using System;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace FastReport.Controls
{
    internal sealed class ExtListView : ListView
    {
        public event EventHandler FetchMoreItems;

        private void OnScroll()
        {
            var scrollInfo = GetFullScrollInfo(false);
            if (scrollInfo.nMax - scrollInfo.nPage < scrollInfo.nPos)
            {
                FetchMoreItems?.Invoke(this, EventArgs.Empty);
            }
        }

        protected override void WndProc(ref Message m)
        {
            base.WndProc(ref m);
            if (m.Msg == 0x115 || (m.Msg == 0x114) || (m.Msg == 0x020A))
            {
                //Trap WM_VSCROLL
                this.OnScroll();
            }
        }

        private const int SIF_RANGE = 0x0001;
        private const int SIF_PAGE = 0x0002;
        private const int SIF_POS = 0x0004;
        private const int SIF_TRACKPOS = 0x0010;
        private const int SIF_ALL = (SIF_RANGE | SIF_PAGE | SIF_POS | SIF_TRACKPOS);
        private const int SB_HORZ = 0;
        private const int SB_VERT = 1;

        [StructLayout(LayoutKind.Sequential)]
        private class SCROLLINFO
        {
            public int cbSize = Marshal.SizeOf(typeof(SCROLLINFO));
            public int fMask;
            public int nMin;
            public int nMax;
            public int nPage;
            public int nPos;
            public int nTrackPos;
        }

        [DllImport("user32.dll", CharSet = CharSet.Auto, ExactSpelling = true)]
        private static extern bool GetScrollInfo(IntPtr hWnd, int fnBar, SCROLLINFO scrollInfo);

        private SCROLLINFO GetFullScrollInfo(bool horizontalBar)
        {
            int fnBar = (horizontalBar ? SB_HORZ : SB_VERT);

            SCROLLINFO scrollInfo = new SCROLLINFO();
            scrollInfo.fMask = SIF_ALL;
            if (GetScrollInfo(Handle, fnBar, scrollInfo))
                return scrollInfo;
            else
                return null;
        }
    }
}