using System;

using UnityEngine;

using Framework.Support;

namespace Framework.Services {

  /// <summary>Manages and provides access to a game object holding the services</summary>
  public static class ServicesRoot {

    /// <summary>Name of the game object that will carry the services</summary>
    public const string ServicesGameObjectName = "Services";

    /// <summary>Retrieves the game object holding the services</summary>
    /// <returns>The game object responsible for holding the services</returns>
    public static GameObject Get() {
      if(GameObjectHelper.IsNullOrDestroyed(servicesGameObject)) {
        servicesGameObject = GameObject.Find("/" + ServicesGameObjectName);
      }

      return servicesGameObject;
    }

    /// <summary>Retrieves or creates the game object holding the services</summary>
    /// <returns>The game object responsible for holding the services</returns>
    public static GameObject GetOrCreate() {
      if(GameObjectHelper.IsNullOrDestroyed(servicesGameObject)) {
        servicesGameObject = GameObject.Find("/" + ServicesGameObjectName);

        // No service container found, create a new one
        if(servicesGameObject == null) {
          servicesGameObject = new GameObject(ServicesGameObjectName);
        }

        // For some reason, this DontDestroyOnLoad() only works in the editor, so to
        // ensure the game object really stays around, we also use a special component.
        GameObject.DontDestroyOnLoad(servicesGameObject);
        servicesGameObject.AddComponent<DontDestroyOnLoadCaller>();
      }

      return servicesGameObject;
    }

    /// <summary>Destroys all services in the specified scope</summary>
    public static void Kill(Scope scope) {

      // It may be that a service container was carried over from the previous scene
      // but it wasn't looked up yet.
      if(GameObjectHelper.IsNullOrDestroyed(servicesGameObject)) {
        servicesGameObject = GameObject.Find("/" + ServicesGameObjectName);
      }

      if(!GameObjectHelper.IsNullOrDestroyed(servicesGameObject)) {
        GameObject.Destroy(servicesGameObject);
        servicesGameObject = null;
      }

    }

    /// <summary>Game object that is holding the services</summary>
    private static GameObject servicesGameObject;

  }

} // namespace Framework.Services