#Jonathan Hudson
#Student Number 12347890
#Date: 2020-08-26
#Lecture Practice

import sys

#Enable one of these to 'hack' the arguments
#sys.argv = ["3_System_Read_File.py"]
#sys.argv = ["3_System_Read_File.py", "-flag"]
#sys.argv = ["3_System_Read_File.py", "input.txt"]
#sys.argv = ["3_System_Read_File.py", "input.txt", "-flag"]

def main():    
    print("Program start")
    
    input_filename, flag = checkArguments()
    
    print("Flag: %s" % flag)
    print("Input filename: %s" % input_filename)
    
    lines = open_file(input_filename)
    
    print("Contents of %s" % input_filename)
    for i in range(len(lines)):
        print("Line %d->%s" % (i, lines[i])
        
    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 3_System_Read_File.py.py\n")
        sys.stderr.write("Usage: python 3_System_Read_File.py.py <input_filename>\n")
        sys.stderr.write("Usage: python 3_System_Read_File.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


def open_file(input_filename):
    #Try to open the file
    input_file = None
    try:
        input_file = open(input_filename, "r")
    except Exception as e:
        sys.stderr.write("Exception message %s.\n" % e)
        sys.stderr.write("Input file %s cannot be opened.\n" % input_filename)
        sys.exit(2)
        
    #If file opens then read in lines and strip white space from right
    lines = []
    try:
        for line in input_file:
            lines.append(line.rstrip())
    except Exception as e:
        sys.stderr.write("Exception message %s.\n" % e)
        sys.stderr.write("Error reading input file %s.\n" % input_file)
        sys.exit(3)
    finally:
        input_file.close()
    return lines

main()