/*
* Copyright (c) 2017 ETH Zürich, Educational Development and Technology (LET)
* 
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*/

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.ComponentModel;
using System.Runtime.InteropServices;
using System.Text;
using SafeExamBrowser.Contracts.WindowsApi;
using SafeExamBrowser.Contracts.WindowsApi.Types;
using SafeExamBrowser.WindowsApi.Constants;

namespace SafeExamBrowser.WindowsApi
{
	public class NativeMethods : INativeMethods
	{
		private ConcurrentDictionary<IntPtr, WinEventDelegate> EventDelegates = new ConcurrentDictionary<IntPtr, WinEventDelegate>();

		public IEnumerable<IntPtr> GetOpenWindows()
		{
			var windows = new List<IntPtr>();
			var success = User32.EnumWindows(delegate (IntPtr hWnd, IntPtr lParam)
			{
				if (hWnd != GetShellWindowHandle() && User32.IsWindowVisible(hWnd) && User32.GetWindowTextLength(hWnd) > 0)
				{
					windows.Add(hWnd);
				}

				return true;
			}, IntPtr.Zero);

			if (!success)
			{
				throw new Win32Exception(Marshal.GetLastWin32Error());
			}

			return windows;
		}

		public uint GetProcessIdFor(IntPtr window)
		{
			User32.GetWindowThreadProcessId(window, out uint processId);

			return processId;
		}

		public IntPtr GetShellWindowHandle()
		{
			return User32.FindWindow("Shell_TrayWnd", null);
		}

		public uint GetShellProcessId()
		{
			var handle = GetShellWindowHandle();
			var threadId = User32.GetWindowThreadProcessId(handle, out uint processId);

			return processId;
		}

		public string GetWindowTitle(IntPtr window)
		{
			var length = User32.GetWindowTextLength(window);

			if (length > 0)
			{
				var builder = new StringBuilder(length);

				User32.GetWindowText(window, builder, length + 1);

				return builder.ToString();
			}

			return string.Empty;
		}

		public RECT GetWorkingArea()
		{
			var workingArea = new RECT();
			var success = User32.SystemParametersInfo(SPI.GETWORKAREA, 0, ref workingArea, SPIF.NONE);

			if (!success)
			{
				throw new Win32Exception(Marshal.GetLastWin32Error());
			}

			return workingArea;
		}

		public void HideWindow(IntPtr window)
		{
			User32.ShowWindow(window, (int)ShowWindowCommand.Hide);
		}

		public void MinimizeAllOpenWindows()
		{
			var handle = GetShellWindowHandle();

			User32.SendMessage(handle, Constant.WM_COMMAND, (IntPtr)Constant.MIN_ALL, IntPtr.Zero);
		}

		public void PostCloseMessageToShell()
		{
			// NOTE: The close message 0x5B4 posted to the shell is undocumented and not officially supported:
			// https://stackoverflow.com/questions/5689904/gracefully-exit-explorer-programmatically/5705965#5705965

			var handle = GetShellWindowHandle();
			var success = User32.PostMessage(handle, 0x5B4, IntPtr.Zero, IntPtr.Zero);

			if (!success)
			{
				throw new Win32Exception(Marshal.GetLastWin32Error());
			}
		}

		public IntPtr RegisterSystemForegroundEvent(Action<IntPtr> callback)
		{
			WinEventDelegate eventProc = (IntPtr hWinEventHook, uint eventType, IntPtr hwnd, int idObject, int idChild, uint dwEventThread, uint dwmsEventTime) =>
			{
				callback(hwnd);
			};

			var handle = User32.SetWinEventHook(Constant.EVENT_SYSTEM_FOREGROUND, Constant.EVENT_SYSTEM_FOREGROUND, IntPtr.Zero, eventProc, 0, 0, Constant.WINEVENT_OUTOFCONTEXT);

			// IMORTANT:
			// Ensures that the callback does not get garbage collected prematurely, as it will be passed to unmanaged code!
			// Not doing so will result in a <c>CallbackOnCollectedDelegate</c> error and subsequent application crash.
			EventDelegates[handle] = eventProc;

			return handle;
		}

		public IntPtr RegisterSystemCaptureStartEvent(Action<IntPtr> callback)
		{
			WinEventDelegate eventProc = (IntPtr hWinEventHook, uint eventType, IntPtr hwnd, int idObject, int idChild, uint dwEventThread, uint dwmsEventTime) =>
			{
				callback(hwnd);
			};

			var handle = User32.SetWinEventHook(Constant.EVENT_SYSTEM_CAPTURESTART, Constant.EVENT_SYSTEM_CAPTURESTART, IntPtr.Zero, eventProc, 0, 0, Constant.WINEVENT_OUTOFCONTEXT);

			// IMORTANT:
			// Ensures that the callback does not get garbage collected prematurely, as it will be passed to unmanaged code!
			// Not doing so will result in a <c>CallbackOnCollectedDelegate</c> error and subsequent application crash.
			EventDelegates[handle] = eventProc;

			return handle;
		}

		public void RestoreWindow(IntPtr window)
		{
			User32.ShowWindow(window, (int)ShowWindowCommand.Restore);
		}

		public void SetWorkingArea(RECT bounds)
		{
			var success = User32.SystemParametersInfo(SPI.SETWORKAREA, 0, ref bounds, SPIF.UPDATEANDCHANGE);

			if (!success)
			{
				throw new Win32Exception(Marshal.GetLastWin32Error());
			}
		}

		public void UnregisterSystemEvent(IntPtr handle)
		{
			var success = User32.UnhookWinEvent(handle);

			if (!success)
			{
				throw new Win32Exception(Marshal.GetLastWin32Error());
			}
			else
			{
				EventDelegates.TryRemove(handle, out WinEventDelegate d);
			}
		}
	}
}