scratch_link.py: Add -s option to specify BLE scan duration

Pyscrlink scans BLE devices for 10 seconds. This is a safe number to
cover various environments and devices. However, this is too long for
specific devices. One example is toio. Toio's Visual Programming
environment has automated connection to toio devices via Scratch-link,
at it assumes that the scan finishes with shorter time. To allow users
to specify shorter scan duration, add -s, or --scan_seconds option.

To simplify this new option support, utilize argparse library. Rewrite
option parser with argparse.

Signed-off-by: Shin'ichiro Kawasaki <kawasaki@juno.dti.ne.jp>

pyscrlink/scratch_link.py

@@ -15,6 +15,7 @@ import logging
 import sys
 import signal
 import traceback
+import argparse
 
 # for Bluetooth (e.g. Lego EV3)
 import bluetooth
@@ -44,6 +45,7 @@ logger.addHandler(handler)
 logger.propagate = False
 
 HOSTNAME="device-manager.scratch.mit.edu"
+scan_seconds=10.0
 
 class Session():
     """Base class for BTSession and BLESession"""
@@ -495,6 +497,7 @@ class BLESession(Session):
         return False
 
     def _scan_devices(self, params):
+        global scan_seconds
         if BLESession.nr_connected > 0:
             return len(BLESession.found_devices) > 0
         found = False
@@ -505,7 +508,8 @@ class BLESession(Session):
                 for i in range(self.MAX_SCANNER_IF):
                     scanner = Scanner(iface=i)
                     try:
-                        devices = scanner.scan(10.0)
+                        logger.debug(f"start BLE scan: {scan_seconds} seconds")
+                        devices = scanner.scan(scan_seconds)
                         for dev in devices:
                             if self.matches(dev, params['filters']):
                                 BLESession.found_devices.append(dev)
@@ -718,18 +722,20 @@ def stack_trace():
          print(line)
 
 def main():
-    opts = [opt for opt in sys.argv[1:] if opt.startswith("-")]
-    if "-h" in opts:
-        print((f"Usage: {sys.argv[0]} [OPTS]\n"
-               "OPTS:\t-h Show this help.\n"
-               "\t-d Print debug messages."
-        ))
-        sys.exit(1)
-    elif "-d" in opts:
+    global scan_seconds
+    parser = argparse.ArgumentParser(description='start Scratch-link')
+    parser.add_argument('-d', '--debug', action='store_true',
+                        help='print debug messages')
+    parser.add_argument('-s', '--scan_seconds', type=float, default=10.0,
+                        help='specifiy duration to scan BLE devices in seconds')
+    args = parser.parse_args()
+    if args.debug:
         print("Print debug messages")
         logLevel = logging.DEBUG
         handler.setLevel(logLevel)
         logger.setLevel(logLevel)
+    scan_seconds = args.scan_seconds
+    logger.debug(f"set scan_seconds: {scan_seconds}")
 
     # Prepare certificate of the WSS server
     gencert.prep_cert()