diff --git a/discover_extensions.py b/discover_extensions.py
index 56abee2..a97d2d4 100755
--- a/discover_extensions.py
+++ b/discover_extensions.py
@@ -1,4 +1,20 @@
 #!/bin/env python3
+#
+# Copyright (C) 2017 The University of Sheffield, UK
+#
+# 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 3 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, see <http://www.gnu.org/licenses/>.
+
 from selenium import webdriver
 import time
 import os
@@ -6,57 +22,65 @@ import re
 import time
 import sys
 import datetime
+import argparse
 
-def scroll(driver):
-    driver.execute_script("window.scrollTo(0, document.body.scrollHeight);")
+class ExtensionExplorer:
+    def scroll(self, driver):
+        driver.execute_script('window.scrollTo(0, document.body.scrollHeight);')
 
-def click_more(driver):
-    more_btn = driver.find_element_by_xpath("//div[text()='See More']")
-    if more_btn and more_btn.is_displayed():
-        more_btn.click()
-        #print("More Button found, seen and clicked")
+    def click_more(self, driver):
+        more_btn = driver.find_element_by_xpath("//div[text()='See More']")
+        if more_btn and more_btn.is_displayed():
+            more_btn.click()
 
-def save_ids(driver, savefile):
-    #This does not give is the complete source, unfortunately:
-    #content = driver.page_source
+    def save_ids(self, driver, savefile):
+        #This does not give us the complete source, unfortunately:
+        #content = driver.page_source
 
-    content = driver.execute_script("return document.body.innerHTML")
-    ids = sorted(set(re.findall("""[a-z]{32}""", content)))
+        content = driver.execute_script('return document.body.innerHTML')
+        ids = sorted(set(re.findall('\/([a-z]{32})"', content)))
 
-    oldids = []
-    try:
-        with open(savefile, "r") as f:
-            for line in f:
-                oldids.append(line.strip())
-        oldids = sorted(set(oldids))
-    except:
-        pass
-    if ids == oldids:
-        return False
+        oldids = []
+        try:
+            with open(savefile, 'r') as f:
+                for line in f:
+                    oldids.append(line.strip())
+            oldids = sorted(set(oldids))
+        except:
+            pass
+        if ids == oldids:
+            return False
 
-    with open(savefile, "w") as f:
-        f.write("\n".join(ids))
-        #print("IDs written")
-    return True
+        with open(savefile, 'w') as f:
+            f.write('\n'.join(ids))
+        return True
+    def run(self, outdir, interval):
+        os.makedirs(outdir, exist_ok=True)
+        savefile = os.path.join(outdir, 'ids-{}.txt'.format(datetime.datetime.now().isoformat()))
 
-savedir = "."
-if len(sys.argv) > 1:
-    savedir = sys.argv[1]
-    os.makedirs(savedir, exist_ok=True)
-savefile = os.path.join(savedir, "ids-{}.txt".format(datetime.datetime.now().isoformat()))
+        driver = webdriver.PhantomJS(service_log_path=os.path.devnull)
+        content = driver.get('https://chrome.google.com/webstore/category/extensions')
 
-driver = webdriver.PhantomJS() 
-content = driver.get('https://chrome.google.com/webstore/category/extensions')
+        last_save = 0
+        while True:
+            try:
+                self.scroll(driver)
+                self.click_more(driver)
+            except Exception as e:
+                print(e, file=sys.stderr)
 
-last_save = 0
-while True:
-    scroll(driver)
-    click_more(driver)
+            if time.time() - last_save > interval:
+                if not self.save_ids(driver, savefile):
+                    driver.quit()
+                    sys.exit(0)
+                last_save = time.time()
 
-    if time.time() - last_save > 30.0:
-        if not save_ids(driver, savefile):
-            #print("No new extension ids since last save, exiting...")
-            sys.exit(0)
-        last_save = time.time()
+            time.sleep(0.5)
 
-    time.sleep(0.5)
+if __name__ == '__main__':
+    parser = argparse.ArgumentParser(
+            description='Crawls the Google Play Store for new extension ids.')
+    parser.add_argument('out', help='The directory where the files with new ids should be stored.')
+    parser.add_argument('-t', '--interval', help='Saves the found ids to file every X seconds. If no new ids have been found within these X seconds, the crawler quits.', default=30.0, type=float)
+    args = parser.parse_args()
+    ExtensionExplorer().run(args.out, args.interval)