using System.Globalization;
using System.Text;

namespace MesETL.App.Helpers;

public static class StringExtensions
{
    /// <summary>
    /// 截断字符串
    /// </summary>
    /// <param name="this"></param>
    /// <param name="maxLength">截断长度</param>
    /// <returns></returns>
    public static string Omit(this ReadOnlySpan<char> @this, int maxLength)
    {
        if (@this.Length > maxLength)
            return @this[..maxLength].ToString() + "...";
        return @this.ToString();
    }

    /// <summary>
    /// 截断字符串
    /// </summary>
    /// <param name="this"></param>
    /// <param name="maxLength">截断长度</param>
    /// <returns></returns>
    public static string Omit(this string @this, int maxLength) => Omit(@this.AsSpan(), maxLength);

    /// <summary>
    /// 将16进制字符串转换为字符串
    /// </summary>
    /// <param name="hexString"></param>
    /// <param name="encoding"></param>
    /// <returns></returns>
    public static string FromHex(ReadOnlySpan<char> hexString, Encoding? encoding = null)
    {
        encoding ??= Encoding.UTF8;

        var realLength = 0;
        for (var i = hexString.Length - 2; i >= 0; i -= 2)
        {
            var b = byte.Parse(hexString.Slice(i, 2), NumberStyles.HexNumber, CultureInfo.InvariantCulture);
            if (b != 0) //not NULL character
            {
                realLength = i + 2;
                break;
            }
        }

        var bytes = new byte[realLength / 2];
        for (var i = 0; i < bytes.Length; i++)
        {
            bytes[i] = byte.Parse(hexString.Slice(i * 2, 2), NumberStyles.HexNumber, CultureInfo.InvariantCulture);
        }

        return encoding.GetString(bytes);
    }
    
    /// <summary>
    /// 检查是否为JSON字符串
    /// </summary>
    /// <param name="hexStr"></param>
    /// <returns></returns>
    public static bool CheckJsonHex(ReadOnlySpan<char> hexStr)
    {
        if (hexStr.Length < 2)
            return false;
        return FromHex(hexStr[..2]) is ['{'] or ['['];
    }
}