Headup h:{days} syntax, usage and date error handling

futureTasks

@@ -3,28 +3,50 @@
 """
 filter incoming lines based on date threshold
 
-hides tasks marked with a date threshold ("t:YYYY-MM-DD") in the future
+Threshold markers are of the form "t:YYYY-MM-DD".
+A headup h:DD will start showing DD days ahead of the t: date.
 
 this is intended to be used as TODOTXT_FINAL_FILTER
 """
 
 import sys
 import re
 
-from datetime import datetime
+import datetime
 
 
 pattern = re.compile(r"t:(\d{4})-(\d{2})-(\d{2})")
+hpattern = re.compile(r"h:(\d+)")
 
 
-def main(args=None):
-	now = datetime.now()
+def usage():
+	print('futureTasks threshold markers are of the form \
+"t:YYYY-MM-DD [h:{days}]"')
+
+
+def main(argv):
+	if len(argv) > 1 and argv[1] == "usage":
+		usage()
+		sys.exit(2)
+	now = datetime.datetime.now()
 	for line in sys.stdin:
 		match = pattern.search(line)
 		if match:
 			threshold = [int(i) for i in match.groups()]
-			if datetime(*threshold) < now:
-				print(line.strip())
+
+			# get pattern of the form h:{days} if present
+			hmatch = hpattern.search(line)
+			if hmatch:
+				headup = int(hmatch.groups()[0])
+			else:
+				headup = 0
+
+			try:
+				if datetime.datetime(*threshold) < now + \
+						datetime.timedelta(days=headup):
+					print(line.strip())
+			except ValueError:
+				print('ERROR: invalid date in line ' + line)
 		else:
 			print(line.strip())
 	return True