ChWebsiteApp/CHDataManagement/Views/Posts/PostImageGalleryView.swift

import SwiftUI
import SFSafeSymbols

private struct NavigationIcon: View {

    let symbol: SFSymbol

    let edge: Edge.Set

    var body: some View {
        SwiftUI.Image(systemSymbol: symbol)
            .resizable()
            .aspectRatio(contentMode: .fit)
            .padding(5)
            .padding(edge, 2)
            .fontWeight(.light)
            .foregroundStyle(Color.white.opacity(0.8))
            .frame(width: 30, height: 30)
            .background(Color.black.opacity(0.7).clipShape(Circle()))
    }
}

struct PostImageGalleryView: View {

    @ObservedObject
    var post: LocalizedPost

    @State private var currentIndex = 0

    @State
    private var showImagePicker = false

    private var imageAtCurrentIndex: Image? {
        guard !post.images.isEmpty else {
            return nil
        }
        guard currentIndex < post.images.count else {
            return post.images.last?.imageToDisplay
        }
        return post.images[currentIndex].imageToDisplay
    }

    var body: some View {
        ZStack(alignment: .center) {
            ZStack(alignment: .bottomTrailing) {
                ZStack(alignment: .bottom) {
                    if let imageAtCurrentIndex {
                        imageAtCurrentIndex
                            .resizable()
                            .scaledToFit()
                    }
                    if post.images.count > 1 {
                        HStack(spacing: 8) {
                            ForEach(0..<post.images.count, id: \.self) { index in
                                Circle()
                                    .fill(index == currentIndex ? Color.white : Color.gray)
                                    .frame(width: 10, height: 10)
                            }
                        }
                        .padding(.bottom, 10)
                    }
                }
                HStack(spacing: 5) {
                    Button(action: shiftBack) {
                        NavigationIcon(symbol: .arrowTurnUpLeft, edge: .trailing)
                    }
                    Button(action: shiftForward) {
                        NavigationIcon(symbol: .arrowTurnUpRight, edge: .leading)
                    }
                    Spacer()
                    Button(action: { showImagePicker = true }) {
                        NavigationIcon(symbol: .plus, edge: .all)
                    }
                    Button(action: removeImage) {
                        NavigationIcon(symbol: .trash, edge: .all)
                    }
                }.padding()
            }
            .buttonStyle(.plain)
            .foregroundStyle(.blue)
            if post.images.count > 1 {
                HStack {
                    Button(action: previous) {
                        NavigationIcon(symbol: .chevronLeft, edge: .trailing)
                    }
                    .buttonStyle(.plain)
                    .padding()

                    Spacer()
                    Button(action: next) {
                        NavigationIcon(symbol: .chevronRight, edge: .leading)
                    }
                    .buttonStyle(.plain)
                    .padding()
                }
            }
        }
        .sheet(isPresented: $showImagePicker) {
            ImagePickerView(
                showImagePicker: $showImagePicker,
                post: post
            )
        }
    }

    private func previous() {
        if currentIndex > 0 {
            currentIndex -= 1
        } else {
            currentIndex = post.images.count - 1
        }
    }

    private func next() {
        if currentIndex < post.images.count - 1 {
            currentIndex += 1
        } else {
            currentIndex = 0
        }
    }

    private func shiftBack() {
        guard currentIndex > 0 else {
            return
        }
        post.images.swapAt(currentIndex, currentIndex-1)
        currentIndex -= 1
    }

    private func shiftForward() {
        guard currentIndex < post.images.count - 1 else {
            return
        }
        post.images.swapAt(currentIndex, currentIndex+1)
        currentIndex += 1
    }

    private func removeImage() {
        post.images.remove(at: currentIndex)
        if currentIndex >= post.images.count {
            currentIndex = post.images.count - 1
        }
    }
}

#Preview(traits: .fixedLayout(width: 300, height: 250)) {
    PostImageGalleryView(post: .german)
}