Detect log file format

sohstationviewer/model/reftek_data/reftek_reader/log_file_reader.py

 from pathlib import Path
-from typing import List
+from typing import List, Literal, Optional
 
+LogFileFormat = Literal['rt2ms', 'logpeek', 'sohstationviewer']
+PACKETS = ['SH', 'SC', 'OM', 'DS', 'AD', 'CD', 'FD', 'EH', 'ET']
+
+
+def detect_log_file_packet_format(packet: List[str]) -> LogFileFormat:
+    """
+    Detect the format of a log file packet. The format can be either rt2ms',
+    logpeek's, or SOHStationViewer's.
+
+    :param packet: a packet extracted from a log file.
+    :return: the format of packet. Can be either 'rt2ms', 'logpeek', or
+        'sohstationviewer'.
+    """
+    # We want to take advantage of the metadata written by the various programs
+    # as much as possible.
+    if packet[0].startswith('logpeek'):
+        return 'logpeek'
+    elif packet[0].startswith('rt2ms'):
+        return 'rt2ms'
+    elif packet[0].startswith('sohstationviewer'):
+        return 'sohstationviewer'
+
+    packet_start = packet[0]
+
+    # The first line of a packet in a log file generated by rt2ms starts with
+    # a 2-letter packet type. That is then followed by an empty space and the
+    # string 'exp'.
+    if packet_start[:2] in PACKETS and packet_start[3:6] == 'exp':
+        return 'rt2ms'
+
+    # SOHStationViewer stores all events' info at the end of its log file, and
+    # so if we see the line
+    # Events:
+    # at the start of a packet, we know the log file is from SOHStationViewer.
+    if packet_start.startswith('Events:'):
+        return 'sohstationviewer'
+
+    # Logpeek write its events' info right after an SH packet.
+    packet_end = packet[-1]
+    packet_end_with_event_info = (packet_end.startswith('DAS') or
+                                  packet_end.startswith('WARNING'))
+    if (packet_start.startswith('State of Health') and
+            packet_end_with_event_info):
+        return 'logpeek'
 
-def detect_log_file_packet_format(packet: List[str]):
-    pass
 
 def read_soh_packet_base(packet: List[str]):
     pass
@@ -51,11 +93,13 @@ class LogFileReader:
     def __init__(self, file_path: Path):
         self.file_path = file_path
         self.packet_reader = None
-        self.log_file_type: LogFileFormat
+        self.log_file_type: Optional[LogFileFormat] = None
 
     def read(self):
         log_file = LogFile(self.file_path)
         for packet in log_file:
+            if self.log_file_type is None:
+                self.log_file_type = detect_log_file_packet_format(packet)
             pass