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

namespace HSchool.Ai;

/// <summary>When this person appears at the yard and when they start walking home today.</summary>
public readonly record struct DayPlan(DateOnly Day, DateTime? AppearAt, DateTime? WalkHomeAt, string? FirstRoom)
{
    public bool Comes => AppearAt is not null;
}

/// <summary>
/// Day plans. Rain and snow arrive as already-counted extra minutes — this project does not
/// know precipitation.
/// </summary>
public static class DayPlans
{
    public static DayPlan Build(
        DefCatalog catalog,
        WalkGraph walks,
        Person person,
        SchoolClass? schoolClass,
        Timetable? timetable,
        DateTime time,
        int weekDays,
        int schoolSeed,
        int extraCommuteMinutes = 0)
    {
        ArgumentNullException.ThrowIfNull(catalog);
        ArgumentNullException.ThrowIfNull(walks);
        ArgumentNullException.ThrowIfNull(person);

        var utc = DateTime.SpecifyKind(time, DateTimeKind.Utc);
        var day = DateOnly.FromDateTime(utc);
        if (!Duty.ComesToday(person, timetable, catalog, utc, weekDays) || catalog.DayFrame is null)
        {
            return new DayPlan(day, null, null, null);
        }

        var weekday = SchoolDay.WeekdayIndex(utc);
        var firstRoom = FirstRoom(person, schoolClass, timetable, catalog, weekday);
        if (firstRoom is null)
        {
            return new DayPlan(day, null, null, null);
        }

        var firstStart = FirstStart(person, schoolClass, timetable, catalog, weekday);
        var lastEnd = LastEnd(person, schoolClass, timetable, catalog, weekday);
        var travel = walks.Minutes(walks.TerritoryId, firstRoom);
        if (float.IsInfinity(travel))
        {
            travel = 0f;
        }

        var slack = SlackMinutes(catalog, person, schoolSeed, day) + Math.Max(0, extraCommuteMinutes);
        var appear = DateTime.SpecifyKind(utc.Date.Add(firstStart.ToTimeSpan()).AddMinutes(-(travel + slack)), DateTimeKind.Utc);
        var walkHome = DateTime.SpecifyKind(utc.Date.Add(lastEnd.ToTimeSpan()), DateTimeKind.Utc);
        return new DayPlan(day, appear, walkHome, firstRoom);
    }

    private static string? FirstRoom(
        Person person,
        SchoolClass? schoolClass,
        Timetable? timetable,
        DefCatalog catalog,
        int weekday)
    {
        if (Duty.IsOtherStaff(person))
        {
            return person.WorkplaceRoomId;
        }

        var lessons = Duty.LessonsToday(person, schoolClass, timetable, weekday);
        return lessons.Count > 0 ? lessons[0].RoomId : schoolClass?.RoomId;
    }

    private static TimeOnly FirstStart(
        Person person,
        SchoolClass? schoolClass,
        Timetable? timetable,
        DefCatalog catalog,
        int weekday)
    {
        var frame = catalog.DayFrame!;
        if (Duty.IsOtherStaff(person))
        {
            return SchoolDay.PeriodStart(frame, 1);
        }

        var lessons = Duty.LessonsToday(person, schoolClass, timetable, weekday);
        return lessons.Count > 0 ? SchoolDay.PeriodStart(frame, lessons[0].Period) : SchoolDay.PeriodStart(frame, 1);
    }

    private static TimeOnly LastEnd(
        Person person,
        SchoolClass? schoolClass,
        Timetable? timetable,
        DefCatalog catalog,
        int weekday)
    {
        var frame = catalog.DayFrame!;
        if (Duty.IsOtherStaff(person))
        {
            return SchoolDay.PeriodEnd(frame, frame.LessonCount);
        }

        var lessons = Duty.LessonsToday(person, schoolClass, timetable, weekday);
        return lessons.Count > 0
            ? SchoolDay.PeriodEnd(frame, lessons[^1].Period)
            : SchoolDay.PeriodEnd(frame, frame.LessonCount);
    }

    private static int SlackMinutes(DefCatalog catalog, Person person, int schoolSeed, DateOnly day)
    {
        var rng = new Random(Seed.Mix(schoolSeed, person.Id, day.DayNumber, Seed.CommuteSalt));
        var min = 0;
        var max = 6;
        if (catalog.BehaviorRules is { } rules)
        {
            min = rules.CommuteSlackMin;
            max = rules.CommuteSlackMax;
        }

        var extra = rng.Next(min, max + 1);
        foreach (var name in person.Traits)
        {
            if (catalog.Traits.TryGetValue(name, out var trait))
            {
                extra += trait.CommuteMinutes;
            }
        }

        return extra;
    }
}