todos/App/Sources/Views/TaskListView.swift

import SwiftData
import SwiftUI

/// A view that displays filtered todo tasks for a specific task group.
///
/// This view provides the presentation layer for displaying and managing tasks within a specific group category.
/// It follows the MVVM pattern, delegating business logic to a view model and data fetching to a separate content view.
struct TaskListView: View {

    // MARK: Properties

    /// The SwiftData model context for performing data operations.
    @Environment(\.modelContext)
    private var modelContext

    /// The view model managing the state and business logic for this view.
    ///
    /// This view model holds the group configuration and completion filter state.
    @State
    private var viewModel: ViewModel

    // MARK: Initialization

    /// Creates a new task list view for a specific group.
    ///
    /// Initializes the view with a view model configured for the specified group.
    /// The view model manages the state for completion filtering and task reordering,
    /// while the view handles the presentation layer including navigation and toolbar.
    ///
    /// - Parameter group: The todo group category to display tasks for.
    /// - Note: The group determines which tasks are fetched, whether
    ///   completion filtering is available, and whether drag and drop reordering is enabled.
    init(group: TodoGroup) {
        _viewModel = .init(initialValue: ViewModel(group: group))
    }

    // MARK: Body

    /// The content and behavior of the view.
    ///
    /// Displays the task list content with navigation title and toolbar controls.
    /// The toolbar includes a completion filter toggle for groups that support it.
    var body: some View {
        Content(
            group: viewModel.group,
            showCompleted: viewModel.showCompleted
        ) { tasks, offsets in
            viewModel.deleteTasks(
                tasks,
                at: offsets,
                from: modelContext
            )
        } onReorder: { tasks, source, destination in
            viewModel.reorderTasks(
                tasks,
                from: source,
                to: destination
            )
        }
        .navigationTitle(viewModel.navigationTitle)
        .toolbar {
            if viewModel.canShowCompleted {
                Menu {
                    Button.init(
                        viewModel.buttonCompleted.title,
                        systemImage: viewModel.buttonCompleted.icon
                    ) {
                        viewModel.toggleCompletedVisibility()
                    }
                } label: {
                    Label(
                        "view.task-list.label.actions",
                        systemImage: "ellipsis"
                    )
                }
            }
        }
    }

}

// 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)
    }
}