#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""\
Tube
"""
from __future__ import absolute_import, division, print_function, unicode_literals
from math import sqrt

__author__ = "Daniel Weschke"
__copyright__ = "Copyright 2019 Daniel Weschke"
__credits__ = ["Daniel Weschke"]
__license__ = "MIT"
__version__ = "2019.02.07"
__maintainer__ = "Daniel Weschke"
__email__ = "daniel.weschke@directbox.de"
__status__ = "Production"  # "Prototype", "Development", "Production"

VERSION = """\
%(prog)s version {version} {copyright}

For Unicode characters check the file encoding that the console is using.
Windows user may execute the command "chcp 65001".""".format(
  version=__version__, copyright=__copyright__)

EPILOG = """\
"""

def critical_buckling_stress(r, nu, E, t):
  """\
  Critical buckling stress of a thin tube loaded with external pressure p.

  r   mean radius (r_a + r_i)/2
  nu  Poisson's ratio
  E   Young's modulus
  t   thickness
  """
  return (E/(4*(1-nu**2))*(t/r)**3)

def allowable_stress(sigma, S):
  """\
  Allowable stress.

  sigma  stress
  S      safety factor, elastic buckling stress state S = 3
  """
  return sigma/S

def main():
  """\
  Main function
  """
  import argparse

  parser = argparse.ArgumentParser(
    description=__doc__, prefix_chars='-', epilog=EPILOG,
    #usage="%(prog)s [OPTION]... NAME",
    formatter_class=argparse.RawTextHelpFormatter,
  )
  parser.add_argument('-v', '--verbose', action="store_true", help="Verbose output")
  parser.add_argument('-V', '--version', action='version', version=VERSION)
  parser.add_argument('-D', '--debug', dest='debug', action='store_true', help=argparse.SUPPRESS)
  subparsers = parser.add_subparsers(help='', dest='case')

  parser_a = subparsers.add_parser(
    'buckling', help="critical buckling stress", prefix_chars='-',
    description="Critical buckling stress of a thin tube loaded with external pressure p.")
  parser_a.add_argument('NU', type=float, help='Poisson\'s ratio')
  parser_a.add_argument('R', type=float, help='mean radius')
  parser_a.add_argument('E', type=float, help='Young\'s modulus')
  parser_a.add_argument('T', type=float, help='thickness')
  parser_a.add_argument('S', nargs='?', type=float, default=3., help='safety factor [default for elastic stress state: 3]')

  args = parser.parse_args()

  if args.debug:
    print(args)

  if args.case == 'buckling':
    p_crit = critical_buckling_stress(args.R, args.NU, args.E, args.T)
    print("p_crit =", p_crit)
    print("p_allow =", allowable_stress(p_crit, args.S))

  return 0

if __name__ == "__main__":
  import sys
  sys.exit(main())