tbf/AppDiagnostic/LogColorizer.cs

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Windows.Forms;

namespace AppDiagnostic
{
    public static class LogColorizer
    {
        public static void Apply(RichTextBox target, int startIndex, int length, string text, IEnumerable<LogColorRule> rules, Font regularFont, Font boldFont)
        {
            if (target == null || length <= 0)
            {
                return;
            }

            target.Select(startIndex, length);
            target.SelectionColor = target.ForeColor;
            target.SelectionBackColor = target.BackColor;
            target.SelectionFont = regularFont;

            foreach (LogColorRule rule in rules)
            {
                if (rule == null || !rule.Enabled || string.IsNullOrEmpty(rule.Pattern))
                {
                    continue;
                }

                int searchIndex = 0;
                while (searchIndex < text.Length)
                {
                    int matchIndex = text.IndexOf(rule.Pattern, searchIndex, StringComparison.OrdinalIgnoreCase);
                    if (matchIndex < 0)
                    {
                        break;
                    }

                    target.Select(startIndex + matchIndex, rule.Pattern.Length);
                    target.SelectionColor = rule.ForeColor;
                    target.SelectionBackColor = rule.UseBackColor ? rule.BackColor : target.BackColor;
                    target.SelectionFont = rule.Bold ? boldFont : regularFont;
                    searchIndex = matchIndex + rule.Pattern.Length;
                }
            }
        }
    }
}