using HSchool.Content;
using HSchool.People;
using HSchool.Schedule;

namespace HSchool.Ai;

/// <summary>
/// Where this person ought to be right now. The timetable and the job, not the walk graph.
/// </summary>
public static class Duty
{
    /// <summary>
    /// The room of the current obligation, or <see langword="null"/> when they should be off campus.
    /// A hole in the class table sends the pupil to their homeroom.
    /// </summary>
    public static string? RoomAt(
        Person person,
        SchoolClass? schoolClass,
        Timetable? timetable,
        DefCatalog catalog,
        DateTime time,
        int weekDays)
    {
        ArgumentNullException.ThrowIfNull(person);
        ArgumentNullException.ThrowIfNull(catalog);

        if (!ComesToday(person, timetable, catalog, time, weekDays))
        {
            return null;
        }

        if (IsOtherStaff(person))
        {
            return person.WorkplaceRoomId;
        }

        var utc = DateTime.SpecifyKind(time, DateTimeKind.Utc);
        if (!SchoolDay.IsWorkday(catalog, utc, weekDays))
        {
            return null;
        }

        var slot = SchoolDay.At(catalog, utc, weekDays);
        var day = SchoolDay.WeekdayIndex(utc);
        var lessons = LessonsToday(person, schoolClass, timetable, day);
        if (lessons.Count == 0)
        {
            return person.WorkplaceRoomId;
        }

        if (slot.Kind == DaySlotKind.Lesson)
        {
            var current = lessons.FirstOrDefault(lesson => lesson.Period == slot.Index);
            if (current is not null)
            {
                return current.RoomId;
            }

            return schoolClass?.RoomId ?? person.WorkplaceRoomId;
        }

        if (slot.Kind == DaySlotKind.Break)
        {
            var next = lessons.Where(lesson => lesson.Period > slot.Index).OrderBy(lesson => lesson.Period).FirstOrDefault();
            return next?.RoomId ?? schoolClass?.RoomId ?? person.WorkplaceRoomId;
        }

        var frame = catalog.DayFrame;
        if (frame is not null
            && SchoolDay.TryParseTime(frame.FirstLesson, out var first)
            && utc.TimeOfDay < first.ToTimeSpan())
        {
            return lessons[0].RoomId;
        }

        if (frame is not null
            && SchoolDay.TryLastBell(catalog, out var last)
            && utc.TimeOfDay >= last.ToTimeSpan())
        {
            return null;
        }

        return lessons[0].RoomId;
    }

    public static bool ComesToday(
        Person person,
        Timetable? timetable,
        DefCatalog catalog,
        DateTime time,
        int weekDays)
    {
        if (person.IsParent && !person.IsStaff && !person.IsStudent)
        {
            return false;
        }

        if (!SchoolDay.IsWorkday(catalog, time, weekDays))
        {
            return false;
        }

        if (IsOtherStaff(person))
        {
            return true;
        }

        var day = SchoolDay.WeekdayIndex(time);
        if (person.IsStudent)
        {
            return timetable?.Lessons.Any(lesson =>
                lesson.ClassId == person.ClassId && lesson.Day == day) == true;
        }

        if (person.IsStaff)
        {
            return timetable?.Lessons.Any(lesson =>
                lesson.TeacherId == person.Id && lesson.Day == day) == true;
        }

        return false;
    }

    public static bool IsOtherStaff(Person person) =>
        person.IsStaff && !Staffing.TeacherPosition.Equals(person.Position, StringComparison.Ordinal);

    public static IReadOnlyList<LessonPlacement> LessonsToday(
        Person person,
        SchoolClass? schoolClass,
        Timetable? timetable,
        int day)
    {
        if (timetable is null)
        {
            return [];
        }

        if (person.IsStudent)
        {
            var classId = person.ClassId ?? schoolClass?.Id;
            return timetable.Lessons
                .Where(lesson => lesson.ClassId == classId && lesson.Day == day)
                .OrderBy(lesson => lesson.Period)
                .ToArray();
        }

        if (person.IsStaff)
        {
            return timetable.Lessons
                .Where(lesson => lesson.TeacherId == person.Id && lesson.Day == day)
                .OrderBy(lesson => lesson.Period)
                .ToArray();
        }

        return [];
    }
}