Implement convoluted encoding of UCS-2 as per TS 102 221 Annex A

TS 102 221 Annex A defines three variants of encoding UCS-2 characters
into byte streams in files on UICC cards: One rather simplistic one, and
two variants for optimizing memory utilization on the card.

Let's impelement a construct "Ucs2Adapter" class for this.

Change-Id: Ic8bc8f71079faec1bf0e538dc0dfa21403869c6d

tests/test_construct.py

@@ -33,5 +33,49 @@ class TestUtils(unittest.TestCase):
         self.assertEqual(filter_dict(inp), out)
 
 
+class TestUcs2Adapter(unittest.TestCase):
+    # the three examples from TS 102 221 Annex A
+    EXAMPLE1 = b'\x80\x00\x30\x00\x31\x00\x32\x00\x33'
+    EXAMPLE2 = b'\x81\x05\x13\x53\x95\xa6\xa6\xff\xff'
+    EXAMPLE3 = b'\x82\x05\x05\x30\x2d\x82\xd3\x2d\x31'
+    ad = Ucs2Adapter(GreedyBytes)
+
+    def test_example1_decode(self):
+        dec = self.ad._decode(self.EXAMPLE1, None, None)
+        self.assertEqual(dec, "0123")
+
+    def test_example2_decode(self):
+        dec = self.ad._decode(self.EXAMPLE2, None, None)
+        self.assertEqual(dec, "S\u0995\u09a6\u09a6\u09ff")
+
+    def test_example3_decode(self):
+        dec = self.ad._decode(self.EXAMPLE3, None, None)
+        self.assertEqual(dec, "-\u0532\u0583-1")
+
+    testdata = [
+        # variant 2 with only GSM alphabet characters
+        ( "mahlzeit", '8108006d61686c7a656974' ),
+        # variant 2 with mixed GSM alphabet + UCS2
+        ( "mahlzeit\u099523", '810b136d61686c7a656974953233' ),
+        # variant 3 due to codepoint exceeding 8 bit
+        ( "mahl\u8023zeit", '820980236d61686c807a656974' ),
+        # variant 1 as there is no common codepoint pointer / prefix
+        ( "\u3000\u2000\u1000", '80300020001000' ),
+    ]
+
+    def test_data_decode(self):
+        for string, encoded_hex in self.testdata:
+            encoded = h2b(encoded_hex)
+            dec = self.ad._decode(encoded, None, None)
+            self.assertEqual(dec, string)
+
+    def test_data_encode(self):
+        for string, encoded_hex in self.testdata:
+            encoded = h2b(encoded_hex)
+            re_enc = self.ad._encode(string, None, None)
+            self.assertEqual(encoded, re_enc)
+
+
+
 if __name__ == "__main__":
 	unittest.main()