import SwiftUI
import PhotosUI

struct NineGridImagePicker: View {
    @Binding var images: [UIImage]
    var maxCount: Int = 9
    var cornerRadius: CGFloat = 16
    var spacing: CGFloat = 8
    var horizontalPadding: CGFloat = 20
    var onTapImage: (Int) -> Void = { _ in }

    @State private var pickerItems: [PhotosPickerItem] = []

    var body: some View {
        GeometryReader { geometry in
            let columns = Array(repeating: GridItem(.flexible(), spacing: spacing), count: 3)
            let columnsCount: CGFloat = 3
            let totalSpacing = spacing * (columnsCount - 1)
            let availableWidth = geometry.size.width - horizontalPadding * 2
            let cellSide = (availableWidth - totalSpacing) / columnsCount

            LazyVGrid(columns: columns, spacing: spacing) {
                ForEach(0..<maxCount, id: \.self) { index in
                    ZStack {
                        // 占位背景（仅 DEBUG 可见）
                        #if DEBUG
                        if index >= images.count && !(index == images.count && images.count < maxCount) {
                            RoundedRectangle(cornerRadius: cornerRadius)
                                .fill(Color.white.opacity(0.08))
                        }
                        #endif

                        if index < images.count {
                            // 图片格子
                            ZStack(alignment: .topTrailing) {
                                Image(uiImage: images[index])
                                    .resizable()
                                    .scaledToFill()
                                    .frame(maxWidth: .infinity, maxHeight: .infinity)
                                    .contentShape(RoundedRectangle(cornerRadius: cornerRadius))
                                    .onTapGesture { onTapImage(index) }

                                Button {
                                    removeImage(at: index)
                                } label: {
                                    Image(systemName: "xmark.circle.fill")
                                        .foregroundColor(.white)
                                        .background(Circle().fill(Color.black.opacity(0.4)))
                                        .font(.system(size: 16, weight: .bold))
                                }
                                .padding(6)
                                .buttonStyle(.plain)
                            }
                        } else if index == images.count && images.count < maxCount {
                            // 添加按钮格子
                            PhotosPicker(
                                selection: $pickerItems,
                                maxSelectionCount: maxCount - images.count,
                                selectionBehavior: .ordered,
                                matching: .images
                            ) {
                                ZStack {
                                    RoundedRectangle(cornerRadius: cornerRadius)
                                        .fill(Color(hex: 0x1C143A))
                                    Image(systemName: "plus")
                                        .foregroundColor(.white.opacity(0.6))
                                        .font(.system(size: 32, weight: .semibold))
                                }
                            }
                            .onChange(of: pickerItems) { _, newItems in
                                handlePickerItems(newItems)
                            }
                        }
                    }
                    .frame(height: cellSide)
                    .clipShape(RoundedRectangle(cornerRadius: cornerRadius))
                    .contentShape(RoundedRectangle(cornerRadius: cornerRadius))
                }
            }
            .padding(.horizontal, horizontalPadding)
        }
        .frame(height: gridHeight(forCount: max(images.count, 1)))
    }

    private func gridHeight(forCount count: Int) -> CGFloat {
        // 通过一个近似：用屏幕宽度估算高度以确保父布局正确测量。
        // 每行 3 个，行数 = ceil(count / 3.0)。在 GeometryReader 中真实高度会覆盖此近似。
        let screenWidth = UIScreen.main.bounds.width
        let columnsCount: CGFloat = 3
        let totalSpacing = spacing * (columnsCount - 1)
        let availableWidth = screenWidth - horizontalPadding * 2
        let side = (availableWidth - totalSpacing) / columnsCount
        let rows = ceil(CGFloat(count) / 3.0)
        let totalRowSpacing = spacing * max(rows - 1, 0)
        return side * rows + totalRowSpacing
    }

    private func handlePickerItems(_ items: [PhotosPickerItem]) {
        guard !items.isEmpty else { return }
        Task { @MainActor in
            var appended: [UIImage] = []
            for item in items {
                if images.count + appended.count >= maxCount { break }
                if let data = try? await item.loadTransferable(type: Data.self),
                   let image = UIImage(data: data) {
                    appended.append(image)
                }
            }
            if !appended.isEmpty {
                images.append(contentsOf: appended)
            }
            pickerItems = []
        }
    }

    private func removeImage(at index: Int) {
        guard images.indices.contains(index) else { return }
        images.remove(at: index)
    }
}