Converting Arabic numerals to Arabic/Persian numbers in html file

I am trying to convert the plain text Arabic Numerals into Eastern Arabic digits. So basically taking 1 2 3... and converting them into ١‎ ٢‎ ٣‎.... The function converts all numbers, including any numbers contained within tags, i.e. H1.

 private void LoadHtmlFile(object sender, EventArgs e)
        {
            var htmlfile = "<html><body><h1>i was born in 1988</h1></body></html>".ToArabicNumber(); ;
            webBrowser1.DocumentText=htmlfile;
        }


    }
    public static class StringHelper
    {
        public static string ToArabicNumber(this string str)
        {
            if (string.IsNullOrEmpty(str)) return "";
            char[] chars;
            chars = str.ToCharArray();
            for (int i = 0; i < str.Length; i++)
            {
                if (str[i] >= '0' && str[i] <= '9')
                {
                    chars[i] += (char)1728;
                }
            }
            return new string(chars);
        }
    }

I also tried targeting only numbers in InnerText, but it also did not work. The code below changes tag numbers as well.

private void LoadHtmlFile(object sender, EventArgs e)
        {
            var htmlfile = "<html><body><h1>i was born in 1988</h1></body></html>" ;
            webBrowser1.DocumentText=htmlfile;
        }

        private void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
        {
            webBrowser1.Document.Body.InnerText = webBrowser1.Document.Body.InnerText.ToArabicNumber();
        }

Any suggestions?

Solution

You can use a regular expression to find the parts of the HTML that are between '>' and '<' characters, and operate on those. This will prevent the code from processing the tag names and attributes (style, etc).

// Convert all English digits in a string to Arabic digit equivalents
public static string ToArabicNums(string src)
{
    const string digits = "۰۱۲۳۴۵۶۷۸۹";
    return string.Join("", 
        src.Select(c => c >= '0' && c <= '9' ? digits[((int)c - (int)'0')] : c)
    );
}

// Convert all English digits in the text segments of an HTML 
// document to Arabic digit equivalents
public static string ToArabicNumsHtml(string src)
{
    string res = src;

    Regex re = new Regex(@">(.*?)<");

    // get Regex matches 
    MatchCollection matches = re.Matches(res);

    // process in reverse in case transformation function returns 
    // a string of a different length
    for (int i = matches.Count - 1; i >= 0; --i)
    {
        Match nxt = matches[i];
        if (nxt.Groups.Count == 2 && nxt.Groups[1].Length > 0)
        {
            Group g = nxt.Groups[1];
            res = res.Substring(0, g.Index) + ToArabicNums(g.Value) +
                res.Substring(g.Index + g.Length);
    }

    return res;
}

This isn't perfect, since it doesn't check at all for HTML character specifiers outside of the tags, such as the construct &#<digits>; (۱ for ۱, etc)to specify a character by Unicode value, and will replace the digits in these. It also won't process any extra text before the first tag or after the last tag.

Sample:

Calling: ToArabicNumsHtml("<html><body><h1>I was born in 1988</h1></body></html>")
Result: "<html><body><h1>I was born in ۱۹۸۸</h1></body></html>"

Use whatever code you prefer in ToArabicNums to do the actual transformation, or generalize it by passing in a transformation function.