#!/usr/bin/env python3
"""Write information into a logfile, like the timestamp and the hostname."""

import os
import socket
from datetime import date
from datetime import datetime


# Determine if the OS is MS Windows
if os.name == 'nt':
    # Set the location of the file to write to, in the user Documents directory
    logfile = os.path.join(os.path.join(os.environ['USERPROFILE']),
                           r'Documents\logoff.log')
# For OS which are not MS Windows
else:
    logfile = os.path.join(os.path.join(os.environ['HOME']),
                           r'Documents/logoff.log')

# Create the file if it does not exist yet
if not os.path.exists(logfile):
    with open(logfile, 'w'):
        pass

# Determine the current date and time
today = date.today()
now = datetime.now()

current_day = today.strftime("%d.%m.%Y")

current_time = now.strftime("%H:%M:%S")

# Determine the client hostname
client_hostname = os.getenv("CLIENTNAME")

# Determine the client hostname via a different method
# in case the first one failed
if client_hostname is None:
    client_hostname = socket.gethostbyaddr(socket.gethostname())[0]


# Class for prepending the date and time to the log file
class Prepender(object):
    def __init__(self,
                 file_path,
                 ):
        # Read in the existing file, so we can write it back later
        with open(file_path, mode='r') as f:
            self.__write_queue = f.readlines()

        self.__open_file = open(file_path, mode='w')

    def write_line(self, line):
        self.__write_queue.insert(0,
                                  "%s\n" % line,
                                  )

    def write_lines(self, lines):
        lines.reverse()
        for line in lines:
            self.write_line(line)

    def close(self):
        self.__exit__(None, None, None)

    def __enter__(self):
        return self

    def __exit__(self, type, value, traceback):
        if self.__write_queue:
            self.__open_file.writelines(self.__write_queue)
        self.__open_file.close()


# Prepend the determined information to the top of the log file
with Prepender(logfile) as f:
    # Must write individual lines in reverse order
    f.write_line(current_day+' - '+current_time+' - '+client_hostname)

# Or, use write_lines instead - that maintains order.
# with Prepender(logfile) as f:
#    f.write_lines(
#        ['This will be line 1',
#         'This will be line 2',
#         'This will be line 3',
#        ]
#    )