import re

from datetime import datetime
from io import BytesIO
import pytz

from pytesseract import image_to_string
from PIL import Image

from lib.config import load_config
from lib.room import Room

__all__ = ["get_room_data"]

config = load_config()

RE_STRING = re.compile(  # https://regex101.com/r/ELsqrO/1
    r"(L-[0-9]{4}): "  # room number (group 1)
    # time-slot (group 2,3,4 - group 5,6,7)
    r"([1-12]{1,2}):([0,3]{2})(am|pm) - ([1-12]{1,2}):([0,3]{2})(am|pm), "
    # weekday (group 8)
    r"(Monday|Tuesday|Wednesday|Thursday|Friday|Saturday|Sunday), "
    # month (group 9)
    r"(January|February|March|April|May|June|July|August|September|October|November|December) "
    r"([1-9][0-9]|[1-9]), ([0-9]{4})",  # day & year (group 10 & 11)
    flags=re.M
)


class NotAMatchException(Exception):
    pass


class NoMatchException(Exception):
    pass


def add_zero_padding(value: str):
    """Adds zero-padding to a single digit value."""
    if int(value) < 10:
        return "0"+str(int(value))  # this removes leading 0 if already present
    return value


def libcal_to_datetime(year: str, month: str, day: str, hour: str, minute: str, am_pm: str) -> datetime:
    """Takes date information as displayed by LibCal and turns it into a datetime object.
    All values should be given in an unmodified string format."""
    date = datetime.strptime(f"{year}-{month}-{add_zero_padding(day)}-"
                             f"{add_zero_padding(hour)}-{add_zero_padding(minute)}-{am_pm}",
                             "%Y-%B-%d-%I-%M-%p")
    tz = pytz.timezone(config.time_zone)
    return tz.localize(date)  # adds timezone info to object


def correct_commas(string: str):
    """Ensures all commas have a space after them in the given string."""
    return re.sub(r"(,)([^ ])", r"\1 \2", string)


def correct_newlines(string: str):
    """Replaces all newlines with a space in the given string."""
    return string.replace("\n", " ")


def get_room_data(img: bytes) -> list[Room]:
    """Gets the room data from a given image"""
    rooms: list[Room] = []
    start_time: datetime | None = None
    end_time: datetime | None = None
    img_string = image_to_string(Image.open(BytesIO(img)))
    img_string = correct_newlines(img_string)
    img_string = correct_commas(img_string)
    matches = re.finditer(RE_STRING, img_string)
    for match in matches:
        if isinstance(match, re.Match):
            room_number = match.group(1)
            start_time = libcal_to_datetime(match.group(11), match.group(
                9), match.group(10), match.group(2), match.group(3), match.group(4))
            end_time = libcal_to_datetime(match.group(11), match.group(
                9), match.group(10), match.group(5), match.group(6), match.group(7))
            room = Room(room_number, start_time, end_time)
            rooms.append(room)
        else:
            raise NotAMatchException(match)
    if len(rooms) == 0:
        raise NoMatchException
    return rooms