Hua.DotNet.Code/Helper/Html/HtmlHelper.cs

using System;
using System.Text;
using System.Text.RegularExpressions;
using System.Web;

namespace Hua.DotNet.Code.Helper.Html;

public class HtmlHelper
{
	private static readonly Regex paragraphStartRegex = new Regex("<p>", RegexOptions.IgnoreCase);

	private static readonly Regex paragraphEndRegex = new Regex("</p>", RegexOptions.IgnoreCase);

	private static string EnsureOnlyAllowedHtml(string text)
	{
		if (string.IsNullOrEmpty(text))
		{
			return string.Empty;
		}
		MatchCollection matchCollection = Regex.Matches(text, "<.*?>", RegexOptions.IgnoreCase);
		for (int num = matchCollection.Count - 1; num >= 0; num--)
		{
			if (!IsValidTag(text.Substring(matchCollection[num].Index + 1, matchCollection[num].Length - 1).Trim().ToLower(), "br,hr,b,i,u,a,div,ol,ul,li,blockquote,img,span,p,em,strong,font,pre,h1,h2,h3,h4,h5,h6,address,cite"))
			{
				text = text.Remove(matchCollection[num].Index, matchCollection[num].Length);
			}
		}
		return text;
	}

	private static bool IsValidTag(string tag, string tags)
	{
		string[] array = tags.Split(',');
		if (tag.IndexOf("javascript") >= 0)
		{
			return false;
		}
		if (tag.IndexOf("vbscript") >= 0)
		{
			return false;
		}
		if (tag.IndexOf("onclick") >= 0)
		{
			return false;
		}
		char[] anyOf = new char[4] { ' ', '>', '/', '\t' };
		int num = tag.IndexOfAny(anyOf, 1);
		if (num > 0)
		{
			tag = tag.Substring(0, num);
		}
		if (tag[0] == '/')
		{
			tag = tag.Substring(1);
		}
		string[] array2 = array;
		foreach (string text in array2)
		{
			if (tag == text)
			{
				return true;
			}
		}
		return false;
	}

	public static string FormatText(string text, bool stripTags, bool convertPlainTextToHtml, bool allowHtml, bool allowBBCode, bool resolveLinks, bool addNoFollowTag)
	{
		if (string.IsNullOrEmpty(text))
		{
			return string.Empty;
		}
		try
		{
			if (stripTags)
			{
				text = StripTags(text);
			}
			text = ((!allowHtml) ? HttpUtility.HtmlEncode(text) : EnsureOnlyAllowedHtml(text));
			if (convertPlainTextToHtml)
			{
				text = ConvertPlainTextToHtml(text);
			}
			if (resolveLinks)
			{
				text = ResolveLinksHelper.FormatText(text);
			}
		}
		catch (Exception ex)
		{
			text = $"Text cannot be formatted. Error: {ex.Message}";
		}
		return text;
	}

	public static string StripTags(string text)
	{
		if (string.IsNullOrEmpty(text))
		{
			return string.Empty;
		}
		text = Regex.Replace(text, "(>)(\\r|\\n)*(<)", "><");
		text = Regex.Replace(text, "(<[^>]*>)([^<]*)", "$2");
		text = Regex.Replace(text, "(&#x?[0-9]{2,4};|&quot;|&amp;|&nbsp;|&lt;|&gt;|&euro;|&copy;|&reg;|&permil;|&Dagger;|&dagger;|&lsaquo;|&rsaquo;|&bdquo;|&rdquo;|&ldquo;|&sbquo;|&rsquo;|&lsquo;|&mdash;|&ndash;|&rlm;|&lrm;|&zwj;|&zwnj;|&thinsp;|&emsp;|&ensp;|&tilde;|&circ;|&Yuml;|&scaron;|&Scaron;)", "@");
		return text;
	}

	public static string ReplaceAnchorTags(string text)
	{
		if (string.IsNullOrEmpty(text))
		{
			return string.Empty;
		}
		text = Regex.Replace(text, "<a\\b[^>]+>([^<]*(?:(?!</a)<[^<]*)*)</a>", "$1", RegexOptions.IgnoreCase);
		return text;
	}

	public static string ConvertPlainTextToHtml(string text)
	{
		if (string.IsNullOrEmpty(text))
		{
			return string.Empty;
		}
		text = text.Replace("\r\n", "<br />");
		text = text.Replace("\r", "<br />");
		text = text.Replace("\n", "<br />");
		text = text.Replace("\t", "&nbsp;&nbsp;");
		text = text.Replace("  ", "&nbsp;&nbsp;");
		return text;
	}

	public static string ConvertHtmlToPlainText(string text, bool decode = false, bool replaceAnchorTags = false)
	{
		if (string.IsNullOrEmpty(text))
		{
			return string.Empty;
		}
		if (decode)
		{
			text = HttpUtility.HtmlDecode(text);
		}
		text = text.Replace("<br>", "\n");
		text = text.Replace("<br >", "\n");
		text = text.Replace("<br />", "\n");
		text = text.Replace("&nbsp;&nbsp;", "\t");
		text = text.Replace("&nbsp;&nbsp;", "  ");
		if (replaceAnchorTags)
		{
			text = ReplaceAnchorTags(text);
		}
		return text;
	}

	public static string ConvertPlainTextToParagraph(string text)
	{
		if (string.IsNullOrEmpty(text))
		{
			return string.Empty;
		}
		text = paragraphStartRegex.Replace(text, string.Empty);
		text = paragraphEndRegex.Replace(text, "\n");
		text = text.Replace("\r\n", "\n").Replace("\r", "\n");
		text += "\n\n";
		text = text.Replace("\n\n", "\n");
		string[] array = text.Split(new char[1] { '\n' });
		StringBuilder stringBuilder = new StringBuilder();
		string[] array2 = array;
		foreach (string text2 in array2)
		{
			if (text2 != null && text2.Trim().Length > 0)
			{
				stringBuilder.AppendFormat("<p>{0}</p>\n", text2);
			}
		}
		return stringBuilder.ToString();
	}
}