"""
Does the following:

1. Generates and saves random secret key
2. Removes the taskapp if celery isn't going to be used

A portion of this code was adopted from Django's standard crypto functions and
utilities, specifically:
    https://github.com/django/django/blob/master/django/utils/crypto.py
"""
import hashlib
import os
import random
import shutil

# Get the root project directory
PROJECT_DIRECTORY = os.path.realpath(os.path.curdir)

# Use the system PRNG if possible
try:
    random = random.SystemRandom()
    using_sysrandom = True
except NotImplementedError:
    # import warnings
    # warnings.warn('A secure pseudo-random number generator is not available '
    #               'on your system. Falling back to Mersenne Twister.')
    using_sysrandom = False

def get_random_string(
        length=50,
        allowed_chars='abcdefghijklmnopqrstuvwxyz0123456789!@#$%^&*(-_=+)'):
    """
    Returns a securely generated random string.
    The default length of 12 with the a-z, A-Z, 0-9 character set returns
    a 71-bit value. log_2((26+26+10)^12) =~ 71 bits
    """
    if not using_sysrandom:
        # This is ugly, and a hack, but it makes things better than
        # the alternative of predictability. This re-seeds the PRNG
        # using a value that is hard for an attacker to predict, every
        # time a random string is required. This may change the
        # properties of the chosen random sequence slightly, but this
        # is better than absolute predictability.
        random.seed(
            hashlib.sha256(
                ("%s%s%s" % (
                    random.getstate(),
                    time.time(),
                    settings.SECRET_KEY)).encode('utf-8')
            ).digest())
    return ''.join(random.choice(allowed_chars) for i in range(length))

def make_secret_key(project_directory):
    """Generates and saves random secret key"""
    # Determine the local_setting_file_location
    local_setting_file_location = os.path.join(
        project_directory,
        'config/settings/local.py'
    )

    # Open locals.py
    with open(local_setting_file_location) as f:
        local_py = f.read()

    # Generate a SECRET_KEY that matches the Django standard
    SECRET_KEY = get_random_string()
    SECRET_KEY = 'CHANGEME!!!' + SECRET_KEY

    # Replace "CHANGEME!!!" with SECRET_KEY
    local_py = local_py.replace('CHANGEME!!!', SECRET_KEY)

    # Write the results to the locals.py module
    with open(local_setting_file_location, 'w') as f:
        f.write(local_py)

def remove_task_app(project_directory):
    """Removes the taskapp if celery isn't going to be used"""
    # Determine the local_setting_file_location
    task_app_location = os.path.join(
        PROJECT_DIRECTORY,
        '{{ cookiecutter.repo_name }}/taskapp'
    )
    shutil.rmtree(task_app_location)

# 1. Generates and saves random secret key
make_secret_key(PROJECT_DIRECTORY)

# 2. Removes the taskapp if celery isn't going to be used
if '{{ cookiecutter.use_celery }}'.lower() == 'n':
    remove_task_app(PROJECT_DIRECTORY)