TaskList.swift

import SwiftUI
import Combine

struct ContentView: View {

    var body: some View {
        TaskList(tasks: [
            Task(id: 1, title: "Task 1", isCompleted: false),
            Task(id: 2, title: "Task 2", isCompleted: false),
            Task(id: 3, title: "Task 3", isCompleted: true),
            Task(id: 4, title: "Task 4", isCompleted: false)
        ])
    }
}

struct TaskList: View {

    @ObservedObject var tasks: ObservableArray<Task>

    var pendingTasks: [Task] {
        tasks.array.filter { !$0.isCompleted }
    }

    var completedTasks: [Task] {
        tasks.array.filter { $0.isCompleted }
    }

    init(tasks: [Task]) {
        self.tasks = ObservableArray(tasks)
    }

    var body: some View {
        List {
            ForEach(Sections.allCases) { section in
                Section(
                    content: {
                        ForEach($tasks.array) { task in
                            if show(task.wrappedValue, for: section) {
                                TaskCell(task: task)
                            }
                        }
                    },
                    header: { Text(section.rawValue) }
                )
            }
        }
    }

    func show(_ task: Task, for section: Sections) -> Bool {
        section == .pending && !task.isCompleted || section == .completed && task.isCompleted
    }
}

class ObservableArray<T: ObservableObject>: ObservableObject {

    @Published var array: [T]
    private var cancellables = Set<AnyCancellable>()

    init(_ array: [T]) {
        self.array = array
        observeChildrenChanges()
    }

    private func observeChildrenChanges() {
        array.forEach {
            $0.objectWillChange
                .sink { _ in
                    self.objectWillChange.send()
                }
                .store(in: &cancellables)
        }
    }
}

struct TaskCell: View {
    @Binding var task: Task

    var body: some View {
        Button(
            action: {
                task.isCompleted.toggle()
                print("\(task.title) is now \(task.isCompleted)")
            },
            label: {
                HStack {
                    Text(task.title)
                    Spacer()
                    Image(systemName: task.isCompleted ? "checkmark.circle.fill" : "circle")
                }
            }
        )
        .buttonStyle(PlainButtonStyle())
    }
}

class Task: ObservableObject, Identifiable {
    let id: Int
    @Published var isCompleted: Bool
    @Published var title: String

    init(id: Int, title: String, isCompleted: Bool) {
        self.id = id
        self.title = title
        self.isCompleted = isCompleted
    }
}

enum Sections: String, CaseIterable, Identifiable {
    case pending
    case completed

    var id: String { rawValue }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        TaskList(
            tasks: [
                Task(id: 1, title: "Task 1", isCompleted: false),
                Task(id: 2, title: "Task 2", isCompleted: false),
                Task(id: 3, title: "Task 3", isCompleted: true),
                Task(id: 4, title: "Task 4", isCompleted: false)
            ]
        )
    }
}