验证码【lazy-captcha】

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace RG3.PF.OssCaptcha.Generator
{
    /// <summary>
    /// 
    /// </summary>
    public enum CaptchaType
    {
        /// <summary>
        /// 默认(英文字符大小写，数字混合)
        /// </summary>
        DEFAULT=0,

        /// <summary>
        /// 中文
        /// </summary>
        CHINESE=1,

        /// <summary>
        /// 数字
        /// </summary>
        NUMBER=2,

        /// <summary>
        /// 中文数字小写
        /// </summary>
        NUMBER_ZH_CN=3,

        /// <summary>
        /// 中文数字大写
        /// </summary>
        NUMBER_ZH_HK=4,

        /// <summary>
        /// 英文字符大小写混合
        /// </summary>
        WORD=5,

        /// <summary>
        /// 英文字符小写
        /// </summary>
        WORD_LOWER=6,

        /// <summary>
        /// 英文字符大写
        /// </summary>
        WORD_UPPER=7,

        /// <summary>
        /// 英文小写，数字混合
        /// </summary>
        WORD_NUMBER_LOWER=8,

        /// <summary>
        /// 英文大写，数字混合
        /// </summary>
        WORD_NUMBER_UPPER=9,

        /// <summary>
        /// 数字计算
        /// </summary>
        ARITHMETIC=10,

        /// <summary>
        /// 数字计算，中文
        /// </summary>
        ARITHMETIC_ZH=11
    }
}

  /// <summary>
        /// 生成
        /// </summary>
        /// <param name="length">长度</param>
        /// <returns>（渲染文本，code）</returns>
        public (string renderText, string code) Generate(int length)
        {
            if (_captchaType == CaptchaType.ARITHMETIC)
            {
                return GenerateaArithmetic(length);
            }
            else if (_captchaType == CaptchaType.ARITHMETIC_ZH)
            {
                return GenerateaArithmeticZh(length);
            }
            else if (_captchaType == CaptchaType.NUMBER_ZH_CN)
            {
                return GenerateaNumberZH(length, false);
            }
            else if (_captchaType == CaptchaType.NUMBER_ZH_HK)
            {
                return GenerateaNumberZH(length, true);
            }
            else
            {
                var chars = GetCharacters(_captchaType);
                var code = Pick(chars, length);
                return (code, code);
            }
        }

   private static IReadOnlyList<char> GetCharacters(CaptchaType captchaType)
        {
            return captchaType switch
            {
                CaptchaType.DEFAULT => Characters.DEFAULT,
                CaptchaType.CHINESE => Characters.CHINESE,
                CaptchaType.NUMBER => Characters.NUMBER,
                CaptchaType.NUMBER_ZH_CN => Characters.NUMBER_ZH_CN,
                CaptchaType.NUMBER_ZH_HK => Characters.NUMBER_ZH_HK,
                CaptchaType.WORD_NUMBER_LOWER => Characters.WORD_NUMBER_LOWER,
                CaptchaType.WORD_NUMBER_UPPER => Characters.WORD_NUMBER_UPPER,
                CaptchaType.WORD => Characters.WORD,
                CaptchaType.WORD_LOWER => Characters.WORD_LOWER,
                CaptchaType.WORD_UPPER => Characters.WORD_UPPER,

                _ => Characters.DEFAULT,
            };
        }