using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.Maui.ApplicationModel;
using Microsoft.Maui.Controls.Internals;
using Microsoft.Maui.Graphics;
using Microsoft.Maui.Handlers;
 
namespace Microsoft.Maui.Controls
{
	/// <include file="../../docs/Microsoft.Maui.Controls/Application.xml" path="Type[@FullName='Microsoft.Maui.Controls.Application']/Docs/*" />
	public partial class Application : Element, IResourcesProvider, IApplicationController, IElementConfiguration<Application>, IVisualTreeElement, IApplication
	{
		readonly WeakEventManager _weakEventManager = new WeakEventManager();
		readonly Lazy<PlatformConfigurationRegistry<Application>> _platformConfigurationRegistry;
 
#pragma warning disable CS0612 // Type or member is obsolete
		readonly Lazy<IResourceDictionary?> _systemResources;
#pragma warning restore CS0612 // Type or member is obsolete
 
		IAppIndexingProvider? _appIndexProvider;
		bool _isStarted;
 
		static readonly SemaphoreSlim SaveSemaphore = new SemaphoreSlim(1, 1);
 
		/// <include file="../../docs/Microsoft.Maui.Controls/Application.xml" path="//Member[@MemberName='.ctor']/Docs/*" />
		public Application() : this(true)
		{
		}
 
		internal Application(bool setCurrentApplication)
		{
			if (setCurrentApplication)
				SetCurrentApplication(this);
 
#pragma warning disable CS0612 // Type or member is obsolete
			_systemResources = new Lazy<IResourceDictionary?>(() =>
			{
				var systemResources = DependencyService.Get<ISystemResourcesProvider>().GetSystemResources();
				if (systemResources is not null)
				{
					systemResources.ValuesChanged += OnParentResourcesChanged;
				}
				return systemResources;
			});
#pragma warning restore CS0612 // Type or member is obsolete
 
			_platformConfigurationRegistry = new Lazy<PlatformConfigurationRegistry<Application>>(() => new PlatformConfigurationRegistry<Application>(this));
 
			_platformAppTheme = AppInfo.RequestedTheme;
			_lastAppTheme = _platformAppTheme;
		}
 
		/// <include file="../../docs/Microsoft.Maui.Controls/Application.xml" path="//Member[@MemberName='Quit']/Docs/*" />
		public void Quit()
		{
			Handler?.Invoke(ApplicationHandler.TerminateCommandKey);
		}
 
		/// <include file="../../docs/Microsoft.Maui.Controls/Application.xml" path="//Member[@MemberName='AppLinks']/Docs/*" />
		public IAppLinks AppLinks
		{
			get
			{
				if (_appIndexProvider == null)
					throw new ArgumentException("No IAppIndexingProvider was provided");
				if (_appIndexProvider.AppLinks == null)
					throw new ArgumentException("No AppLinks implementation was found, if in Android make sure you installed the Microsoft.Maui.Controls.AppLinks");
				return _appIndexProvider.AppLinks;
			}
		}
 
		/// <include file="../../docs/Microsoft.Maui.Controls/Application.xml" path="//Member[@MemberName='SetCurrentApplication']/Docs/*" />
		[EditorBrowsable(EditorBrowsableState.Never)]
		public static void SetCurrentApplication(Application value) => Current = value;
 
		/// <include file="../../docs/Microsoft.Maui.Controls/Application.xml" path="//Member[@MemberName='Current']/Docs/*" />
		public static Application? Current { get; set; }
 
		Page? _singleWindowMainPage;
 
		/// <include file="../../docs/Microsoft.Maui.Controls/Application.xml" path="//Member[@MemberName='MainPage']/Docs/*" />
		public Page? MainPage
		{
			[Obsolete("This property has been deprecated. For single-window applications, use Windows[0].Page. For multi-window applications, identify and use the appropriate Window object to access the desired Page. Additionally, each element features a Window property, accessible when it's part of the current window.")]
			get
			{
				if (Windows.Count == 0)
					return _singleWindowMainPage;
 
				return Windows[0].Page;
			}
			[Obsolete("This property is deprecated. Initialize your application by overriding Application.CreateWindow rather than setting MainPage. To modify the root page in an active application, use Windows[0].Page for applications with a single window. For applications with multiple windows, use Application.Windows to identify and update the root page on the correct window.  Additionally, each element features a Window property, accessible when it's part of the current window.")]
			set
			{
				if (MainPage == value)
					return;
 
				OnPropertyChanging();
 
				if (MainPage is not null)
				{
					((IElementDefinition)this).RemoveResourcesChangedListener(MainPage.OnParentResourcesChanged);
				}
 
				_singleWindowMainPage = value;
 
				if (value is not null)
				{
					value.OnResourcesChanged(this.GetMergedResources());
					((IElementDefinition)this).AddResourcesChangedListener(value.OnParentResourcesChanged);
				}
 
				if (Windows.Count == 1)
				{
					Windows[0].Page = value;
				}
 
				OnPropertyChanged();
			}
		}
 
		/// <include file="../../docs/Microsoft.Maui.Controls/Application.xml" path="//Member[@MemberName='NavigationProxy']/Docs/*" />
		[EditorBrowsable(EditorBrowsableState.Never)]
		public NavigationProxy? NavigationProxy { get; private set; }
 
		internal IResourceDictionary? SystemResources => _systemResources.Value;
 
		/// <include file="../../docs/Microsoft.Maui.Controls/Application.xml" path="//Member[@MemberName='SetAppIndexingProvider']/Docs/*" />
		[EditorBrowsable(EditorBrowsableState.Never)]
		public void SetAppIndexingProvider(IAppIndexingProvider provider)
		{
			_appIndexProvider = provider;
		}
 
		ResourceDictionary? _resources;
		bool IResourcesProvider.IsResourcesCreated => _resources != null;
 
		/// <include file="../../docs/Microsoft.Maui.Controls/Application.xml" path="//Member[@MemberName='Resources']/Docs/*" />
		public ResourceDictionary Resources
		{
			get
			{
				if (_resources != null)
					return _resources;
 
				_resources = new ResourceDictionary();
				((IResourceDictionary)_resources).ValuesChanged += OnResourcesChanged;
				return _resources;
			}
			set
			{
				if (_resources == value)
					return;
				OnPropertyChanging();
				if (_resources != null)
					((IResourceDictionary)_resources).ValuesChanged -= OnResourcesChanged;
				_resources = value;
				OnResourcesChanged(value);
				if (_resources != null)
					((IResourceDictionary)_resources).ValuesChanged += OnResourcesChanged;
				OnPropertyChanged();
			}
		}
 
		/// <include file="../../docs/Microsoft.Maui.Controls/Application.xml" path="//Member[@MemberName='UserAppTheme']/Docs/*" />
		public AppTheme UserAppTheme
		{
			get => _userAppTheme;
			set
			{
				if (_userAppTheme == value)
					return;
 
				_userAppTheme = value;
 
				TriggerThemeChangedActual();
			}
		}
 
		public AppTheme PlatformAppTheme
		{
			get => _platformAppTheme;
			private set
			{
				if (_platformAppTheme == value)
					return;
 
				_platformAppTheme = value;
 
				TriggerThemeChangedActual();
			}
		}
 
		/// <include file="../../docs/Microsoft.Maui.Controls/Application.xml" path="//Member[@MemberName='RequestedTheme']/Docs/*" />
		public AppTheme RequestedTheme =>
			UserAppTheme != AppTheme.Unspecified
				? UserAppTheme
				: PlatformAppTheme;
 
		static Color? _accentColor;
		public static Color? AccentColor
		{
			get => _accentColor ??= GetAccentColor();
			set => _accentColor = value;
		}
 
 
		static Color? GetAccentColor()
		{
#if WINDOWS
			if (UI.Xaml.Application.Current.Resources.TryGetValue("SystemColorControlAccentBrush", out object accent) &&
				accent is UI.Xaml.Media.SolidColorBrush scb)
			{
				return scb.ToColor();
			}
 
			return null;
#elif ANDROID
			var context = (Current?.Windows?.Count > 0 && Current.Windows[0].MauiContext is not null) ? Current.Windows[0].MauiContext.Context : Current?.FindMauiContext()?.Context;
			if (context is not null)
				return context?.GetAccentColor();
 
			return null;
#elif IOS
			return ColorExtensions.AccentColor.ToColor();
#else
			return Color.FromRgba(50, 79, 133, 255);
#endif
		}
 
		public event EventHandler<AppThemeChangedEventArgs> RequestedThemeChanged
		{
			add => _weakEventManager.AddEventHandler(value);
			remove => _weakEventManager.RemoveEventHandler(value);
		}
 
		bool _themeChangedFiring;
		AppTheme _platformAppTheme = AppTheme.Unspecified;
		AppTheme _lastAppTheme = AppTheme.Unspecified;
		AppTheme _userAppTheme = AppTheme.Unspecified;
 
		void TriggerThemeChangedActual()
		{
			var newTheme = RequestedTheme;
 
			// On iOS the event is triggered more than once.
			// To minimize that for us, we only do it when the theme actually changes and it's not currently firing
			if (_themeChangedFiring || newTheme == _lastAppTheme)
				return;
 
			try
			{
				_themeChangedFiring = true;
				_lastAppTheme = newTheme;
 
				OnParentResourcesChanged([new KeyValuePair<string, object>(AppThemeBinding.AppThemeResource, newTheme)]);
				_weakEventManager.HandleEvent(this, new AppThemeChangedEventArgs(newTheme), nameof(RequestedThemeChanged));
				OnPropertyChanged(nameof(UserAppTheme));
			}
			finally
			{
				_themeChangedFiring = false;
			}
		}
 
		public event EventHandler<ModalPoppedEventArgs>? ModalPopped;
 
		public event EventHandler<ModalPoppingEventArgs>? ModalPopping;
 
		public event EventHandler<ModalPushedEventArgs>? ModalPushed;
 
		public event EventHandler<ModalPushingEventArgs>? ModalPushing;
 
		internal void NotifyOfWindowModalEvent(EventArgs eventArgs)
		{
			switch (eventArgs)
			{
				case ModalPoppedEventArgs poppedEvents:
					ModalPopped?.Invoke(this, poppedEvents);
					break;
				case ModalPoppingEventArgs poppingEvents:
					ModalPopping?.Invoke(this, poppingEvents);
					break;
				case ModalPushedEventArgs pushedEvents:
					ModalPushed?.Invoke(this, pushedEvents);
					break;
				case ModalPushingEventArgs pushingEvents:
					ModalPushing?.Invoke(this, pushingEvents);
					break;
				default:
					break;
			}
		}
 
		public event EventHandler<Page>? PageAppearing;
 
		public event EventHandler<Page>? PageDisappearing;
 
		/// <inheritdoc/>
		public IPlatformElementConfiguration<T, Application> On<T>() where T : IConfigPlatform
		{
			return _platformConfigurationRegistry.Value.On<T>();
		}
 
		protected virtual void OnAppLinkRequestReceived(Uri uri)
		{
		}
 
		protected override void OnParentSet()
		{
			throw new InvalidOperationException("Setting a Parent on Application is invalid.");
		}
 
		protected virtual void OnResume()
		{
		}
 
		protected virtual void OnSleep()
		{
		}
 
		protected virtual void OnStart()
		{
		}
 
		internal static void ClearCurrent() => Current = null;
 
		internal static bool IsApplicationOrNull(object? element) =>
			element == null || element is IApplication;
 
		internal static bool IsApplicationOrWindowOrNull(object? element) =>
			element == null || element is IApplication || element is IWindow;
 
		internal override void OnParentResourcesChanged(IEnumerable<KeyValuePair<string, object>> values)
		{
			if (!((IResourcesProvider)this).IsResourcesCreated || Resources.Count == 0)
			{
				base.OnParentResourcesChanged(values);
				return;
			}
 
			var innerKeys = new HashSet<string>(StringComparer.Ordinal);
			var changedResources = new List<KeyValuePair<string, object>>();
			foreach (KeyValuePair<string, object> c in Resources)
				innerKeys.Add(c.Key);
			foreach (KeyValuePair<string, object> value in values)
			{
				if (innerKeys.Add(value.Key))
					changedResources.Add(value);
			}
			OnResourcesChanged(changedResources);
		}
 
		/// <include file="../../docs/Microsoft.Maui.Controls/Application.xml" path="//Member[@MemberName='SendOnAppLinkRequestReceived']/Docs/*" />
		[EditorBrowsable(EditorBrowsableState.Never)]
		public void SendOnAppLinkRequestReceived(Uri uri)
		{
			OnAppLinkRequestReceived(uri);
		}
 
		internal void SendResume()
		{
			if (Current is null)
				Current = this;
 
			OnResume();
		}
 
		internal void SendSleep()
		{
			OnSleep();
		}
 
		internal void SendStart()
		{
			if (_isStarted)
				return;
 
			_isStarted = true;
			OnStart();
		}
 
		internal void OnPageAppearing(Page page)
			=> PageAppearing?.Invoke(this, page);
 
		internal void OnPageDisappearing(Page page)
			=> PageDisappearing?.Invoke(this, page);
 
		protected internal virtual void CleanUp()
		{
			// Unhook everything that's referencing the main page so it can be collected
			// This only comes up if we're disposing of an embedded Forms app, and will
			// eventually go away when we fully support multiple windows
			// TODO MAUI
			//if (_mainPage != null)
			//{
			//	InternalChildren.Remove(_mainPage);
			//	_mainPage.Parent = null;
			//	_mainPage = null;
			//}
 
			NavigationProxy = null;
		}
 
		IReadOnlyList<Maui.IVisualTreeElement> IVisualTreeElement.GetVisualChildren() => this.Windows;
 
		internal const string MauiWindowIdKey = "__MAUI_WINDOW_ID__";
 
		readonly List<Window> _windows = new();
		readonly Dictionary<string, WeakReference<Window>> _requestedWindows = new(StringComparer.Ordinal);
		ILogger<Application>? _logger;
 
		ILogger<Application>? Logger =>
			_logger ??= Handler?.MauiContext?.CreateLogger<Application>();
 
		IReadOnlyList<IWindow> IApplication.Windows => _windows;
 
		public IReadOnlyList<Window> Windows => _windows;
 
		IWindow IApplication.CreateWindow(IActivationState? activationState)
		{
			Window? window = null;
 
			// try get the window that is pending
			if (activationState?.State?.TryGetValue(MauiWindowIdKey, out var requestedWindowId) ?? false)
			{
				if (requestedWindowId != null && _requestedWindows.TryGetValue(requestedWindowId, out var r))
				{
					if (r.TryGetTarget(out var w))
					{
						window = w;
					}
					_requestedWindows.Remove(requestedWindowId);
				}
			}
 
			// create a new one if there is no pending windows
			if (window == null)
			{
				window = CreateWindow(activationState);
 
				if (_singleWindowMainPage != null && window.Page != null && window.Page != _singleWindowMainPage)
					throw new InvalidOperationException($"Both {nameof(MainPage)} was set and {nameof(Application.CreateWindow)} was overridden to provide a page.");
			}
 
			// make sure it is added to the windows list
			if (!_windows.Contains(window))
				AddWindow(window);
 
			return window;
		}
 
		void IApplication.OpenWindow(IWindow window)
		{
			if (window is Window cwindow)
			{
				OpenWindow(cwindow);
			}
		}
 
		void IApplication.CloseWindow(IWindow window)
		{
			Handler?.Invoke(nameof(IApplication.CloseWindow), window);
		}
 
		void IApplication.ActivateWindow(IWindow window)
		{
			if (window is Window cwindow)
			{
				ActivateWindow(cwindow);
			}
		}
 
		internal void RemoveWindow(Window window)
		{
			// Do not attempt to close the "MainPage" window
			if (_singleWindowMainPage != null && window.Page == _singleWindowMainPage)
				return;
 
			// Window was closed, stop tracking it
			if (window is null)
				return;
 
			if (window is NavigableElement ne)
				ne.NavigationProxy.Inner = null;
 
			if (window is Element windowElement)
			{
				RemoveLogicalChild(windowElement);
			}
 
			_windows.Remove(window);
		}
 
		public virtual void OpenWindow(Window window)
		{
			var id = Guid.NewGuid().ToString("n");
			_requestedWindows.Add(id, new WeakReference<Window>(window));
 
			var state = new PersistedState
			{
				[MauiWindowIdKey] = id
			};
 
			Handler?.Invoke(nameof(IApplication.OpenWindow), new OpenWindowRequest(State: state));
		}
 
		public virtual void CloseWindow(Window window)
		{
			Handler?.Invoke(nameof(IApplication.CloseWindow), window);
		}
 
		public virtual void ActivateWindow(Window window)
		{
			Handler?.Invoke(nameof(IApplication.ActivateWindow), window);
		}
 
		void IApplication.ThemeChanged()
		{
			PlatformAppTheme = AppInfo.RequestedTheme;
		}
 
		protected virtual Window CreateWindow(IActivationState? activationState)
		{
			var windowCreator = activationState?.Context.Services.GetService<IWindowCreator>();
			var window = windowCreator?.CreateWindow(this, activationState);
			if (window is not null)
				return window;
 
			if (Windows.Count > 1)
#pragma warning disable CS0618 // Type or member is obsolete
				throw new NotImplementedException($"Either set {nameof(MainPage)} or override {nameof(Application.CreateWindow)}.");
#pragma warning restore CS0618 // Type or member is obsolete
 
			if (Windows.Count > 0)
				return Windows[0];
 
			if (_singleWindowMainPage is not null)
				return new Window(_singleWindowMainPage);
 
#pragma warning disable CS0618 // Type or member is obsolete
			throw new NotImplementedException($"Either set {nameof(MainPage)} or override {nameof(Application.CreateWindow)}.");
#pragma warning restore CS0618 // Type or member is obsolete
		}
 
		internal void AddWindow(Window window)
		{
			_windows.Add(window);
 
			if (window is Element windowElement)
			{
				AddLogicalChild(windowElement);
			}
 
			if (window is NavigableElement ne)
				ne.NavigationProxy.Inner = NavigationProxy;
 
			// Once the window has been attached to the application. 
			// The window will finish propagating events like `Appearing`.
			//
			// I could fire this from 'OnParentSet` inside Window but
			// I'd rather wait until Application is done wiring itself
			// up to the window before triggering any down stream life cycle
			// events.
			window.FinishedAddingWindowToApplication(this);
		}
	}
}