Caps-iOS/Caps/Views/GridView.swift

import SwiftUI
import SFSafeSymbols

struct GridView: View {

    let database: Database


    @AppStorage("currentGridName")
    private(set) var currentGridName = "default"

    private var defaultImageGrid: ImageGrid {
        .init(columns: 40, capPlacements: database.caps.keys.sorted())
    }

    var imageSize: CGFloat {
        CapsApp.thumbnailImageSize
    }

    private let verticalInsetFactor: CGFloat = cos(.pi / 6)

    private let minScale: CGFloat = 1.0

    private let maxScale: CGFloat = 0.5

    private let cancelButtonSize: CGFloat = 75
    private let cancelIconSize: CGFloat = 25

    @Binding
    var isPresented: Bool

    var image: ImageGrid

    @State var scale: CGFloat = 1.0

    @State var lastScaleValue: CGFloat = 1.0

    init(isPresented: Binding<Bool>, database: Database) {
        self._isPresented = isPresented
        self.database = database
        self.image = .init(columns: 1, capPlacements: [])

        if let image = database.load(grid: currentGridName) {
            self.image = image
        } else {
            self.image = defaultImageGrid
            currentGridName = "default"
        }
    }

    var columnCount: Int {
        image.columns
    }

    var capCount: Int {
        image.capCount
    }

    var imageHeight: CGFloat {
        (CGFloat(capCount) / CGFloat(columnCount)).rounded(.up) * verticalInsetFactor * imageSize + (1-verticalInsetFactor) * imageSize
    }

    var imageWidth: CGFloat {
        imageSize * (CGFloat(columnCount) + 0.5)
    }

    var magnificationGesture: some Gesture {
        MagnificationGesture()
            .onChanged { val in
                let delta = val / self.lastScaleValue
                self.lastScaleValue = val
                self.scale = max(min(self.scale * delta, minScale), maxScale)
            }
            .onEnded { val in
                // without this the next gesture will be broken
                self.lastScaleValue = 1.0
            }
    }

    var gridView: some View {
        let gridItems = Array(repeating: GridItem(.fixed(imageSize), spacing: 0), count: columnCount)

        return LazyVGrid(columns: gridItems, alignment: .leading, spacing: 0) {
            ForEach(image.items) { item in
                CachedCapImage(
                    item.id,
                    check: { cachedImage(item.cap) },
                    fetch: { await fetchImage(item.cap) },
                    content: { $0.resizable() },
                    placeholder: { ProgressView() })
                .frame(width: imageSize,
                       height: imageSize)
                .clipShape(Circle())
                .offset(x: isEvenRow(item.id) ? 0 : imageSize / 2)
                .frame(width: imageSize,
                       height: imageSize * verticalInsetFactor)
            }
        }
        .frame(width: imageWidth)
    }

    var body: some View {
        ZStack {
            ScrollView([.vertical, .horizontal]) {
                gridView
                .scaleEffect(scale)
                .frame(
                    width: imageWidth * scale,
                    height: imageHeight * scale
                )
            }
            .gesture(magnificationGesture)
            .onDisappear {
                database.save(image, named: currentGridName)
            }
            
            VStack {
                Spacer()
                HStack {
                    Spacer()
                    IconButton(action: saveScreenshot,
                               icon: .squareAndArrowDown,
                               iconSize: cancelIconSize,
                               buttonSize: cancelButtonSize)
                    .padding()
                    IconButton(action: dismiss,
                               icon: .xmark,
                               iconSize: cancelIconSize,
                               buttonSize: cancelButtonSize)
                    .padding()
                }
            }
        }
    }

    func isEvenRow(_ idx: Int) -> Bool {
        (idx / columnCount) % 2 == 0
    }

    private func cachedImage(_ cap: Int) -> UIImage? {
        let image = CapImage(
            cap: cap,
            version: database
                .mainImage(for: cap))
        return database.images.cachedImage(image)
    }

    private func fetchImage(_ cap: Int) async -> UIImage? {
        let image = CapImage(
            cap: cap,
            version: database
                .mainImage(for: cap))
        return await database.images.image(image, download: true)
    }

    private func dismiss() {
        isPresented = false
    }

    private func saveScreenshot() {
        let image = gridView.snapshot()
        UIImageWriteToSavedPhotosAlbum(image, nil, nil, nil)
    }
}

struct GridView_Previews: PreviewProvider {
    static var previews: some View {
        GridView(isPresented: .constant(true), database: .largeMock)
    }
}