import SwiftData
import SwiftUI

/// A view that displays all todo tasks for a specific task group.
///
/// This view shows a filtered list of tasks based on the selected group (today, upcoming, past, or completed).
/// The view uses a view model to separate business logic from presentation.
struct TaskListView: View {
    
    // MARK: Properties
    
    /// Query to fetch todos filtered by the current group.
    @Query
    private var tasks: [Todo]
    
    /// The view model managing the business logic for this view.
    @State
    private var viewModel: ViewModel

    // MARK: Initialization
    
    /// Creates a new task list view for a specific group.
    /// - Parameter group: The todo group to display tasks for.
    init(group: TodoGroup) {
        _tasks = .init(FetchDescriptor<Todo>(group: group))
        _viewModel = .init(initialValue: ViewModel(group: group))
    }
    
    // MARK: Body
    
    /// The content and behavior of the view.
    ///
    /// Displays a list of tasks filtered by the current group.
    var body: some View {
        Group {
            if tasks.isEmpty {
                ContentUnavailableView(
                    "view.task-list.content-unavailable.title",
                    systemImage: "checkmark.circle"
                )
            } else {
                List {
                    ForEach(tasks) { todo in
                        Item(todo)
                    }
                }
                .listStyle(.grouped)
            }
        }
        .navigationTitle(viewModel.navigationTitle)
    }
}

// MARK: - Previews

#Preview(
    "Task list with empty tasks",
    traits: .emptyContainer
) {
    NavigationStack {
        TaskListView(group: .today)
    }
}

#Preview(
    "Task list - today",
    traits: .sampleTasks
) {
    NavigationStack {
        TaskListView(group: .today)
    }
}

#Preview(
    "Task list - upcoming",
    traits: .sampleTasks
) {
    NavigationStack {
        TaskListView(group: .upcoming)
    }
}

#Preview(
    "Task list - overdue",
    traits: .sampleTasks
) {
    NavigationStack {
        TaskListView(group: .overdue)
    }
}

#Preview(
    "Task list - completed",
    traits: .sampleTasks
) {
    NavigationStack {
        TaskListView(group: .completed)
    }
}