C# Online Compiler | .NET Fiddle

<no name> by Anonymous

using System;
using System.Text.RegularExpressions;
					
public class Program {
	public static void Main() {
		var html = "<html><head></head><body><p>Hi try this link: <a href='https://example.com/Test'>Test</a><p></body></html>";
		var plainText = HtmlToPlainText(html);
		Console.WriteLine(plainText);
	}
	
	private static string HtmlToPlainText(string html) {
		/* Todo: Rob - Find a safe method to strip the HTML down to plain text */
		/* Ref: https://stackoverflow.com/a/16407272 */

		const string
			tagWhiteSpace =
			@"(>|$)(\W|\n|\r)+<"; //matches one or more (white space or line breaks) between '>' and '<'
		const string
			stripFormatting =
			@"<[^>]*(>|$)"; //match any character between '<' and '>', even when end tag is missing
		const string
			lineBreak =
			@"<(br|BR|/div)\s{0,1}\/{0,1}>"; //matches: <br>,<br/>,<br />,<BR>,<BR/>,<BR /> ALSO matches </div> as Exchange uses it for line breaks

		var lineBreakRegex = new Regex(lineBreak, RegexOptions.Multiline);
		var stripFormattingRegex = new Regex(stripFormatting, RegexOptions.Multiline);
		var tagWhiteSpaceRegex = new Regex(tagWhiteSpace, RegexOptions.Multiline);

		var headStartIndex = html.IndexOf("<head>");
		var headEndIndex = html.IndexOf("</head>") + 7;

		//Remove the head
		var text = string.Concat(html.Substring(0, headStartIndex), html.Substring(headEndIndex));
		//var text = $"{html.Substring(0, headStartIndex)}{html.Substring(headEndIndex)}";
		//Decode html specific characters
		text = System.Net.WebUtility.HtmlDecode(text);

		//Remove tag whitespace/line breaks
		text = tagWhiteSpaceRegex.Replace(text, "><");
		//Replace <br /> with line breaks
		//text = lineBreakRegex.Replace(text, Environment.NewLine);

		text = (text
				.Replace("p>", "p>\r\n")
				.Replace("a>", "a>\r\n")
			   );

		//Strip formatting
		text = stripFormattingRegex.Replace(text, string.Empty);

		text = string.Join(
			"\r\n\r\n",
			text.Split(new[] { '\r', '\n', '\r', '\n' }, StringSplitOptions.RemoveEmptyEntries)
		);

		if (text == null) {
			return null;
		}
		
		return text.Trim();
	}
}

​x
 
using System;
using System.Text.RegularExpressions;
                    
public class Program {
    public static void Main() {
        var html = "<html><head></head><body><p>Hi try this link: <a href='https://example.com/Test'>Test</a><p></body></html>";
        var plainText = HtmlToPlainText(html);
        Console.WriteLine(plainText);
    }
    
    private static string HtmlToPlainText(string html) {
        /* Todo: Rob - Find a safe method to strip the HTML down to plain text */
        /* Ref: https://stackoverflow.com/a/16407272 */
​
        const string
            tagWhiteSpace =
            @"(>|$)(\W|\n|\r)+<"; //matches one or more (white space or line breaks) between '>' and '<'
        const string
            stripFormatting =
            @"<[^>]*(>|$)"; //match any character between '<' and '>', even when end tag is missing
        const string
            lineBreak =
            @"<(br|BR|/div)\s{0,1}\/{0,1}>"; //matches: <br>,<br/>,<br />,<BR>,<BR/>,<BR /> ALSO matches </div> as Exchange uses it for line breaks
​
        var lineBreakRegex = new Regex(lineBreak, RegexOptions.Multiline);
        var stripFormattingRegex = new Regex(stripFormatting, RegexOptions.Multiline);
        var tagWhiteSpaceRegex = new Regex(tagWhiteSpace, RegexOptions.Multiline);
​
        var headStartIndex = html.IndexOf("<head>");
        var headEndIndex = html.IndexOf("</head>") + 7;
​
        //Remove the head
        var text = string.Concat(html.Substring(0, headStartIndex), html.Substring(headEndIndex));
        //var text = $"{html.Substring(0, headStartIndex)}{html.Substring(headEndIndex)}";
        //Decode html specific characters
        text = System.Net.WebUtility.HtmlDecode(text);
​
        //Remove tag whitespace/line breaks
        text = tagWhiteSpaceRegex.Replace(text, "><");
        //Replace <br /> with line breaks
        //text = lineBreakRegex.Replace(text, Environment.NewLine);
​
        text = (text
                .Replace("p>", "p>\r\n")
                .Replace("a>", "a>\r\n")
               );
​
        //Strip formatting
        text = stripFormattingRegex.Replace(text, string.Empty);
​
        text = string.Join(
            "\r\n\r\n",
            text.Split(new[] { '\r', '\n', '\r', '\n' }, StringSplitOptions.RemoveEmptyEntries)
        );
​
        if (text == null) {
            return null;
        }
        
        return text.Trim();
    }
}

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