From ee48d286c2f59a1b43bfabf12f81c86217c5c753 Mon Sep 17 00:00:00 2001
From: Adam Goldsmith <adam@adamgoldsmith.name>
Date: Sun, 1 Sep 2024 21:35:58 -0400
Subject: [PATCH] doorcontrol: Fix Credential odd parity calculation

whoops!
---
 doorcontrol/hid/Credential.py            | 18 +++++++++++++-----
 doorcontrol/hid/tests/test_Credential.py | 10 ++++++++++
 2 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/doorcontrol/hid/Credential.py b/doorcontrol/hid/Credential.py
index 5bc3248..2ba1af9 100644
--- a/doorcontrol/hid/Credential.py
+++ b/doorcontrol/hid/Credential.py
@@ -25,15 +25,23 @@ class InvalidParity(InvalidHexCode):
 class Credential:
     bits: bitstring.Bits
 
+    @staticmethod
+    def even_parity(bits: bitstring.Bits) -> bool:
+        return bool(bits[7:19].count(1) % 2)
+
+    @staticmethod
+    def odd_parity(bits: bitstring.Bits) -> bool:
+        return (bits[19:31].count(1) % 2) == 0
+
     @classmethod
-    def from_code(cls, facility=int, card_number=int) -> "Credential":
+    def from_code(cls, facility: int, card_number: int) -> "Credential":
         bits = bitstring.pack(
             "0b000000, 0b0, uint:8=facility, uint:16=card_number, 0b0",
             facility=facility,
             card_number=card_number,
         )
-        bits[6] = bits[7:19].count(1) % 2  # even parity
-        bits[31] = bits[19:31].count(0) % 2  # odd parity
+        bits[6] = cls.even_parity(bits)
+        bits[31] = cls.odd_parity(bits)
         return cls(bitstring.Bits(bits))
 
     @classmethod
@@ -42,9 +50,9 @@ class Credential:
 
         if bits[:6].any(1):
             raise Not26Bit(bits)
-        if bits[6] != bits[7:19].count(1) % 2:
+        if bits[6] != cls.even_parity(bits):
             raise InvalidParity(bits, "even")
-        if bits[31] != (bits[19:31].count(0) % 2):
+        if bits[31] != (cls.odd_parity(bits)):
             raise InvalidParity(bits, "odd")
 
         return cls(bits)
diff --git a/doorcontrol/hid/tests/test_Credential.py b/doorcontrol/hid/tests/test_Credential.py
index 7e9b240..fe9bde7 100644
--- a/doorcontrol/hid/tests/test_Credential.py
+++ b/doorcontrol/hid/tests/test_Credential.py
@@ -18,3 +18,13 @@ class CredentialTestCase(TestCase):
         cred = Credential.from_code(facility_code, card_number)
         hex_cred = Credential.from_hex(cred.hex)
         self.assertEqual(cred, hex_cred)
+
+    def test_example_numbers(self):
+        examples = [
+            (100, 12345, "02C86073"),
+        ]
+
+        for facility_code, card_number, hex_number in examples:
+            code_cred = Credential.from_code(facility_code, card_number)
+            hex_cred = Credential.from_hex(hex_number)
+            self.assertEqual(code_cred, hex_cred)