#!/usr/bin/env python3

import email
import getpass
import imaplib
import os

username = input("Gmail username: ")
seekrit = getpass.getpass("Gmail password: ")

m = imaplib.IMAP4_SSL("imap.gmail.com")
m.login(username, seekrit)

# This could be "/INBOX" or whatever instead.  Use m.list() 
# to see all available mailboxes.
mailbox = "Spam"

# The actual response is something like ('OK', [b'1234']).  I do not
# understand why imaplib handles numbers this way.
ignored_response, num_msgs = m.select(f"[Gmail]/{mailbox}", readonly=True) 
# Just convert num_msgs to something sane right away.  I.e., let's all
# pretend this never happened.
num_msgs = int(num_msgs[0].decode("utf-8"))
print(f"{num_msgs} messages to retrieve from mailbox '{mailbox}'")
width = len(str(num_msgs))

# After this, 'items' will be a tuple with a single element: a 
# bytestring of space-separated decimal integers, each of which
# identifies a mail message.  E.g.,: [b'1 2 3 4 5 6 7 8 9 10 ...']
#
# By the way, one could filter with IMAP rules here; see
# http://www.example-code.com/csharp/imap-search-critera.asp.
ignored_response, items = m.search(None, "ALL")

# Turn that bytestring into a list of bytestrings, each representing
# a number.  We're leaving them as bytestrings because apparently
# imaplib.fetch() wants that?  Further research required.
items = items[0].split()

for emailid in items:
    fpath = emailid.decode("utf-8").zfill(width) + ".txt"
    print("CHECKING %s" % fpath)
    if not os.path.isfile(fpath):
        # Fetch the mail.  I believe "(RFC822)" means something like
        # "get headers and body (but not attachments)."  We don't
        # don't need the attachments to determine whether something
        # is spam or ham, so we don't fetch them by default.
        ignored_response, data = m.fetch(emailid, "(RFC822)")
        # Get mail body, presumably sans attachments
        headers_and_body = data[0][1]
        print("SAVING %s" % fpath)
        with open(fpath, 'wb') as f:
            f.write(headers_and_body)

m.close()
m.logout()