@@ -1,54 +1,126 @@
 #!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
 """
-Test example to take a ping and save it into an sqlite3 database
-https://docs.python.org/3/library/sqlite3.html
+Is the website alive? This could be tested at a regular interval by retrieving 
+a url and checking its status. These tests can be stored in a database which makes
+it easy to accumulate statistics and to query for various patterns.
+
+Manual:
+  https://docs.python.org/3/library/sqlite3.html
+
+The database is named "ping.db" and is stored in the current directory.
+
+If you have the command "sqlite3" installed you could use that to connect to the 
+database and inspect it.
+
+$ sqlite3 ping.db 
+
 """
-# pip install requests
+
 import requests
 import sqlite3
 import time
 import sys
 
+
+
+def isSQLite3(filename):
+    """
+    Check if a file is a SQLite3 database.
+    http://stackoverflow.com/questions/12932607/how-to-check-with-python-and-sqlite3-if-one-sqlite-database-file-exists
+    """
+    from os.path import isfile, getsize
+
+    if not isfile(filename):
+        return False
+    if getsize(filename) < 100: # SQLite database file header is 100 bytes
+        return False
+    else:
+        fd = open(filename, 'rb')
+        Header = fd.read(100)
+        fd.close()
+
+        if Header[0:16] == b'SQLite format 3\000':
+            return True
+        else:
+            return False
+
+
+#
 # Get argument if there is one and use that as url
+#
 if len(sys.argv) == 2:
     url = sys.argv[1]
 else:
-    url = "http://dbwebb.se/"
+    sys.stderr.write("Add the url (for example http://bth.se) to check as a command line argument.\n")
+    sys.stderr.write("{command} http://bth.se.\n\n".format(command=sys.argv[0]))
+    sys.exit(1)
+
+
+
+print(__doc__)
+_ = input("Press enter to continue.")
 
-# connect to the database and set a cursor
-conn = sqlite3.connect("ping.sqlite3")
-cur = conn.cursor()
 
-# init database incase it's lost
-cur.execute("""
-CREATE TABLE IF NOT EXISTS Pings
-(url TEXT, time TEXT PRIMARY KEY, repsonse INTEGER)""")
 
+#
+# Connect to the database and set a cursor
+#
+dbFile = "ping.db"
+
+db = sqlite3.connect(dbFile)
+dbc = db.cursor()
+
+
+#
+# Init a new database if needed
+#
+dbc.execute("CREATE TABLE IF NOT EXISTS Pings (url TEXT, time TEXT, repsonse INTEGER)")
+
+
+#
+# Check if the database is valid
+#
+if not isSQLite3(dbFile):
+    sys.stderr.write("The file '{}' is not a valid SQLite database.\n".format(dbFile))
+    sys.exit(1)
+
+
+
+#
 # get current time for logging
+#
 rTime = time.ctime(time.time())
 
 try:
     # url must start with "http://" or the request fails
+    print("Connecting to: {}".format(url))
     r = requests.head(url)
     code = r.status_code
+
 except requests.ConnectionError:
     code = 0
 
-# create the values to be added as tuple
-values = (url, rTime, code)
+
+
+#
 # insert values into database
-cur.execute("""
-INSERT INTO Pings (url, time, repsonse)
-VALUES (?, ?, ?)
-""", values)
-
-print("Rows in db:")
-# get all the rows in database
-cur.execute("SELECT url, time, repsonse FROM Pings")
-# loop through the result
-for row in cur:
+#
+print("Storing log entry in database")
+dbc.execute("INSERT INTO Pings (url, time, repsonse) VALUES (?, ?, ?)", (url, rTime, code))
+
+print("Retrieving all rows in database:")
+dbc.execute("SELECT url, time, repsonse FROM Pings")
+
+# Loop through a resultset from a SELECT query
+for row in dbc:
     print(row)
 
-# commit the changes and close the connection
-conn.commit()
-conn.close()
+
+
+#
+# Commit the changes and close the connection
+#
+db.commit()
+db.close()