// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Printing;
 
namespace System.Windows.Forms;
 
/// <summary>
///  Provides data for the <see cref="Control.Paint"/> event.
/// </summary>
/// <remarks>
///  <para>
///   Please keep this class consistent with <see cref="PrintPageEventArgs"/>.
///  </para>
/// </remarks>
public partial class PaintEventArgs : EventArgs, IDisposable, IDeviceContext, IGraphicsHdcProvider, IHdcContext
{
    private readonly DrawingEventArgs _event;
 
    /// <remarks>
    ///  <para>
    ///   This is only needed for <see cref="ResetGraphics"/> callers and applies in the following places:
    ///  </para>
    ///  <list type="number">
    ///   <item><description>In <see cref="Control.WmPaint(ref Message)"/> when we are painting the background.</description></item>
    ///   <item><description>In <see cref="Control.WmPrintClient(ref Message)"/>.</description></item>
    ///  </list>
    ///  <para>
    ///   We can potentially optimize further by skipping the save when we only use <see cref="GraphicsInternal"/>
    ///   as we shouldn't have messed with the clipping there.
    ///  </para>
    /// </remarks>
    private GraphicsState? _savedGraphicsState;
 
    public PaintEventArgs(Graphics graphics, Rectangle clipRect) : this(
        graphics,
        clipRect,
        // If Graphics comes in on the public constructor we don't know that it has no transform or clip
        flags: DrawingEventFlags.GraphicsStateUnclean)
    {
    }
 
    internal PaintEventArgs(
        PaintEventArgs e,
        Rectangle clipRect)
    {
        HDC hdc = e.HDC;
        _event = hdc.IsNull
            ? new DrawingEventArgs(e.GraphicsInternal, clipRect, e._event.Flags)
            : new DrawingEventArgs(hdc, clipRect, e._event.Flags);
    }
 
    internal PaintEventArgs(
        Graphics graphics,
        Rectangle clipRect,
        DrawingEventFlags flags)
    {
        _event = new DrawingEventArgs(graphics, clipRect, flags);
        SaveStateIfNeeded(graphics);
    }
 
    /// <summary>
    ///  Internal version of constructor for performance. We try to avoid getting the graphics object until needed.
    /// </summary>
    internal PaintEventArgs(
        HDC hdc,
        Rectangle clipRect,
        DrawingEventFlags flags = DrawingEventFlags.CheckState)
    {
        _event = new DrawingEventArgs(hdc, clipRect, flags);
    }
 
    ~PaintEventArgs() => Dispose(false);
 
    /// <summary>
    ///  Gets the rectangle in which to paint.
    /// </summary>
    public Rectangle ClipRectangle => _event.ClipRectangle;
 
    /// <summary>
    ///  Gets the <see cref="Drawing.Graphics"/> object used to paint.
    /// </summary>
    public Graphics Graphics => _event.Graphics;
 
    /// <summary>
    ///  Disposes of the resources (other than memory) used by the <see cref="PaintEventArgs"/>.
    /// </summary>
    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }
 
    protected virtual void Dispose(bool disposing) => _event?.Dispose(disposing);
 
    /// <summary>
    ///  If ControlStyles.AllPaintingInWmPaint, we call this method after OnPaintBackground so it appears to
    ///  OnPaint that it's getting a fresh Graphics. We want to make sure AllPaintingInWmPaint is purely an
    ///  optimization, and doesn't change behavior, so we need to make sure any clipping regions established in
    ///  OnPaintBackground don't apply to OnPaint.
    /// </summary>
    internal void ResetGraphics()
    {
        Graphics? graphics = _event.GetGraphics(create: false);
        if (_event.Flags.HasFlag(DrawingEventFlags.SaveState) && graphics is not null)
        {
            if (_savedGraphicsState is not null)
            {
                graphics.Restore(_savedGraphicsState);
                _savedGraphicsState = null;
            }
            else
            {
                Debug.Fail("Called ResetGraphics more than once?");
            }
        }
    }
 
    private void SaveStateIfNeeded(Graphics graphics)
        => _savedGraphicsState = _event.Flags.HasFlag(DrawingEventFlags.SaveState) ? graphics.Save() : default;
 
    /// <summary>
    ///  For internal use to improve performance. DO NOT use this method if you modify the Graphics Clip or Transform.
    /// </summary>
    internal Graphics GraphicsInternal => _event.GetOrCreateGraphicsInternal(SaveStateIfNeeded);
 
    /// <summary>
    ///  Returns the <see cref="HDC"/> the event was created off of, if any.
    /// </summary>
    internal HDC HDC => _event.HDC;
 
    IntPtr IDeviceContext.GetHdc() => Graphics?.GetHdc() ?? IntPtr.Zero;
    HDC IHdcContext.GetHdc() => (HDC)((IDeviceContext)this).GetHdc();
    void IDeviceContext.ReleaseHdc() => Graphics?.ReleaseHdc();
    void IHdcContext.ReleaseHdc() => ((IDeviceContext)this).ReleaseHdc();
    IGraphics? IGraphicsHdcProvider.GetGraphics(bool createIfNeeded) => _event.GetGraphics(createIfNeeded);
    HDC IGraphicsHdcProvider.GetHdc() => _event.GetHDC();
    bool IGraphicsHdcProvider.IsGraphicsStateClean => _event.IsStateClean;
}