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;
    private readonly List<PersonLogEvent> _dayLog = [];
    private readonly HashSet<string> _lessonLogOnce = new(StringComparer.Ordinal);
    private readonly HashSet<string> _lessonMarkOnce = new(StringComparer.Ordinal);
    private readonly List<WorldEvent> _worldEvents = [];

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

    /// <summary>Climate preset rolled at birth. Weather reads it; it cannot change on a live school.</summary>
    public string? ClimatePresetId { get; private set; }

    /// <summary>Street temperature and precipitation last committed for the clock and warmth.</summary>
    public OutdoorWeather Weather { get; private set; } = OutdoorWeather.None;

    /// <summary>Student and staff dress rules. Pending pair applies on the next work morning.</summary>
    public SchoolDressRules DressRules { get; set; } = new();

    /// <summary>Student and staff speech-topic rules. Pending ids apply on the next work morning.</summary>
    public SchoolSpeechRules SpeechRules { get; set; } = new();

    /// <summary>Skill everyone generated for this school speaks natively.</summary>
    public string? NativeLanguage { 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; }

    /// <summary>Last slot <see cref="AttendanceSystem"/> observed — detects leaving a lesson to finalize absents.</summary>
    internal DaySlot? LastAttendanceSlot { get; set; }

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

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

    internal int DecisionBudget { get; set; }

    internal int HeavySystemsInvocations { get; private set; }

    internal double LastHeavyGameMinutes { get; private set; }

    private int _impulseCounter;

    public int PendingDecisionCount => DecisionQueue.Count;

    /// <summary>
    /// Today's history for the person card. Cleared at six in the morning. Not written to disk.
    /// </summary>
    public IReadOnlyList<PersonLogEvent> DayLog => _dayLog;

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

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

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

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

    /// <summary>
    /// Auto director summons FIFO. Worker thread only — never HTTP. Cleared on morning / skip.
    /// </summary>
    internal List<DirectorSummonTicket> DirectorSummons { get; } = [];

    internal int NextSummonOrder { get; set; }

    /// <summary>
    /// Active parent meetings. Worker thread only — never HTTP. Cleared on morning / skip.
    /// </summary>
    internal List<ParentMeetingSession> ActiveParentMeetings { get; } = [];

    /// <summary>Class ids that already rolled a meeting chance today (pass or fail).</summary>
    internal HashSet<string> ParentMeetingRolledToday { get; } = new(StringComparer.Ordinal);

    /// <summary>
    /// A finished or interrupted circle wrote opinions onto the roster. <see cref="Tick"/>
    /// returns this so the worker persists <c>people.json</c> — same seam as morning dress.
    /// </summary>
    internal bool RosterTalkDirty { get; set; }

    internal void ResetDayLog()
    {
        _dayLog.Clear();
        LoggedActivity.Clear();
        _lessonLogOnce.Clear();
        _lessonMarkOnce.Clear();
        LastAttendanceSlot = null;
    }

    internal void AppendDayLog(PersonLogEvent row) => _dayLog.Add(row);

    /// <summary>
    /// Lesson-quality rows fire every tick the condition holds. One key per person per day is enough.
    /// </summary>
    internal bool TryLogLessonOnce(string personId, string type, string subject)
    {
        var key = string.Concat(personId, "\0", type, "\0", subject);
        if (!_lessonLogOnce.Add(key))
        {
            return false;
        }

        AppendDayLog(new PersonLogEvent(personId, Clock.Time, type, subject));
        return true;
    }

    /// <summary>
    /// One lesson mark per person per calendar day and period. Survives teacher arriving mid-slot.
    /// </summary>
    internal bool TryClaimLessonMark(string personId, DateTime day, int period)
    {
        var key = string.Concat(personId, "\0", day.ToString("yyyy-MM-dd"), "\0", period.ToString());
        return _lessonMarkOnce.Add(key);
    }

    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? countryId = null, ApplicantPool? applicants = null, string? nativeLanguage = null, string? climatePresetId = null)
    {
        ObjectDisposedException.ThrowIf(_disposed, this);
        ArgumentNullException.ThrowIfNull(roster);

        Roster = roster;
        PeopleSeed = seed;
        CountryId = countryId;
        ClimatePresetId = climatePresetId;
        NativeLanguage = nativeLanguage;
        Applicants = applicants;
        RosterSpawner.Spawn(World, roster, Catalog);
        PlanDay = null;
        LastDecisionSlot = null;
        LastAttendanceSlot = null;
        Plans.Clear();
        DecisionQueue.Clear();
        LoggedActivity.Clear();
        SyncWeather(force: true);
    }

    public bool TryStartAction(string personId, string actionId)
    {
        ObjectDisposedException.ThrowIf(_disposed, this);
        ArgumentException.ThrowIfNullOrWhiteSpace(personId);
        ArgumentException.ThrowIfNullOrWhiteSpace(actionId);
        var started = ActivitySystem.TryStart(this, personId, actionId);
        if (started)
        {
            PersonDayLog.Sync(this);
        }

        return started;
    }

    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);

    /// <summary>
    /// Live circle for the presence frame and the person card. Null when this person is not talking.
    /// Member ids include self and are sorted; names stay off the wire.
    /// </summary>
    public TalkCirclePresence? TalkCircleOf(string personId)
    {
        if (!TalkCircleByPerson.TryGetValue(personId, out var circleId)
            || !TalkCirclesById.TryGetValue(circleId, out var circle))
        {
            return null;
        }

        var members = circle.Members.ToArray();
        Array.Sort(members, StringComparer.Ordinal);
        return new TalkCirclePresence(circle.TopicId, members);
    }

    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);
        TalkCircleSystem.AbandonAll(this);
        DirectorSummonSystem.ClearAll(this);
        ParentMeetingSystem.ClearAll(this);
        ResetDayLog();
        var peopleChanged = TryYearlyIntake(before, next.Value);
        peopleChanged |= TryApplicantRefresh();
        PlanDay = null;
        LastDecisionSlot = null;
        NeedDecay.Apply(World, Catalog, (next.Value - before).TotalMinutes);
        peopleChanged |= ApparelWear.Apply(this, gameMinutes: 0, before);
        SyncWeather(force: true);
        RecordWorldEvents(before, next.Value);
        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, Catalog);
        PresenceSystem.Restore(this, snapshot);
        TimetableDirty = true;
    }

    /// <summary>
    /// Writes roster fields that do not change who is in the World (class-teacher slots). No
    /// respawn and no timetable dirty — unlike <see cref="ApplyStaffing"/>.
    /// </summary>
    public void ApplyRosterData(Roster roster)
    {
        ObjectDisposedException.ThrowIf(_disposed, this);
        ArgumentNullException.ThrowIfNull(roster);
        Roster = roster;
    }

    public void SetTimetable(Timetable timetable)
    {
        ObjectDisposedException.ThrowIf(_disposed, this);
        ArgumentNullException.ThrowIfNull(timetable);
        Timetable = timetable;
        TimetableDirty = false;
        // Duty rooms and AppearAt come from this table. EnsurePlans only rebuilds when the day
        // or the roster size changes, so a pin or an assign would otherwise keep yesterday's
        // empty-staff plans and leave the campus empty.
        PlanDay = null;
        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, need decay, apparel wear, then health conditions.</summary>
    /// <returns><see langword="true"/> when the roster, applicant pool or wardrobe 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)
        {
            if (PersonDayLog.CrossedDayStart(before, Clock.Time))
            {
                ResetDayLog();
                // Hung summons do not survive the work morning — same clear as skip empty.
                DirectorSummonSystem.ClearAll(this);
        ParentMeetingSystem.ClearAll(this);
            }

            peopleChanged = TryYearlyIntake(before, Clock.Time);
            peopleChanged |= TryApplicantRefresh();
            if (peopleChanged)
            {
                PlanDay = null;
                LastDecisionSlot = null;
            }

            SyncWeather(force: false);

            _impulseCounter++;
            var stride = ClockSpeed.HeavySystemsStride(Clock.SpeedIndex);
            if (_impulseCounter % stride == 0)
            {
                var heavyMinutes = ClockSpeed.HeavyGameMinutes(Clock.SpeedIndex, gameMinutes);
                peopleChanged |= ApplyHeavySystems(heavyMinutes);
            }

            RecordWorldEvents(before, Clock.Time);
        }
        else
        {
            SyncWeather(force: false);
        }

        return peopleChanged;
    }

    /// <summary>Facts raised since the last drain. The worker maps them to notices; simulation has no UI.</summary>
    public IReadOnlyList<WorldEvent> DrainWorldEvents()
    {
        if (_worldEvents.Count == 0)
        {
            return [];
        }

        var copy = _worldEvents.ToArray();
        _worldEvents.Clear();
        return copy;
    }

    /// <summary>Queue a fact for the worker's notice board. Simulation never builds UI itself.</summary>
    internal void RaiseWorldEvent(in WorldEvent fact) => _worldEvents.Add(fact);

    /// <summary>
    /// Presence wire tag for auto director summons. Values match <c>DirectorSummons.Presence*</c>
    /// and <see cref="Protocol.PresenceSummonPhase"/>.
    /// </summary>
    public byte DirectorSummonPresencePhase(string personId) =>
        DirectorSummonSystem.ResolvePresencePhase(this, personId);

    /// <summary>ActionDef id for the person card when summoned but the live activity is idle.</summary>
    public string? DirectorSummonPresenceActionId(string personId) =>
        DirectorSummonSystem.PresenceActionId(DirectorSummonPresencePhase(personId));

    /// <summary>
    /// Card label while walking to / sitting in a parent meeting without a live activity yet.
    /// </summary>
    public string? ParentMeetingPresenceActionId(string personId)
    {
        if (!ParentMeetingSystem.IsInMeeting(this, personId))
        {
            return null;
        }

        var session = ActiveParentMeetings.FirstOrDefault(row =>
            row.TeacherId.Equals(personId, StringComparison.Ordinal)
            || row.AttendeeIds.Contains(personId));
        if (session is null)
        {
            return null;
        }

        return session.InProgress && session.TeacherId.Equals(personId, StringComparison.Ordinal)
            ? HSchool.Ai.ParentMeetings.MeetingAction
            : HSchool.Ai.ParentMeetings.GoingAction;
    }

    private void RecordWorldEvents(DateTime before, DateTime after)
    {
        _worldEvents.AddRange(EventSystem.Detect(this, before, after));
    }

    private bool ApplyHeavySystems(double gameMinutes)
    {
        HeavySystemsInvocations++;
        LastHeavyGameMinutes = gameMinutes;

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

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

        DirectorSummonSystem.Apply(this);
        ParentMeetingSystem.Apply(this);

        PersonDayLog.Sync(this);

        if (Catalog is not null)
        {
            var below = PresenceSystem.BelowThreshold(this);
            NeedDecay.Apply(World, Catalog, gameMinutes);
            WarmthDecay.Apply(this, gameMinutes);
            PresenceSystem.EnqueueNewlyUrgent(this, below);
            PresenceSystem.DrainDecisions(this);
            LessonLearningSystem.Apply(this, gameMinutes);
            AttendanceSystem.Apply(this);
            peopleChanged |= ApparelWear.Apply(this, gameMinutes, Clock.Time.AddMinutes(-gameMinutes));
            peopleChanged |= AffinitySystem.Apply(this, talked);
        }

        peopleChanged |= HealthConditionSystem.Apply(this, gameMinutes);
        peopleChanged |= RosterTalkDirty;
        RosterTalkDirty = false;
        return peopleChanged;
    }

    /// <summary>
    /// Recomputes the street from the preset, seed and current time. Commits when the clock
    /// tenths or precipitation change, so warmth does not jitter every tick. A skip must force
    /// the morning sample — yesterday's evening must not stick.
    /// </summary>
    public void SyncWeather(bool force)
    {
        ObjectDisposedException.ThrowIf(_disposed, this);
        CommitWeather(EvaluateWeather(), force);
    }

    /// <summary>
    /// Test hook: the vanilla diurnal never crosses <c>outerBelowC</c> during a school day, so a
    /// mid-day frost has to be injected to prove jackets walk to the locker room instead of
    /// appearing on the body.
    /// </summary>
    internal void ForceWeather(OutdoorWeather weather) => CommitWeather(weather, force: true);

    private void CommitWeather(OutdoorWeather next, bool force)
    {
        if (force || next.Tenths != Weather.Tenths || next.Precipitation != Weather.Precipitation)
        {
            var before = Weather;
            Weather = next;
            if (Roster is not null && Catalog is not null)
            {
                ApparelPresence.EnqueueOnWeatherChange(this, before, next);
            }
        }
    }

    private OutdoorWeather EvaluateWeather()
    {
        if (Catalog is null
            || ClimatePresetId is null
            || !Catalog.ClimatePresets.TryGetValue(ClimatePresetId, out var preset)
            || preset.Abstract)
        {
            return OutdoorWeather.None;
        }

        return WeatherSampler.Sample(preset, PeopleSeed, Clock.Time);
    }

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

        var changed = false;
        foreach (var date in YearlyIntake.DatesBetween(before, after))
        {
            Roster = YearlyIntake.Apply(Catalog, Roster, PeopleSeed, CountryId, date, NativeLanguage);
            if (Map is not null)
            {
                Roster = LockerAssigner.Apply(Catalog, Map, Roster);
            }

            changed = true;
        }

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

        return changed;
    }

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

        var next = Applicants.Advance(Catalog, Roster, PeopleSeed, CountryId, Clock.Time, NativeLanguage);
        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);
}

internal readonly record struct ApologyDebt(string FromId, string ToId, int Baseline, int Lost);