#! /usr/bin/env python3
#
def char_to_num ( ch ):

#*****************************************************************************80
#
## char_to_num() ???
#
  "Assumes all characters are digits or capital letters."
  n = ord ( ch )

  if n <= ord('9'): # digits 
    return n - ord('0')

  if n < ord('I'): # A-I
    return n - ord('A') + 1

  if n <= ord('R'): # J-R
    return n - ord('J') + 1    

  return n - ord('S') + 2 # S-Z
        
def checksum ( vin ):

#*****************************************************************************80
#
## checksum() computes the checksum of a VIN.
#
  assert ( len ( vin ) == 17 )

  w = [ 8, 7, 6, 5, 4, 3, 2, 10, 0, 9, 8, 7, 6, 5, 4, 3, 2 ]

  t = 0
  for i, c in enumerate(vin):
    t = t + char_to_num(c)*w[i]
  t = ( t % 11 )
  check = 'X' if t == 10 else str(t)
  return check

def validate ( vin ):

#*****************************************************************************80
#
## validate() ???
#
  return checksum(vin) == vin[8]

def vin_test ( ):

#*****************************************************************************80
#
## vin_test() tests vin().
#
#  Licensing:
#
#    This code is distributed under the MIT license. 
#
#  Modified:
#
#    05 September 2022
#
#  Author:
#
#    John Burkardt
#
#  Reference:
#
#    John D Cook,
#    Vehicle Identification Number (VIN) Check Sum,
#    https://www.johndcook.com/blog/2019/09/12/vin-check-sum/
#    12 September 2019.
#
#    John D Cook,
#    Computing VIN Checksums,
#    https://www.johndcook.com/blog/2022/09/04/computing-vin-checksums/
#    04 September 2022.
#
  import platform

  vin_data = [ \
    "11111111111111111", \
    "5GZCZ43D13S812715", \
    "1M8GDM9AXKP042788" ]

  print ( '' )
  print ( 'vin_test():' )
  print ( '  Python version: ' + platform.python_version ( ) )
  print ( '  vin() verifies a Vehicle Identifical Number (VIN).' )

  for vin in vin_data:
    print ( '"' + vin + '"', end = '' )
    print ( '  ', checksum ( vin ), end = '' )
    print ( '  ', validate ( vin ) )
#
#  Terminate.
#
  print ( '' )
  print ( 'vin_test():' )
  print ( '  Normal end of execution.' )

  return

def timestamp ( ):

#*****************************************************************************80
#
## timestamp() prints the date as a timestamp.
#
#  Licensing:
#
#    This code is distributed under the MIT license. 
#
#  Modified:
#
#    21 August 2019
#
#  Author:
#
#    John Burkardt
#
  import time

  t = time.time ( )
  print ( time.ctime ( t ) )

  return

if ( __name__ == "__main__" ):
  timestamp ( )
  vin_test ( )
  timestamp ( )