using System;
using System.IO;
using System.ComponentModel;
using System.ComponentModel.Design;
using System.Collections;
using System.Diagnostics;
using System.Drawing;
using System.Windows.Forms;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Binary;
using Microsoft.Win32; // Registry
using System.Runtime.InteropServices;
using System.Reflection;
using System.Text;

namespace DragAndDropFileControlLibrary {

  [DefaultEventAttribute("FileDropped")]
  public partial class DragAndDropFileComponent : Component, ISupportInitialize, IMessageFilter {

    [DllImport("shell32.dll")]
    static extern long DragAcceptFiles(IntPtr hwnd, Boolean accept);

    [DllImport("shell32.dll")]
    static extern int DragQueryFile(IntPtr hdrop, int iFile, StringBuilder fileName, int fileSize);

    [DllImport("shell32.dll")]
    static extern void DragFinish(IntPtr hdrop);

    const int WM_DROPFILES = 563;

    private Form host;

    public DragAndDropFileComponent() { }
    public DragAndDropFileComponent(IContainer container)
      : this() {
      // Integrate with container
      if( container != null ) container.Add(this);
    }

    #region ISupportInitialize Members
    public void BeginInit() { }

    public void EndInit() {
      // Filter file drop associated messages
      Application.AddMessageFilter(this);
      DragAcceptFiles(this.host.Handle, true);
    }

    #endregion

    // From Ian Griffiths (thanks, Ian!)
    [Browsable(false)]
    public Form HostingForm {
      get {
        if( (host == null) && this.DesignMode ) {
          // See if we're being hosted in VS.NET (or something similar)
          IDesignerHost designer = this.GetService(typeof(IDesignerHost)) as IDesignerHost;
          if( designer != null ) host = designer.RootComponent as Form;
        }

        return host;
      }
      set {
        // Cache the hosting form
        host = value;
      }
    }

    [Category("Action")]
    [Description("Occurs when a file is dropped onto the host form.")]
    public event FileDroppedEventHandler FileDropped;

    public bool PreFilterMessage(ref Message m) {

      if( m.Msg == WM_DROPFILES ) {

        // This code handles multiple dropped files.
        int filecount = DragQueryFile(m.WParam, -1, null, 0);
        
        // Extract files
        if( filecount > 0 ) {
          string[] filenames = new string[filecount];
          for( int i = 0; i < filecount; i++ ) {
            StringBuilder sb = new StringBuilder(256);
            DragQueryFile(m.WParam, i, sb, 256);
            filenames[i] = sb.ToString();
            
          }
          // Process files
          HandleDroppedFiles(filenames);
        }

        // Release system allocated memory
        DragFinish(m.WParam);

        return true;
      }

      return false;
    }

    public void HandleDroppedFiles(string[] filenames) {
      FileDroppedEventArgs e = new FileDroppedEventArgs(filenames);
      OnFileDropped(e);
    }

    protected virtual void OnFileDropped(FileDroppedEventArgs e) {
      if( FileDropped != null ) {
        FileDropped(this, e);
      }
    }
  }
}