#! /usr/bin/env python3
#
def json_test ( ):

#*****************************************************************************80
#
## json_test() makes some simple tests involving JSON files.
#
  print ( '' )
  print ( 'json_test():' )
  print ( '  Some simple tests involving JSON files.' )

  collatz_json_test ( )
  image_json_test ( )

  print ( '' )
  print ( 'json_test():' )
  print ( '  Normal end of execution.' )

  return

def collatz_json_test ( ):

#*****************************************************************************80
#
## collatz_json_test() reads a collatz dict from a JSON file and updates it.
#
  import json

  print ( '' )
  print ( 'collatz_json_test ( ):' )
  print ( '  Read the collatz dict from a JSON file.' )
  print ( '  Verify that it has information in it already.' )
  print ( '  Add some more.' )
#
#  Read the json file.
#
  filename = 'collatz_dict.json'
  input = open ( filename, 'r' )
  collatz_dict = json.load ( input )
  input.close ( )

  print ( '' )
  print ( '  After retrieval from json file "' + filename + '", collatz_dict' )
  print ( '  has "length" (number of entries) = ', len ( collatz_dict ) )
#
#  Now add data for n = 100
#
  n = 100
  collatz_add_to_dict ( collatz_dict, n )

  print ( '' )
  print ( '  After adding data for n = ', n, 'the Collatz dict' )
  print ( '  has "length" (number of entries) = ', len ( collatz_dict ) )

  return

def image_json_test ( ):

#*****************************************************************************80
#
## image_json_test() reads a little information from a JSON file.
#
  import json

  print ( '' )
  print ( 'image_json_test ( ):' )
  print ( '  Read some information from a JSON file.' )

  filename = 'cake.json'
  input = open ( filename, 'r' )
  my_image = json.load ( input )
  id = my_image["id"]
  print ( '  Cake image id = ', id )
  image = my_image["image"]
  url = image["url"]
  print ( '  Cake image url = "' + url + '"' )
  input.close ( )

  return

def collatz_add_to_dict ( collatz_dict, n ):

#*****************************************************************************80
#
## collatz_add_to_dict() adds information to a Collatz dict.
#
  while ( not ( n in collatz_dict ) ):
    n2 = collatz ( n )
    collatz_dict[n] = n2
    n = n2

  return

def collatz ( n ):

#*****************************************************************************80
#
## collatz() applies one step of the Collatz iteration to an integer.
#
#  Licensing:
#
#    This code is distributed under the GNU LGPL license. 
#
#  Modified:
#
#    11 June 2022
#
#  Author:
#
#    John Burkardt
#
#  Input:
#
#    integer n: the starting value.
#
#  Output:
#
#    integer n2: the transformed value.
#
  if ( not isinstance ( n, int ) ):
    raise Exception ( 'collatz: type(n) = ', type ( n ), \
      ', but n must be an integer.' )
  elif ( n < 1 ):
    raise Exception ( 'collatz: n =', n, ', but 1 <= n required.' )
  elif ( n == 1 ):
    n2 = 1
  elif ( ( n % 2 ) == 0 ):
    n2 = n // 2
  else:
    n2 = 3 * n + 1

  return n2

if ( __name__ == '__main__' ):
  json_test ( )