutils.support import construct_extras
+
+
+_TEST_DATE1 = datetime.datetime(1970, 1, 2, 0, 0)
+_TEST_DATE2 = datetime.datetime(1971, 1, 1, 0, 0)
+_TEST_DATE3 = datetime.datetime(1970, 1, 1, 0, 0)
+
+_NEW_EPOCH = 31536000  # datetime.datetime(1971, 1, 1, 0, 0)
+
+class TestTimestamp(unittest.TestCase):
+
+    def test_build_unix_epoch(self):
+        self.assertEqual(
+            construct_extras.Timestamp(construct.Int32ul).build(_TEST_DATE1),
+            b'\x80\x51\x01\x00')
+
+    def test_parse_unix_epoch(self):
+        self.assertEqual(
+            construct_extras.Timestamp(construct.Int32ul).parse(
+                b'\x803\xe1\x01'),
+            _TEST_DATE2)
+
+    def test_build_custom_epoch(self):
+        self.assertEqual(
+            construct_extras.Timestamp(
+                construct.Int32ul, epoch=_NEW_EPOCH).build(_TEST_DATE2),
+            b'\x00\x00\x00\x00')
+
+    def test_parse_custom_epoch(self):
+        self.assertEqual(
+            construct_extras.Timestamp(
+                construct.Int32ul, epoch=_NEW_EPOCH).parse(
+                    b'\x00\x00\x00\x00'),
+            _TEST_DATE2)
+
+    def test_build_custom_epoch_negative_failure(self):
+        with self.assertRaises(construct.core.FieldError):
+            construct_extras.Timestamp(
+                construct.Int32ul, epoch=_NEW_EPOCH).build(_TEST_DATE1)
+
+    def test_build_custom_epoch_negative_success(self):
+        self.assertEqual(
+            construct_extras.Timestamp(
+                construct.Int32sl, epoch=_NEW_EPOCH).build(_TEST_DATE1),
+            b'\x00\x1e\x20\xfe')
+
+    def test_build_varint(self):
+        self.assertEqual(
+            construct_extras.Timestamp(construct.VarInt).build(_TEST_DATE3),
+            b'\x00')
+
+    def test_invalid_value(self):
+        with self.assertRaises(AssertionError):
+            construct_extras.Timestamp(construct.Int32ul).build('foo')
+
+
+if __name__ == '__main__':
+        unittest.main()