import os

import sys

def fatal(msg):

    print >> sys.stderr, msg

    sys.exit(2)

def get_list_from_file(file_path, list_name):

    '''Looks for a Python list called list_name in the file specified

    by file_path and returns it.

    If the file or list name aren't found, this function will return

    an empty list.

    '''

    list = []

    # Read in the file if it exists.

    if os.path.exists(file_path):

        file_in = open(file_path, "r")

        # Look for the list.

        list_string = ""

        parsing_multiline_list = False

        for line in file_in:

            if list_name in line or parsing_multiline_list:

                list_string += line

                # Handle multiline lists.

                if ']' not in list_string:

                    parsing_multiline_list = True

                else:

                    # Evaluate the list once its end is reached.

                    # Make the split function only split it once.

                    list = eval(list_string.split('=', 1)[1].strip())

                    break

        # Close the file

        file_in.close()

    return list

def read_config_file():

    '''Reads the NS-3 configuration file and returns a list of enabled modules.

    This function first looks for the ns3 configuration file (.ns3rc)

    in the current working directory and then looks in the ~

    directory.

    '''

    # See if the ns3 configuration file exists in the current working

    # directory and then look for it in the ~ directory.

    dot_ns3rc_name = '.ns3rc'

    dot_ns3rc_path = dot_ns3rc_name

    if not os.path.exists(dot_ns3rc_path):

        dot_ns3rc_path = os.path.expanduser('~/') + dot_ns3rc_name

        if not os.path.exists(dot_ns3rc_path):

            # Enable all modules if the .ns3rc file can't be found.

            return ['all_modules']

    # Read in the ns3 configuration file.

    modules_enabled = get_list_from_file(dot_ns3rc_path, 'modules_enabled')

    if not modules_enabled:

        # Enable all modules if the modules_enabled line can't be found.

        return ['all_modules']

    return modules_enabled