import re
from datetime import datetime, timedelta, timezone
from zoneinfo import ZoneInfo

from .models import ReminderParseResult
from .time_utils import utc_now


def unit_to_timedelta(amount: int, unit: str) -> timedelta | None:
    normalized = unit.lower().strip(".")
    if normalized in {"s", "sec", "secs", "second", "seconds", "с", "сек", "секунд"}:
        return timedelta(seconds=amount)
    if normalized in {"m", "min", "mins", "minute", "minutes", "м"} or normalized.startswith("мин"):
        return timedelta(minutes=amount)
    if normalized in {"h", "hr", "hrs", "hour", "hours", "ч"} or normalized.startswith("час"):
        return timedelta(hours=amount)
    if normalized in {"d", "day", "days", "д"} or normalized.startswith(("дн", "ден")):
        return timedelta(days=amount)
    return None


def parse_reminder(raw_text: str, tz: ZoneInfo) -> ReminderParseResult | None:
    text = raw_text.strip()
    if not text:
        return None

    relative_match = re.match(r"^(?:через\s+)?(\d+)\s*([a-zа-я.]+)\s+(.+)$", text, re.IGNORECASE)
    if relative_match:
        amount = int(relative_match.group(1))
        delta = unit_to_timedelta(amount, relative_match.group(2))
        reminder_text = relative_match.group(3).strip()
        if delta and reminder_text:
            return ReminderParseResult(utc_now() + delta, reminder_text)

    now_local = datetime.now(tz)
    absolute_patterns = (
        (r"^(\d{4}-\d{2}-\d{2})\s+(\d{1,2}:\d{2})\s+(.+)$", "%Y-%m-%d %H:%M"),
        (r"^(\d{1,2}\.\d{1,2}\.\d{4})\s+(\d{1,2}:\d{2})\s+(.+)$", "%d.%m.%Y %H:%M"),
    )

    for pattern, date_format in absolute_patterns:
        match = re.match(pattern, text)
        if not match:
            continue

        naive = datetime.strptime(f"{match.group(1)} {match.group(2)}", date_format)
        remind_at = naive.replace(tzinfo=tz)
        reminder_text = match.group(3).strip()
        if reminder_text:
            return ReminderParseResult(remind_at.astimezone(timezone.utc), reminder_text)

    time_match = re.match(r"^(\d{1,2}:\d{2})\s+(.+)$", text)
    if time_match:
        hour, minute = (int(part) for part in time_match.group(1).split(":", 1))
        if 0 <= hour <= 23 and 0 <= minute <= 59:
            remind_at = now_local.replace(hour=hour, minute=minute, second=0, microsecond=0)
            if remind_at <= now_local:
                remind_at += timedelta(days=1)
            reminder_text = time_match.group(2).strip()
            if reminder_text:
                return ReminderParseResult(remind_at.astimezone(timezone.utc), reminder_text)

    return None