from __future__ import annotations

import logging
import secrets
import time

logger = logging.getLogger(__name__)

CODE_CHARS = "ABCDEFGHJKLMNPQRSTUVWXYZ23456789"
CODE_LENGTH = 6
CODE_TTL_SECONDS = 600
MAX_PENDING = 3
REQUEST_COOLDOWN_S = 3600


class ILinkPairing:
    def __init__(self):
        self._pending: dict[str, dict] = {}
        self._paired: dict[str, float] = {}
        self._last_request: dict[str, float] = {}

    def generate_code(self, user_id: str) -> str | None:
        now = time.time()
        last = self._last_request.get(user_id, 0)
        if now - last < REQUEST_COOLDOWN_S:
            return None

        if len(self._pending) >= MAX_PENDING:
            return None

        code = "".join(secrets.choice(CODE_CHARS) for _ in range(CODE_LENGTH))
        self._pending[user_id] = {"code": code, "created_at": now}
        self._last_request[user_id] = now
        return code

    def verify(self, user_id: str, code: str) -> bool:
        entry = self._pending.get(user_id)
        if not entry:
            return False

        if time.time() - entry["created_at"] > CODE_TTL_SECONDS:
            del self._pending[user_id]
            return False

        if entry["code"] == code.upper().strip():
            del self._pending[user_id]
            self._paired[user_id] = time.time()
            return True

        return False

    def is_paired(self, user_id: str) -> bool:
        return user_id in self._paired

    def revoke(self, user_id: str) -> None:
        self._paired.pop(user_id, None)
        self._pending.pop(user_id, None)