todos/App/Sources/Views/TaskGroupListView.swift

import SwiftData
import SwiftUI

/// A view that displays todo tasks grouped by date and completion categories.
///
/// This view serves as the main interface for browsing tasks organized into four groups:
/// - **Today**: Tasks due today that are not yet completed
/// - **Upcoming**: Tasks due in the future that are not yet completed
/// - **Overdue**: Tasks due in the past that are not yet completed
/// - **Completed**: Tasks that have been marked as done
struct TaskGroupListView: View {

    // MARK: Properties

    /// Binding to the currently selected todo task group.
    ///
    /// When provided, the view will use this binding for navigation split view selection.
    @Binding
    private var group: TodoGroup?

    /// Query to monitor all todo tasks for changes.
    ///
    /// This query triggers view updates whenever todo tasks are inserted, updated, or deleted,
    /// ensuring the task counts displayed in the view remain accurate.
    @Query
    private var todos: [Todo]

    /// The view model managing the state and logic for this view.
    ///
    /// Handles task counting and provides access to all task groups.
    /// Initialized with the default calendar for date calculations.
    @State
    private var viewModel = ViewModel()

    // MARK: Initializers

    /// Creates a task group list view with a binding to the selected group.
    ///
    /// This initializer configures the view for use in a navigation split view,
    /// where the binding tracks which task group is currently selected in the sidebar.
    ///
    /// - Parameter group: A binding to the currently selected task group.
    init(_ group: Binding<TodoGroup?>) {
        self._group = group
    }

    // MARK: Body

    /// The content and behavior of the view.
    ///
    /// Displays a scrollable vertical list of task group cards. Each card shows:
    /// - The group's icon in its associated color
    /// - The group's title
    /// - The current count of tasks in that group
    ///
    /// Cards are tappable and update the selected group binding for navigation split view.
    /// Task counts are fetched on-demand from the model context for each render.
    var body: some View {
        List(
            viewModel.groups,
            selection: $group
        ) { group in
            Card(
                group: group,
                count: viewModel.count(
                    todos,
                    for: group
                )
            )
            .listRowBackground(Color.clear)
            .listRowSeparator(.hidden)
            .tag(group)
        }
        .listStyle(.plain)
        .navigationTitle("view.task-group-list.navigation.title")
        .sensoryFeedback(
            .selection,
            trigger: group
        )
    }
}

// MARK: - Previews

#Preview(
    "Task group list with empty tasks",
    traits: .emptyContainer
) {
    @Previewable
    @State
    var group: TodoGroup?

    NavigationStack {
        TaskGroupListView($group)
    }
}

#Preview(
    "Task group list with sample tasks",
    traits: .sampleTasks
) {
    @Previewable
    @State
    var group: TodoGroup?

    NavigationStack {
        TaskGroupListView($group)
    }
}