#!/usr/bin/env python3

import os

display_env = 'DISPLAY='
dbus_env = 'DBUS_SESSION_BUS_ADDRESS='
user_env = 'USER='


def re_pid_environ(pid):
    """
    read environ of 1 process
    returns tuple with USER, DBUS, DISPLAY like follow:
    ('user', 'DISPLAY=:0',
     'DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus')
    returns None if these vars is not in /proc/[pid]/environ
    """

    try:
        with open('/proc/' + pid + '/environ', 'rb') as f:
            env = f.read().decode('utf-8', 'ignore')
    except FileNotFoundError:
        return None
    except ProcessLookupError:
        return None

    if display_env in env and dbus_env in env and user_env in env:

        env_list = env.split('\x00')

        print(pid, env_list, '\n')

        # iterating over a list of process environment variables
        for i in env_list:

            # exclude Display Manager's user
            if i.startswith('HOME=/var'):
                return None

            if i.startswith(user_env):
                user = i
                if user == 'USER=root':
                    return None
                continue

            if i.startswith(display_env):
                display = i[:10]
                continue

            if i.startswith(dbus_env):
                dbus = i
                continue

        try:
            return user.partition('USER=')[2], display, dbus
        except UnboundLocalError:
            return None


def root_notify_env():
    """return set(user, display, dbus)"""
    unsorted_envs_list = []
    # iterates over processes, find processes with suitable env
    for pid in os.listdir('/proc'):

        # os.path.exists('/proc/[pid]/exe') indicates process existanse
        if os.path.exists('/proc/' + pid + '/exe') is True:
            one_env = re_pid_environ(pid)
            unsorted_envs_list.append(one_env)

    env = set(unsorted_envs_list)
    env.discard(None)

    # deduplicate dbus
    new_env = []
    end = []
    for i in env:
        key = i[0] + i[1]
        if key not in end:
            end.append(key)
            new_env.append(i)
        else:
            continue

    return new_env


print(root_notify_env())