ios-tracker/HabitTracker/Support/ModelContext+Habit.swift

import Foundation
import SwiftData

extension ModelContext {
    /// Toggles completion for a habit on a given day: removes the entry if it
    /// exists, otherwise inserts one normalized to the start of that day.
    func toggleCompletion(for habit: Habit, on day: Date) {
        let calendar = Calendar.current
        if let entry = habit.entries.first(where: { calendar.isDate($0.date, inSameDayAs: day) }) {
            delete(entry)
        } else {
            let entry = HabitEntry(date: calendar.startOfDay(for: day), habit: habit)
            insert(entry)
        }
        WidgetSync.refresh(self)
    }
}