using System.Security.Cryptography;
using System.Text;
namespace LMS.Common.Password
{
    public static class PasswordGenerator
    {
        private const string LowercaseChars = "abcdefghijklmnopqrstuvwxyz";
        private const string UppercaseChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        private const string NumberChars = "0123456789";
        private const string SpecialChars = "@$!%*?.&";
        private const string AllChars = LowercaseChars + UppercaseChars + NumberChars + SpecialChars;

        /// <summary>
        /// 生成指定长度的随机密码
        /// </summary>
        /// <param name="length">密码长度</param>
        /// <returns>随机生成的密码</returns>
        public static string GeneratePassword(int length)
        {
            if (length < 4)
            {
                throw new ArgumentException("密码长度必须至少为4个字符", nameof(length));
            }

            // 使用加密安全的随机数生成器
            using var rng = RandomNumberGenerator.Create();
            // 确保密码包含至少一个小写字母、一个大写字母、一个数字和一个特殊字符
            var password = new StringBuilder();

            // 添加每种类型的至少一个字符
            password.Append(GetRandomChar(LowercaseChars, rng));
            password.Append(GetRandomChar(UppercaseChars, rng));
            password.Append(GetRandomChar(NumberChars, rng));
            password.Append(GetRandomChar(SpecialChars, rng));

            // 添加剩余的随机字符
            for (int i = 4; i < length; i++)
            {
                password.Append(GetRandomChar(AllChars, rng));
            }

            // 打乱字符顺序
            return ShuffleString(password.ToString(), rng);
        }

        /// <summary>
        /// 从指定字符集中获取一个随机字符
        /// </summary>
        private static char GetRandomChar(string chars, RandomNumberGenerator rng)
        {
            byte[] data = new byte[1];
            rng.GetBytes(data);
            return chars[data[0] % chars.Length];
        }

        /// <summary>
        /// 打乱字符串中字符的顺序
        /// </summary>
        private static string ShuffleString(string input, RandomNumberGenerator rng)
        {
            char[] array = input.ToCharArray();
            int n = array.Length;

            while (n > 1)
            {
                byte[] box = new byte[1];
                rng.GetBytes(box);
                int k = box[0] % n;
                n--;
                char temp = array[n];
                array[n] = array[k];
                array[k] = temp;
            }

            return new string(array);
        }
    }
}