using UnityEngine;
using UnityEngine.UI;

/// <summary>
/// 计算 Sprite 的非透明可见区域（基于 sprite.rect），
/// 将其中心与 Image 矩形中心对齐，并把偏移应用到「父物体」的 anchoredPosition.y。
/// 同时缓存上下左右边界，避免重复扫描，并提供 UI 尺寸下的边界/宽度。
/// </summary>
[DisallowMultipleComponent]
public class ImageAlphaBounds : MonoBehaviour
{
    [Range(0f, 1f)]
    public float alphaThreshold = 0.1f;

    private Sprite cachedSprite;
    private int cachedTop;
    private int cachedBottom;
    private int cachedLeft;
    private int cachedRight;
    private bool cachedValid;

    private void EnsureBounds(Image img)
    {
        Sprite sp = img.sprite;
        if (cachedValid && cachedSprite == sp) return;

        cachedSprite = sp;
        cachedValid = false;

        if (sp == null) return;

        Texture2D tex = sp.texture;
        if (tex == null || !tex.isReadable)
        {
            Debug.LogWarning($"{name}: Texture not readable. Enable Read/Write in import settings.");
            return;
        }

        Rect r = sp.rect;
        int sx = Mathf.RoundToInt(r.x);
        int sy = Mathf.RoundToInt(r.y);
        int sw = Mathf.RoundToInt(r.width);
        int sh = Mathf.RoundToInt(r.height);

        Color[] pixels = tex.GetPixels(sx, sy, sw, sh);

        int top = -1, bottom = -1, left = -1, right = -1;

        for (int y = 0; y < sh; y++)
        {
            int rowStart = y * sw;
            for (int x = 0; x < sw; x++)
            {
                if (pixels[rowStart + x].a > alphaThreshold)
                {
                    if (top == -1) top = y;
                    bottom = y;

                    if (left == -1 || x < left) left = x;
                    if (right == -1 || x > right) right = x;
                }
            }
        }

        if (top == -1 || bottom == -1)
        {
            cachedTop = cachedBottom = cachedLeft = cachedRight = -1;
        }
        else
        {
            cachedTop = top;
            cachedBottom = bottom;
            cachedLeft = left;
            cachedRight = right;
        }

        cachedValid = true;
    }

    public void AdjustY()
    {
        Image img = GetComponent<Image>();
        if (img == null || img.sprite == null) return;

        EnsureBounds(img);

        if (!cachedValid || cachedBottom < cachedTop) return;

        RectTransform imgRT = img.rectTransform;
        float fullHeightUI = imgRT.sizeDelta.y;
        float spriteHeightPx = img.sprite.rect.height;
        float scaleY = fullHeightUI / spriteHeightPx;

        float centerVisibleFromTopPx = (cachedTop + cachedBottom + 1) * 0.5f;
        float centerVisibleFromTopUI = centerVisibleFromTopPx * scaleY;
        float imageCenterFromTopUI = fullHeightUI * 0.5f;

        float deltaY = centerVisibleFromTopUI - imageCenterFromTopUI;

        RectTransform parentRT = img.transform.parent as RectTransform;
        if (parentRT != null)
        {
            Vector2 p = parentRT.anchoredPosition;
            float parentScaleY = parentRT.localScale.y;
            parentRT.anchoredPosition = new Vector2(p.x, -deltaY * parentScaleY);
        }
    }

    public float GetOpaqueHeight()
    {
        if (!cachedValid || cachedBottom < cachedTop) return 0f;
        return cachedBottom - cachedTop + 1;
    }

    public float GetOpaqueWidth()
    {
        if (!cachedValid || cachedRight < cachedLeft) return 0f;
        return cachedRight - cachedLeft + 1;
    }

    public float GetOpaqueLeftUI()
    {
        Image img = GetComponent<Image>();
        if (img == null || !cachedValid || cachedRight < cachedLeft) return 0f;

        RectTransform rt = img.rectTransform;
        float spriteWidthPx = img.sprite.rect.width;
        float scaleX = rt.sizeDelta.x / spriteWidthPx;
        return cachedLeft * scaleX;
    }

    public float GetOpaqueRightUI()
    {
        Image img = GetComponent<Image>();
        if (img == null || !cachedValid || cachedRight < cachedLeft) return 0f;

        RectTransform rt = img.rectTransform;
        float spriteWidthPx = img.sprite.rect.width;
        float scaleX = rt.sizeDelta.x / spriteWidthPx;
        return cachedRight * scaleX;
    }

    /// <summary>
    /// 返回不透明宽度的 UI 尺寸（换算自 sprite.rect 像素宽度）
    /// </summary>
    public float GetOpaqueWidthUI()
    {
        Image img = GetComponent<Image>();
        if (img == null || !cachedValid || cachedRight < cachedLeft) return 0f;

        RectTransform rt = img.rectTransform;
        float spriteWidthPx = img.sprite.rect.width;
        float scaleX = rt.sizeDelta.x / spriteWidthPx;
        return (cachedRight - cachedLeft + 1) * scaleX;
    }
}