using Unosquare.Swan.Formatters;
using Unosquare.Swan.Reflection;
using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;

namespace Unosquare.Swan.Abstractions {
  /// <summary>
  /// Represents a provider to save and load settings using a plain JSON file.
  /// </summary>
  /// <example>
  /// The following example shows how to save and load settings.
  /// <code>
  /// using Unosquare.Swan.Abstractions;
  /// 
  /// public class Example
  /// { 
  ///     public static void Main()
  ///     {
  ///         // get user from settings
  ///         var user = SettingsProvider&lt;Settings&gt;.Instance.Global.User;
  ///             
  ///         // modify the port
  ///         SettingsProvider&lt;Settings&gt;.Instance.Global.Port = 20;
  ///             
  ///         // if we want these settings to persist
  ///         SettingsProvider&lt;Settings&gt;.Instance.PersistGlobalSettings();
  ///     }
  ///         
  ///     public class Settings
  ///     {
  ///         public int Port { get; set; } = 9696;
  ///         
  ///         public string User { get; set; } = "User";
  ///     }
  /// }
  /// </code>
  /// </example>
  /// <typeparam name="T">The type of settings model.</typeparam>
  public sealed class SettingsProvider<T>
      : SingletonBase<SettingsProvider<T>> {
    private readonly Object _syncRoot = new Object();

    private T _global;

    /// <summary>
    /// Gets or sets the configuration file path. By default the entry assembly directory is used
    /// and the filename is 'appsettings.json'.
    /// </summary>
    /// <value>
    /// The configuration file path.
    /// </value>
    public String ConfigurationFilePath {
      get; set;
    } =
#if NETSTANDARD1_3
            Path.Combine(Runtime.LocalStoragePath, "appsettings.json");
#else
            Path.Combine(Runtime.EntryAssemblyDirectory, "appsettings.json");
#endif

    /// <summary>
    /// Gets the global settings object.
    /// </summary>
    /// <value>
    /// The global settings object.
    /// </value>
    public T Global {
      get {
        lock(this._syncRoot) {
          if(Equals(this._global, default(T))) {
            this.ReloadGlobalSettings();
          }

          return this._global;
        }
      }
    }

    /// <summary>
    /// Reloads the global settings.
    /// </summary>
    public void ReloadGlobalSettings() {
      if(File.Exists(this.ConfigurationFilePath) == false || File.ReadAllText(this.ConfigurationFilePath).Length == 0) {
        this.ResetGlobalSettings();
        return;
      }

      lock(this._syncRoot) {
        this._global = Json.Deserialize<T>(File.ReadAllText(this.ConfigurationFilePath));
      }
    }

    /// <summary>
    /// Persists the global settings.
    /// </summary>
    public void PersistGlobalSettings() => File.WriteAllText(this.ConfigurationFilePath, Json.Serialize(this.Global, true));

    /// <summary>
    /// Updates settings from list.
    /// </summary>
    /// <param name="propertyList">The list.</param>
    /// <returns>
    /// A list of settings of type ref="ExtendedPropertyInfo".
    /// </returns>
    /// <exception cref="ArgumentNullException">propertyList.</exception>
    public List<String> RefreshFromList(List<ExtendedPropertyInfo<T>> propertyList) {
      if(propertyList == null) {
        throw new ArgumentNullException(nameof(propertyList));
      }

      List<String> changedSettings = new List<String>();
      IEnumerable<PropertyInfo> globalProps = Runtime.PropertyTypeCache.RetrieveAllProperties<T>();

      foreach(ExtendedPropertyInfo<T> property in propertyList) {
        PropertyInfo propertyInfo = globalProps.FirstOrDefault(x => x.Name == property.Property);

        if(propertyInfo == null) {
          continue;
        }

        Object originalValue = propertyInfo.GetValue(this.Global);
        Boolean isChanged = propertyInfo.PropertyType.IsArray
            ? property.Value is IEnumerable enumerable && propertyInfo.TrySetArray(enumerable.Cast<Object>(), this.Global)
            : this.SetValue(property.Value, originalValue, propertyInfo);

        if(!isChanged) {
          continue;
        }

        changedSettings.Add(property.Property);
        this.PersistGlobalSettings();
      }

      return changedSettings;
    }

    /// <summary>
    /// Gets the list.
    /// </summary>
    /// <returns>A List of ExtendedPropertyInfo of the type T.</returns>
    public List<ExtendedPropertyInfo<T>> GetList() {
      Dictionary<String, Object> jsonData = Json.Deserialize(Json.Serialize(this.Global)) as Dictionary<String, Object>;

      return jsonData?.Keys
          .Select(p => new ExtendedPropertyInfo<T>(p) { Value = jsonData[p] })
          .ToList();
    }

    /// <summary>
    /// Resets the global settings.
    /// </summary>
    public void ResetGlobalSettings() {
      lock(this._syncRoot) {
        this._global = Activator.CreateInstance<T>();
      }

      this.PersistGlobalSettings();
    }

    private Boolean SetValue(Object property, Object originalValue, PropertyInfo propertyInfo) {
      switch(property) {
        case null when originalValue == null:
          break;
        case null:
          propertyInfo.SetValue(this.Global, null);
          return true;
        default:
          if(propertyInfo.PropertyType.TryParseBasicType(property, out Object propertyValue) &&
              !propertyValue.Equals(originalValue)) {
            propertyInfo.SetValue(this.Global, propertyValue);
            return true;
          }

          break;
      }

      return false;
    }
  }
}