from __future__ import annotations

import os

ALLOWED_MIME_TYPES = {
    "application/pdf",
    "text/plain",
    "text/csv",
    "image/jpeg",
    "image/png",
    "image/gif",
    "image/webp",
    "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
    "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
    "application/msword",
    "application/vnd.ms-excel",
}

BLOCKED_EXTENSIONS = {
    ".exe",
    ".dll",
    ".bat",
    ".cmd",
    ".ps1",
    ".vbs",
    ".js",
    ".scr",
    ".pif",
    ".msi",
    ".com",
}

MAX_TOTAL_SIZE = 25 * 1024 * 1024
MAX_PER_ATTACHMENT = 10 * 1024 * 1024
MAX_TEXT_FOR_AI = 200 * 1024


def is_attachment_safe(filename: str, content_type: str, size: int) -> tuple[bool, str]:
    ext = os.path.splitext(filename)[1].lower()
    if ext in BLOCKED_EXTENSIONS:
        return False, f"禁止的文件类型: {ext}"
    if size > MAX_PER_ATTACHMENT:
        return False, f"附件过大 ({size} bytes > {MAX_PER_ATTACHMENT})"
    if content_type not in ALLOWED_MIME_TYPES:
        return False, f"不支持的 MIME 类型: {content_type}"
    return True, "ok"