OpenTween.TweenMain.ListTab_DragDrop C# (CSharp) Method

        private void ListTab_DragDrop(object sender, DragEventArgs e)
        {
            if (!e.Data.GetDataPresent(typeof(TabPage))) return;

            _tabDrag = false;
            string tn = "";
            bool bef = false;
            Point cpos = new Point(e.X, e.Y);
            Point spos = ListTab.PointToClient(cpos);
            int i;
            for (i = 0; i < ListTab.TabPages.Count; i++)
            {
                Rectangle rect = ListTab.GetTabRect(i);
                if (rect.Left <= spos.X && spos.X <= rect.Right &&
                    rect.Top <= spos.Y && spos.Y <= rect.Bottom)
                {
                    tn = ListTab.TabPages[i].Text;
                    if (spos.X <= (rect.Left + rect.Right) / 2)
                        bef = true;
                    else
                        bef = false;

                    break;
                }
            }

            //タブのないところにドロップ->最後尾へ移動
            if (string.IsNullOrEmpty(tn))
            {
                tn = ListTab.TabPages[ListTab.TabPages.Count - 1].Text;
                bef = false;
                i = ListTab.TabPages.Count - 1;
            }

            TabPage tp = (TabPage)e.Data.GetData(typeof(TabPage));
            if (tp.Text == tn) return;

            ReOrderTab(tp.Text, tn, bef);
        }