"""Copy user messages without losing Telegram entities, including custom emoji."""
import asyncio
from functools import wraps

from aiogram.types import Message, MessageEntity

COPY_TIMEOUT = 15.0


def bounded_copy(func):
    @wraps(func)
    async def wrapped(*args, **kwargs):
        async with asyncio.timeout(COPY_TIMEOUT):
            return await func(*args, **kwargs)
    return wrapped


def utf16_length(text: str) -> int:
    """Telegram entity offsets count UTF-16 code units, not Python characters."""
    return len(text.encode("utf-16-le")) // 2


@bounded_copy
async def copy_preserving_entities(message: Message, recipient_id: int, sender_name: str | None = None):
    if sender_name is None:
        # Native copy keeps the original body/caption and its entities unchanged.
        return await message.copy_to(recipient_id)

    prefix = "📨 "
    header = f"{prefix}{sender_name}:\n\n"
    header_entities = [MessageEntity(type="bold", offset=utf16_length(prefix),
                                     length=utf16_length(sender_name + ":"))]
    offset = utf16_length(header)
    has_caption = any((message.photo, message.video, message.document,
                       message.animation, message.audio, message.voice))
    body = message.text if message.text is not None else (message.caption or "")
    original = message.entities if message.text is not None else message.caption_entities
    entities = header_entities + [entity.model_copy(update={"offset": entity.offset + offset})
                                  for entity in original or ()]
    limit = 4096 if message.text is not None else 1024
    if (message.text is not None or has_caption) and offset + utf16_length(body) <= limit:
        if message.text is not None:
            return await message.bot.send_message(recipient_id, header + body,
                                                   entities=entities, parse_mode=None)
        return await message.copy_to(recipient_id, caption=header + body,
                                     caption_entities=entities, parse_mode=None)

    # Do not trim a long body/caption: send the header separately and copy the original.
    await message.bot.send_message(recipient_id, header, entities=header_entities, parse_mode=None)
    return await message.copy_to(recipient_id)