import SwiftUI
import Photos

struct ThumbnailImageInner: View {
    @ObservedObject var assetImage: PHAssetImage
    var size: CGFloat
    
    var body: some View {
        Image(nsImage: assetImage.image)
            .resizable()
            .scaledToFill()
            .clipped()
            .frame(width: size, height: size, alignment: .center)
    }
}

/// Render a single thumbnail image in the thumbnail picker.
///
/// Thumbnails are square, and they expand to fill the square.  This may
/// mean some information gets cropped out -- that's okay, these are only
/// small previews, not complete images.
struct ThumbnailImage: View {
    
    // Implementation note: the reason we pass in a bunch of individual
    // properties rather than the whole asset is because we need an
    // @EnvironmentObject (the PhotosLibrary) to create the PHAssetImage,
    // so we can stick the latter in an @ObservedObject.
    //
    // But EnvironmentObject values aren't passed down until you call the
    // `body` method, which is too late!  So instead we have the parent
    // view call into PhotosLibrary and pass in the relevant values here.
    //
    // The `getAssetImage` is a callback so we can load those assets somewhat
    // lazily; the ThumbnailImageInner is separate so it can subscribe to
    // updates to the PHAssetImage.
    @State var assetImage: PHAssetImage? = nil
    
    var index: Int
    var state: ReviewState?
    var isFocused: Bool
    var isFavorite: Bool
    private var getAssetImage: () -> PHAssetImage
    
    init(index: Int, state: ReviewState?, isFavorite: Bool, isFocused: Bool, getAssetImage: @escaping () -> PHAssetImage) {
        self.index = index
        
        self.isFavorite = isFavorite
        self.state = state
        
        self.isFocused = isFocused
        self.getAssetImage = getAssetImage
    }
    
    private func size() -> CGFloat {
        isFocused ? 70 : 50
    }
    
    private func cornerRadius() -> CGFloat {
        isFocused ? 7 : 5
    }
    
    var body: some View {
        if let thisAssetImage = assetImage {
            ThumbnailImageInner(assetImage: thisAssetImage, size: size())
                .cornerRadius(cornerRadius())
                .reviewStateColor(isRejected: state == .Rejected)
                .reviewStateBorder(for: state, with: cornerRadius())
                .reviewStateIcon(for: state, isFocused)
                .favoriteHeartIcon(isFavorite, isFocused)
                
        } else {
            ProgressView()
                .onAppear {
                    self.assetImage = getAssetImage()
                }
        }
        
    }
}