Impressia/Vernissage/Views/HomeFeedView.swift

//
//  https://mczachurski.dev
//  Copyright © 2022 Marcin Czachurski and the repository contributors.
//  Licensed under the MIT License.
//

import SwiftUI

struct HomeFeedView: View {
    @Environment(\.managedObjectContext) private var viewContext
    @EnvironmentObject var applicationState: ApplicationState
    
    @State private var firstLoadFinished = false
    @State private var allItemsBottomLoaded = false
    
    private static let initialColumns = 1
    @State private var gridColumns = Array(repeating: GridItem(.flexible()), count: initialColumns)
        
    @FetchRequest var dbStatuses: FetchedResults<StatusData>
    
    init(accountId: String) {
        _dbStatuses = FetchRequest<StatusData>(
            sortDescriptors: [SortDescriptor(\.id, order: .reverse)],
            predicate: NSPredicate(format: "pixelfedAccount.id = %@", accountId))
    }
    
    var body: some View {
        ScrollView {
            LazyVGrid(columns: gridColumns) {
                ForEach(dbStatuses, id: \.self) { item in
                    NavigationLink(destination: StatusView(statusId: item.id,
                                                           imageBlurhash: item.attachments().first?.blurhash,
                                                           imageWidth: item.attachments().first?.metaImageWidth,
                                                           imageHeight: item.attachments().first?.metaImageHeight)
                        .environmentObject(applicationState)) {
                        ImageRow(status: item)
                    }
                    .buttonStyle(EmptyButtonStyle())
                }
                
                if allItemsBottomLoaded == false && firstLoadFinished == true {
                    LoadingIndicator()
                        .task {
                            do {
                                if let accountData = self.applicationState.accountData {
                                    let newStatusesCount = try await TimelineService.shared.onBottomOfList(for: accountData)
                                    if newStatusesCount == 0 {
                                        allItemsBottomLoaded = true
                                    }
                                }
                            } catch {
                                print("Error", error)
                            }
                        }
                }
            }
        }
        .overlay(alignment: .center) {
            if firstLoadFinished == false {
                LoadingIndicator()
            } else {
                if self.dbStatuses.isEmpty {
                    VStack {
                        Image(systemName: "photo.on.rectangle.angled")
                            .font(.largeTitle)
                            .padding(.bottom, 4)
                        Text("Unfortunately, there are no photos here.")
                            .font(.title3)
                    }.foregroundColor(.lightGrayColor)
                }
            }
        }
        .refreshable {
            do {
                if let accountData = self.applicationState.accountData {
                    _ = try await TimelineService.shared.onTopOfList(for: accountData)
                }
            } catch {
                print("Error", error)
            }
        }
        .task {
            do {
                defer {
                    Task { @MainActor in
                        self.firstLoadFinished = true
                    }
                }

                if self.dbStatuses.isEmpty == false {
                    return
                }

                if let accountData = self.applicationState.accountData {
                    _ = try await TimelineService.shared.onTopOfList(for: accountData)
                }
            } catch {
                print("Error", error)
            }
        }
    }
}

struct HomeFeedView_Previews: PreviewProvider {
    static var previews: some View {
        HomeFeedView(accountId: "")
    }
}