using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;

namespace AibisDream
{
    /// <summary>
    /// 画板组件，支持鼠标拖动绘制（UI Space）
    /// 需要挂载在带有RectTransform和RawImage的GameObject上
    /// </summary>
    [RequireComponent(typeof(RectTransform))]
    [RequireComponent(typeof(RawImage))]
    public class SignBoard : MonoBehaviour, IPointerDownHandler, IDragHandler, IPointerUpHandler
    {
        [Header("画板设置")]
        [SerializeField] private int textureWidth = 512;
        [SerializeField] private int textureHeight = 512;
        [SerializeField] private Color backgroundColor = Color.white;
        
        [Header("画笔设置")]
        [SerializeField] private Color drawColor = Color.black;
        [SerializeField] private int brushSize = 5;
        [SerializeField] private bool smoothDrawing = true; // 是否平滑绘制（连接两点之间的所有点）
        
        private Texture2D drawTexture;
        private RawImage drawImage;
        private RectTransform rectTransform;
        
        private Vector2 lastDrawPoint;
        private bool isDrawing = false;
        
        private void Awake()
        {
            drawImage = GetComponent<RawImage>();
            rectTransform = GetComponent<RectTransform>();
        }
        
        private void Start()
        {
            InitializeTexture();
        }
        
        /// <summary>
        /// 初始化画布纹理
        /// </summary>
        private void InitializeTexture()
        {
            // 创建可读写的纹理
            drawTexture = new Texture2D(textureWidth, textureHeight, TextureFormat.RGBA32, false);
            drawTexture.filterMode = FilterMode.Bilinear;
            
            // 填充背景色
            Color[] pixels = new Color[textureWidth * textureHeight];
            for (int i = 0; i < pixels.Length; i++)
            {
                pixels[i] = backgroundColor;
            }
            drawTexture.SetPixels(pixels);
            drawTexture.Apply();
            
            // 设置到RawImage
            drawImage.texture = drawTexture;
        }
        
        /// <summary>
        /// 将屏幕坐标转换为纹理坐标
        /// </summary>
        private bool ScreenToTextureCoord(Vector2 screenPos, out Vector2 textureCoord)
        {
            textureCoord = Vector2.zero;
            
            // 将屏幕坐标转换为UI本地坐标
            if (UIManager.Instance.ScreenPointToLocalPointInRectangle(rectTransform, screenPos, out Vector2 localPoint))
            {
                // 检查是否在RectTransform范围内
                Rect rect = rectTransform.rect;
                if (!rect.Contains(localPoint))
                {
                    return false;
                }
                
                // 转换为纹理坐标 (0,0) 到 (textureWidth, textureHeight)
                // localPoint的范围是 (-rect.width/2, -rect.height/2) 到 (rect.width/2, rect.height/2)
                float normalizedX = (localPoint.x + rect.width / 2) / rect.width;
                float normalizedY = (localPoint.y + rect.height / 2) / rect.height;
                
                textureCoord.x = normalizedX * textureWidth;
                textureCoord.y = normalizedY * textureHeight;
                
                return true;
            }
            
            return false;
        }
        
        /// <summary>
        /// 在指定位置绘制
        /// </summary>
        private void DrawAtPoint(Vector2 point)
        {
            int centerX = Mathf.RoundToInt(point.x);
            int centerY = Mathf.RoundToInt(point.y);
            
            // 绘制圆形笔刷
            for (int x = -brushSize; x <= brushSize; x++)
            {
                for (int y = -brushSize; y <= brushSize; y++)
                {
                    // 检查是否在圆形范围内
                    float distance = Mathf.Sqrt(x * x + y * y);
                    if (distance <= brushSize)
                    {
                        int px = centerX + x;
                        int py = centerY + y;
                        
                        // 检查边界
                        if (px >= 0 && px < textureWidth && py >= 0 && py < textureHeight)
                        {
                            // 根据距离计算透明度，实现柔和的笔刷效果
                            float alpha = 1f - (distance / brushSize);
                            Color finalColor = drawColor;
                            finalColor.a *= alpha;
                            
                            // 混合颜色
                            Color existingColor = drawTexture.GetPixel(px, py);
                            Color blendedColor = Color.Lerp(existingColor, finalColor, finalColor.a);
                            drawTexture.SetPixel(px, py, blendedColor);
                        }
                    }
                }
            }
        }
        
        /// <summary>
        /// 在两点之间绘制线条（平滑绘制）
        /// </summary>
        private void DrawLine(Vector2 start, Vector2 end)
        {
            float distance = Vector2.Distance(start, end);
            int steps = Mathf.CeilToInt(distance);
            
            for (int i = 0; i <= steps; i++)
            {
                float t = steps > 0 ? (float)i / steps : 0;
                Vector2 point = Vector2.Lerp(start, end, t);
                DrawAtPoint(point);
            }
        }
        
        /// <summary>
        /// 应用绘制更改到纹理
        /// </summary>
        private void ApplyDrawing()
        {
            if (drawTexture != null)
            {
                drawTexture.Apply();
                // 确保RawImage显示更新
                if (drawImage != null && drawImage.texture != drawTexture)
                {
                    drawImage.texture = drawTexture;
                }
            }
        }
        
        /// <summary>
        /// 清除画布
        /// </summary>
        public void Clear()
        {
            Color[] pixels = new Color[textureWidth * textureHeight];
            for (int i = 0; i < pixels.Length; i++)
            {
                pixels[i] = backgroundColor;
            }
            drawTexture.SetPixels(pixels);
            drawTexture.Apply();
        }
        
        /// <summary>
        /// 设置画笔颜色
        /// </summary>
        public void SetDrawColor(Color color)
        {
            drawColor = color;
        }
        
        /// <summary>
        /// 设置画笔大小
        /// </summary>
        public void SetBrushSize(int size)
        {
            brushSize = Mathf.Max(1, size);
        }
        
        /// <summary>
        /// 设置背景颜色
        /// </summary>
        public void SetBackgroundColor(Color color)
        {
            backgroundColor = color;
        }
        
        /// <summary>
        /// 保存画布为PNG图片
        /// </summary>
        public byte[] SaveToPNG()
        {
            return drawTexture.EncodeToPNG();
        }
        
        // EventSystem接口实现
        public void OnPointerDown(PointerEventData eventData)
        {
            if (eventData.button != PointerEventData.InputButton.Left)
                return;
            
            if (ScreenToTextureCoord(eventData.position, out Vector2 textureCoord))
            {
                isDrawing = true;
                // 确保第一次点击也能绘制
                lastDrawPoint = textureCoord;
                DrawAtPoint(textureCoord);
                ApplyDrawing();
                
                // 强制更新RawImage显示
                if (drawImage != null && drawTexture != null)
                {
                    drawImage.texture = drawTexture;
                }
            }
        }
        
        public void OnDrag(PointerEventData eventData)
        {
            if (!isDrawing)
                return;
            
            if (ScreenToTextureCoord(eventData.position, out Vector2 textureCoord))
            {
                if (smoothDrawing)
                {
                    // 平滑绘制：连接两点之间的所有点
                    // 如果两点距离太近，直接绘制当前点（避免DrawLine计算出错）
                    float distance = Vector2.Distance(lastDrawPoint, textureCoord);
                    if (distance < 0.1f)
                    {
                        DrawAtPoint(textureCoord);
                    }
                    else
                    {
                        DrawLine(lastDrawPoint, textureCoord);
                    }
                }
                else
                {
                    // 直接绘制当前点
                    DrawAtPoint(textureCoord);
                }
                
                ApplyDrawing();
                lastDrawPoint = textureCoord;
            }
        }
        
        public void OnPointerUp(PointerEventData eventData)
        {
            isDrawing = false;
        }
        
        private void OnDestroy()
        {
            // 清理纹理资源
            if (drawTexture != null)
            {
                Destroy(drawTexture);
            }
        }
    }
}