import SwiftUI

struct CachedAsyncImage<Placeholder: View>: View {
    let url: URL?
    @ViewBuilder let placeholder: () -> Placeholder

    @State private var image: Image?
    @State private var isLoading = false

    var body: some View {
        Group {
            if let image {
                image
                    .resizable()
                    .aspectRatio(contentMode: .fill)
            } else {
                placeholder()
                    .task(id: url) {
                        await loadImage()
                    }
            }
        }
    }

    private func loadImage() async {
        guard let url, !isLoading else { return }

        // 检查内存缓存
        if let cached = ImageCache.shared.get(url) {
            self.image = cached
            return
        }

        isLoading = true
        defer { isLoading = false }

        do {
            let (data, _) = try await ImageCache.shared.session.data(from: url)
            #if os(macOS)
            if let nsImage = NSImage(data: data) {
                let img = Image(nsImage: nsImage)
                ImageCache.shared.set(img, for: url)
                self.image = img
            }
            #else
            if let uiImage = UIImage(data: data) {
                let img = Image(uiImage: uiImage)
                ImageCache.shared.set(img, for: url)
                self.image = img
            }
            #endif
        } catch {
            // 加载失败保持 placeholder
        }
    }
}

// MARK: - 图片内存缓存

private final class ImageCache: @unchecked Sendable {
    static let shared = ImageCache()

    private let cache = NSCache<NSURL, CacheEntry>()
    let session: URLSession

    private init() {
        cache.countLimit = 200
        cache.totalCostLimit = 100 * 1024 * 1024 // 100MB

        // 配置磁盘缓存
        let config = URLSessionConfiguration.default
        config.urlCache = URLCache(
            memoryCapacity: 50 * 1024 * 1024,  // 50MB 内存
            diskCapacity: 200 * 1024 * 1024      // 200MB 磁盘
        )
        config.requestCachePolicy = .returnCacheDataElseLoad
        session = URLSession(configuration: config)
    }

    func get(_ url: URL) -> Image? {
        cache.object(forKey: url as NSURL)?.image
    }

    func set(_ image: Image, for url: URL) {
        cache.setObject(CacheEntry(image: image), forKey: url as NSURL)
    }
}

private final class CacheEntry {
    let image: Image
    init(image: Image) { self.image = image }
}