"""
客户端工具函数
"""
import json
import os
from datetime import datetime, timezone, timedelta


def beijing_now_str(fmt='%Y-%m-%d %H:%M:%S'):
    """返回北京时间字符串"""
    return datetime.now(timezone(timedelta(hours=8))).strftime(fmt)


def validate_username(username):
    """验证用户名"""
    if not username or len(username) < 4 or len(username) > 20:
        return False, "用户名长度必须为4-20个字符"
    if not username.replace('_', '').isalnum():
        return False, "用户名只能包含字母、数字和下划线"
    return True, ""


def validate_password(password):
    """验证密码"""
    if not password or len(password) < 6 or len(password) > 20:
        return False, "密码长度必须为6-20个字符"
    return True, ""


def create_default_config():
    """创建默认配置文件（仅在不存在时创建）"""
    if os.path.exists('config.json'):
        return
    default_config = {
        'server_host': '127.0.0.1',
        'server_port': 8888,
        'auto_login': False,
        'username': '',
        'save_password': False,
        'theme': 'light',
        'font_size': 12,
        'notify_new_message': True,
        'notify_sound': True
    }
    with open('config.json', 'w', encoding='utf-8') as f:
        json.dump(default_config, f, ensure_ascii=False, indent=2)