From 0c5539be3a22c28c7ea290bfecc48e11a4cf0eb4 Mon Sep 17 00:00:00 2001
From: Junzi Sun <junzisun@gmail.com>
Date: Sat, 23 May 2020 21:07:23 +0200
Subject: [PATCH] update BDS61 decoder

---
 pyModeS/decoder/adsb.py      |   2 +-
 pyModeS/decoder/bds/bds61.py | 113 +++++++++++++++--------------------
 tests/test_adsb.py           |   5 +-
 3 files changed, 53 insertions(+), 67 deletions(-)

diff --git a/pyModeS/decoder/adsb.py b/pyModeS/decoder/adsb.py
index d9ed7fd..1d65849 100644
--- a/pyModeS/decoder/adsb.py
+++ b/pyModeS/decoder/adsb.py
@@ -28,7 +28,7 @@ from pyModeS.decoder.bds.bds06 import (
 )
 from pyModeS.decoder.bds.bds08 import category, callsign
 from pyModeS.decoder.bds.bds09 import airborne_velocity, altitude_diff
-from pyModeS.decoder.bds.bds61 import is_emergency, emergency, emergency_squawk
+from pyModeS.decoder.bds.bds61 import is_emergency, emergency_state, emergency_squawk
 
 
 def df(msg):
diff --git a/pyModeS/decoder/bds/bds61.py b/pyModeS/decoder/bds/bds61.py
index 495382e..05dc649 100644
--- a/pyModeS/decoder/bds/bds61.py
+++ b/pyModeS/decoder/bds/bds61.py
@@ -4,95 +4,80 @@
 #   Aircraft Airborne status
 # ------------------------------------------
 
-from __future__ import absolute_import, print_function, division
-
 from pyModeS import common
 
 
-def is_emergency(msg):
-    """
-    Check if the aircraft is reporting an emergency
+def is_emergency(msg: str) -> bool:
+    """Check if the aircraft is reporting an emergency.
+
     Non-emergencies are either a subtype of zero (no information) or
     subtype of one and a value of zero (no emergency).
     Subtype = 2 indicates an ACAS RA broadcast, look in BDS 3,0
-    :param msg:
+
+    :param msg: 28 bytes hexadecimal message string
     :return: if the aircraft has declared an emergency
     """
     if common.typecode(msg) != 28:
         raise RuntimeError("%s: Not an airborne status message, expecting TC=28" % msg)
 
     mb = common.hex2bin(msg)[32:]
-
     subtype = common.bin2int(mb[5:8])
-    emergency_state = common.bin2int(mb[8:11])
 
     if subtype == 2:
         raise RuntimeError("%s: Emergency message is ACAS-RA, not implemented")
 
-    if subtype == 0:
-        return False
-    elif subtype == 1 and emergency_state == 0:
-        return False
-    else:
+    emergency_state = common.bin2int(mb[8:11])
+
+    if subtype == 1 and emergency_state == 1:
         return True
-
-
-def emergency(msg):
-    """
-    Return the aircraft emergency
-
-    ===== =======
-    Value Meaning
-    ===== =======
-    1     General emergency
-    2     Lifeguard/Medical
-    3     Minimum fuel
-    4     No communications
-    5     Unlawful communications
-    6     Reserved
-    7     Reserved
-    :param msg:
-    :return: If the aircraft has declared an emergency, the type
-    """
-    if not is_emergency(msg):
-        raise RuntimeError("%s: Aircraft not declared an emergency" % msg)
     else:
-        mb = common.hex2bin(msg)[32:]
-
-        subtype = common.bin2int(mb[5:8])
-        emergency_state = common.bin2int(mb[8:11])
-
-        return emergency_state
+        return False
 
 
-def emergency_squawk(msg):
+def emergency_state(msg: str) -> int:
+    """Decode aircraft emergency state.
+
+    Value   Meaning
+    -----   -----------------------
+    0       No emergency
+    1       General emergency
+    2       Lifeguard/Medical
+    3       Minimum fuel
+    4       No communications
+    5       Unlawful communications
+    6-7     Reserved
+
+    :param msg: 28 bytes hexadecimal message string
+    :return: emergency state
     """
-    Squawk code of the transmitting aircraft
-    Emergency value 1 will be squawk 7700
-    Emergency value 4 will be squawk 7600
-    Emergency value 5 will be squawk 7500
-    :param msg:
+
+    mb = common.hex2bin(msg)[32:]
+    subtype = common.bin2int(mb[5:8])
+
+    if subtype == 2:
+        raise RuntimeError("%s: Emergency message is ACAS-RA, not implemented")
+
+    emergency_state = common.bin2int(mb[8:11])
+    return emergency_state
+
+
+def emergency_squawk(msg: str) -> str:
+    """Decode squawk code.
+
+    Emergency value 1: squawk 7700.
+    Emergency value 4: squawk 7600.
+    Emergency value 5: squawk 7500.
+
+    :param msg: 28 bytes hexadecimal message string
     :return: aircraft squawk code
     """
     if common.typecode(msg) != 28:
         raise RuntimeError("%s: Not an airborne status message, expecting TC=28" % msg)
 
-    mb = common.hex2bin(msg)[32:]
-    C1 = mb[11]
-    A1 = mb[12]
-    C2 = mb[13]
-    A2 = mb[14]
-    C4 = mb[15]
-    A4 = mb[16]
-    B1 = mb[17]
-    D1 = mb[18]
-    B2 = mb[19]
-    D2 = mb[20]
-    B4 = mb[21]
-    D4 = mb[22]
+    msgbin = common.hex2bin(msg)
 
-    byte1 = int(A4 + A2 + A1, 2)
-    byte2 = int(B4 + B2 + B1, 2)
-    byte3 = int(C4 + C2 + C1, 2)
-    byte4 = int(D4 + D2 + D1, 2)
-    return str(byte1) + str(byte2) + str(byte3) + str(byte4)
+    # construct the 13 bits Mode A ID code
+    idcode = msgbin[43:49] + "0" + msgbin[49:55]
+
+    squawk = common.squawk(idcode)
+    return squawk
diff --git a/tests/test_adsb.py b/tests/test_adsb.py
index 45db5fa..c6e6de0 100644
--- a/tests/test_adsb.py
+++ b/tests/test_adsb.py
@@ -81,8 +81,9 @@ def test_adsb_velocity():
 
 
 def test_adsb_emergency():
-    assert not adsb.is_emergency('8DA2C1B6E112B600000000760759')
-    assert adsb.emergency_squawk('8DA2C1B6E112B600000000760759') == '6615'
+    assert not adsb.is_emergency("8DA2C1B6E112B600000000760759")
+    assert adsb.emergency_state("8DA2C1B6E112B600000000760759") == 0
+    assert adsb.emergency_squawk("8DA2C1B6E112B600000000760759") == "6615"
 
 
 # def test_nic():