using System;
using System.Collections.Generic;
using System.Linq;
using System.Numerics;

namespace AcDream.Core.Physics.Motion;

/// <summary>
/// R5 — port of retail's <c>TargetManager</c> (acclient.h:31024, struct #3484;
/// decomp 0x0051a370-0x0051ad90, <c>r5-targetmanager-decomp.md</c>). A
/// peer-to-peer <b>voyeur subscription</b> system with two roles per object:
///
/// <list type="bullet">
/// <item><b>Watcher</b> (<see cref="TargetInfo"/>): <see cref="SetTarget"/>
/// registers this object as a voyeur ON a target; the target's per-tick
/// <see cref="HandleTargetting"/> pushes position updates back here via
/// <see cref="ReceiveUpdate"/>, which fans them to the owning host's
/// MoveToManager + PositionManager (sticky) through
/// <see cref="IPhysicsObjHost.HandleUpdateTarget"/>.</item>
/// <item><b>Watched</b> (<see cref="VoyeurTable"/>): other objects'
/// <see cref="AddVoyeur"/> subscribe to THIS object; each tick
/// <see cref="HandleTargetting"/> → <see cref="CheckAndUpdateVoyeur"/> sends a
/// dead-reckoned update to any subscriber the object has drifted past the
/// subscriber's radius from.</item>
/// </list>
///
/// <para>This REPLACES the AP-79 minimal TargetTracker adapter (GameWindow
/// polling the entity table). It is a faithful superset: the same
/// move-to tracking (distance &gt; radius → HandleUpdateTarget(Ok)) plus the
/// correct sticky, 10 s timeout, and exit/teleport event handling.</para>
///
/// <para>Owned 1:1 by an <see cref="IPhysicsObjHost"/> (retail
/// <c>CPhysicsObj::target_manager</c>, lazily created on first
/// <c>set_target</c>/<c>add_voyeur</c>). The two throttle constants
/// (<see cref="ThrottleSeconds"/>=0.5, <see cref="StalenessSeconds"/>=10) are
/// ACE's, verified against the retail x87 mush — port-plan §2d.</para>
/// </summary>
public sealed class TargetManager
{
    /// <summary>Retail <c>HandleTargetting</c> per-tick throttle (ACE: 0.5s) —
    /// the voyeur sweep runs at most this often.</summary>
    public const double ThrottleSeconds = 0.5;

    /// <summary>Retail target-info staleness timeout (ACE: 10.0s) — an
    /// Undefined-status target with no update for this long is marked
    /// TimedOut.</summary>
    public const double StalenessSeconds = 10.0;

    private readonly IPhysicsObjHost _host;

    private TargetInfo? _targetInfo;                          // retail target_info (watcher role)
    private Dictionary<uint, TargettedVoyeurInfo>? _voyeurTable; // retail voyeur_table (watched role)
    private double _lastUpdateTime;                            // retail last_update_time (throttle base)

    public TargetManager(IPhysicsObjHost host)
        => _host = host ?? throw new ArgumentNullException(nameof(host));

    /// <summary>The current watched-target info, or null when tracking
    /// nothing.</summary>
    public TargetInfo? TargetInfo => _targetInfo;

    /// <summary>The subscriber table (null until the first
    /// <see cref="AddVoyeur"/>).</summary>
    public IReadOnlyDictionary<uint, TargettedVoyeurInfo>? VoyeurTable => _voyeurTable;

    /// <summary>Retail <c>get_target_quantum</c> — the current target's
    /// quantum, 0 when tracking nothing.</summary>
    public double GetTargetQuantum() => _targetInfo?.Quantum ?? 0.0;

    // ── watcher role ───────────────────────────────────────────────────────

    /// <summary>
    /// Retail <c>TargetManager::SetTarget</c> (0x0051ac30). Tear down any
    /// existing target, then: if <paramref name="objectId"/> is 0, synthesize a
    /// TimedOut clear-update to the host and leave <see cref="TargetInfo"/>
    /// null; otherwise create a fresh <see cref="TargetInfo"/> (status
    /// Undefined) and subscribe as a voyeur ON the target
    /// (<c>target.add_voyeur(self.id, radius, quantum)</c>). The target's live
    /// position arrives asynchronously via <see cref="ReceiveUpdate"/>.
    /// </summary>
    public void SetTarget(uint contextId, uint objectId, float radius, double quantum)
    {
        ClearTarget();

        if (objectId == 0)
        {
            // Clear/cancel: report a TimedOut update carrying the context,
            // leave _targetInfo null. (Retail var_10_1 = 6 = TimedOut.)
            var cleared = new TargetInfo(
                ObjectId: 0, Status: TargetStatus.TimedOut,
                TargetPosition: default, InterpolatedPosition: default,
                ContextId: contextId);
            _host.HandleUpdateTarget(cleared);
            return;
        }

        _targetInfo = new TargetInfo(
            ObjectId: objectId, Status: TargetStatus.Undefined,
            TargetPosition: default, InterpolatedPosition: default,
            ContextId: contextId, Radius: radius, Quantum: quantum,
            LastUpdateTime: _host.CurTime);

        var target = _host.GetObjectA(objectId);
        target?.AddVoyeur(_host.Id, radius, quantum);
    }

    /// <summary>
    /// Retail <c>TargetManager::SetTargetQuantum</c> (0x0051a4a0). Update the
    /// current target's resend interval and re-register the voyeur subscription
    /// on the target with the new quantum.
    /// </summary>
    public void SetTargetQuantum(double quantum)
    {
        if (_targetInfo is not { } ti)
            return;

        _targetInfo = ti with { Quantum = quantum };
        var target = _host.GetObjectA(ti.ObjectId);
        target?.AddVoyeur(_host.Id, ti.Radius, quantum);
    }

    /// <summary>
    /// Retail <c>TargetManager::ClearTarget</c> (0x0051a7e0). Unsubscribe from
    /// the current target's voyeur table and drop <see cref="TargetInfo"/>.
    /// </summary>
    public void ClearTarget()
    {
        if (_targetInfo is not { } ti)
            return;

        var target = _host.GetObjectA(ti.ObjectId);
        target?.RemoveVoyeur(_host.Id);
        _targetInfo = null;
    }

    /// <summary>
    /// Retail <c>TargetManager::ReceiveUpdate</c> (0x0051a930). The inbound
    /// handler when a target we watch sends us its position (via
    /// <c>SendVoyeurUpdate</c> → <c>receive_target_update</c>). Ignores updates
    /// for anything but our current target. Copies the payload, stamps receipt
    /// time, recomputes the self→target interpolated heading (falls back to +Z
    /// when degenerate), fans the snapshot to the host, and drops the
    /// subscription on an ExitWorld status.
    /// </summary>
    public void ReceiveUpdate(TargetInfo update)
    {
        if (_targetInfo is not { } ti || ti.ObjectId != update.ObjectId)
            return;

        // Copy radius/quantum/positions/velocity/status from the wire; keep our
        // object_id; stamp receipt time.
        Vector3 interpHeading = update.InterpolatedPosition.Frame.Origin
                              - _host.Position.Frame.Origin;
        if (MoveToMath.NormalizeCheckSmall(ref interpHeading))
            interpHeading = Vector3.UnitZ;

        var updated = ti with
        {
            Radius = update.Radius,
            Quantum = update.Quantum,
            TargetPosition = update.TargetPosition,
            InterpolatedPosition = update.InterpolatedPosition,
            Velocity = update.Velocity,
            Status = update.Status,
            InterpolatedHeading = interpHeading,
            LastUpdateTime = _host.CurTime,
        };
        _targetInfo = updated;

        _host.HandleUpdateTarget(updated);

        if (update.Status == TargetStatus.ExitWorld)
            ClearTarget();
    }

    // ── watched role ───────────────────────────────────────────────────────

    /// <summary>
    /// Retail <c>TargetManager::AddVoyeur</c> (0x0051a830). A subscriber
    /// registers to watch this object. If already subscribed, updates its
    /// radius/quantum in place (no immediate send); otherwise creates the entry
    /// and pushes an immediate initial snapshot (<c>Ok</c>).
    /// </summary>
    public void AddVoyeur(uint watcherId, float radius, double quantum)
    {
        _voyeurTable ??= new Dictionary<uint, TargettedVoyeurInfo>();

        if (_voyeurTable.TryGetValue(watcherId, out var existing))
        {
            existing.Radius = radius;
            existing.Quantum = quantum;
            return;
        }

        var voyeur = new TargettedVoyeurInfo(watcherId, radius, quantum);
        _voyeurTable[watcherId] = voyeur;
        SendVoyeurUpdate(voyeur, _host.Position, TargetStatus.Ok);
    }

    /// <summary>Retail <c>TargetManager::RemoveVoyeur</c> (0x0051ad90).</summary>
    public bool RemoveVoyeur(uint watcherId)
        => _voyeurTable?.Remove(watcherId) ?? false;

    /// <summary>
    /// Retail <c>TargetManager::HandleTargetting</c> (0x0051aa90). THE per-tick
    /// driver (no separate <c>UseTime</c>): self-throttled to
    /// <see cref="ThrottleSeconds"/>, promotes a stale target to TimedOut after
    /// <see cref="StalenessSeconds"/>, then sweeps every subscriber through
    /// <see cref="CheckAndUpdateVoyeur"/>.
    /// </summary>
    public void HandleTargetting()
    {
        if (_host.PhysicsTimerTime - _lastUpdateTime < ThrottleSeconds)
            return;

        if (_targetInfo is { } ti)
        {
            if (ti.Status == TargetStatus.Undefined
                && ti.LastUpdateTime + StalenessSeconds < _host.CurTime)
            {
                var timedOut = ti with { Status = TargetStatus.TimedOut };
                _targetInfo = timedOut;
                _host.HandleUpdateTarget(timedOut);
            }
        }

        if (_voyeurTable != null)
        {
            foreach (var voyeur in _voyeurTable.Values.ToList())
                CheckAndUpdateVoyeur(voyeur);
        }

        _lastUpdateTime = _host.PhysicsTimerTime;
    }

    /// <summary>
    /// Retail <c>TargetManager::CheckAndUpdateVoyeur</c> (0x0051a650). Push an
    /// update to <paramref name="voyeur"/> only if this object's dead-reckoned
    /// position has drifted more than the voyeur's radius since the last send.
    /// </summary>
    public void CheckAndUpdateVoyeur(TargettedVoyeurInfo voyeur)
    {
        Position newPos = GetInterpolatedPosition(voyeur.Quantum);
        float drift = Vector3.Distance(
            newPos.Frame.Origin, voyeur.LastSentPosition.Frame.Origin);
        if (drift > voyeur.Radius)
            SendVoyeurUpdate(voyeur, newPos, TargetStatus.Ok);
    }

    /// <summary>
    /// Retail <c>TargetManager::GetInterpolatedPosition</c> (0x0051a5e0).
    /// Dead-reckon this object's position forward by <paramref name="quantum"/>
    /// seconds using its current velocity.
    /// </summary>
    public Position GetInterpolatedPosition(double quantum)
    {
        var pos = _host.Position;
        Vector3 origin = pos.Frame.Origin + _host.Velocity * (float)quantum;
        return new Position(pos.ObjCellId, origin, pos.Frame.Orientation);
    }

    /// <summary>
    /// Retail <c>TargetManager::SendVoyeurUpdate</c> (0x0051a4f0). Record the
    /// sent position on the voyeur, build a <see cref="TargetInfo"/> carrying
    /// this object's CURRENT authoritative position + the extrapolated
    /// <paramref name="pos"/> + velocity + status, and deliver it to the
    /// subscriber's <see cref="ReceiveUpdate"/> (via its host).
    /// </summary>
    public void SendVoyeurUpdate(TargettedVoyeurInfo voyeur, Position pos, TargetStatus status)
    {
        voyeur.LastSentPosition = pos;

        var info = new TargetInfo(
            ObjectId: _host.Id,
            Status: status,
            TargetPosition: _host.Position,          // current authoritative
            InterpolatedPosition: pos,               // the extrapolated position
            ContextId: 0,
            Radius: voyeur.Radius,
            Quantum: voyeur.Quantum,
            Velocity: _host.Velocity);

        var voyeurObj = _host.GetObjectA(voyeur.ObjectId);
        voyeurObj?.ReceiveTargetUpdate(info);
    }

    /// <summary>
    /// Retail <c>TargetManager::NotifyVoyeurOfEvent</c> (0x0051a6f0). Broadcast
    /// a discrete status event (e.g. ExitWorld, Teleported) to every subscriber
    /// with this object's CURRENT position — no distance gate.
    /// </summary>
    public void NotifyVoyeurOfEvent(TargetStatus status)
    {
        if (_voyeurTable == null)
            return;

        foreach (var voyeur in _voyeurTable.Values.ToList())
            SendVoyeurUpdate(voyeur, _host.Position, status);
    }
}