- igc/reader: add "datetime" and "datetime_local" to fix_records to (#…

…307)

* - igc/reader: add "datetime" and "datetime_local" to fix_records to
              deal with UTC and local time correctly. Please read "How
              to read an IGC file" for a detailed explanation.

* Added missing timezone.py

* Fix datetime.UTC, which is only available in python 3.11

CHANGELOG.rst

@@ -6,6 +6,9 @@ Here you can see the full list of changes between each aerofiles release.
 aerofiles vXXX, 2024-XX-YYYY
 ----------------------------
 - igc/reader: fix for HFTZN to handle timezone that is not integer
+- igc/reader: add "datetime" and "datetime_local" to fix_records to
+              deal with UTC and local time correctly. Please read "How
+              to read an IGC file" for a detailed explanation.
 
 aerofiles v1.3.1, 2024-08-12
 ----------------------------

aerofiles/igc/reader.py

@@ -1,5 +1,7 @@
 import datetime
 
+from aerofiles.util.timezone import TimeZoneFix
+
 
 class Reader:
     """
@@ -57,6 +59,23 @@ def read(self, file_obj):
                         fix_records[0].append(MissingExtensionsError)
 
                     fix_record = LowLevelReader.process_B_record(line, fix_record_extensions[1])
+
+                    # To create "datetime" we need a date. Take it from header or previous fix:
+                    if len(fix_records[1]) == 0:
+                        date = header[1]["utc_date"]
+                    else:
+                        previous_fix = fix_records[1][-1]
+                        date = previous_fix["datetime"].date()
+                        time = previous_fix["datetime"].time()
+                        # If time of next fix is _before_ last fix, we are now on next day
+                        if fix_record["time"] < time:
+                            date = date + datetime.timedelta(days=1)
+
+                    fix_record["datetime"] = datetime.datetime.combine(date, fix_record["time"]).replace(tzinfo=TimeZoneFix(0))
+                    if "time_zone_offset" in header[1]:
+                        timezone = TimeZoneFix(header[1]["time_zone_offset"])
+                        fix_record["datetime_local"] = fix_record["datetime"].astimezone(timezone)
+
                     fix_records[1].append(fix_record)
             elif record_type == 'C':
                 task_item = line
@@ -653,28 +672,15 @@ def decode_date(date_str):
         elif date_str == '000000':
             return None
 
-        dd = int(date_str[0:2])
-        mm = int(date_str[2:4])
-        yy = int(date_str[4:6])
-
-        current_year_yyyy = datetime.date.today().year
-        current_year_yy = current_year_yyyy % 100
-        current_century = current_year_yyyy - current_year_yy
-        yyyy = current_century + yy if yy <= current_year_yy else current_century - 100 + yy
-
-        return datetime.date(yyyy, mm, dd)
+        return datetime.datetime.strptime(date_str, "%d%m%y").date()
 
     @staticmethod
     def decode_time(time_str):
 
         if len(time_str) != 6:
             raise ValueError('Time string does not have correct size')
 
-        h = int(time_str[0:2])
-        m = int(time_str[2:4])
-        s = int(time_str[4:6])
-
-        return datetime.time(h, m, s)
+        return datetime.datetime.strptime(time_str, "%H%M%S").time()
 
     @staticmethod
     def decode_extension_record(line):

aerofiles/igc/writer.py

@@ -1,6 +1,7 @@
 import datetime
 
 from aerofiles.igc import patterns
+from aerofiles.util.timezone import TimeZoneFix
 
 
 class Writer:
@@ -513,7 +514,7 @@ def write_task_metadata(
         """
 
         if declaration_datetime is None:
-            declaration_datetime = datetime.datetime.utcnow()
+            declaration_datetime = datetime.datetime.now(TimeZoneFix(0))
 
         if isinstance(declaration_datetime, datetime.datetime):
             declaration_datetime = (
@@ -687,7 +688,7 @@ def write_fix(self, time=None, latitude=None, longitude=None, valid=False,
         """
 
         if time is None:
-            time = datetime.datetime.utcnow()
+            time = datetime.datetime.now(TimeZoneFix(0))
 
         record = self.format_time(time)
         record += self.format_latitude(latitude)
@@ -754,7 +755,7 @@ def write_event(self, *args):
             time = None
 
         if time is None:
-            time = datetime.datetime.utcnow()
+            time = datetime.datetime.now(TimeZoneFix(0))
 
         if not patterns.THREE_LETTER_CODE.match(code):
             raise ValueError('Invalid event code')
@@ -790,7 +791,7 @@ def write_satellites(self, *args):
             time, satellites = args
 
         if time is None:
-            time = datetime.datetime.utcnow()
+            time = datetime.datetime.now(TimeZoneFix(0))
 
         record = self.format_time(time)
 

aerofiles/util/timezone.py

@@ -0,0 +1,16 @@
+import datetime
+
+
+class TimeZoneFix(datetime.tzinfo):
+
+    def __init__(self, fix):
+        self.fix = fix
+
+    def utcoffset(self, dt):
+        return datetime.timedelta(hours=self.fix)
+
+    def dst(self, dt):
+        return datetime.timedelta(0)
+
+    def tzname(self, dt):
+        return str(self.fix)

docs/contents.rst.inc

@@ -7,6 +7,7 @@ This part of the documentation explains typical use cases with `aerofiles`.
    :maxdepth: 2
 
    installation
+   guide/igc-reading
    guide/igc-writing
 
 API Reference

tests/igc/data/example.igc

@@ -6,6 +6,7 @@ HFCM2CREW2: Smith-Barry John A
 HFGTYGLIDERTYPE: Schleicher ASH-25
 HFGIDGLIDERID: ABCD-1234
 HFDTM100GPSDATUM: WGS-1984
+HFTZNTIMEZONE:+3.00
 HFRFWFIRMWAREVERSION:6.4
 HFRHWHARDWAREVERSION:3.0
 HFFTYFRTYPE: Manufacturer, Model
@@ -43,7 +44,7 @@ E160305PEV
 B1603055107180N00149185WA002910043521008015
 B1603105107212N00149174WA002930043519608024
 K16024800090
-B1602485107220N00149150WA004940043619008018
+B2202485107220N00149150WA004940043619008018
 B1602525107330N00149127WA004960043919508015
 LXXXRURITANIAN STANDARD NATIONALS DAY 1
 LXXXFLIGHT TIME: 4:14:25, TASK SPEED:58.48KTS

tests/igc/test_reader.py

@@ -632,7 +632,15 @@ def test_highlevel_reader():
         'manufacturer': 'XXX'
     }
 
-    assert len(result['fix_records'][1]) == 9
+    fixes = result['fix_records'][1]
+    assert len(fixes) == 9
+
+    assert fixes[0]["datetime"] == datetime.datetime(2001, 7, 16, 16, 2, 40, tzinfo=datetime.timezone(datetime.timedelta(0)))
+    # check that timezone is +3
+    assert fixes[0]["datetime_local"].time() == datetime.time(19, 2, 40)
+
+    # Check, that we have the next day, because the time is lower than the previous fix
+    assert fixes[8]["datetime"].date() == datetime.date(2001, 7, 17)
 
     assert result['task'][1]['declaration_date'] == datetime.date(2001, 7, 15)
     assert result['task'][1]['declaration_time'] == datetime.time(21, 38, 41)
@@ -674,6 +682,7 @@ def test_highlevel_reader():
         'pressure_sensor_max_alt': {
             'unit': 'm',
             'value': 11000},
+        'time_zone_offset': 3,
         'utc_date': datetime.date(2001, 7, 16)
     }