"""Keyset cursor helpers for thread listings (SPEC §9.1: cursor = last_message_at,id)."""

from __future__ import annotations

import base64
import datetime as dt
import uuid


def encode_cursor(last_message_at: dt.datetime, thread_id: uuid.UUID) -> str:
    raw = f"{last_message_at.isoformat()}|{thread_id}"
    return base64.urlsafe_b64encode(raw.encode()).decode()


def decode_cursor(cursor: str | None) -> tuple[dt.datetime, uuid.UUID] | None:
    if not cursor:
        return None
    try:
        raw = base64.urlsafe_b64decode(cursor.encode()).decode()
        date_str, id_str = raw.split("|", 1)
        return dt.datetime.fromisoformat(date_str), uuid.UUID(id_str)
    except (ValueError, TypeError):
        return None