import binascii
import random

from email import policy
from email.parser import BytesParser
from email.generator import BytesGenerator

# Two sample policies, 1 is more linient coming to/from disk, 2 being an crude
# example of a destination that cannot handle utf-8.  Basically testing how the
# email package handles the conversions.  There are other policy options,
# including changing between \r\n and \n.  I am not an expert on the IMAP
# protocol, but I imagine the servers capabilities can be mapped to some sort of
# policy.
p1 = policy.default.clone(cte_type='8bit',utf8=True,refold_source='none')
p2 = policy.default.clone(cte_type='7bit',utf8=False,refold_source='none')

# Name of a sample input file that contains several different encodings.
input_file='testmail-mime'

# Establish a parser that can be used to to read messages stored on disk
my_parser = BytesParser(policy=p1)

# Establish a generator that can convert a message based on policy and write it
# to disk.  I believe this is equivalent to msg.as_bytes(policy=p1)
my_p1_generator = BytesGenerator(open('{}-P1'.format(input_file),'wb'),
        mangle_from_=None, maxheaderlen=None, policy=p1)
my_p2_generator = BytesGenerator(open('{}-P2'.format(input_file),'wb'),
        mangle_from_=None, maxheaderlen=None, policy=p2)

# Parse the test message.  Note that the file is read as binary ('rt') and not
# text ('rt') as is currently done in OfflineIMAP
msg = my_parser.parse(open(input_file, 'rb'))

# Generate a random header the same way OfflineIMAP does currently and add it to
# the message - retaining the multiple encoding.
rand_header = '{}-{}'.format((binascii.crc32(msg.as_bytes(policy=p1)) &
        0xffffffff),random.randrange(9999999999))
msg.add_header('X-OfflineIMAP',rand_header)

# Display/save the message retaining the original format
# A diff between 'testmail-mime' and 'testmail-mime-P1' should show two changes,
# 1) The lack of the initial 'From ' mbox delimeter and
# 2) The addtional 'X-OfflineIMAP' header
print(msg.as_bytes(policy=p1))
my_p1_generator.flatten(msg)

# Display/save the message retaining the original format
# A diff between 'testmail-mime' and 'testmail-mime-P2' should show the same
# changes as -P1 and additional changes to attachments 2 and 3
print(msg.as_bytes(policy=p2))
my_p2_generator.flatten(msg)