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

namespace BNG {
    public class ScreenFader : MonoBehaviour {

        [Tooltip("Should the screen fade in when a new level is loaded")]
        public bool FadeOnSceneLoaded = true;

        [Tooltip("Color of the fade. Alpha will be modified when fading in / out")]
        public Color FadeColor = Color.black;

        [Tooltip("How fast to fade in / out")]
        public float FadeInSpeed = 6f;

        public float FadeOutSpeed = 6f;

        [Tooltip("Wait X seconds before fading scene in")]
        public float SceneFadeInDelay = 1f;

        GameObject fadeObject;
        RectTransform fadeObjectRect;
        Canvas fadeCanvas;
        CanvasGroup canvasGroup;
        Image fadeImage;
        IEnumerator fadeRoutine;
        string faderName = "ScreenFader";


        void Awake() {
            initialize();
        }

        protected virtual void initialize() {
            // Create a Canvas that will be placed directly over the camera
            if (fadeObject == null) {
                Canvas childCanvas = GetComponentInChildren<Canvas>();

                // Found existing item, no need to initialize this one
                if (childCanvas != null && childCanvas.transform.name == faderName) {
                    GameObject.Destroy(this.gameObject);
                    return;
                }
                fadeObject = new GameObject();
                fadeObject.transform.parent = Camera.main.transform;
                fadeObject.transform.localPosition = new Vector3(0, 0, 0.03f);
                fadeObject.transform.localEulerAngles = Vector3.zero;
                fadeObject.transform.name = faderName;

                fadeCanvas = fadeObject.AddComponent<Canvas>();
                fadeCanvas.renderMode = RenderMode.WorldSpace;
                fadeCanvas.sortingOrder = 100; // Make sure the canvas renders on top

                canvasGroup = fadeObject.AddComponent<CanvasGroup>();
                canvasGroup.interactable = false;

                fadeImage = fadeObject.AddComponent<Image>();
                fadeImage.color = FadeColor;
                fadeImage.raycastTarget = false;

                // Stretch the image
                fadeObjectRect = fadeObject.GetComponent<RectTransform>();
                fadeObjectRect.anchorMin = new Vector2(1, 0);
                fadeObjectRect.anchorMax = new Vector2(0, 1);
                fadeObjectRect.pivot = new Vector2(0.5f, 0.5f);
                fadeObjectRect.sizeDelta = new Vector2(0.2f, 0.2f);
                fadeObjectRect.localScale = new Vector2(2f, 2f);

            }
        }

        void OnEnable() {
            SceneManager.sceneLoaded += OnSceneLoaded;
        }

        void OnDisable() {
            SceneManager.sceneLoaded -= OnSceneLoaded;
        }

        void OnSceneLoaded(Scene scene, LoadSceneMode mode) {

            if (FadeOnSceneLoaded && fadeObject != null) {
                // Start screen at fade
                updateImageAlpha(FadeColor.a);

                StartCoroutine(fadeOutWithDelay(SceneFadeInDelay));
            }
        }

        IEnumerator fadeOutWithDelay(float delaySeconds) {
            yield return new WaitForSeconds(delaySeconds);

            DoFadeOut();
        }

        /// <summary>
        /// Fade from transparent to solid color
        /// </summary>
        public virtual void DoFadeIn() {

            // Stop if currently running
            if (fadeRoutine != null) {
                StopCoroutine(fadeRoutine);
            }

            // Do the fade routine
            if (canvasGroup != null) {
                fadeRoutine = doFade(canvasGroup.alpha, 1);
                StartCoroutine(fadeRoutine);
            }
        }

        /// <summary>
        /// Fade from solid color to transparent
        /// </summary>
        public virtual void DoFadeOut() {
            if (fadeRoutine != null) {
                StopCoroutine(fadeRoutine);
            }

            fadeRoutine = doFade(canvasGroup.alpha, 0);
            StartCoroutine(fadeRoutine);
        }

        public virtual void SetFadeLevel(float fadeLevel) {
            if (fadeRoutine != null) {
                StopCoroutine(fadeRoutine);
                // Debug.Log("----- Stopped Routine");
            }

            // No Canvas available to fade
            if (canvasGroup == null) {
                return;
            }

            fadeRoutine = doFade(canvasGroup.alpha, fadeLevel);
            StartCoroutine(fadeRoutine);
        }

        IEnumerator doFade(float alphaFrom, float alphaTo) {

            float alpha = alphaFrom;

            updateImageAlpha(alpha);

            while (alpha != alphaTo) {

                if (alphaFrom < alphaTo) {
                    alpha += Time.deltaTime * FadeInSpeed;
                    if (alpha > alphaTo) {
                        alpha = alphaTo;
                    }
                }
                else {
                    alpha -= Time.deltaTime * FadeOutSpeed;
                    if (alpha < alphaTo) {
                        alpha = alphaTo;
                    }
                }

                updateImageAlpha(alpha);

                yield return new WaitForEndOfFrame();
            }

            yield return new WaitForEndOfFrame();

            // Ensure alpha is always applied
            updateImageAlpha(alphaTo);
        }

        protected virtual void updateImageAlpha(float alphaValue) {

            // Canvas Group was Destroyed.
            if (canvasGroup == null) {
                return;
            }

            // Enable canvas if necessary
            if (!canvasGroup.gameObject.activeSelf) {
                canvasGroup.gameObject.SetActive(true);
            }

            canvasGroup.alpha = alphaValue;

            // Disable Canvas if we're done
            if (alphaValue == 0 && canvasGroup.gameObject.activeSelf) {
                canvasGroup.gameObject.SetActive(false);
            }
        }
    }
}