From c47277ad2d6146e8612080fbf4fe5632f58297e3 Mon Sep 17 00:00:00 2001
From: Cody Mitchell <codyshanemitchell@gmail.com>
Date: Sun, 13 Sep 2026 23:08:43 -0500
Subject: [PATCH] Ignore corrupt trailing timestamps when filling idle sleep

---
 pygt3x/reader.py               |  7 ++--
 tests/test_ism_corrupt_tail.py | 63 ++++++++++++++++++++++++++++++++++
 2 files changed, 68 insertions(+), 2 deletions(-)
 create mode 100644 tests/test_ism_corrupt_tail.py

diff --git a/pygt3x/reader.py b/pygt3x/reader.py
index f4674ac..aefee88 100644
--- a/pygt3x/reader.py
+++ b/pygt3x/reader.py
@@ -144,6 +144,7 @@ def _get_data_default(self, num_rows=None):
         last_idsm_ts = 0
         # Initialize evt in case there are no events in the GT3x file
         evt = None
+        last_valid_timestamp = None
         for evt in self.read_events(num_rows):
 
             if not evt.is_checksum_valid:
@@ -152,6 +153,8 @@ def _get_data_default(self, num_rows=None):
                 )
                 continue
 
+            last_valid_timestamp = evt.header.timestamp
+
             try:
                 type = Types(evt.header.event_type)
             except ValueError:
@@ -279,8 +282,8 @@ def _get_data_default(self, num_rows=None):
             # Idle sleep mode was started but not finished before the recording
             # ended. This means that we might be missing some records at the end of
             # the file.
-            assert evt is not None
-            idle_sleep_mode_ended = evt.header.timestamp
+            assert last_valid_timestamp is not None
+            idle_sleep_mode_ended = last_valid_timestamp
             payload = self._validate_payload(
                 self._fill_ism(
                     idle_sleep_mode_started - (dt_idm - 1),
diff --git a/tests/test_ism_corrupt_tail.py b/tests/test_ism_corrupt_tail.py
new file mode 100644
index 0000000..0e1018e
--- /dev/null
+++ b/tests/test_ism_corrupt_tail.py
@@ -0,0 +1,63 @@
+from functools import reduce
+from operator import xor
+import struct
+from zipfile import ZipFile
+
+import numpy as np
+import pandas as pd
+import pytest
+
+from pygt3x.reader import FileReader
+
+
+START = 1600000000
+
+
+def _record(event_type, second, payload, corrupt=False):
+    header = struct.pack("<BBIH", 0x1E, event_type, START + second, len(payload))
+    checksum = reduce(xor, header + payload, 0) ^ 0xFF
+    if corrupt:
+        checksum ^= 1
+    return header + payload + bytes([checksum])
+
+
+def _read(tmp_path, sample_rate, tail):
+    params = _record(21, 0, bytes([0, 0, 2, 0, 4, 0, 0, 0]))
+    activity = _record(26, 0, struct.pack("<hhh", 10, 20, 30) * sample_rate)
+    sleep = _record(3, 1, b"\x08")
+    battery = _record(2, 5, struct.pack("<H", 3700))
+    path = tmp_path / "synthetic.gt3x"
+    with ZipFile(path, "w") as archive:
+        archive.writestr(
+            "info.txt", f"Sample Rate: {sample_rate}\nAcceleration Scale: 1\n"
+        )
+        archive.writestr("log.bin", params + activity + sleep + battery + tail)
+    with FileReader(str(path)) as reader:
+        return reader.to_pandas(calibrate=False)
+
+
+@pytest.mark.parametrize("sample_rate", [30, 100])
+@pytest.mark.parametrize("second", [3, 9])
+@pytest.mark.parametrize("repeat", [1, 2])
+def test_bad_checksum_tail_preserves_sleep_boundary(
+    tmp_path, sample_rate, second, repeat
+):
+    expected = _read(tmp_path, sample_rate, b"")
+    assert len(expected) == 5 * sample_rate
+    assert expected.IdleSleepMode.sum() == 4 * sample_rate
+    np.testing.assert_allclose(
+        expected.index, START + np.arange(5 * sample_rate) / sample_rate,
+        rtol=0, atol=5e-7,
+    )
+    tail = _record(2, second, struct.pack("<H", 3700), corrupt=True) * repeat
+    actual = _read(tmp_path, sample_rate, tail)
+    pd.testing.assert_frame_equal(actual, expected)
+
+
+@pytest.mark.parametrize("sample_rate", [30, 100])
+@pytest.mark.parametrize("length", [4, 9, 10])
+def test_incomplete_tail_preserves_sleep_boundary(tmp_path, sample_rate, length):
+    expected = _read(tmp_path, sample_rate, b"")
+    tail = _record(2, 9, struct.pack("<H", 3700))[:length]
+    actual = _read(tmp_path, sample_rate, tail)
+    pd.testing.assert_frame_equal(actual, expected)