#!/usr/local/cpython-3.7/bin/python3

"""Compute maximum heart rate as a function of age."""

import sys


def usage(retval):
    """Output a usage message."""
    if retval:
        write = sys.stderr.write
    else:
        write = sys.stdout.write

    write(f'{sys.argv[0]} --age 50 --help\n')

    sys.exit(retval)


def main():
    """Compute maximum heart rate as a function of age."""
    age = -1
    while sys.argv[1:]:
        if sys.argv[1] == '--age':
            age = float(sys.argv[2])
            del sys.argv[1]
        elif sys.argv[1] in ('-h', '--help'):
            usage(0)
        else:
            sys.stderr.write(f'{sys.argv[0]}: unrecognized option: {sys.argv[1]}\n')
            usage(1)
        del sys.argv[1]

    if age == -1:
        sys.stderr.write('--age is a required option\n')
        usage(1)

    max_heart_rate = 205.8 - (0.685 * age)

    print(f'max heart rate is: {max_heart_rate}')
    print(f'90% is: {max_heart_rate * 0.9}')
    print(f'80% is: {max_heart_rate * 0.8}')


main()