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

    /// The SwiftData model context for database operations.
    ///
    /// This context is used by the view model to perform efficient database-level queries for counting tasks in each group.
    @Environment(\.modelContext)
    private var modelContext

    /// 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: 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 navigate to a detailed task list for the selected group.
    /// Task counts are fetched on-demand from the model context for each render.
    var body: some View {
        ScrollView {
            VStack(spacing: 16) {
                ForEach(viewModel.groups) { group in
                    NavigationLink(destination: TaskListView(group: group)) {
                        Card(
                            group: group,
                            count: viewModel.count(
                                for: group,
                                in: modelContext
                            )
                        )
                    }
                    .buttonStyle(.plain)
                }
            }
            .padding(.horizontal)
        }
        .navigationTitle("view.task-group-list.navigation.title")
    }
}

// MARK: - Previews

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

#Preview(
    "Task group list with sample tasks",
    traits: .sampleTasks
) {
    NavigationStack {
        TaskGroupListView()
    }
}