using HSchool.Content;

namespace HSchool.Simulation;

/// <summary>
/// Turns clock edges into world facts. One dayStart per morning crossing, one lessonStart per
/// school when the bell enters a lesson period — not one per class.
/// </summary>
internal static class EventSystem
{
    public static IReadOnlyList<WorldEvent> Detect(School school, DateTime before, DateTime after)
    {
        if (school.Catalog is null || after <= before)
        {
            return [];
        }

        var facts = new List<WorldEvent>(2);
        if (CrossedWorkMorning(school.Catalog, before, after, school.SchoolWeekDays))
        {
            facts.Add(new WorldEvent(EventTriggers.DayStart));
        }

        if (EnteredLessonPeriod(school.Catalog, before, after, school.SchoolWeekDays))
        {
            facts.Add(new WorldEvent(EventTriggers.LessonStart));
        }

        return facts;
    }

    private static bool CrossedWorkMorning(DefCatalog catalog, DateTime before, DateTime after, int weekDays)
    {
        if (!PersonDayLog.CrossedDayStart(before, after))
        {
            return false;
        }

        return SchoolDay.IsWorkday(catalog, after, weekDays);
    }

    private static bool EnteredLessonPeriod(DefCatalog catalog, DateTime before, DateTime after, int weekDays)
    {
        var beforeSlot = SchoolDay.At(catalog, before, weekDays);
        var afterSlot = SchoolDay.At(catalog, after, weekDays);
        return afterSlot.Kind == DaySlotKind.Lesson && beforeSlot != afterSlot;
    }
}