using System;
using global::System.IO;
using global::Newtonsoft.Json.Linq;

namespace Pilz.Configuration
{
    public sealed class SettingsManager<T> : ISettingsManager where T : SettingsBase
    {
        public event EventHandler AutoSavingSettings;
        public event EventHandler SavingSettings;
        public event EventHandler SavedSettings;

        private T defaultInstance = null;
        private bool enableAutoSave = false;
        private bool addedHandler = false;

        public string ConfigFilePath { get; set; }

        public bool AutoSaveOnExit
        {
            get
            {
                return enableAutoSave;
            }

            set
            {
                if (enableAutoSave != value)
                {
                    enableAutoSave = value;
                    switch (enableAutoSave)
                    {
                        case true:
                            {
                                if (!addedHandler)
                                {
                                    AddAutoSaveHandler();
                                }

                                break;
                            }

                        case false:
                            {
                                if (addedHandler)
                                {
                                    RemoveAutoSaveHandler();
                                }

                                break;
                            }
                    }
                }
            }
        }

        private void AddAutoSaveHandler()
        {
            System.Windows.Forms.Application.ApplicationExit += AutoSaveSettingsOnExit;
            addedHandler = true;
        }

        private void RemoveAutoSaveHandler()
        {
            System.Windows.Forms.Application.ApplicationExit -= AutoSaveSettingsOnExit;
            addedHandler = false;
        }

        public T Instance
        {
            get
            {
                if (defaultInstance is null)
                {
                    Load();
                }

                return defaultInstance;
            }
        }

        public SettingsManager()
        {
            ConfigFilePath = "";
            AutoSaveOnExit = false;
        }

        public SettingsManager(string fileName, bool autoSaveOnExit)
        {
            ConfigFilePath = fileName;
            AutoSaveOnExit = autoSaveOnExit;
        }

        private void AutoSaveSettingsOnExit(object sender, EventArgs e)
        {
            AutoSavingSettings?.Invoke(this, new EventArgs());
            Save();
        }

        public void Save()
        {
            if (!string.IsNullOrEmpty(ConfigFilePath) && defaultInstance is object)
            {
                SavePrivate();
            }
        }

        public void Load()
        {
            if (!string.IsNullOrEmpty(ConfigFilePath) && File.Exists(ConfigFilePath))
            {
                LoadPrivate();
            }
            else
            {
                CreateNewInstance();
            }

            if (defaultInstance is object)
            {
                defaultInstance._settingsManager = this;
            }
        }

        public void Reset()
        {
            Instance.ResetValues();
        }

        private void CreateNewInstance()
        {
            var ctor = typeof(T).GetConstructor(Array.Empty<Type>());
            if (ctor is object)
            {
                defaultInstance = (T)ctor.Invoke(Array.Empty<object>());
                defaultInstance.ResetValues();
            }
            else
            {
                throw new Exception("The base type has no constructor with no parameters.");
            }
        }

        private void LoadPrivate()
        {
            defaultInstance = JObject.Parse(File.ReadAllText(ConfigFilePath)).ToObject<T>();
        }

        private void SavePrivate()
        {
            SavingSettings?.Invoke(this, new EventArgs());
            var obj = JObject.FromObject(defaultInstance);
            if (obj is object)
            {
                File.WriteAllText(ConfigFilePath, obj.ToString());
            }

            SavedSettings?.Invoke(this, new EventArgs());
        }
    }
}