using System.Drawing;
using System.Windows.Forms;

namespace Developpez.Dotnet.Windows.Forms
{
    /// <summary>
    /// Un TabControl dont les onglets peuvent être réordonnés en les glissant avec la souris
    /// </summary>
    public class TabControlEx : TabControl
    {
        /// <summary>
        /// Redéfinit la propriété <see cref="Control.AllowDrop"/>
        /// Renvoie toujours true
        /// </summary>
        public override bool AllowDrop
        {
            get { return true; }
            set { }
        }

        private bool _dragging;

        /// <summary>
        /// Redéfinit la méthode <see cref="Control.OnMouseDown"/>
        /// </summary>
        /// <param name="e">Paramètres de l'évènement</param>
        protected override void OnMouseMove(MouseEventArgs e)
        {
            base.OnMouseMove(e);

            if (!_dragging)
            {
                if (e.Button == MouseButtons.Left)
                {
                    int idx = GetTabIndexAtPosition(e.X, e.Y);
                    if (idx >= 0)
                    {
                        _dragging = true;
                        this.DoDragDrop(idx, DragDropEffects.Move);
                        return;
                    }
                }
            }
            _dragging = false;
        }

        /// <summary>
        /// Redéfinit la méthode <see cref="Control.OnDragEnter"/>
        /// </summary>
        /// <param name="e">Paramètres de l'évènement</param>
        protected override void OnDragEnter(DragEventArgs e)
        {
            base.OnDragEnter(e);

            if (e.Data.GetDataPresent(typeof(int)))
                e.Effect = DragDropEffects.Move;
        }

        /// <summary>
        /// Redéfinit la méthode <see cref="Control.OnDragDrop"/>
        /// </summary>
        /// <param name="e">Paramètres de l'évènement</param>
        protected override void OnDragDrop(DragEventArgs e)
        {
            base.OnDragDrop(e);

            int idxOld;
            if (e.Data.GetDataPresent(typeof(int)))
                idxOld = (int)e.Data.GetData(typeof(int));
            else
                return;

            Point pos = this.PointToClient(new Point(e.X, e.Y));
            int idxNew = GetNewTabIndexForPosition(pos.X, pos.Y);
            if (idxNew < 0)
                idxNew = this.TabCount;

            if (idxNew == idxOld)
                return;

            TabPage tp = this.TabPages[idxOld];
            this.TabPages.Remove(tp);

            if (idxOld < idxNew)
                idxNew--;

            this.TabPages.Insert(idxNew, tp);
            this.SelectedTab = tp;
        }

        private int GetTabIndexAtPosition(int x, int y)
        {
            for (int i = 0; i < this.TabCount; i++)
            {
                Rectangle rect = this.GetTabRect(i);
                if (rect.Contains(x, y))
                {
                    return i;
                }
            }
            return -1;
        }

        private int GetNewTabIndexForPosition(int x, int y)
        {
            int idx = GetTabIndexAtPosition(x, y);
            Rectangle rect = this.GetTabRect(idx);
            if (x < rect.Left + rect.Width / 2)
                return idx;
            return idx + 1;
        }
    }
}