# Copyright 2017  Lars Wirzenius
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
# =*= License: GPL-3+ =*=


import email


def get_ids_from_message(msg):
    return set(_yield_ids(msg))


def _yield_ids(msg):
    header_names = ('Message-Id', 'In-Reply-To', 'References')
    for header_name in header_names:
        for msg_id in _yield_ids_from_header(msg, header_name):
            yield msg_id


def _yield_ids_from_header(msg, header_name):
    values = msg.get_all(header_name)
    if values:
        for _, msg_id in email.utils.getaddresses(values):
            yield msg_id