import Foundation
import SwiftData

/// Extension providing convenient initializers for fetching todos by group category.
///
/// This extension allows creating fetch descriptors that automatically filter and sort todos
/// based on their completion status and due dates according to the specified `TodoGroup`.
extension FetchDescriptor where T == Todo {

    /// Creates a fetch descriptor for todos filtered and sorted by a specific group.
    ///
    /// This initializer provides a convenient way to fetch todos categorized by their temporal
    /// relevance and completion status. Each group applies appropriate predicates and sort orders:
    ///
    /// - **Completed**: All tasks marked as done, sorted by completion date (most recent first)
    /// - **Overdue**: Incomplete tasks with due dates before today, sorted by due date (most recent first)
    /// - **Today**: Incomplete tasks due today, sorted by due date (earliest first)
    /// - **Upcoming**: Incomplete tasks due after today, sorted by due date (earliest first)
    ///
    /// - Parameters:
    ///   - group: The todo group category to filter by.
    ///   - calendar: The calendar to use for date calculations. Defaults to `.current`.
    init(
        group: TodoGroup,
        calendar: Calendar = .current
    ) {
        let today = calendar.startOfDay(for: .now)
        let tomorrow = calendar.date(byAdding: .day, value: 1, to: today) ?? today

        switch group {
            case .completed:
                self.init(
                    predicate: #Predicate { $0.completed != nil },
                    sortBy: [.init(\.completed, order: .reverse)]
                )
            case .overdue:
                self.init(
                    predicate: #Predicate { $0.completed == nil && $0.due < today },
                    sortBy: [.init(\.due, order: .reverse)]
                )
            case .today:
                self.init(
                    predicate: #Predicate { $0.completed == nil && $0.due >= today && $0.due < tomorrow },
                    sortBy: [.init(\.due, order: .forward)]
                )
            case .upcoming:
                self.init(
                    predicate: #Predicate { $0.completed == nil && $0.due >= tomorrow },
                    sortBy: [.init(\.due, order: .forward)]
                )
        }
    }

}