global using static Terminal.Gui.ConfigurationManager;
global using CM = Terminal.Gui.ConfigurationManager;

using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Text.Json;
using System.Text.Json.Serialization;
using static Terminal.Gui.SpinnerStyle;


#nullable enable

namespace Terminal.Gui;

/// <summary>
/// Provides settings and configuration management for Terminal.Gui applications. 
/// <para>
/// Users can set Terminal.Gui settings on a global or per-application basis by providing JSON formatted configuration files.
/// The configuration files can be placed in at <c>.tui</c> folder in the user's home directory (e.g. <c>C:/Users/username/.tui</c>, 
/// or <c>/usr/username/.tui</c>),
/// the folder where the Terminal.Gui application was launched from (e.g. <c>./.tui</c>), or as a resource
/// within the Terminal.Gui application's main assembly. 
/// </para>
/// <para>
/// Settings are defined in JSON format, according to this schema: 
///	https://gui-cs.github.io/Terminal.Gui/schemas/tui-config-schema.json
/// </para>
/// <para>
/// Settings that will apply to all applications (global settings) reside in files named <c>config.json</c>. Settings 
/// that will apply to a specific Terminal.Gui application reside in files named <c>appname.config.json</c>,
/// where <c>appname</c> is the assembly name of the application (e.g. <c>UICatalog.config.json</c>).
/// </para>
/// Settings are applied using the following precedence (higher precedence settings
/// overwrite lower precedence settings):
/// <para>
///	1. Application configuration found in the users's home directory (<c>~/.tui/appname.config.json</c>) -- Highest precedence 
/// </para>
/// <para>
///	2. Application configuration found in the directory the app was launched from (<c>./.tui/appname.config.json</c>).
/// </para>
/// <para>
///	3. Application configuration found in the applications's resources (<c>Resources/config.json</c>). 
/// </para>
/// <para>
///	4. Global configuration found in the user's home directory (<c>~/.tui/config.json</c>).
/// </para>
/// <para>
///	5. Global configuration found in the directory the app was launched from (<c>./.tui/config.json</c>).
/// </para>
/// <para>
///     6. Global configuration in <c>Terminal.Gui.dll</c>'s resources (<c>Terminal.Gui.Resources.config.json</c>) -- Lowest Precidence.
/// </para>
/// </summary>
public static partial class ConfigurationManager {

	private static readonly string _configFilename = "config.json";

	internal static readonly JsonSerializerOptions _serializerOptions = new JsonSerializerOptions {
		ReadCommentHandling = JsonCommentHandling.Skip,
		PropertyNameCaseInsensitive = true,
		DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
		WriteIndented = true,
		Converters = {
				// We override the standard Rune converter to support specifying Glyphs in
				// a flexible way
				new RuneJsonConverter(),
			},
	};

	/// <summary>
	/// A dictionary of all properties in the Terminal.Gui project that are decorated with the <see cref="SerializableConfigurationProperty"/> attribute.
	/// The keys are the property names pre-pended with the class that implements the property (e.g. <c>Application.UseSystemConsole</c>).
	/// The values are instances of <see cref="ConfigProperty"/> which hold the property's value and the
	/// <see cref="PropertyInfo"/> that allows <see cref="ConfigurationManager"/> to get and set the property's value.
	/// </summary>
	/// <remarks>
	/// Is <see langword="null"/> until <see cref="Initialize"/> is called. 
	/// </remarks>
	internal static Dictionary<string, ConfigProperty>? _allConfigProperties;

	/// <summary>
	/// The backing property for <see cref="Settings"/>. 
	/// </summary>
	/// <remarks>
	/// Is <see langword="null"/> until <see cref="Reset"/> is called. Gets set to a new instance by
	/// deserialization (see <see cref="Load"/>).
	/// </remarks>
	private static SettingsScope? _settings;

	/// <summary>
	/// The root object of Terminal.Gui configuration settings / JSON schema. Contains only properties with the <see cref="SettingsScope"/>
	/// attribute value.
	/// </summary>
	public static SettingsScope? Settings {
		get {
			if (_settings == null) {
				throw new InvalidOperationException ("ConfigurationManager has not been initialized. Call ConfigurationManager.Reset() before accessing the Settings property.");
			}
			return _settings;
		}
		set {
			_settings = value!;
		}
	}

	/// <summary>
	/// The root object of Terminal.Gui themes manager. Contains only properties with the <see cref="ThemeScope"/>
	/// attribute value.
	/// </summary>
	public static ThemeManager? Themes => ThemeManager.Instance;

	/// <summary>
	/// Application-specific configuration settings scope.
	/// </summary>
	[SerializableConfigurationProperty (Scope = typeof (SettingsScope), OmitClassName = true), JsonPropertyName ("AppSettings")]
	public static AppScope? AppSettings { get; set; }

	/// <summary>
	/// The set of glyphs used to draw checkboxes, lines, borders, etc...See also <seealso cref="Terminal.Gui.GlyphDefinitions"/>.
	/// </summary>
	[SerializableConfigurationProperty (Scope = typeof (SettingsScope), OmitClassName = true),
		JsonPropertyName ("Glyphs")]
	public static GlyphDefinitions Glyphs { get; set; } = new GlyphDefinitions ();

	/// <summary>
	/// Initializes the internal state of ConfigurationManager. Nominally called once as part of application
	/// startup to initialize global state. Also called from some Unit Tests to ensure correctness (e.g. Reset()).
	/// </summary>
	internal static void Initialize ()
	{
		_allConfigProperties = new Dictionary<string, ConfigProperty> ();
		_settings = null;

		Dictionary<string, Type> classesWithConfigProps = new Dictionary<string, Type> (StringComparer.InvariantCultureIgnoreCase);
		// Get Terminal.Gui.dll classes

		var types = from assembly in AppDomain.CurrentDomain.GetAssemblies ()
			    from type in assembly.GetTypes ()
			    where type.GetProperties ().Any (prop => prop.GetCustomAttribute (typeof (SerializableConfigurationProperty)) != null)
			    select type;

		foreach (var classWithConfig in types) {
			classesWithConfigProps.Add (classWithConfig.Name, classWithConfig);
		}

		Debug.WriteLine ($"ConfigManager.getConfigProperties found {classesWithConfigProps.Count} classes:");
		classesWithConfigProps.ToList ().ForEach (x => Debug.WriteLine ($"  Class: {x.Key}"));

		foreach (var p in from c in classesWithConfigProps
				  let props = c.Value.GetProperties (BindingFlags.Instance | BindingFlags.Static | BindingFlags.NonPublic | BindingFlags.Public).Where (prop =>
					prop.GetCustomAttribute (typeof (SerializableConfigurationProperty)) is SerializableConfigurationProperty)
				  let enumerable = props
				  from p in enumerable
				  select p) {
			if (p.GetCustomAttribute (typeof (SerializableConfigurationProperty)) is SerializableConfigurationProperty scp) {
				if (p.GetGetMethod (true)!.IsStatic) {
					// If the class name is omitted, JsonPropertyName is allowed. 
					_allConfigProperties!.Add (scp.OmitClassName ? ConfigProperty.GetJsonPropertyName (p) : $"{p.DeclaringType?.Name}.{p.Name}", new ConfigProperty {
						PropertyInfo = p,
						PropertyValue = null
					});
				} else {
					throw new Exception ($"Property {p.Name} in class {p.DeclaringType?.Name} is not static. All SerializableConfigurationProperty properties must be static.");
				}
			}
		}

		_allConfigProperties = _allConfigProperties!.OrderBy (x => x.Key).ToDictionary (x => x.Key, x => x.Value, StringComparer.InvariantCultureIgnoreCase);

		Debug.WriteLine ($"ConfigManager.Initialize found {_allConfigProperties.Count} properties:");
		//_allConfigProperties.ToList ().ForEach (x => Debug.WriteLine ($"  Property: {x.Key}"));

		AppSettings = new AppScope ();
	}

	/// <summary>
	/// Creates a JSON document with the configuration specified. 
	/// </summary>
	/// <returns></returns>
	internal static string ToJson ()
	{
		Debug.WriteLine ($"ConfigurationManager.ToJson()");
		return JsonSerializer.Serialize<SettingsScope> (Settings!, _serializerOptions);
	}

	internal static Stream ToStream ()
	{
		var json = JsonSerializer.Serialize<SettingsScope> (Settings!, _serializerOptions);
		// turn it into a stream
		var stream = new MemoryStream ();
		var writer = new StreamWriter (stream);
		writer.Write (json);
		writer.Flush ();
		stream.Position = 0;
		return stream;
	}

	/// <summary>
	/// Gets or sets whether the <see cref="ConfigurationManager"/> should throw an exception if it encounters 
	/// an error on deserialization. If <see langword="false"/> (the default), the error is logged and printed to the 
	/// console when <see cref="Application.Shutdown"/> is called. 
	/// </summary>
	[SerializableConfigurationProperty (Scope = typeof (SettingsScope))]
	public static bool? ThrowOnJsonErrors { get; set; } = false;

	internal static StringBuilder jsonErrors = new StringBuilder ();

	internal static void AddJsonError (string error)
	{
		Debug.WriteLine ($"ConfigurationManager: {error}");
		jsonErrors.AppendLine (error);
	}

	/// <summary>
	/// Prints any Json deserialization errors that occurred during deserialization to the console.
	/// </summary>
	public static void PrintJsonErrors ()
	{
		if (jsonErrors.Length > 0) {
			Console.WriteLine ($"Terminal.Gui ConfigurationManager encountered the following errors while deserializing configuration files:");
			Console.WriteLine (jsonErrors.ToString ());
		}
	}

	private static void ClearJsonErrors ()
	{
		jsonErrors.Clear ();
	}

	/// <summary>
	/// Called when the configuration has been updated from a configuration file. Invokes the <see cref="Updated"/>
	/// event.
	/// </summary>
	public static void OnUpdated ()
	{
		Debug.WriteLine ($"ConfigurationManager.OnApplied()");
		Updated?.Invoke (null, new ConfigurationManagerEventArgs ());
	}

	/// <summary>
	/// Event fired when the configuration has been updated from a configuration source.  
	/// application.
	/// </summary>
	public static event EventHandler<ConfigurationManagerEventArgs>? Updated;

	/// <summary>
	/// Resets the state of <see cref="ConfigurationManager"/>. Should be called whenever a new app session
	/// (e.g. in <see cref="Application.Init(ConsoleDriver)"/> starts. Called by <see cref="Load"/>
	/// if the <c>reset</c> parameter is <see langword="true"/>.
	/// </summary>
	/// <remarks>
	/// 
	/// </remarks>
	public static void Reset ()
	{
		Debug.WriteLine ($"ConfigurationManager.Reset()");
		if (_allConfigProperties == null) {
			ConfigurationManager.Initialize ();
		}

		ClearJsonErrors ();

		Settings = new SettingsScope ();
		ThemeManager.Reset ();
		AppSettings = new AppScope ();

		// To enable some unit tests, we only load from resources if the flag is set
		if (Locations.HasFlag (ConfigLocations.DefaultOnly)) {
			Settings.UpdateFromResource (typeof (ConfigurationManager).Assembly, $"Terminal.Gui.Resources.{_configFilename}");
		}
		Apply ();
		ThemeManager.Themes? [ThemeManager.SelectedTheme]?.Apply ();
		AppSettings?.Apply ();
	}

	/// <summary>
	/// Retrieves the hard coded default settings from the Terminal.Gui library implementation. Used in development of
	/// the library to generate the default configuration file. Before calling Application.Init, make sure
	/// <see cref="Locations"/> is set to <see cref="ConfigLocations.None"/>.
	/// </summary>
	/// <remarks>
	/// <para>
	/// This method is only really useful when using ConfigurationManagerTests
	/// to generate the JSON doc that is embedded into Terminal.Gui (during development). 
	/// </para>
	/// <para>
	/// WARNING: The <c>Terminal.Gui.Resources.config.json</c> resource has setting definitions (Themes)
	/// that are NOT generated by this function. If you use this function to regenerate <c>Terminal.Gui.Resources.config.json</c>,
	/// make sure you copy the Theme definitions from the existing <c>Terminal.Gui.Resources.config.json</c> file.
	/// </para>		
	/// </remarks>
	internal static void GetHardCodedDefaults ()
	{
		if (_allConfigProperties == null) {
			throw new InvalidOperationException ("Initialize must be called first.");
		}
		Settings = new SettingsScope ();
		ThemeManager.GetHardCodedDefaults ();
		AppSettings?.RetrieveValues ();
		foreach (var p in Settings!.Where (cp => cp.Value.PropertyInfo != null)) {
			Settings! [p.Key].PropertyValue = p.Value.PropertyInfo?.GetValue (null);
		}
	}

	/// <summary>
	/// Applies the configuration settings to the running <see cref="Application"/> instance.
	/// </summary>
	public static void Apply ()
	{
		var settings = false;
		var themes = false;
		var appSettings = false;
		try {
			settings = Settings?.Apply () ?? false;
			themes = !string.IsNullOrEmpty (ThemeManager.SelectedTheme) && (ThemeManager.Themes? [ThemeManager.SelectedTheme]?.Apply () ?? false);
			appSettings = AppSettings?.Apply () ?? false;

		} catch (JsonException e) {
			if (ThrowOnJsonErrors ?? false) {
				throw;
			} else {
				AddJsonError ($"Error applying Configuration Change: {e.Message}");
			}
		} finally {
			if (settings || themes || appSettings) {
				OnApplied ();
			}
		}
	}

	/// <summary>
	/// Called when an updated configuration has been applied to the  
	/// application. Fires the <see cref="Applied"/> event.
	/// </summary>
	public static void OnApplied ()
	{
		Debug.WriteLine ($"ConfigurationManager.OnApplied()");
		Applied?.Invoke (null, new ConfigurationManagerEventArgs ());

		// TODO: Refactor ConfigurationManager to not use an event handler for this.
		// Instead, have it call a method on any class appropriately attributed
		// to update the cached values. See Issue #2871
	}

	/// <summary>
	/// Event fired when an updated configuration has been applied to the  
	/// application.
	/// </summary>
	public static event EventHandler<ConfigurationManagerEventArgs>? Applied;

	/// <summary>
	/// Name of the running application. By default this property is set to the application's assembly name.
	/// </summary>
	public static string AppName { get; set; } = Assembly.GetEntryAssembly ()?.FullName?.Split (',') [0]?.Trim ()!;

	/// <summary>
	/// Describes the location of the configuration files. The constants can be
	/// combined (bitwise) to specify multiple locations.
	/// </summary>
	[Flags]
	public enum ConfigLocations {
		/// <summary>
		/// No configuration will be loaded.
		/// </summary>
		/// <remarks>
		///  Used for development and testing only. For Terminal,Gui to function properly, at least
		///  <see cref="DefaultOnly"/> should be set.
		/// </remarks>
		None = 0,

		/// <summary>
		/// Global configuration in <c>Terminal.Gui.dll</c>'s resources (<c>Terminal.Gui.Resources.config.json</c>) -- Lowest Precidence.
		/// </summary>
		DefaultOnly,

		/// <summary>
		/// This constant is a combination of all locations
		/// </summary>
		All = -1

	}

	/// <summary>
	/// Gets and sets the locations where <see cref="ConfigurationManager"/> will look for config files.
	/// The value is <see cref="ConfigLocations.All"/>.
	/// </summary>
	public static ConfigLocations Locations { get; set; } = ConfigLocations.All;

	/// <summary>
	/// Loads all settings found in the various configuration storage locations to 
	/// the <see cref="ConfigurationManager"/>. Optionally,
	/// resets all settings attributed with <see cref="SerializableConfigurationProperty"/> to the defaults.
	/// </summary>
	/// <remarks>
	/// Use <see cref="Apply"/> to cause the loaded settings to be applied to the running application.
	/// </remarks>
	/// <param name="reset">If <see langword="true"/> the state of <see cref="ConfigurationManager"/> will
	/// be reset to the defaults.</param>
	public static void Load (bool reset = false)
	{
		Debug.WriteLine ($"ConfigurationManager.Load()");

		if (reset) Reset ();

		// LibraryResources is always loaded by Reset
		if (Locations == ConfigLocations.All) {
			var embeddedStylesResourceName = Assembly.GetEntryAssembly ()?
				.GetManifestResourceNames ().FirstOrDefault (x => x.EndsWith (_configFilename));
			if (string.IsNullOrEmpty (embeddedStylesResourceName)) {
				embeddedStylesResourceName = _configFilename;
			}

			Settings = Settings?
				// Global current directory
				.Update ($"./.tui/{_configFilename}")?
				// Global home directory
				.Update ($"~/.tui/{_configFilename}")?
				// App resources
				.UpdateFromResource (Assembly.GetEntryAssembly ()!, embeddedStylesResourceName!)?
				// App current directory
				.Update ($"./.tui/{AppName}.{_configFilename}")?
				// App home directory
				.Update ($"~/.tui/{AppName}.{_configFilename}");
		}
	}

	/// <summary>
	/// Returns an empty Json document with just the $schema tag.
	/// </summary>
	/// <returns></returns>
	public static string GetEmptyJson ()
	{
		var emptyScope = new SettingsScope ();
		emptyScope.Clear ();
		return JsonSerializer.Serialize<SettingsScope> (emptyScope, _serializerOptions);
	}

	/// <summary>
	/// System.Text.Json does not support copying a deserialized object to an existing instance.
	/// To work around this, we implement a 'deep, memberwise copy' method. 
	/// </summary>
	/// <remarks>
	/// TOOD: When System.Text.Json implements `PopulateObject` revisit
	///	https://github.com/dotnet/corefx/issues/37627
	/// </remarks>
	/// <param name="source"></param>
	/// <param name="destination"></param>
	/// <returns><paramref name="destination"/> updated from <paramref name="source"/></returns>
	internal static object? DeepMemberwiseCopy (object? source, object? destination)
	{
		if (destination == null) {
			throw new ArgumentNullException (nameof (destination));
		}

		if (source == null) {
			return null!;
		}

		if (source.GetType () == typeof (SettingsScope)) {
			return ((SettingsScope)destination).Update ((SettingsScope)source);
		}
		if (source.GetType () == typeof (ThemeScope)) {
			return ((ThemeScope)destination).Update ((ThemeScope)source);
		}
		if (source.GetType () == typeof (AppScope)) {
			return ((AppScope)destination).Update ((AppScope)source);
		}

		// If value type, just use copy constructor.
		if (source.GetType ().IsValueType || source.GetType () == typeof (string)) {
			return source;
		}

		// Dictionary
		if (source.GetType ().IsGenericType && source.GetType ().GetGenericTypeDefinition ().IsAssignableFrom (typeof (Dictionary<,>))) {
			foreach (var srcKey in ((IDictionary)source).Keys) {
				if (srcKey is string) {

				}
				if (((IDictionary)destination).Contains (srcKey))
					((IDictionary)destination) [srcKey] = DeepMemberwiseCopy (((IDictionary)source) [srcKey], ((IDictionary)destination) [srcKey]);
				else {
					((IDictionary)destination).Add (srcKey, ((IDictionary)source) [srcKey]);
				}
			}
			return destination;
		}

		// ALl other object types
		var sourceProps = source?.GetType ().GetProperties ().Where (x => x.CanRead).ToList ();
		var destProps = destination?.GetType ().GetProperties ().Where (x => x.CanWrite).ToList ()!;
		foreach (var (sourceProp, destProp) in
			from sourceProp in sourceProps
			where destProps.Any (x => x.Name == sourceProp.Name)
			let destProp = destProps.First (x => x.Name == sourceProp.Name)
			where destProp.CanWrite
			select (sourceProp, destProp)) {

			var sourceVal = sourceProp.GetValue (source);
			var destVal = destProp.GetValue (destination);
			if (sourceVal != null) {
				if (destVal != null) {
					// Recurse
					destProp.SetValue (destination, DeepMemberwiseCopy (sourceVal, destVal));
				} else {
					destProp.SetValue (destination, sourceVal);
				}
			}
		}
		return destination!;
	}

	//public class ConfiguraitonLocation
	//{
	//	public string Name { get; set; } = string.Empty;

	//	public string? Path { get; set; }

	//	public async Task<SettingsScope> UpdateAsync (Stream stream)
	//	{
	//		var scope = await JsonSerializer.DeserializeAsync<SettingsScope> (stream, serializerOptions);
	//		if (scope != null) {
	//			ConfigurationManager.Settings?.UpdateFrom (scope);
	//			return scope;
	//		}
	//		return new SettingsScope ();
	//	}

	//}

	//public class StreamConfiguration {
	//	private bool _reset;

	//	public StreamConfiguration (bool reset)
	//	{
	//		_reset = reset;
	//	}

	//	public StreamConfiguration UpdateAppResources ()
	//	{
	//		if (Locations.HasFlag (ConfigLocations.AppResources)) LoadAppResources ();
	//		return this;
	//	}

	//	public StreamConfiguration UpdateAppDirectory ()
	//	{
	//		if (Locations.HasFlag (ConfigLocations.AppDirectory)) LoadAppDirectory ();
	//		return this;
	//	}

	//	// Additional update methods for each location here

	//	private void LoadAppResources ()
	//	{
	//		// Load AppResources logic here
	//	}

	//	private void LoadAppDirectory ()
	//	{
	//		// Load AppDirectory logic here
	//	}
	//}
}