#!/usr/bin/env python3

"""Watch a few mbox folders from Thunderbird and notify when there are
new messages. This should be a builtin feature in Thunderbird, but it
is not."""

# TODO:
#  - handle emails received at the same second
#  - add an action to Open TB (thunderbird mid:....)

import sys
import argparse
import pyinotify
import os
import email.parser
import email.header
from pydbus import SessionBus

parser = argparse.ArgumentParser(description=sys.modules[__name__].__doc__)
parser.add_argument("root", metavar="FILE", help="path to Thunderbird mail folder")
parser.add_argument("folder", metavar="FOLDER", help="folder to monitor", nargs="+")
options = parser.parse_args()

watermarks = {}
notify = SessionBus().get(".Notifications")


class EventHandler(pyinotify.ProcessEvent):
    def process_IN_CLOSE_WRITE(self, event):
        watermark = process(event.pathname, watermarks[event.pathname])
        watermarks[event.pathname] = watermark


def process(path, watermark):
    new_watermark = None
    with open(path, "rb") as mbox:
        marker = b"\nFrom "
        chunk = 1024

        mbox.seek(0, os.SEEK_END)
        begin = mbox.tell()
        while begin > 0:
            while True:
                begin -= 1024
                if begin < 0:
                    begin = 0
                    break
                mbox.seek(begin)
                buffer = mbox.read(chunk)
                idx = buffer.rfind(marker)
                if idx == -1:
                    continue
                begin = begin + idx
                break
            end = begin + 1
            while True:
                mbox.seek(end)
                buffer = mbox.read(chunk)
                if len(buffer) < chunk:
                    end = end + len(buffer)
                    break
                idx = buffer.find(marker)
                if idx == -1:
                    end += chunk
                    continue
                end = end + idx
                break
            mbox.seek(begin + 1)
            message = mbox.read(end - begin).split(b"\n")
            if message[0] == watermark:
                return new_watermark
            if new_watermark is None:
                new_watermark = message[0]
            if watermark is None:
                return new_watermark
            message = b"\n".join(message[1:])
            parsed = email.parser.BytesParser().parsebytes(message, headersonly=True)
            subject = parsed.get("subject")
            author = parsed.get("from")
            if subject is not None and author is not None:
                subject, charset = email.header.decode_header(subject)
                if charset is not None:
                    subject = subject.decode(charset)
                author, charset = email.header.decode_header(author)
                if charset is not None:
                    author = author.decode(charset)
                notify.Notify(
                    "Thunderbird",
                    0,
                    "thunderbird",
                    f"Mail from {author}",
                    subject,
                    [],
                    {},
                    10000,
                )
    return new_watermark


wm = pyinotify.WatchManager()
mask = pyinotify.IN_CLOSE_WRITE
handler = EventHandler()
notifier = pyinotify.Notifier(wm, handler)
for folder in options.folder:
    folder = folder.split("/")
    folder = [f"{f}.sbd" for f in folder[:-1]] + [folder[-1]]
    folder = os.path.join(os.path.expanduser(options.root), *folder)
    print(f"Watch {folder}...", flush=True)
    watermarks[folder] = process(folder, None)
    wm.add_watch(folder, mask)
notifier.loop()