#Jonathan Hudson
#Student Number 12347890
#Date: 2021-05-03
#Lecture Practice

import sys

#Enable one of these to 'hack' the arguments 
#sys.argv = ["2_System_Args.py"]
#sys.argv = ["2_System_Args.py", "-flag"]
#sys.argv = ["2_System_Args.py", "input.txt"]
#sys.argv = ["2_System_Args.py", "input.txt", "-flag"]

def main():  
    print("Program start")
    
    input_filename, flag = checkArguments()
    
    print("Flag: %s" % flag)
    print("Input filename: %s" % input_filename)
    
    print("Program done")

def checkArguments():
    
    print("These are the %d arguments you entered." % len(sys.argv))
    print(sys.argv)
    
    input_filename = None
    flag = False
    #No arguments, will handle getting filename from prompt later
    if len(sys.argv) == 1:
        pass
    
    #1 Argument get either flag or assume argument is filename
    elif len(sys.argv) == 2:
        if(sys.argv[1] == "-flag"):
            flag = True
        else:
            input_filename = sys.argv[1]
            
    #More than 2 arguments error and exit
    else:
        sys.stderr.write("Too many arguments!\n")
        sys.stderr.write("Usage: python 2_System_Args.py.py\n")
        sys.stderr.write("Usage: python 2_System_Args.py.py <input_filename>\n")
        sys.stderr.write("Usage: python 2_System_Args.py.py -flag\n")
        sys.exit(1)

    #Get filename if not in any argument
    if input_filename == None:
        input_filename = input("Enter input filename:")
        
    return input_filename, flag

main()