From bbceb8429c5e1dde488d7463a100863885041654 Mon Sep 17 00:00:00 2001
From: Richard Senior <richard.j.senior@gmail.com>
Date: Wed, 27 Apr 2016 17:10:51 +0100
Subject: [PATCH] Add script to recreate metar.dat.gz

---
 create_metar_dat.py | 80 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 80 insertions(+)
 create mode 100755 create_metar_dat.py

diff --git a/create_metar_dat.py b/create_metar_dat.py
new file mode 100755
index 0000000..e05554d
--- /dev/null
+++ b/create_metar_dat.py
@@ -0,0 +1,80 @@
+#!/usr/bin/env python3
+#
+# create_metar_dat.py
+#
+# Script to create metar.dat.gz by checking weather.noaa.gov for stations
+# that have reported recently.
+#
+# Usage: create_metar_dat.py [OUTPUT_FILENAME]
+#
+# If OUTPUT_FILENAME is omitted, creates metar.dat.gz in working directory.
+#
+# Copyright (c) 2016 Richard Senior
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
+# MA 02110-1301, USA.
+
+import datetime
+import dateutil.parser
+import gzip
+import os
+import re
+import sys
+import urllib.request
+
+filename = "metar.dat.gz" if len(sys.argv) <= 1 else sys.argv[1]
+max_age_days = 7
+url = "http://weather.noaa.gov/pub/data/observations/metar/stations/"
+
+now = datetime.datetime.now()
+script = os.path.basename(__file__)
+
+class ParseException(Exception):
+    pass
+
+def stations():
+    for line in urllib.request.urlopen(url).readlines():
+        if line.startswith(b"<img"):
+            yield line
+
+def active_stations():
+    cutoff = now - datetime.timedelta(max_age_days)
+    icao_pattern = re.compile("[A-Z][A-Z0-9]{3}")
+    for station in stations():
+        tokens = station.split()
+        last_modified = tokens[5]
+        if dateutil.parser.parse(last_modified) > cutoff:
+            icao = tokens[4][16:20:].decode()
+            # Sanity check on parsed ICAO code.
+            if not icao_pattern.match(icao):
+                raise ParseException("Dubious ICAO code: " + icao)
+            yield icao
+
+# Run through the active stations before opening the file so that a file
+# is not created (or overwritten) if an exception is thrown.
+active = [icao + "\n" for icao in active_stations()]
+
+# Sanity check on the number of stations.
+if len(active) < 5000:
+    raise ParseException("Expected more than " + str(len(active)) + " stations")
+
+with gzip.open(filename, "wt") as f:
+    print("# List of airports known to have metar data available", file=f)
+    print("# Generated by", script, "on", now.strftime("%Y-%m-%d"), file=f)
+    print("#", url, file=f)
+    f.writelines(active)
+
+print(script + ": Wrote", len(active), "stations to", filename)
+