using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.IO;
using System.Linq;
using System.Text;
using BepInEx.Logging;

namespace BepInEx.Configuration
{
	/// <summary>
	/// A helper class to handle persistent data.
	/// </summary>
	public class ConfigFile
	{
		private readonly BepInPlugin _ownerMetadata;

		internal static ConfigFile CoreConfig { get; } = new ConfigFile(Paths.BepInExConfigPath, true);

		/// <summary>
		/// All config entries inside 
		/// </summary>
		protected Dictionary<ConfigDefinition, ConfigEntry> Entries { get; } = new Dictionary<ConfigDefinition, ConfigEntry>();

		/// <summary>
		/// Create a list with all config entries inside of this config file.
		/// </summary>
		[Obsolete("Use GetConfigEntries instead")]
		public ReadOnlyCollection<ConfigDefinition> ConfigDefinitions => Entries.Keys.ToList().AsReadOnly();

		/// <summary>
		/// Create an array with all config entries inside of this config file. Should be only used for metadata purposes.
		/// If you want to access and modify an existing setting then use <see cref="Wrap{T}(ConfigDefinition,T,ConfigDescription)"/> 
		/// instead with no description.
		/// </summary>
		public ConfigEntry[] GetConfigEntries() => Entries.Values.ToArray();

		/// <summary>
		/// Full path to the config file. The file might not exist until a setting is added and changed, or <see cref="Save"/> is called.
		/// </summary>
		public string ConfigFilePath { get; }

		/// <summary>
		/// If enabled, writes the config to disk every time a value is set. 
		/// If disabled, you have to manually use <see cref="Save"/> or the changes will be lost!
		/// </summary>
		public bool SaveOnConfigSet { get; set; } = true;

		/// <summary>
		/// Create a new config file at the specified config path.
		/// </summary>
		/// <param name="configPath">Full path to a file that contains settings. The file will be created as needed.</param>
		/// <param name="saveOnInit">If the config file/directory doesn't exist, create it immediately.</param>
		/// <param name="owner">The plugin that owns this setting.</param>
		public ConfigFile(string configPath, bool saveOnInit, BaseUnityPlugin owner = null)
		{
			_ownerMetadata = owner?.Metadata;

			if (configPath == null) throw new ArgumentNullException(nameof(configPath));
			configPath = Path.GetFullPath(configPath);
			ConfigFilePath = configPath;

			if (File.Exists(ConfigFilePath))
			{
				Reload();
			}
			else if (saveOnInit)
			{
				Save();
			}

			StartWatching();
		}

		#region Save/Load

		private readonly object _ioLock = new object();

		/// <summary>
		/// Reloads the config from disk. Unsaved changes are lost.
		/// </summary>
		public void Reload()
		{
			lock (_ioLock)
			{
				string currentSection = string.Empty;

				foreach (string rawLine in File.ReadAllLines(ConfigFilePath))
				{
					string line = rawLine.Trim();

					if (line.StartsWith("#")) //comment
						continue;

					if (line.StartsWith("[") && line.EndsWith("]")) //section
					{
						currentSection = line.Substring(1, line.Length - 2);
						continue;
					}

					string[] split = line.Split('='); //actual config line
					if (split.Length != 2)
						continue; //empty/invalid line

					string currentKey = split[0].Trim();
					string currentValue = split[1].Trim();

					var definition = new ConfigDefinition(currentSection, currentKey);

					Entries.TryGetValue(definition, out ConfigEntry entry);
					if (entry == null)
					{
						entry = new ConfigEntry(this, definition);
						Entries[definition] = entry;
					}

					entry.SetSerializedValue(currentValue, true, this);
				}
			}

			OnConfigReloaded();
		}

		/// <summary>
		/// Writes the config to disk.
		/// </summary>
		public void Save()
		{
			lock (_ioLock)
			{
				StopWatching();

				string directoryName = Path.GetDirectoryName(ConfigFilePath);
				if (directoryName != null) Directory.CreateDirectory(directoryName);

				using (var writer = new StreamWriter(File.Create(ConfigFilePath), Encoding.UTF8))
				{
					if (_ownerMetadata != null)
					{
						writer.WriteLine($"## Settings file was created by plugin {_ownerMetadata.Name} v{_ownerMetadata.Version}");
						writer.WriteLine($"## Plugin GUID: {_ownerMetadata.GUID}");
						writer.WriteLine();
					}

					foreach (var sectionKv in Entries.GroupBy(x => x.Key.Section).OrderBy(x => x.Key))
					{
						// Section heading
						writer.WriteLine($"[{sectionKv.Key}]");

						foreach (var configEntry in sectionKv.Select(x => x.Value))
						{
							writer.WriteLine();

							configEntry.WriteDescription(writer);

							writer.WriteLine($"{configEntry.Definition.Key} = {configEntry.GetSerializedValue()}");
						}

						writer.WriteLine();
					}
				}

				StartWatching();
			}
		}

		#endregion

		#region Wraps

		/// <summary>
		/// Create a new setting or access one of the existing ones. The setting is saved to drive and loaded automatically.
		/// If you are the creator of the setting, provide a ConfigDescription object to give user information about the setting.
		/// If you are using a setting created by another plugin/class, do not provide any ConfigDescription.
		/// </summary>
		/// <typeparam name="T">Type of the value contained in this setting.</typeparam>
		/// <param name="configDefinition">Section and Key of the setting.</param>
		/// <param name="defaultValue">Value of the setting if the setting was not created yet.</param>
		/// <param name="configDescription">Description of the setting shown to the user.</param>
		/// <returns></returns>
		public ConfigWrapper<T> Wrap<T>(ConfigDefinition configDefinition, T defaultValue, ConfigDescription configDescription = null)
		{
			if (!TomlTypeConverter.CanConvert(typeof(T)))
				throw new ArgumentException($"Type {typeof(T)} is not supported by the config system. Supported types: {string.Join(", ", TomlTypeConverter.GetSupportedTypes().Select(x => x.Name).ToArray())}");

			Entries.TryGetValue(configDefinition, out var entry);

			if (entry == null)
			{
				entry = new ConfigEntry(this, configDefinition, typeof(T), defaultValue);
				Entries[configDefinition] = entry;
			}
			else
			{
				entry.SetTypeAndDefaultValue(typeof(T), defaultValue, !Equals(defaultValue, default(T)));
			}

			if (configDescription != null)
			{
				if (entry.Description != null)
					Logger.Log(LogLevel.Warning, $"Tried to add configDescription to setting {configDefinition} when it already had one defined. Only add configDescription once or a random one will be used.");

				if (configDescription.AcceptableValues != null)
				{
					var genericArguments = configDescription.AcceptableValues.GetType().GetGenericArguments();
					if (genericArguments.Length > 0 && genericArguments[0] != typeof(T))
						throw new ArgumentException("AcceptableValues has a different type than the setting type", nameof(configDefinition));
				}

				entry.SetDescription(configDescription);
			}

			return new ConfigWrapper<T>(entry);
		}

		/// <summary>
		/// Create a new setting or access one of the existing ones. The setting is saved to drive and loaded automatically.
		/// If you are the creator of the setting, provide a ConfigDescription object to give user information about the setting.
		/// If you are using a setting created by another plugin/class, do not provide any ConfigDescription.
		/// </summary>
		[Obsolete("Use other Wrap overloads instead")]
		public ConfigWrapper<T> Wrap<T>(string section, string key, string description = null, T defaultValue = default(T))
			=> Wrap(new ConfigDefinition(section, key), defaultValue, string.IsNullOrEmpty(description) ? null : new ConfigDescription(description));

		/// <summary>
		/// Create a new setting or access one of the existing ones. The setting is saved to drive and loaded automatically.
		/// If you are the creator of the setting, provide a ConfigDescription object to give user information about the setting.
		/// If you are using a setting created by another plugin/class, do not provide any ConfigDescription.
		/// </summary>
		/// <typeparam name="T">Type of the value contained in this setting.</typeparam>
		/// <param name="section">Section/category/group of the setting. Settings are grouped by this.</param>
		/// <param name="key">Name of the setting.</param>
		/// <param name="defaultValue">Value of the setting if the setting was not created yet.</param>
		/// <param name="configDescription">Description of the setting shown to the user.</param>
		/// <returns></returns>
		public ConfigWrapper<T> Wrap<T>(string section, string key, T defaultValue, ConfigDescription configDescription = null)
			=> Wrap(new ConfigDefinition(section, key), defaultValue, configDescription);

		#endregion

		#region Events

		/// <summary>
		/// An event that is fired every time the config is reloaded.
		/// </summary>
		public event EventHandler ConfigReloaded;

		/// <summary>
		/// Fired when one of the settings is changed.
		/// </summary>
		public event EventHandler<SettingChangedEventArgs> SettingChanged;

		internal void OnSettingChanged(object sender, ConfigEntry changedEntry)
		{
			if (changedEntry == null) throw new ArgumentNullException(nameof(changedEntry));

			if (SettingChanged != null)
			{
				var args = new SettingChangedEventArgs(changedEntry);

				foreach (var callback in SettingChanged.GetInvocationList().Cast<EventHandler<SettingChangedEventArgs>>())
				{
					try
					{
						callback(sender, args);
					}
					catch (Exception e)
					{
						Logger.Log(LogLevel.Error, e);
					}
				}
			}

			// Check sender to prevent infinite loops
			// todo batching / async?
			if (sender != this && SaveOnConfigSet)
				Save();
		}

		private void OnConfigReloaded()
		{
			if (ConfigReloaded != null)
			{
				foreach (var callback in ConfigReloaded.GetInvocationList().Cast<EventHandler>())
				{
					try
					{
						callback(this, EventArgs.Empty);
					}
					catch (Exception e)
					{
						Logger.Log(LogLevel.Error, e);
					}
				}
			}
		}

		#endregion

		#region File watcher

		private FileSystemWatcher _watcher;

		/// <summary>
		/// Start watching the config file on disk for changes.
		/// </summary>
		public void StartWatching()
		{
			lock (_ioLock)
			{
				if (_watcher != null) return;

				_watcher = new FileSystemWatcher
				{
					Path = Path.GetDirectoryName(ConfigFilePath) ?? throw new ArgumentException("Invalid config path"),
					Filter = Path.GetFileName(ConfigFilePath),
					IncludeSubdirectories = false,
					NotifyFilter = NotifyFilters.LastWrite,
					EnableRaisingEvents = true
				};

				_watcher.Changed += (sender, args) => Reload();
			}
		}

		/// <summary>
		/// Stop watching the config file on disk for changes.
		/// </summary>
		public void StopWatching()
		{
			lock (_ioLock)
			{
				if (_watcher != null)
				{
					_watcher.EnableRaisingEvents = false;
					_watcher.Dispose();
					_watcher = null;
				}
			}
		}

		/// <inheritdoc />
		~ConfigFile()
		{
			StopWatching();
		}

		#endregion
	}
}