#!/usr/bin/env python3
"""Print your future lessons in a specific class"""

import argparse
from dataclasses import dataclass
import datetime
import fnmatch
from getpass import getpass
import pathlib
import os
import sys
import typing as t

import icalevents
from icalevents.icalevents import events
import toml
import webuntis


def die(msg: str, status=1) -> t.NoReturn:
    """print a message and exit"""
    print(msg, file=sys.stderr)
    sys.exit(status)


@dataclass
class Period:
    """Data representing a period where a lesson could take place"""
    start: datetime.datetime
    code = None


@dataclass
class WebuntisSessionCredentials:
    """Data required to create a new webuntis session"""
    school: str
    server: str
    username: str
    password: str

    def __init__(self, config: dict):
        self.school = config.get('school') or input('Webuntis School: ')
        self.server = config.get('server') or input('Webuntis Server: ')
        self.username = config.get('user') or input('Webuntis User: ')
        self.password = config.get('password') or getpass(
            prompt='Webuntis Password: ')


def find_config() -> t.Optional[pathlib.Path]:
    """Search for a config file"""

    path = pathlib.Path('config')
    if path.is_file():
        return path

    config_dir = pathlib.Path(
        os.environ.get('XDG_CONFIG_HOME', os.environ['HOME'] + '/.config'))
    path = config_dir / 'avail-lessons' / 'config'
    if path.is_file():
        return path

    return None


def load_config(path="") -> dict:
    """Load a toml config file"""
    path = path or find_config()
    if not path:
        return {}

    with open(path, 'r', encoding='utf-8') as config_file:
        config = toml.load(config_file)

    return config


def load_events(config: dict) -> list[icalevents.icalparser.Event]:
    """Retrieve all events from the specified ics calendars"""
    evs = []
    for uri in config['icalendars']:
        if uri.startswith("http"):
            evs += events(url=uri, start=config['start'], end=config['end'])
        elif pathlib.Path(uri).is_file():
            evs += events(file=uri, start=config['start'], end=config['end'])

    return evs


def filter_special_events(
    evs: list[icalevents.icalparser.Event],
    special_events_definitions: dict[str, dict[str, str]]
) -> list[tuple[icalevents.icalparser.Event, str]]:
    """Filter all events for special events and return a sorted list"""

    special_events = []
    for special_event in special_events_definitions:
        pattern, fmt = special_events_definitions[special_event].values()
        for event in evs:
            if not fnmatch.fnmatch(event.summary, pattern):
                continue

            special_events.append((event, eval('f' + f'"{fmt}"')))  # pylint: disable=eval-used

    # Sort the special events by their start datetime
    special_events.sort(key=lambda t: t[0].start)
    return special_events


def format_period(period: webuntis.objects.PeriodObject,
                  evs: list[icalevents.icalparser.Event], config: dict) -> str:
    """Format a given period"""
    # Provide some useful shortcuts for the output format
    date = period.start.date()
    week = date.isocalendar().week  # pylint: disable=unused-variable

    period_events = ""
    period_evs = [
        ev for ev in evs if
        ev.start.timestamp() <= period.start.timestamp() <= ev.end.timestamp()
        # Detect early end of classes
        or (ev.summary == 'Unterrichtsschluss' and ev.start.date() == date
            and ev.start.timestamp() <= period.start.timestamp())
    ]
    if period_evs:
        for event in period_evs:
            period_events += f' {event.summary} |'
        # strip the leading ' ' and trailing ' |'
        period_events = period_events[1:-2]

    fmt = config.get(
        'fmt') or '{week} {date.strftime(\'%d.%m\')} {period_events}'
    # Using eval here instead of string.format() is potentially dangerous.
    # However, I do not consider this an actual thread because this is an
    # obscure script run with only trusted inputs (cli arguments, manual written
    # config), therefore potential code execution is not a real concern.
    line = eval('f' + f'"{fmt}"')  # pylint: disable=eval-used

    # Apply event_line_formats
    event_line_formats = config.get('event_line_formats', [])
    for event in period_evs:
        if event.summary in event_line_formats:
            # Same eval reasoning as above.
            line = eval('f' + f'"{event_line_formats[event.summary]}"')  # pylint: disable=eval-used

    return line


def filter_periods(timetable: webuntis.objects.PeriodList,
                   config: dict) -> list[webuntis.objects.PeriodObject]:
    """Filter the timetable for our periods"""
    return [
        p for p in timetable if p.subjects.filter(  # type: ignore # pylint: disable=no-member
            name=config['subject']) and p.teachers.filter(  # pylint: disable=no-member
                name=config['teacher'])
    ]


DAYS_MAP = {'Mo': 1, 'Di': 2, 'Mi': 3, 'Do': 4, 'Fr': 5}

TIME_SLOTS = {
    '1': datetime.timedelta(hours=8),
    '2': datetime.timedelta(hours=8, minutes=45),
    '3': datetime.timedelta(hours=9, minutes=45),
    '4': datetime.timedelta(hours=10, minutes=30),
    '5': datetime.timedelta(hours=11, minutes=30),
    '6': datetime.timedelta(hours=12, minutes=15),
    '7': datetime.timedelta(hours=13),
    '8': datetime.timedelta(hours=13, minutes=45),
    '9': datetime.timedelta(hours=14, minutes=30),
    '10': datetime.timedelta(hours=15, minutes=20),
    '11': datetime.timedelta(hours=16),
    '12': datetime.timedelta(hours=16, minutes=45),
}


def build_periods(config: str, start: datetime.datetime,
                  end: datetime.datetime) -> list[Period]:
    """Build a list of periods from a configuration string"""

    periods = []
    week = start.isocalendar().week
    while True:
        year = start.year if week >= start.isocalendar().week else end.year
        for period in config.split(';'):
            weekday, slot = period.split(':')
            period_day = datetime.datetime.fromisocalendar(
                year=year, week=week, day=DAYS_MAP[weekday])
            period_start = period_day + TIME_SLOTS[slot]
            periods.append(Period(period_start))

        week = week % 52 + 1
        if week > end.isocalendar().week and year == end.isocalendar().year:
            break

    return periods


def main():
    """Programm entry point loading data from webuntis and printing the remaining lessons"""
    parser = argparse.ArgumentParser()
    parser.add_argument('--school',
                        help='The shool identifier used by webuntis')
    parser.add_argument('--server', help='The webuntis server')
    parser.add_argument('--user', help='The webuntis login username')
    parser.add_argument('--password', help='The webuntis login password')
    parser.add_argument('--config', help='Path to a configuration file')
    parser.add_argument('--teacher',
                        help='The teacher abbreviation used in webuntis')
    parser.add_argument('--subject',
                        help='The subject abbreviation used in webuntis')
    parser.add_argument('--class', help='The class name')
    parser.add_argument('--periods',
                        help=('The periods when you teach the class.'
                              'Format: <Day>:<Slot>[;<Day><Slot>]*'),
                        type=str)
    parser.add_argument('--show-events',
                        action='store_true',
                        help='Show ICS calendar events during the lessons')
    args = parser.parse_args()

    config = {'start': datetime.datetime.now()}

    config.update(load_config(args.config))
    # command line arguments override the values in the config file
    config.update({k: v for k, v in args.__dict__.items() if v})

    if 'class' not in config or 'subject' not in config:
        die('Class and subject must be provided')

    periods = None
    if 'webuntis' in config:
        # use the webuntis username as teacher fallback
        if 'teacher' not in config:
            config['teacher'] = config['webuntis']['username']

        session_info = WebuntisSessionCredentials(config['webuntis'])
        with webuntis.Session(useragent="muhq's avail-lessons script",
                              **session_info.__dict__).login() as session:

            # Unfortunately pylint does not understand the type (_itemclass)
            # of the webuntis ListResults, therfore we supress the errors when
            # accessing members of the _itemclass.
            year = [
                y for y in session.schoolyears()
                if y.start <= config['start'] <= y.end  # pylint: disable=no-member
            ]
            if not year:
                die('No school year is active')
            year = year[0]

            if 'end' not in config:
                config['end'] = year.end

            klasse = session.klassen().filter(name=config['class'])[0]  # pylint: disable=no-member

            timetable = session.timetable_extended(klasse=klasse,
                                                   start=config['start'],
                                                   end=config['end'])

            periods = filter_periods(timetable, config)
    elif args.periods:
        start = config.setdefault(
            'start', datetime.datetime.fromisocalendar(2023, 37, 2))
        end = config.setdefault('end',
                                datetime.datetime.fromisocalendar(2024, 30, 5))
        periods = build_periods(args.periods, start, end)

    if not periods:
        die('Webuntis credentials or manual periods must be provided')

    # load ICS events
    evs = load_events(config)

    # filter special events
    special_events = filter_special_events(evs,
                                           config.get('special_events', {}))

    lines = []
    for period in periods:
        # Insert formatted prior special event
        if special_events and special_events[0][0].start.timestamp(
        ) <= period.start.timestamp():
            lines.append(special_events[0][1])
            special_events = special_events[1:]

        if period.code:
            print(f'WARNING: period {period.start} is {period.code}',
                  file=sys.stderr)

        lines.append(format_period(period, evs, config))

    if 'output_header' in config:
        print(config['output_header'])

    for line in lines:
        print(line)

    if 'output_footer' in config:
        print(config['output_footer'])


if __name__ == '__main__':
    main()