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

/// <summary>
/// 判定线旁的实时偏移条：每次判定在横条上生成一个彩色点，
/// x 位置表示偏移大小（左=偏晚 Late，右=偏早 Early），随后淡出。
/// 纯显示组件，订阅 ScoreManager.OnOffsetRecorded，不参与任何判定/计分逻辑。
/// 用法：挂到一个 RectTransform 上，作为横条容器；在 Inspector 指定 dotPrefab。
/// </summary>
[RequireComponent(typeof(RectTransform))]
public class OffsetBarDisplay : MonoBehaviour
{
    [Header("References")]
    [Tooltip("单个偏移点的预制（应带 Image/RectTransform）。若留空则运行时自动生成一个圆点。")]
    public RectTransform dotPrefab;
    [Tooltip("横条容器；留空则用本物体的 RectTransform。")]
    public RectTransform barContainer;
    [Tooltip("可选：中线（完美判定 0ms）指示线，仅用于视觉参考。")]
    public RectTransform centerMarker;

    [Header("Mapping")]
    [Tooltip("映射到横条边缘的最大偏移（毫秒）。超出按此裁剪。")]
    public float maxOffsetMs = 120f;
    [Tooltip("横条半宽（像素）。点的 x 在 [-halfWidth, halfWidth] 内。留 <=0 则用容器宽度的一半。")]
    public float halfWidthPixels = 0f;

    [Header("Appearance")]
    public float dotLifetime = 0.9f;
    public float dotStartSize = 14f;
    public Color earlyColor = new Color(0.35f, 0.7f, 1f, 1f);
    public Color lateColor = new Color(1f, 0.55f, 0.35f, 1f);
    public Color perfectColor = new Color(0.6f, 1f, 0.6f, 1f);
    [Tooltip("|偏移| 小于此值视为完美，用 perfectColor。")]
    public float perfectThresholdMs = 8f;
    [Tooltip("对象池上限，避免高连击时无限实例化。")]
    public int maxPooledDots = 48;

    private class Dot
    {
        public RectTransform rect;
        public Image image;
        public float age;
        public bool active;
    }

    private readonly List<Dot> pool = new List<Dot>();

    private void OnEnable()
    {
        ScoreManager.OnOffsetRecorded += HandleOffset;
    }

    private void OnDisable()
    {
        ScoreManager.OnOffsetRecorded -= HandleOffset;
    }

    private void Awake()
    {
        if (barContainer == null) barContainer = GetComponent<RectTransform>();
    }

    private float HalfWidth()
    {
        if (halfWidthPixels > 0f) return halfWidthPixels;
        if (barContainer != null) return barContainer.rect.width * 0.5f;
        return 200f;
    }

    // 正数 = 偏早(Early)，负数 = 偏晚(Late)。见 ScoreManager.RecordOffset。
    private void HandleOffset(float offsetMs)
    {
        if (!isActiveAndEnabled) return;

        Dot dot = GetPooledDot();
        if (dot == null) return;

        float clamped = Mathf.Clamp(offsetMs, -maxOffsetMs, maxOffsetMs);
        float norm = maxOffsetMs > 0f ? clamped / maxOffsetMs : 0f; // [-1,1]
        // Early(正) 放右侧，Late(负) 放左侧。
        float x = norm * HalfWidth();

        Vector2 pos = dot.rect.anchoredPosition;
        pos.x = x;
        pos.y = 0f;
        dot.rect.anchoredPosition = pos;
        dot.rect.sizeDelta = new Vector2(dotStartSize, dotStartSize);

        Color c;
        if (Mathf.Abs(offsetMs) < perfectThresholdMs) c = perfectColor;
        else c = offsetMs > 0f ? earlyColor : lateColor;
        dot.image.color = c;

        dot.age = 0f;
        dot.active = true;
        dot.rect.gameObject.SetActive(true);
    }

    private void Update()
    {
        float dt = Time.unscaledDeltaTime;
        float life = Mathf.Max(0.01f, dotLifetime);

        for (int i = 0; i < pool.Count; i++)
        {
            Dot d = pool[i];
            if (!d.active) continue;

            d.age += dt;
            float t = d.age / life;
            if (t >= 1f)
            {
                d.active = false;
                d.rect.gameObject.SetActive(false);
                continue;
            }

            Color c = d.image.color;
            c.a = 1f - t;
            d.image.color = c;
        }
    }

    private Dot GetPooledDot()
    {
        for (int i = 0; i < pool.Count; i++)
        {
            if (!pool[i].active) return pool[i];
        }

        if (pool.Count >= maxPooledDots)
        {
            // 全部占用：复用最老的一个。
            Dot oldest = pool[0];
            for (int i = 1; i < pool.Count; i++)
                if (pool[i].age > oldest.age) oldest = pool[i];
            return oldest;
        }

        return CreateDot();
    }

    private Dot CreateDot()
    {
        RectTransform rect;
        Image img;

        if (dotPrefab != null)
        {
            rect = Instantiate(dotPrefab, barContainer);
            img = rect.GetComponent<Image>();
            if (img == null) img = rect.gameObject.AddComponent<Image>();
        }
        else
        {
            GameObject go = new GameObject("OffsetDot", typeof(RectTransform), typeof(Image));
            rect = go.GetComponent<RectTransform>();
            rect.SetParent(barContainer, false);
            img = go.GetComponent<Image>();
        }

        rect.anchorMin = rect.anchorMax = new Vector2(0.5f, 0.5f);
        rect.pivot = new Vector2(0.5f, 0.5f);
        rect.gameObject.SetActive(false);

        Dot dot = new Dot { rect = rect, image = img, age = 0f, active = false };
        pool.Add(dot);
        return dot;
    }
}