#!/usr/bin/env python3

"""qmauth.py

Extract delivers information about emails from a maildir.
Runs with elevated privileges.

This program is started by qmail-authuser with elevated privileges after
a successful login.
Input directives are provided as command line arguments.
Output is delivered via STDOUT as json and log information via STDERR.

Exit codes::

      1  reserved
      2  reserved
      3  operational error       (error message in output)
      4  user error              (no output)
      5  issue switching to user (no output)
    110  reserved
    111  reserved
"""

import email.parser
import email.policy
import json
import logging
import re

from argparse  import ArgumentParser
from base64    import b64encode
from datetime  import datetime
from glob      import glob
from itertools import islice
from mailbox   import Maildir, MaildirMessage
from os        import environ, getpid, path, setuid
from pathlib   import Path
from pwd       import getpwnam
from sys       import exit as sysexit, stdout


class MyMaildir(Maildir):

    def __init__(self, dirname, *args, **kwargs):
        self.__path = dirname
        super().__init__(dirname, *args, **kwargs)

    def get_filename(self, mid):
        p_cur = glob(path.join(self.__path, 'cur', mid + '*'))
        p_new = glob(path.join(self.__path, 'new', mid + '*'))
        res = p_cur + p_new
        if len(res) != 1:
            raise LookupError(f"could not uniquely identify file for mail-id {mid!r}", mid)
        return res[0]

    def get_folder(self, folder):
        # copy from internal implementation
        return MyMaildir(
            path.join(self._path, '.' + folder), factory=self._factory, create=False,
        )


class QMAuthError(Exception):

    def __init__(self, msg, **args):
        self.msg = msg
        self.info = args


def _adr(addrs):
    if addrs is None:
        return None
    return [
        {'address': addr.addr_spec, 'display_name': addr.display_name}
        for addr in addrs.addresses
    ]


def _get_rcv_time(mid):
    idx = mid.find('.')
    assert idx >= 0
    return float(mid[:idx])


def startup(maildir, su, user, mode):

    del environ['PATH']

    netfehcom_uid = getpwnam(su).pw_uid
    if not netfehcom_uid:
        logging.error("user must not be root")
        sysexit(5)
    try:
        setuid(netfehcom_uid)
    except OSError:
        logging.exception("error setting uid")
        sysexit(5)

    def create_messages(mail_file):
        if mode == count_mails:
            msg = MaildirMessage(None)
        elif mode == list_mails:
            msg = MaildirMessage(email.parser.BytesHeaderParser(policy=email.policy.default).parse(mail_file))
        else:
            msg = email.parser.BytesParser(policy=email.policy.default).parse(mail_file)

        return msg

    return MyMaildir(
        maildir / user,
        create=False,
        factory=create_messages,
    )


def _sort_by_sender(midmsg):
    _, msg = midmsg

    if len(addrs := msg['from'].addresses) == 1:
        return addrs[0].addr_spec
    else:
        return msg['sender'].address.addr_spec


def _sort_mails(f, sort):

    reverse = False
    if sort.startswith('!'):
        reverse = True
        sort = sort[1:]

    by_rec_date = lambda midmsg: float(re.match(r"\d+\.\d+", midmsg[0], re.ASCII)[0])

    if   sort == 'date':    keyfn = by_rec_date
    elif sort == 'sender':  keyfn = _sort_by_sender
    elif sort == 'subject': keyfn = lambda midmsg: midmsg[1]['subject']
    elif sort == 'size':    keyfn = lambda midmsg: path.getsize(f.get_filename(midmsg[0]))
    elif sort == '':        keyfn = by_rec_date
    else:
        logging.warning("unknown sort-verb %r", sort)
        reverse = False
        keyfn = by_rec_date

    return keyfn, reverse


def _get_mime_head_info(msg):
    return {
        'content_maintype':    msg.get_content_maintype(),
        'content_subtype':     msg.get_content_subtype(),
        'content_disposition': msg.get_content_disposition(),
        'filename':            msg.get_filename(),
    }


def _get_head_info(msg):
    return {
        'date': msg['date'].datetime.isoformat(),

        'from':     _adr(msg['from']),
        'sender':   _adr(msg['sender']),
        'reply_to': _adr(msg['reply-to']),

        'to':  _adr(msg['to']),
        'cc':  _adr(msg['cc']),
        'bcc': _adr(msg['bcc']),

        'subject':  msg['subject'],
        'comments': msg['comments'],
        'keywords': msg['keywords'],

        'mime': _get_mime_head_info(msg),
    }


def list_mails(f, start, end, sortby, folder):

    assert 0 <= start <= end

    if folder:
        f = f.get_folder(folder)

    if start == end:
        return []

    kfn, reverse = _sort_mails(f, sortby)
    msgs = list(f.items())
    msgs.sort(key=kfn, reverse=reverse)
    msgs = msgs[start : min(len(msgs), end)]

    return [
        {
            'message_handle': mid,
            'byte_size':      path.getsize(f.get_filename(mid)),
            'unread':         'S' in msg.get_flags(),
            'date_received':  datetime.fromtimestamp(_get_rcv_time(mid)).isoformat(),
            'head':           _get_head_info(msg),
        }
        for mid, msg in msgs
    ]


def count_mails(f, subfolder):
    if subfolder:
        f = f.get_folder(subfolder)

    return {
        'total_mails':  len(f),
        'byte_size':    sum(path.getsize(f.get_filename(mid)) for mid in f.keys()),
        'unread_mails': len([1 for m in f if 'S' in m.get_flags()]),
    }


def _get_body(mail):
    if not mail.is_multipart():
        if mail.get_content_maintype() == 'text':
            return mail.get_content()
        else:
            ret = mail.get_content()
            if ret.isascii():
                return ret.decode(encoding='ascii')
            elif len(ret) <= 512*1024:
                return b64encode(ret).decode(encoding='ascii')
            else:
                raise QMAuthError("non attachment part too large (>512kB)", size=len(ret))

    if (mctype := mail.get_content_maintype()) == 'message':
        msg = mail.get_content()
        return {
            'head': _get_head_info(msg),
            'body': _get_body(msg),
        }
    elif mctype == 'multipart':
        ret = {
            'preamble': mail.preamble,
            'parts': [],
            'epilogue': mail.epilogue,
        }
        for part in mail.iter_parts():
            head = _get_mime_head_info(part)
            if head['content_disposition'] != 'attachment':
                body = _get_body(part)
            else:
                body = None
            ret['parts'].append({
                'head': head,
                'body': body,
            })
        return ret
    else:
        raise ValueError(f"unknown major content-type {mctype!r}")


def read_mail(f, subfolder, mid):
    if subfolder:
        f = f.get_folder(subfolder)

    msg = f.get(mid, None)
    if not msg:
        raise QMAuthError("no such message", mid=mid)

    return {
        'head': _get_head_info(msg),
        'body': _get_body(msg),
    }


def _descent(xx):
    head = _get_mime_head_info(xx)
    if (mctype := head['content_maintype']) == 'message':
        body = xx.get_content()
    elif mctype == 'multipart':
        body = xx.iter_parts()
    else:
        body = xx.get_content()
    return {
        'head': head,
        'body': body,
    }


def raw_mail(f, subfolder, mid, path):
    if subfolder:
        f = f.get_folder(subfolder)
    
    msg = f.get(mid, None)
    if not msg:
        raise QMAuthError("no such message", mid=mid)

    pth = [int(seg) for seg in path.split('.')] if path else []
    mail = {
        'head': {"content_maintype": "message", "content_subtype": "rfc822"},
        'body': msg,
    }

    for n in pth:
        mctype = mail['head']['content_maintype']

        if mctype == 'multipart':
            try:
                res = next(islice(mail['body'], n, None))
            except StopIteration:
                raise QMAuthError("out of bounds path for mail", path=pth)
            mail = _descent(res)
        elif mctype == 'message':
            assert n == 0
            mail = _descent(mail['body'])
        else:
            raise QMAuthError(f"can not descent into non multipart content type {mctype}")

    if hasattr(mail['body'], '__next__'):
        raise QMAuthError("can not stop at multipart section", path=pth)

    json.dump(mail['head'], stdout)
    stdout.write("\n")
    if type(mail['body']) is str:
        stdout.write(mail['body'])
    elif type(mail['body']) is bytes:
        stdout.flush()
        stdout.buffer.write(mail['body'])
    else:
        stdout.write(str(mail['body']))
    sysexit(0)


def _matches(m, pattern):
    if m.is_multipart():
        return any(
            1
            for part in m.body.parts
            if re.search(pattern, part.decoded()) or re.search(pattern, part.subject)
        )
    return re.search(pattern, m.body.decoded()) or re.search(pattern, m.subject)


def search_mails(f, pattern: str, subfolder: str):
    if subfolder:
        f = f.get_folder(subfolder)

    return [
        {
            'head': _get_head_info(msg),
            'body': _get_body(msg),
        }
        for msg in f.values()
        if _matches(msg, pattern)
    ]


def folders(f):
    return f.list_folders()


def move_mail(f, mid, from_, to):
    if from_:
        f = f.get_folder(from_)

    fname = Path(f.get_filename(mid))

    assert to in f.list_folders()

    sep = -2 if not from_ else -3

    if to:
        res = fname.parts[:sep] + ('.' + to,) + fname.parts[-2:]
    else:
        res = fname.parts[:sep] + fname.parts[-2:]

    fname.rename(Path(*res))

    return 1


ap = ArgumentParser(allow_abbrev=False)
ap.add_argument('maildir_path', type=Path)
ap.add_argument('os_user')
ap.add_argument('mail_user')
sp = ap.add_subparsers(title='methods', required=True)

sp_list = sp.add_parser('list')
sp_list.add_argument('folder', metavar='subfolder')
sp_list.add_argument('start', type=int)
sp_list.add_argument('end', type=int)
sp_list.add_argument('sortby', metavar='sort_by')
sp_list.set_defaults(run=list_mails)

sp_count = sp.add_parser('count')
sp_count.add_argument('subfolder')
sp_count.set_defaults(run=count_mails)

sp_read = sp.add_parser('read')
sp_read.add_argument('subfolder')
sp_read.add_argument('mid', metavar='message')
sp_read.set_defaults(run=read_mail)

sp_raw = sp.add_parser('raw')
sp_raw.add_argument('subfolder')
sp_raw.add_argument('mid', metavar='message')
sp_raw.add_argument('path', default='')
sp_raw.set_defaults(run=raw_mail)

sp_folders = sp.add_parser('folders')
sp_folders.set_defaults(run=folders)

sp_move = sp.add_parser('move')
sp_move.add_argument('mid', metavar='message')
sp_move.add_argument('from_', metavar='from')
sp_move.add_argument('to')
sp_move.set_defaults(run=move_mail)

sp_search = sp.add_parser('search')
sp_search.add_argument('pattern')
sp_search.add_argument('subfolder')
sp_search.set_defaults(run=search_mails)


if __name__ == '__main__':
    try:
        logging.basicConfig(
            level='INFO',
            format="%(levelname)s:"+str(getpid())+":%(message)s",
        )
        args = vars(ap.parse_args())
        logging.debug("started with %s", args)
        s = startup(
            args.pop('maildir_path'),
            args.pop('os_user'),
            args.pop('mail_user'),
            args['run'],
        )
        logging.debug("setuid successful")
        run = args.pop('run')
        reply = run(s, **args)
        json.dump(reply, stdout)
    except QMAuthError as qerr:
        errmsg = dict(error=qerr.msg, **qerr.info)
        json.dump(errmsg, stdout)
        sysexit(3)
    except Exception:
        logging.exception("qmauth.py error")
        sysexit(4)