using System.Numerics;
using AcDream.Core.Vfx;

namespace AcDream.App.Rendering.Vfx;

internal interface IWorldSceneParticleVisibility
{
    void MarkVisibleCells(HashSet<uint> cellIds);

    void CompleteFrame();

    void AbortFrame();
}

/// <summary>
/// Bridges the retained retail PView result into the next physics update's
/// <c>CObjCell::IsInView</c> particle gate. The controller owns only immutable
/// frame meaning: one completed viewer position plus the AC cells admitted by
/// that completed view. It neither creates emitters nor performs rendering.
/// </summary>
public sealed class ParticleVisibilityController : IWorldSceneParticleVisibility
{
    public const float ExtendedRangeMultiplier = 2f;

    private readonly HashSet<uint> _buildingCellIds = new();
    private readonly HashSet<uint> _completedCellIds = new();
    private Vector3 _buildingViewerPosition;
    private Vector3 _completedViewerPosition;
    private bool _frameOpen;
    private bool _frameUsesWorldView;
    private bool _hasCompletedWorldView;

    public void BeginFrame(Vector3 viewerPosition)
    {
        _buildingCellIds.Clear();
        _buildingViewerPosition = viewerPosition;
        _frameUsesWorldView = false;
        _frameOpen = true;
    }

    /// <summary>
    /// Declares that this frame has an authoritative world-visibility product.
    /// That product can come from the unified retail PView or from the outdoor
    /// landscape fallback. Login and portal-space frames deliberately omit it;
    /// dedicated pass and examination emitters carry explicit bypass policies.
    /// </summary>
    public void UseWorldView()
    {
        if (_frameOpen)
            _frameUsesWorldView = true;
    }

    public void MarkVisibleCells(HashSet<uint> cellIds)
    {
        ArgumentNullException.ThrowIfNull(cellIds);
        if (!_frameOpen || !_frameUsesWorldView)
            return;

        _buildingCellIds.UnionWith(cellIds);
    }

    public void CompleteFrame()
    {
        if (!_frameOpen)
            return;

        _frameOpen = false;
        if (!_frameUsesWorldView)
        {
            _completedCellIds.Clear();
            _completedViewerPosition = _buildingViewerPosition;
            _hasCompletedWorldView = false;
            return;
        }

        _completedCellIds.Clear();
        _completedCellIds.UnionWith(_buildingCellIds);
        _completedViewerPosition = _buildingViewerPosition;
        _hasCompletedWorldView = true;
    }

    /// <summary>Discards the in-progress visibility product while preserving
    /// the last completed view consumed by the update thread.</summary>
    public void AbortFrame()
    {
        _buildingCellIds.Clear();
        _frameUsesWorldView = false;
        _frameOpen = false;
    }

    public void Apply(ParticleSystem particles, float rangeMultiplier)
    {
        ArgumentNullException.ThrowIfNull(particles);
        particles.ApplyRetailView(
            _completedViewerPosition,
            _completedCellIds,
            _hasCompletedWorldView,
            rangeMultiplier);
    }

    public void Reset()
    {
        _buildingCellIds.Clear();
        _completedCellIds.Clear();
        _frameOpen = false;
        _frameUsesWorldView = false;
        _hasCompletedWorldView = false;
        _buildingViewerPosition = default;
        _completedViewerPosition = default;
    }
}