from exceptions import IOError

"""
input: phone book filename
output: reads phone book file and creates a phone book from it. If the file
doesn't exist, it creates an empty phone book. Returns the phone book.
"""
def read_phone_book(filename):
    # If the file doesn't exist (i.e. we haven't saved it yet), we don't want to
    # crash. This code prevents that and returns an empty dictionary in that case
    try:
        fh = open(filename, 'r')
    except IOError:
        print 'Error opening file. Using empty directory.'
        return {}

    # The file does exist. Read it and create the phone book from its contents
    phone_book = {}
    for line in fh:
        line = line.strip(' \n\r\t')
        print line
        if line == '':
            continue
        data = line.split(':')
        phone_book[data[0]] = data[1]

    fh.close()
    return phone_book


"""
input: filename and phone book
output: writes the phone book to file; returns nothing
"""
def save_phone_book(filename, phone_book):
    fh = open(filename, 'w')
    for entry in phone_book:
        string = entry + ':' + phone_book[entry] + '\n' # Need a newline character!
        fh.write(string)

    fh.close()
    return None


"""
input: none
output: (name, number) entered by user to add to phone book
"""
def get_user_input():
    name =  raw_input('Enter name to add (q to quit adding names): ')
    if name.lower() == 'q':
        return None

    number = raw_input('Enter number for ' + name + ': ')
    return (name, number)


"""
input: phone book
output: allows user to add multiple names and returns phone book
"""
def build_phone_book(phone_book):
    while True:
        entry = get_user_input()
        if entry == None:
            break

        phone_book = add_entry(entry, phone_book)

    return phone_book


"""
input: tuple with name and number; phone book
output: adds the tuple entry and returns phone book
"""
def add_entry(info, phone_book):
    if info[0] in phone_book:
        print info[0] + " exists. Overwriting."

    phone_book[info[0]] = info[1]
    return phone_book


"""
input: name to search for, phone_book
ouput: returns number belonging to name or None if name not found
"""
def retrieve_entry(name, phone_book):
    if name in phone_book:
        return phone_book[name]

    print name + " not found."
    return None


"""
input: number to search for, phone_book
output: returns name belonging to number or None if number not found
"""
def retrieve_entry_by_number(number, phone_book):
    name_found = False
    for name in phone_book:
        if phone_book[name] == number:
            return name

    if not name_found:
        print number + ' not found.'
        return None

"""
input: name to delete, phone_book
output: deletes entry for name and returns updated phone book
"""
def delete_entry(name, phone_book):
    if not name in phone_book:
        print name + ' not found.'
        return phone_book

    del(phone_book[name])
    print name, 'deleted.'
    return phone_book


# Tests #

#p = {}
#p = add_entry(('Chris', 123), p)
#print p
#
## Overwrite existing entry
#p = add_entry(('Chris', 456), p)
#print p
#
## Retrieve valid entry
#print retrieve_entry('Chris', p)
#
## Attempt to retrieve invalid entry
#print retrieve_entry('Bob', p)
#
## Add Bob
#p =add_entry(('Bob', 345), p)
#
## Sort by key and print entries
#keys = sorted(p.keys())
#for key in keys:
#    print key, p[key]
#
## Delete a valid entry
#print delete_entry('Bob', p)
#
## Attempt to delete an invalid entry (already been removed)
#print delete_entry('Bob', p)
#
## Reading file tests
#print read_abook('abook.txt')
#print read_abook('does_not_exist.txt')