using UnityEngine;
using UnityEngine.SceneManagement;
using System.Collections;
using UnityEngine.UI;

/// <summary>
/// A global helper to seamlessly load levels using a dedicated Loading Scene.
/// </summary>
public class LevelLoader : MonoBehaviour
{
    // The static variable that remembers where we want to go!
    public static string targetSceneName = "";

    [Header("Loading UI")]
    [Tooltip("The UI Slider used as a visual loading progress bar.")]
    public Slider loadingProgressBar;

    private void Start()
    {
        // If this script wakes up and there's a target scene defined, it means 
        // we are currently sitting in the LoadingScene and should start the heavy lifting!
        if (!string.IsNullOrEmpty(targetSceneName))
        {
            StartCoroutine(LoadSceneAsynchronously(targetSceneName));
        }
    }

    /// <summary>
    /// Call this from anywhere in your game to trigger the loading screen and go to a new level!
    /// Example: LevelLoader.LoadLevel("HouseInterior");
    /// </summary>
    public static void LoadLevel(string sceneName)
    {
        targetSceneName = sceneName;
        // Asynchronously load the Loading Scene to prevent the Main Menu from freezing!
        SceneManager.LoadSceneAsync("LoadingScene");
    }

    private IEnumerator LoadSceneAsynchronously(string sceneName)
    {
        // Start loading the heavy scene in the background
        AsyncOperation operation = SceneManager.LoadSceneAsync(sceneName);

        // Update the loading bar while the scene is loading
        while (!operation.isDone)
        {
            float progress = Mathf.Clamp01(operation.progress / 0.9f);
            
            if (loadingProgressBar != null)
            {
                loadingProgressBar.value = progress;
            }

            yield return null;
        }
    }
}