from subprocess import Popen, PIPE
from io import BytesIO

# The hack of all hacks...
# The python mbox parser fails to split some messages from mj2
# correctly - they appear to be too far out of spec. However,
# formail does it right. So open a formail pipe on the mbox,
# reassemble it to one long stream with a unique separator,
# and then split it apart again in python.. Isn't it cute?
SEPARATOR = "ABCARCHBREAK123" * 50
bSEPARATOR = bytes(SEPARATOR, 'ascii')


class MailboxBreakupParser(object):
    def __init__(self, fn):
        self.EOF = False

        if fn.endswith(".gz"):
            cat = "zcat"
        else:
            cat = "cat"
        cmd = "%s %s | formail -s /bin/sh -c 'cat && echo %s'" % (cat, fn, SEPARATOR)
        self.pipe = Popen(cmd, shell=True, stdout=PIPE, stderr=PIPE)

    def returncode(self):
        self.pipe.wait()
        return self.pipe.returncode

    def stderr_output(self):
        return self.pipe.stderr.read()

    def __next__(self):
        sio = BytesIO()
        while True:
            try:
                l = next(self.pipe.stdout)
            except StopIteration:
                # End of file!
                self.EOF = True
                if sio.tell() == 0:
                    # Nothing read yet, so return None instead of an empty
                    # bytesio
                    return None
                sio.seek(0)
                return sio
            if l.rstrip() == bSEPARATOR:
                # Reached a separator. Meaning we're not at end of file,
                # but we're at end of message.
                sio.seek(0)
                return sio
            # Otherwise, append it to where we are now
            sio.write(l)