using Arch.Core;
using HSchool.Ai;
using HSchool.Content;
using HSchool.People;
using HSchool.Schedule;

namespace HSchool.Simulation;

/// <summary>
/// One save: a name, a calendar, a frozen def catalog, a map instance, the ECS world, and — once
/// people exist — the roster those entities were built from.
/// </summary>
public sealed class School : IDisposable
{
    /// <summary>Longest name a school may carry, in characters.</summary>
    public const int MaxNameLength = 40;

    private bool _disposed;

    internal School(int id, string name, DateTime startDate, DefCatalog? catalog, MapLayout? map)
    {
        Id = id;
        Name = name;
        Clock = new GameClock(startDate);
        Catalog = catalog;
        Map = map;
        World = World.Create();
    }

    /// <summary>A brand-new school: calendar running at the start date, empty world.</summary>
    public static School Create(
        int id,
        string name,
        DateTime startDate,
        DefCatalog? catalog = null,
        MapLayout? map = null) =>
        new(id, name, startDate, catalog, map);

    /// <summary>Rebuilds a school from a save. Time, pause and speed come from disk, not defaults.</summary>
    public static School Load(
        int id,
        string name,
        DateTime time,
        bool running,
        int speedIndex,
        DefCatalog? catalog = null,
        MapLayout? map = null)
    {
        var school = new School(id, name, time, catalog, map);
        school.Clock.IsRunning = running;
        school.Clock.SpeedIndex = speedIndex;
        return school;
    }

    public int Id { get; }

    public string Name { get; }

    public GameClock Clock { get; }

    /// <summary>Frozen at create/load. Null only in clock-only unit tests.</summary>
    public DefCatalog? Catalog { get; }

    /// <summary>The school's map instance. Null only in clock-only unit tests.</summary>
    public MapLayout? Map { get; }

    /// <summary>The Arch world backing this school. Only this school's worker thread may touch it.</summary>
    public World World { get; }

    /// <summary>Composition snapshot. Null in clock-only tests or before <see cref="InstallPeople"/>.</summary>
    public Roster? Roster { get; private set; }

    /// <summary>People looking for work. Not in the roster and not in the World until hired.</summary>
    public ApplicantPool? Applicants { get; private set; }

    public int PeopleSeed { get; private set; }

    /// <summary>Name pack used to generate this school's people. Needed again on 1 September.</summary>
    public string? NameSetId { get; private set; }

    /// <summary>Last built table. Null until the worker installs people.</summary>
    public Timetable? Timetable { get; private set; }

    /// <summary>True after yearly intake until the worker rebuilds around remaining locks.</summary>
    public bool TimetableDirty { get; private set; }

    /// <summary>Walk matrix for this map. Null in clock-only tests.</summary>
    internal WalkGraph? Walks { get; private set; }

    internal int SchoolWeekDays { get; private set; } = 5;

    internal int MaxDecisionsPerTick { get; private set; } = 64;

    internal int MaxSkipDays { get; private set; } = 400;

    internal DateOnly? PlanDay { get; set; }

    internal DaySlot? LastDecisionSlot { get; set; }

    internal Dictionary<string, DayPlan> Plans { get; } = new(StringComparer.Ordinal);

    internal Queue<string> DecisionQueue { get; } = new();

    internal int DecisionBudget { get; set; }

    public int PendingDecisionCount => DecisionQueue.Count;

    public void QueueDecision(string personId)
    {
        ObjectDisposedException.ThrowIf(_disposed, this);
        ArgumentException.ThrowIfNullOrWhiteSpace(personId);
        PresenceSystem.Enqueue(this, personId);
    }

    /// <summary>
    /// Installs a roster that already matches the map. Spawns entities; does not write to disk.
    /// </summary>
    public void InstallPeople(Roster roster, int seed, string? nameSetId = null, ApplicantPool? applicants = null)
    {
        ObjectDisposedException.ThrowIf(_disposed, this);
        ArgumentNullException.ThrowIfNull(roster);

        Roster = roster;
        PeopleSeed = seed;
        NameSetId = nameSetId;
        Applicants = applicants;
        RosterSpawner.Spawn(World, roster);
        PlanDay = null;
        LastDecisionSlot = null;
        Plans.Clear();
        DecisionQueue.Clear();
    }

    public bool TryStartAction(string personId, string actionId)
    {
        ObjectDisposedException.ThrowIf(_disposed, this);
        ArgumentException.ThrowIfNullOrWhiteSpace(personId);
        ArgumentException.ThrowIfNullOrWhiteSpace(actionId);
        return ActivitySystem.TryStart(this, personId, actionId);
    }

    public void ConfigurePresence(int weekDays = 5, int maxDecisionsPerTick = 64, int maxSkipDays = 400)
    {
        ObjectDisposedException.ThrowIf(_disposed, this);
        SchoolWeekDays = weekDays;
        MaxDecisionsPerTick = maxDecisionsPerTick;
        MaxSkipDays = maxSkipDays;
        if (Catalog is not null && Map is not null)
        {
            Walks = WalkGraph.Build(Catalog, Map);
        }
    }

    public IReadOnlyList<PresenceSnapshot> CapturePresence() => PresenceSystem.Capture(this);

    public void RestorePresence(IReadOnlyList<PresenceSnapshot>? saved) => PresenceSystem.Restore(this, saved);

    public bool IsCampusEmpty() => PresenceSystem.IsEmpty(this);

    public SkipEmptyPeek PeekSkipEmpty()
    {
        ObjectDisposedException.ThrowIf(_disposed, this);
        if (Catalog is null || !IsCampusEmpty() || SchoolDay.InWorkWindow(Catalog, Clock.Time, SchoolWeekDays))
        {
            return SkipEmptyPeek.Refused;
        }

        var next = SchoolDay.NextWorkMorning(Catalog, Clock.Time, SchoolWeekDays, MaxSkipDays);
        return next is null ? SkipEmptyPeek.Refused : new SkipEmptyPeek(true, next.Value);
    }

    public SkipEmptyResult TrySkipEmpty()
    {
        ObjectDisposedException.ThrowIf(_disposed, this);
        if (Catalog is null)
        {
            return SkipEmptyResult.Fail(SkipEmptyError.NoMorning);
        }

        if (!IsCampusEmpty())
        {
            return SkipEmptyResult.Fail(SkipEmptyError.PeoplePresent);
        }

        if (SchoolDay.InWorkWindow(Catalog, Clock.Time, SchoolWeekDays))
        {
            return SkipEmptyResult.Fail(SkipEmptyError.InWorkWindow);
        }

        var next = SchoolDay.NextWorkMorning(Catalog, Clock.Time, SchoolWeekDays, MaxSkipDays);
        if (next is null)
        {
            return SkipEmptyResult.Fail(SkipEmptyError.NoMorning);
        }

        var before = Clock.Time;
        Clock.JumpTo(next.Value);
        var peopleChanged = TryYearlyIntake(before, next.Value);
        peopleChanged |= TryApplicantRefresh();
        PlanDay = null;
        LastDecisionSlot = null;
        NeedDecay.Apply(World, Catalog, (next.Value - before).TotalMinutes);
        return new SkipEmptyResult(SkipEmptyError.None, next.Value, peopleChanged);
    }

    /// <summary>
    /// Replaces the roster and applicant pool after hire or a subject change. The World is rebuilt
    /// so the people list and card match; needs reset to the roster snapshot, same as yearly intake.
    /// </summary>
    public void ApplyStaffing(Roster roster, ApplicantPool applicants)
    {
        ObjectDisposedException.ThrowIf(_disposed, this);
        ArgumentNullException.ThrowIfNull(roster);
        ArgumentNullException.ThrowIfNull(applicants);

        Roster = roster;
        Applicants = applicants;
        var snapshot = PresenceSystem.Capture(this);
        RosterSpawner.Replace(World, roster);
        PresenceSystem.Restore(this, snapshot);
        TimetableDirty = true;
    }

    public void SetTimetable(Timetable timetable)
    {
        ObjectDisposedException.ThrowIf(_disposed, this);
        ArgumentNullException.ThrowIfNull(timetable);
        Timetable = timetable;
        TimetableDirty = false;
        LastDecisionSlot = null;
        foreach (var id in Roster?.People.Select(person => person.Id) ?? [])
        {
            DecisionQueue.Enqueue(id);
        }
    }

    /// <summary>Runs one fixed step of the school: calendar, yearly intake, applicant refresh, presence, actions, then need decay.</summary>
    /// <returns><see langword="true"/> when the roster or the applicant pool changed this step.</returns>
    public bool Tick(double deltaTime, double gameMinutesPerRealSecond)
    {
        ObjectDisposedException.ThrowIf(_disposed, this);

        var before = Clock.Time;
        var gameMinutes = Clock.Advance(deltaTime, gameMinutesPerRealSecond);
        var peopleChanged = false;
        if (gameMinutes > 0)
        {
            peopleChanged = TryYearlyIntake(before, Clock.Time);
            peopleChanged |= TryApplicantRefresh();
            if (peopleChanged)
            {
                PlanDay = null;
                LastDecisionSlot = null;
            }

            PresenceSystem.Apply(this, gameMinutes);
            foreach (var id in ActivitySystem.Apply(this, gameMinutes))
            {
                PresenceSystem.Enqueue(this, id);
            }

            if (Catalog is not null)
            {
                var below = PresenceSystem.BelowThreshold(this);
                NeedDecay.Apply(World, Catalog, gameMinutes);
                PresenceSystem.EnqueueNewlyUrgent(this, below);
                PresenceSystem.DrainDecisions(this);
                LessonLearningSystem.Apply(this, gameMinutes);
            }
        }

        return peopleChanged;
    }

    private bool TryYearlyIntake(DateTime before, DateTime after)
    {
        if (Roster is null || Catalog is null || NameSetId is null)
        {
            return false;
        }

        var changed = false;
        foreach (var date in YearlyIntake.DatesBetween(before, after))
        {
            Roster = YearlyIntake.Apply(Catalog, Roster, PeopleSeed, NameSetId, date);
            changed = true;
        }

        if (changed)
        {
            var snapshot = PresenceSystem.Capture(this);
            RosterSpawner.Replace(World, Roster);
            PresenceSystem.Restore(this, snapshot);
            TimetableDirty = true;
        }

        return changed;
    }

    private bool TryApplicantRefresh()
    {
        if (Applicants is null || Roster is null || Catalog is null || NameSetId is null || Catalog.StaffingRules is null)
        {
            return false;
        }

        var next = Applicants.Advance(Catalog, Roster, PeopleSeed, NameSetId, Clock.Time);
        if (next.Week == Applicants.Week)
        {
            return false;
        }

        Applicants = next;
        return true;
    }

    public void Dispose()
    {
        if (_disposed)
        {
            return;
        }

        _disposed = true;

        // Fully qualified: the `World` property would otherwise shadow the type.
        Arch.Core.World.Destroy(World);
    }
}

public enum SkipEmptyError
{
    None,
    PeoplePresent,
    InWorkWindow,
    NoMorning,
}

public readonly record struct SkipEmptyPeek(bool Allowed, DateTime? Time)
{
    public static SkipEmptyPeek Refused { get; } = new(false, null);
}

public readonly record struct SkipEmptyResult(SkipEmptyError Error, DateTime? Time, bool PeopleChanged)
{
    public bool Succeeded => Error == SkipEmptyError.None;

    public static SkipEmptyResult Fail(SkipEmptyError error) => new(error, null, false);
}