import SwiftUI

struct AsyncImageView: View {
    let url: String
    let nums: [Int]
    let index: Int
    @State private var image: UIImage?
    @State private var isLoading = false
    @State private var error: Error?
    
    // 静态属性，用于维护当前加载的索引范围
    private static var currentlyLoadingIndices: Set<Int> = []
    private static let maxConcurrentLoads = 4

    var body: some View {
        Group {
            if let image = image {
                Image(uiImage: image)
                    .resizable()
                    .aspectRatio(contentMode: .fit)
            } else if isLoading {
                ProgressView()
            } else if error != nil {
                VStack {
                    Image(systemName: "exclamationmark.triangle")
                        .foregroundColor(.red)
                    Text(error?.localizedDescription ?? "未知错误")
                        .font(.caption)
                }
            } else {
                Color.gray.opacity(0.3)
            }
        }
        .onAppear {
            loadImage()
        }
    }
    
    private func loadImage() {
        // 如果已经在加载中，或者超出最大加载限制，直接返回
        guard !Self.currentlyLoadingIndices.contains(index),
              Self.currentlyLoadingIndices.count < Self.maxConcurrentLoads else {
            return
        }
        
        // 添加当前索引到加载集合
        Self.currentlyLoadingIndices.insert(index)
        isLoading = true
        error = nil
        
        // 确保 nums 和 index 对齐，避免越界
        guard let decodeNum = nums[safe: index] else {
            print("错误：nums 中未找到索引 \(index) 对应的值，可能 API 数据不一致")
            Self.currentlyLoadingIndices.remove(index)
            return
        }
        
        print("调试信息：图片 URL: \(url), 解密参数 num: \(decodeNum), 索引: \(index)")
        
        guard let imageUrl = URL(string: url) else {
            self.error = NSError(domain: "无效的URL", code: 1, userInfo: nil)
            isLoading = false
            Self.currentlyLoadingIndices.remove(index)
            return
        }
        
        // 加载图片数据
        URLSession.shared.dataTask(with: imageUrl) { data, response, error in
            DispatchQueue.main.async {
                // 移除当前索引
                Self.currentlyLoadingIndices.remove(index)
                self.isLoading = false
                
                if let error = error {
                    self.error = error
                    print("图片加载失败，错误: \(error.localizedDescription)")
                    return
                }
                
                guard let httpResponse = response as? HTTPURLResponse,
                      (200...299).contains(httpResponse.statusCode),
                      let data = data, !data.isEmpty else {
                    self.error = NSError(domain: "无效响应", code: 2, userInfo: nil)
                    print("图片加载失败，无效响应或数据为空")
                    return
                }
                
                if let loadedImage = UIImage(data: data) {
                    print("图片加载成功，开始解密...")
                    let decodedImage = loadedImage.decodeImage(num: decodeNum)
                    self.image = decodedImage
                    print("解密完成，图片已更新")
                } else {
                    self.error = NSError(domain: "图片数据解码失败", code: 4, userInfo: nil)
                    print("图片数据解码失败")
                }
            }
        }.resume()
    }
}

extension Array {
    subscript(safe index: Int) -> Element? {
        return indices.contains(index) ? self[index] : nil
    }
}