import sys
import collections
import os

try:
    create = open('studentlist.txt', 'x')
    create.close()

except:
    print('Student file already exists')

def optionHandler(option):
    if option == 'a':
        addStudent()
    elif option == 'd':
        deleteStudent()
    elif option == 'r':
        readList()
    elif option == 'q':

        sys.exit()
    else:
        return -1


def addStudent():
    studentDict = {}
    ID = input('Student ID number? ')
    try:
        ID = int(ID)
    except:
        return print('ID not a number')
    fName = input('Student first name? ')
    lName = input('Student last name? ')
    major = input('Student major? ')
    studentfile = open('studentlist.txt', 'r')
    line = studentfile.readline()
    while line:
        curStudent = line.split(',')
        curStudent = list(map(str.strip, curStudent))
        curStudentIDNum = int(curStudent[0])
        curStudentDict = {'fName': curStudent[1], 'lName' : curStudent[2], 'Major' : curStudent[3]}
        studentDict[curStudentIDNum] = {'fName': curStudent[1], 'lName' : curStudent[2], 'Major' : curStudent[3]}
        line = studentfile.readline()
    studentDict[ID] = {'fName': fName, 'lName' : lName, 'Major' : major}
    studentfile.close()
    newfile = open('studentlist.txt', 'w').close()
    newfile = open('studentlist.txt', 'w')
    studentDict = collections.OrderedDict(sorted(studentDict.items(), key=lambda x: int(x[0])))
    for ID in studentDict:
        newfile.write(str(ID)+','+studentDict[ID]['fName']+','+studentDict[ID]['lName']+','+studentDict[ID]['Major']+'\n')
    newfile.close()


def deleteStudent():
    studentDict = {}
    studentfile = open('studentlist.txt', 'r')
    line = studentfile.readline()
    while line:
        curStudent = line.split(',')
        curStudent = list(map(str.strip, curStudent))
        curStudentIDNum = int(curStudent[0])
        curStudentDict = {'fName': curStudent[1], 'lName' : curStudent[2], 'Major' : curStudent[3]}
        studentDict[curStudentIDNum] = {'fName': curStudent[1], 'lName' : curStudent[2], 'Major' : curStudent[3]}
        line = studentfile.readline()
    studentID = input('Student ID to remove? ')
    try:
        studentID = int(studentID)
    except:
        print('Invalid ID: not a number')

    try:
        del studentDict[studentID]
    except:
        print('Invalid ID: key not found')
    newfile = open('studentlist.txt', 'w').close()
    newfile = open('studentlist.txt', 'w')
    studentDict = collections.OrderedDict(sorted(studentDict.items(), key=lambda x: int(x[0])))
    for ID in studentDict:
        newfile.write(str(ID)+','+studentDict[ID]['fName']+','+studentDict[ID]['lName']+','+studentDict[ID]['Major']+'\n')
    newfile.close()


def readList():
    studentDict= {}
    studentfile = open('studentlist.txt', 'r')
    line = studentfile.readline()
    while line:
        curStudent = line.split(',')
        curStudent = list(map(str.strip, curStudent))
        curStudentIDNum = int(curStudent[0])
        curStudentDict = {'fName': curStudent[1], 'lName' : curStudent[2], 'Major' : curStudent[3]}
        studentDict[curStudentIDNum] = {'fName': curStudent[1], 'lName' : curStudent[2], 'Major' : curStudent[3]}
        line = studentfile.readline()
    print("{:<9} {:<10} {:<10} {:<10}"
                            .format('ID', 'First Name', 'Last Name', 'Major'))
    for ID in studentDict:
        print("{:<10} {:<10} {:<10} {:<10}"
                            .format(str(ID),studentDict[ID]['fName'],studentDict[ID]['lName'],studentDict[ID]['Major']))
while(True):
    option = input('Pick an option:\nAdd a student-(a)\nDelete a student-(d)\nRead the student list-(r)\nQuit-(q)\nInput: ')
    if optionHandler(option) == -1:
        print('Invalid Option')