DisplayManager.cs

// These 'using' statements are necessary for file operations, P/Invoke, and JSON serialization.
// Add them at the very top of your file.
using System;
using System.IO;
using System.Runtime.InteropServices;
using System.Text.Json;

// This is the namespace for your project.
namespace MonPro
{
    /// <summary>
    /// Handles saving, loading, and applying monitor display configurations.
    /// All P/Invoke calls and display logic are contained within this class.
    /// </summary>
    public static class DisplayManager // Making this 'static' as it only contains utility methods.
    {
        #region Public Methods (What the UI will use)

        /// <summary>
        /// Queries the current display configuration and saves it to a JSON file.
        /// </summary>
        /// <param name="filePath">The full path for the profile file to be saved.</param>
        public static void SaveCurrentProfile(string filePath)
        {
            // 1. Get the required buffer sizes for the configuration arrays.
            DisplayApi.GetDisplayConfigBufferSizes(
                DisplayApi.QdcFlags.QDC_ONLY_ACTIVE_PATHS,
                out uint pathCount,
                out uint modeCount);

            // 2. Create the arrays to hold the configuration data.
            var pathArray = new DisplayApi.DISPLAYCONFIG_PATH_INFO[pathCount];
            var modeArray = new DisplayApi.DISPLAYCONFIG_MODE_INFO[modeCount];

            // 3. Query the actual display configuration from Windows.
            DisplayApi.QueryDisplayConfig(
                DisplayApi.QdcFlags.QDC_ONLY_ACTIVE_PATHS,
                ref pathCount, pathArray,
                ref modeCount, modeArray,
                IntPtr.Zero);

            // 4. Create a profile object, serialize it to JSON, and write it to a file.
            var profile = new MonitorProfile { PathArray = pathArray, ModeArray = modeArray };
            string json = JsonSerializer.Serialize(profile, new JsonSerializerOptions { WriteIndented = true });
            File.WriteAllText(filePath, json);
        }

        /// <summary>
        /// Loads a display configuration from a JSON file and applies it.
        /// </summary>
        /// <param name="filePath">The full path of the profile file to load.</param>
        public static void LoadProfile(string filePath)
        {
            if (!File.Exists(filePath)) return;

            string json = File.ReadAllText(filePath);
            var profile = JsonSerializer.Deserialize<MonitorProfile>(json);

            if (profile == null) return;

            // Apply the loaded configuration.
            DisplayApi.SetDisplayConfig(
                (uint)profile.PathArray.Length,
                profile.PathArray,
                (uint)profile.ModeArray.Length,
                profile.ModeArray,
                DisplayApi.SdcFlags.SDC_APPLY | DisplayApi.SdcFlags.SDC_TOPOLOGY_CLONE | DisplayApi.SdcFlags.SDC_TOPOLOGY_EXTEND);
        }

        #endregion

        #region Nested Classes (Data Structures)

        /// <summary>
        /// A helper class that defines the structure of our saved JSON profile file.
        /// </summary>
        public class MonitorProfile
        {
            public DisplayApi.DISPLAYCONFIG_PATH_INFO[] PathArray { get; set; }
            public DisplayApi.DISPLAYCONFIG_MODE_INFO[] ModeArray { get; set; }
        }

        #endregion

        #region P/Invoke Definitions (The Core Windows API Logic)

        /// <summary>
        /// This static class holds all the low-level Windows API structures, enums, and function imports.
        /// It's nested here to keep everything neatly organized.
        /// </summary>
        public static class DisplayApi
        {
            [Flags]
            public enum SdcFlags : uint { SDC_TOPOLOGY_INTERNAL = 0x00000001, SDC_TOPOLOGY_CLONE = 0x00000002, SDC_TOPOLOGY_EXTEND = 0x00000004, SDC_TOPOLOGY_EXTERNAL = 0x00000008, SDC_APPLY = 0x00000080 }
            [Flags]
            public enum QdcFlags : uint { QDC_ALL_PATHS = 0x00000001, QDC_ONLY_ACTIVE_PATHS = 0x00000002, QDC_DATABASE_CURRENT = 0x00000004 }
            public enum DISPLAYCONFIG_VIDEO_OUTPUT_TECHNOLOGY : uint { OTHER = 0xFFFFFFFF, HD15 = 0, SVIDEO = 1, COMPOSITE_VIDEO = 2, COMPONENT_VIDEO = 3, DVI = 4, HDMI = 5, LVDS = 6, D_JPN = 8, SDI = 9, DISPLAYPORT_EXTERNAL = 10, DISPLAYPORT_EMBEDDED = 11, UDI_EXTERNAL = 12, UDI_EMBEDDED = 13, SDTVDONGLE = 14, MIRACAST = 15, INTERNAL = 0x80000000, FORCED_UINT32 = 0xFFFFFFFF }
            public enum DISPLAYCONFIG_ROTATION : uint { IDENTITY = 1, ROTATE90 = 2, ROTATE180 = 3, ROTATE270 = 4, FORCED_UINT32 = 0xFFFFFFFF }
            public enum DISPLAYCONFIG_SCALING : uint { IDENTITY = 1, CENTERED = 2, STRETCHED = 3, ASPECTRATIOCENTEREDMAX = 4, CUSTOM = 5, PREFERRED = 128, FORCED_UINT32 = 0xFFFFFFFF }
            public enum DISPLAYCONFIG_SCANLINE_ORDERING : uint { UNSPECIFIED = 0, PROGRESSIVE = 1, INTERLACED = 2, INTERLACED_UPPERFIELDFIRST = INTERLACED, INTERLACED_LOWERFIELDFIRST = 3, FORCED_UINT32 = 0xFFFFFFFF }
            public enum DISPLAYCONFIG_MODE_INFO_TYPE : uint { SOURCE = 1, TARGET = 2, FORCE_UINT32 = 0xFFFFFFFF }

            [StructLayout(LayoutKind.Sequential)] public struct LUID { public long LowPart; public long HighPart; }
            [StructLayout(LayoutKind.Sequential)] public struct POINTL { public long x; public long y; }
            [StructLayout(LayoutKind.Sequential)] public struct RECTL { public int left; public int top; public int right; public int bottom; }
            [StructLayout(LayoutKind.Sequential)] public struct DISPLAYCONFIG_RATIONAL { public uint Numerator; public uint Denominator; }
            [StructLayout(LayoutKind.Sequential)] public struct DISPLAYCONFIG_PATH_SOURCE_INFO { public LUID adapterId; public uint id; public uint modeInfoIdx; public ushort statusFlags; }
            [StructLayout(LayoutKind.Sequential)] public struct DISPLAYCONFIG_SOURCE_MODE { public uint width; public uint height; public DISPLAYCONFIG_PIXEL_FORMAT pixelFormat; public POINTL position; }
            [StructLayout(LayoutKind.Sequential)] public struct DISPLAYCONFIG_TARGET_MODE { public DISPLAYCONFIG_VIDEO_SIGNAL_INFO videoSignalInfo; }
            [StructLayout(LayoutKind.Sequential)] public struct DISPLAYCONFIG_VIDEO_SIGNAL_INFO { public ulong totalSize; public ulong activeSize; public DISPLAYCONFIG_RATIONAL VSyncFreq; public DISPLAYCONFIG_RATIONAL HSyncFreq; public DISPLAYCONFIG_SCANLINE_ORDERING scanLineOrdering; }
            public enum DISPLAYCONFIG_PIXEL_FORMAT : uint { PIXELFORMAT_8BPP = 1, PIXELFORMAT_16BPP = 2, PIXELFORMAT_24BPP = 3, PIXELFORMAT_32BPP = 4, PIXELFORMAT_NONGDI = 5, PIXELFORMAT_FORCE_UINT32 = 0xffffffff }

            [StructLayout(LayoutKind.Sequential)]
            public struct DISPLAYCONFIG_PATH_INFO
            {
                public DISPLAYCONFIG_PATH_SOURCE_INFO sourceInfo;
                public DISPLAYCONFIG_PATH_TARGET_INFO targetInfo;
                public uint flags;
            }

            [StructLayout(LayoutKind.Sequential)]
            public struct DISPLAYCONFIG_PATH_TARGET_INFO
            {
                public LUID adapterId;
                public uint id;
                public uint modeInfoIdx;
                public DISPLAYCONFIG_VIDEO_OUTPUT_TECHNOLOGY outputTechnology;
                public DISPLAYCONFIG_ROTATION rotation;
                public DISPLAYCONFIG_SCALING scaling;
                public DISPLAYCONFIG_RATIONAL refreshRate;
                public DISPLAYCONFIG_SCANLINE_ORDERING scanLineOrdering;
                public bool targetAvailable;
                public uint statusFlags;
            }

            [StructLayout(LayoutKind.Explicit)]
            public struct DISPLAYCONFIG_MODE_INFO_UNION
            {
                [FieldOffset(0)] public DISPLAYCONFIG_TARGET_MODE targetMode;
                [FieldOffset(0)] public DISPLAYCONFIG_SOURCE_MODE sourceMode;
            }

            [StructLayout(LayoutKind.Sequential)]
            public struct DISPLAYCONFIG_MODE_INFO
            {
                public DISPLAYCONFIG_MODE_INFO_TYPE infoType;
                public uint id;
                public LUID adapterId;
                public DISPLAYCONFIG_MODE_INFO_UNION modeInfo;
            }

            [DllImport("user32.dll")]
            public static extern int GetDisplayConfigBufferSizes(QdcFlags flags, out uint numPathArrayElements, out uint numModeInfoArrayElements);

            [DllImport("user32.dll")]
            public static extern int QueryDisplayConfig(QdcFlags flags, ref uint numPathArrayElements, [Out] DISPLAYCONFIG_PATH_INFO[] pathInfoArray, ref uint numModeInfoArrayElements, [Out] DISPLAYCONFIG_MODE_INFO[] modeInfoArray, IntPtr currentTopologyId);

            [DllImport("user32.dll")]
            public static extern int SetDisplayConfig(uint numPathArrayElements, [In] DISPLAYCONFIG_PATH_INFO[] pathInfoArray, uint numModeInfoArrayElements, [In] DISPLAYCONFIG_MODE_INFO[] modeInfoArray, SdcFlags flags);
        }

        #endregion
    }
}