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

public class UINavigator : MonoBehaviour
{
    [SerializeField] string firstSelectButtonTagName = "EntryButton";

    float pulseRate = 8f;
    float amplitude = .2f;
    Image image = null;
    Color color;

    Selectable lastSelected;

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

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

    void SelectFirstButton(Scene s, LoadSceneMode m)
    {
        StartCoroutine(SelectFirstButtonCoroutine());
    }

    IEnumerator SelectFirstButtonCoroutine()
    {
        if (!string.IsNullOrEmpty(firstSelectButtonTagName))
        {
            float startTime = Time.time;
            while (Time.time < startTime + 1f)
            {
                yield return new WaitForEndOfFrame();

                GameObject go = GameObject.FindGameObjectWithTag(firstSelectButtonTagName);

                if (go == null)
                {
                    continue;
                }

                if (go.GetComponent<Selectable>() == null)
                {
                    continue;
                }

                EventSystem.current.SetSelectedGameObject(go);
                break;
            }
        }
    }

    void Update()
    {
        EventSystem eventSys = EventSystem.current;

        // 鼠标点击取消
        if (Input.GetMouseButtonDown(0))
        {
            UnSelect();
        }

        if (Input.GetKeyDown(KeyCode.Escape))
        {
            Application.Quit();
        }


        if(eventSys.currentSelectedGameObject == null)
        {
            return;
        }

        Selectable selected = eventSys.currentSelectedGameObject?.GetComponent<Selectable>();
        if (selected != null && image != null)
        {
            float pulse = .5f + .5f * Mathf.Sin(Time.unscaledTime * pulseRate);
            float value = 1 - amplitude * pulse;

            Color col = color * value;
            col.a = 1f;
            image.color = col;

            //Debug.Log(selected.gameObject);
        }

        if (selected != lastSelected)
        {
            UnSelect();

            if (selected)
            {
                image = selected.GetComponent<Image>();
                if (image != null)
                {
                    color = image.color;
                }
            }

            lastSelected = selected;
        }

        KeyCode keyCode = KeyCode.None;
        if (Input.GetKeyDown(KeyCode.LeftArrow))
        {
            keyCode = KeyCode.LeftArrow;
        }
        else if (Input.GetKeyDown(KeyCode.RightArrow))
        {
            keyCode = KeyCode.RightArrow;
        }
        else if (Input.GetKeyDown(KeyCode.UpArrow))
        {
            keyCode = KeyCode.UpArrow;
        }
        else if (Input.GetKeyDown(KeyCode.DownArrow))
        {
            keyCode = KeyCode.DownArrow;
        }

        if (keyCode != KeyCode.None)
        {
            // 没有已选择的UI，寻找第一个
            if (selected == null || !selected.isActiveAndEnabled)
            {
                Selectable firstSelectable = FindObjectOfType<Selectable>();
                if (firstSelectable != null)
                {
                    eventSys.SetSelectedGameObject(firstSelectable.gameObject);
                }
            }
            // 通过已选择的UI，寻找下一个
            else 
            {
                switch (keyCode)
                {
                    case KeyCode.LeftArrow:
                        selected = selected.FindSelectableOnLeft();
                        break;
                    case KeyCode.RightArrow:
                        selected = selected.FindSelectableOnRight();
                        break;
                    case KeyCode.UpArrow:
                        selected = selected.FindSelectableOnUp();
                        break;
                    case KeyCode.DownArrow:
                        selected = selected.FindSelectableOnDown();
                        break;
                }
            }
        }
    }

    void UnSelect()
    {
        if (image != null)
        {
            image.color = color;
            image = null;
        }
    }
}