PrintCustomSelectionTextBox

//https://stackoverflow.com/questions/61099950/how-to-textbox-inputs-of-custom-format-in-c?noredirect=1#comment108120129_61099950
//April 4, 2020

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Windows.Forms;
using System.Text.RegularExpressions;
using System.Drawing;

namespace JQ
{
    [DesignerCategory("Code")]
    class PrintPageRangeTB : TextBox
    {
        #region Private Fields

        private const int WM_PAINT = 0xF;

        #endregion

        #region Constructors

        public PrintPageRangeTB() : base() { }

        #endregion

        #region Properties

        public int Min { get; set; } = 0;
        public int Max { get; set; } = 1000;
        public string CueText { get; set; } = "e.g. 1-5, 8, 15-20";
        public bool ShowCue { get; set; } = true;
        [Browsable(false)]
        public IEnumerable<int> Pages
        {
            get
            {
                var pages = new HashSet<int>();

                if (IsValidInput())
                {
                    var pat = @"(\d+)-(\d+)";
                    var parts = Text.Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries);

                    foreach(var part in parts)
                    {
                        var m = Regex.Match(part, pat);

                        if (m != null && m.Groups.Count == 3)
                        {
                            var x = int.Parse(m.Groups[1].Value);
                            var y = int.Parse(m.Groups[2].Value);

                            for (var i = Math.Min(x, y); i <= Math.Max(x, y); i++)
                                pages.Add(i);
                        }
                        else if (int.TryParse(part.Replace("-", ""), out int v))
                            pages.Add(v);
                    }
                }
                return pages.OrderBy(x => x);
            }
        }

        [Browsable(false)]
        public bool IsValidPageRange => TextLength > 0 && IsValidInput();

        #endregion

        #region Base

        protected override void OnKeyPress(KeyPressEventArgs e)
        {
            base.OnKeyPress(e);
            if (!char.IsControl(e.KeyChar) &&
                !char.IsDigit(e.KeyChar) &&
                e.KeyChar != '-' &&
                e.KeyChar != ',')
                e.Handled = true;
        }

        protected override void OnTextChanged(EventArgs e)
        {
            base.OnTextChanged(e);

            if (!IsValidInput())
                SendKeys.SendWait("{BS}");
        }

        protected override void WndProc(ref Message m)
        {
            base.WndProc(ref m);

            if (m.Msg == WM_PAINT)
            {
                if (!Focused &&
                    string.IsNullOrEmpty(Text) &&
                    ShowCue &&
                    !string.IsNullOrEmpty(CueText))
                {
                    using (var graphics = CreateGraphics())
                    {
                        TextRenderer.DrawText(
                            graphics,
                            CueText,
                            Font,
                            ClientRectangle,
                            SystemColors.GrayText,
                            Enabled ? BackColor : SystemColors.Control,
                            TextFormatFlags.Top | TextFormatFlags.Left);
                    }
                }
            }
        }

        #endregion

        #region Private Methods

        private bool IsValidInput()
        {
            var parts = Text.Split(new[] { '-', ',' }, StringSplitOptions.RemoveEmptyEntries);
            var pages = parts.Where(x => int.TryParse(x, out _)).Select(x => int.Parse(x));

            return !parts.Any(x => x.Length > 1 && x.StartsWith("0")) &&
                !Regex.IsMatch(Text, @"^-|^,|--|,,|,-|-,|\d+-\d+-|-\d+-") &&
                !pages.Any(x => x < Min || x > Max);
        }

        #endregion
    }

        #region Public Methods

        public string PagesString(string separator = ", ") =>
            string.Join(separator, Pages);

        #endregion
}