generate_password

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""Simple password generator

Generates a random password. Length is passed as an argument, default is 8.

Password length and complexity (weather it contains non-alphanumeric chars) can
also be configured using $GENERATE_PASSWORD_INCLUDE_SPECIAL and
$GENERATE_PASSWORD_LENGTH.
"""

import random
import sys
import os
from io import IOBase  # Only used for type hints


def usage(destination: IOBase = sys.stdout) -> None:
	"""Show a usage help message."""
	print("""generate_password
	Small secure password generator

Usage:
	generate_password [<length>]

	You can pass the desired password length as an argument.
	


Fine-Tuning password generation:

By setting environment variables, you can now fine-tune the
generation behaviour (default values also shown below):

	GENERATE_PASSWORD_INCLUDE_SPECIAL=1
		Set to 0 to exclude special characters.

	GENERATE_PASSWORD_LENGTH=16
		Password length. If a password length was given as an argument,
		this value is ignored.

""", file=destination)
	

def get_random_password(length: int, include_special: bool = True) -> str:
	"""Generate a new random password

	Uses random.choice to construct the password char by char.

	Args:
		length (int): Number of random characters to select.
		include_special (bool): Choose from a wider range of characters

	Returns:
		str: A total of length characters randomly generated.
	"""
	allowed_chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
	allowed_chars += 'abcdefghijklmnopqrstuvwxyz'
	allowed_chars += '0123456789'
	if include_special:
		allowed_chars += '.,-_!?()/='

	word = ''
	for i in range(length):
		word += random.choice(allowed_chars)

	return word


def getenv_int(var_name: str, fallback_value: int) -> int:
	"""
	Try to get the value of an environment variable, and
	convert it to an int().

	If the variable is not defined, or can not be converted to
	an integer, return the fallback value.
	"""
	try:
		my_var = int(os.getenv(var_name, fallback_value))

	except ValueError:
		my_var = fallback_value

	return my_var


def getenv_bool(var_name: str, fallback_value: bool) -> bool:
	"""
	Get a boolean environment variable and uses the fallback_value
	on errors.
	NOTE: uses Python's bool(), so everything except 0 (or None)
	is treated as True.
	"""
	return bool(
		getenv_int(
			var_name,
			int(
				fallback_value
			)
		)
	)


def stringIsSignedInt(value: str) -> bool:
	return False in [char not in "0123456789" for char in value]


def main():
	passwd_cfg = {
		"length": getenv_int("GENERATE_PASSWORD_LENGTH", 16),
		"includeSpecial": getenv_bool("GENERATE_PASSWORD_INCLUDE_SPECIAL", True)
	}

	if len(sys.argv) > 1:
		if "--help" in sys.argv or "-h" in sys.argv:
			# Show help and exit
			usage()
			sys.exit(0)

		elif len(sys.argv) > 1 and "/?" in sys.argv:
			"""
			EASTER EGG

			If "/?" is given as argument (parameter in ancient Windows style to show usage
			help; Microsoft uses Unix-like parameters almost everywhere for years now.

			GIVEN AN OLD SCHOOL STYLE PARAMETER?

			 	- TIME TO APPLY SOME STRICT LIMITS TO PASSWORD LENGTH AND CONTENT!
			"""
			passwd_cfg["length"] = 6
			passwd_cfg["includeSpecial"] = False

		elif len(sys.argv) == 2 and stringIsSignedInt(sys.argv[1]):
			"""
			Password length given as argument
			Overrides value of os.environ["GENERATE_PASSWORD_LENGTH"] !
			"""
			passwd_cfg["length"] = int(sys.argv[1])

		else:
			# Unknown argument
			usage(sys.stderr)
			sys.exit(1)

	# No trailing newline if stdout is piped/redirected
	line_end = "\n" if sys.stdout.isatty() else ""

	print(
		get_random_password(
			passwd_cfg["length"],
			passwd_cfg["includeSpecial"]
		),
		end=line_end
	)


if __name__ == "__main__":
	main()