using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Imaging;
using System.Runtime.InteropServices;

namespace SetWallpapers
{
    internal class Program
    {
        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        private static extern Int32 SystemParametersInfo(UInt32 uiAction, UInt32 uiParam, String pvParam, UInt32 fWinIni);

        private static UInt32 SPI_SETDESKWALLPAPER = 20;
        private static UInt32 SPIF_UPDATEINIFILE = 0x1;

        public void SetImage(string filename)
        {
            SystemParametersInfo(SPI_SETDESKWALLPAPER, 0, filename, SPIF_UPDATEINIFILE);
        }

        private static void Main(string[] args)
        {
            var images = new Dictionary<string, Image>
            {
                { @"\\.\DISPLAY1", Image.FromFile(@"C:\Users\Public\Pictures\Sample Pictures\Lighthouse.jpg") },
                { @"\\.\DISPLAY2", Image.FromFile(@"C:\Users\Public\Pictures\Sample Pictures\Jellyfish.jpg") },
                { @"\\.\DISPLAY3", Image.FromFile(@"C:\Users\Public\Pictures\Sample Pictures\Koala.jpg") }
            };

            CreateBackgroundImage(images);

        }

        private static void CreateBackgroundImage(Dictionary<string, Image> imageFiles)
        {
            const string defaultBackgroundFile = @"C:\Users\Public\Pictures\Sample Pictures\DefaultBackground.bmp";

            using (var virtualScreenBitmap = new Bitmap((int)System.Windows.SystemParameters.VirtualScreenWidth, (int)System.Windows.SystemParameters.VirtualScreenHeight))
            {
                using (var virtualScreenGraphic = Graphics.FromImage(virtualScreenBitmap))
                {
                    foreach (var screen in System.Windows.Forms.Screen.AllScreens)
                    {
                        var image = (imageFiles.ContainsKey(screen.DeviceName)) ? imageFiles[screen.DeviceName] : null;

                        var monitorDimensions = screen.Bounds;
                        var width = monitorDimensions.Width;
                        var monitorBitmap = new Bitmap(width, monitorDimensions.Height);
                        var fromImage = Graphics.FromImage(monitorBitmap);
                        fromImage.FillRectangle(SystemBrushes.Desktop, 0, 0, monitorBitmap.Width, monitorBitmap.Height);

                        if (image != null)
                            DrawImageCentered(fromImage, image, new Rectangle(0, 0, monitorBitmap.Width, monitorBitmap.Height));

                        Rectangle rectangle;
                        if (monitorDimensions.Top == 0 && monitorDimensions.Left == 0)
                        {
                            rectangle = monitorDimensions;
                        }
                        else
                        {
                            if ((monitorDimensions.Left < 0 && monitorDimensions.Width > -monitorDimensions.Left) ||
                                (monitorDimensions.Top < 0 && monitorDimensions.Height > -monitorDimensions.Top))
                            {
                                var isMain = (monitorDimensions.Top < 0 && monitorDimensions.Bottom > 0);

                                var left = (monitorDimensions.Left < 0)
                                               ? (int) System.Windows.SystemParameters.VirtualScreenWidth + monitorDimensions.Left
                                               : monitorDimensions.Left;

                                var top = (monitorDimensions.Top < 0)
                                              ? (int) System.Windows.SystemParameters.VirtualScreenHeight + monitorDimensions.Top
                                              : monitorDimensions.Top;

                                Rectangle srcRect;
                                if (isMain)
                                {
                                    rectangle = new Rectangle(left, 0, monitorDimensions.Width, monitorDimensions.Bottom);
                                    srcRect = new Rectangle(0, -monitorDimensions.Top, monitorDimensions.Width, monitorDimensions.Height + monitorDimensions.Top);
                                }
                                else
                                {
                                    rectangle = new Rectangle(0, top, monitorDimensions.Right, monitorDimensions.Height);
                                    srcRect = new Rectangle(-monitorDimensions.Left, 0, monitorDimensions.Width + monitorDimensions.Left,
                                                            monitorDimensions.Height);
                                }

                                virtualScreenGraphic.DrawImage(monitorBitmap, rectangle, srcRect, GraphicsUnit.Pixel);
                                rectangle = new Rectangle(left, top, monitorDimensions.Width, monitorDimensions.Height);
                            }
                            else
                            {
                                var left = (monitorDimensions.Left < 0)
                                               ? (int) System.Windows.SystemParameters.VirtualScreenWidth + monitorDimensions.Left
                                               : monitorDimensions.Left;
                                var top = (monitorDimensions.Top < 0)
                                              ? (int) System.Windows.SystemParameters.VirtualScreenHeight + monitorDimensions.Top
                                              : monitorDimensions.Top;
                                rectangle = new Rectangle(left, top, monitorDimensions.Width, monitorDimensions.Height);
                            }
                        }
                        virtualScreenGraphic.DrawImage(monitorBitmap, rectangle);
                    }

                    virtualScreenBitmap.Save(defaultBackgroundFile, ImageFormat.Bmp);
                }
            }

            SystemParametersInfo(SPI_SETDESKWALLPAPER, 0u, defaultBackgroundFile, SPIF_UPDATEINIFILE);
        }


        private static void DrawImageCentered(Graphics g, Image img, Rectangle monitorRect)
        {
            float heightRatio = (float)monitorRect.Height / (float)img.Height;
            float widthRatio = (float)monitorRect.Width / (float)img.Width;
            int height = monitorRect.Height;
            int width = monitorRect.Width;
            int x = 0;
            int y = 0;

            if (heightRatio > 1f && widthRatio > 1f)
            {
                height = img.Height;
                width = img.Width;
                x = (int)((float)(monitorRect.Width - width) / 2f);
                y = (int)((float)(monitorRect.Height - height) / 2f);
            }
            else
            {
                if (heightRatio < widthRatio)
                {
                    width = (int)((float)img.Width * heightRatio);
                    height = (int)((float)img.Height * heightRatio);
                    x = (int)((float)(monitorRect.Width - width) / 2f);
                }
                else
                {
                    width = (int)((float)img.Width * widthRatio);
                    height = (int)((float)img.Height * widthRatio);
                    y = (int)((float)(monitorRect.Height - height) / 2f);
                }
            }

            Rectangle rect = new Rectangle(x, y, width, height);
            g.DrawImage(img, rect);
        }
    }
}