using System;

namespace AcDream.Core.Physics.Motion;

/// <summary>
/// R5 — port of retail's <c>PositionManager</c> facade (acclient.h:30952,
/// struct #3468; decomp 0x00555160-0x005553d0,
/// <c>r5-positionmanager-sticky-decomp.md</c>). A thin fan-out over three
/// sub-managers: Interpolation, Sticky, Constraint. Owned 1:1 by the entity's
/// <see cref="IPhysicsObjHost"/> (retail <c>CPhysicsObj::position_manager</c>,
/// lazily created).
///
/// <para><b>Interpolation note:</b> retail's <c>adjust_offset</c> chains
/// Interpolation → Sticky → Constraint. acdream's interpolation stage lives in
/// <see cref="RemoteMotionCombiner"/> (the R5-renamed remote-motion combiner,
/// formerly the misnamed <c>Physics.PositionManager</c>) and is NOT chained
/// here in V1 — this facade owns only the two R5 targets (Sticky retires TS-39;
/// Constraint is structural — see <see cref="ConstraintManager"/>). Folding the
/// combiner in as the interp stage is a wiring-slice cleanup.</para>
/// </summary>
public sealed class PositionManager
{
    private readonly IPhysicsObjHost _host;

    // Lazily created (retail: sticky on first StickTo, constraint on first
    // ConstrainTo — 0x00555230 / 0x00555280).
    private StickyManager? _sticky;
    private ConstraintManager? _constraint;

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

    /// <summary>Exposed for wiring/tests — the lazily-created sub-managers
    /// (null until first use).</summary>
    public StickyManager? Sticky => _sticky;
    public ConstraintManager? Constraint => _constraint;

    /// <summary>Retail <c>PositionManager::StickTo</c> (0x00555230) — lazily
    /// create the <see cref="StickyManager"/> and begin following
    /// <paramref name="objectId"/>.</summary>
    public void StickTo(uint objectId, float radius, float height)
    {
        _sticky ??= new StickyManager(_host);
        _sticky.StickTo(objectId, radius, height);
    }

    /// <summary>Retail <c>PositionManager::UnStick</c> (0x005551e0) — forward
    /// to the sticky sub-manager if it exists.</summary>
    public void UnStick() => _sticky?.UnStick();

    /// <summary>Retail <c>PositionManager::GetStickyObjectID</c>
    /// (0x00555270).</summary>
    public uint GetStickyObjectId() => _sticky?.TargetId ?? 0u;

    /// <summary>Retail <c>PositionManager::ConstrainTo</c> (0x00555280) —
    /// lazily create the <see cref="ConstraintManager"/> and arm the leash.
    /// (Unused in acdream — no arming call site; see
    /// <see cref="ConstraintManager"/>.)</summary>
    public void ConstrainTo(Position anchor, float startDistance, float maxDistance)
    {
        _constraint ??= new ConstraintManager(_host);
        _constraint.ConstrainTo(anchor, startDistance, maxDistance);
    }

    /// <summary>Retail <c>PositionManager::UnConstrain</c>
    /// (0x005552b0).</summary>
    public void UnConstrain() => _constraint?.UnConstrain();

    /// <summary>Retail <c>PositionManager::IsFullyConstrained</c>
    /// (0x005552c0) — false when no constraint sub-manager exists.</summary>
    public bool IsFullyConstrained() => _constraint?.IsFullyConstrained() ?? false;

    /// <summary>
    /// Retail <c>PositionManager::HandleUpdateTarget</c> (0x005553d0) — only
    /// the sticky sub-manager cares about live target positions (interpolation
    /// and constraint don't). Fanned out from
    /// <c>CPhysicsObj::HandleUpdateTarget</c>.
    /// </summary>
    public void HandleUpdateTarget(TargetInfo info) => _sticky?.HandleUpdateTarget(info);

    /// <summary>
    /// Retail <c>PositionManager::adjust_offset</c> (0x00555190) — chains the
    /// sub-managers' contributions into the SAME <paramref name="offset"/>
    /// accumulator, in retail order. Retail runs Interpolation → Sticky →
    /// Constraint; acdream's interpolation stays in the separate remote-motion
    /// combiner (see class note), so this chains Sticky → Constraint only.
    /// Constraint is LAST because it clamps the already-composed displacement.
    /// </summary>
    public void AdjustOffset(MotionDeltaFrame offset, double quantum)
    {
        _sticky?.AdjustOffset(offset, quantum);
        _constraint?.AdjustOffset(offset, quantum);
    }

    /// <summary>
    /// Retail <c>PositionManager::UseTime</c> (0x00555160) — per-tick pump.
    /// Retail order Interpolation → Constraint → Sticky; acdream runs the two
    /// owned managers (constraint's UseTime is a retail no-op, so effectively
    /// just the sticky 1 s watchdog).
    /// </summary>
    public void UseTime() => _sticky?.UseTime();
}