"""
 atm.py

 Implements an ATM simulation with data stored in 
 a "list of dictionaries", an example of a python data structure.

 Accounts are dictionaries
 with keys (person, password, checking, savings).

 The bank is a list of accounts.
 
   bank = [ 
           {'person': 'Jack', 'password': 'jackpass',    # account 0
            'checking': 100.00, 'savings': 500.00 },     #

           {'person': 'Jill', 'password': 'janepass',    # account 1
            'checking': 243.56, 'savings': 876.54 }      #
          ]

 The initial data for the bank is read from 
 a CSV (comma separated value) file that looks like this:

 -- atm_data.txt --
 person,password,checking,savings
 Jack,jackpass,100.00,500.00
 Jill,jillpass,243.56,876.54

 Notice that 
  * the only global variable is a constant
    which sets the name of the data file,
  * all the functions have docstrings which 
    describes their arguments and return value, and
  * the main() function is short and sweet.

 There is a built-in library in python for reading and 
 writing to CSV files, but here that file is processed
 explicitly instead.

 TODO : 
  * Write the modified data back out to the file, 
    so that repeated execution remembers the transactions.
  * Rewrite this wholel thing using classes for Person, Account, Bank
    rather than a data structure. (Just as a learning exercise.)
  * For a really good time, implement more realistic passwords :
    * Add counter to login attempts & quit if too many.
    * Use the python getpass library. (Alternative input without display.)
    * Hide the passwords in the data file with hashlib library.
    * Add a "salt" to the stored password so that duplicate passwords
      don't have the same hash.

 Jim Mahoney | Nov 2016 | MIT License
"""

datafilename = 'data_atm.csv'

def get_bank_from_file(filename = datafilename):
    """ Return a 'bank' data structure as described 
        at the top of the file, by reading its data from a CSV file """
    # Yet another function that follows the "accumulator pattern".
    bank = []                        # Start with an empty bank.
    datafile = open(filename, 'r')
    firstline = datafile.readline()  # Read & do nothing with first line.
    while True:                      # Loop over remaing lines in file.
        line = datafile.readline()
        if line == '':               # At end of file, readline() returns ''
            return bank              # ... so the bank is filled with accounts.
        else:
            (person, password, checking, savings) = line.split(',')
            bank.append( {'person': person,               # Make a new dict
                          'password': password,           # account, and put
                          'checking': float(checking),    # it in the bank.
                          'savings': float(savings) }     # 
                       )

def login(bank):
    """ Prompt the user to login to a bank account. 
        If succesful, return id = index of account in bank list.
        If user types 'QUIT', return 'QUIT'.
    """
    while True:                          # Allow repeated login attempts.
        # print "DEBUG: {}:format(bank)"

        print
        who = raw_input('Login with your name (or QUIT to exit): ')

        if who == 'QUIT':
            print 'Bye.'
            return 'QUIT'

        password = raw_input('Password? ') 

        for id in range(len(bank)):   # search accounts for user,passwd
            account = bank[id]
            #print "DEBUG: id={} account={}".format(id, account)
            #print "DEBUG: passwd='{}'".format(password)
            #print "DEBUG: who='{}'".format(who)
            #print "DEBUG: person match? ", account['person'] == who
            #print "DEBUG: passwd match? ", account['password'] == password
            if account['person'] == who and account['password'] == password:
               return id

        print " OOPS: name or password is wrong - try again. "

def transaction(account):
    """ Prompt user for transactions to apply to given account, which is
        a dictionary with keys ('person', 'password', 'checking', 'savings')
        Return the modified account. """
    while True:

        # show account status
        print " status: {} has {} in checking, {} in savings.".format(
            account['person'], account['checking'], account['savings'])

        # do one transaction
        what = raw_input(' transaction (deposit, withdraw, transfer, end) ? ')

        if what[0] == 'e':    # end
            return account

        elif what[0] == 'w':  # withdraw
            which = raw_input('  account (checking, savings) ? ')
            amount = float(raw_input('  amount (xxx.xx) ? '))
            account[which] = account[which] - amount

        elif what[0] == 'd':  # deposit
            which = raw_input('  account (checking, savings) ? ')
            amount = float(raw_input('  amount (xxx.xx) ? '))
            account[which] = account[which] + amount

        elif what[0] == 't':  # transfer
            which = raw_input(' 1 (check to save) or 2 (save -> check) ? ')
            amount = float(raw_input('  amount (xxx.xx) ? '))
            if which == '1':
                account['checking'] = account['checking'] - amount
                account['savings'] = account['savings'] + amount
            if which == '2':
                account['checking'] = account['checking'] + amount
                account['savings'] = account['savings'] - amount

def main():
    print "-- ATM simulation --"
    bank = get_bank_from_file()
    while True:
        id = login(bank)
        if id == 'QUIT':
            return
        else:
            bank[id] = transaction( bank[id] )

if __name__ == '__main__':
    main()