using System;
using System.Collections.Concurrent;
using System.Numerics;

namespace AcDream.Core.Vfx;

/// <summary>
/// Resolves <see cref="EmitterDesc"/> instances by their retail emitter
/// dat id (<c>0x32xxxxxx</c> range). The current build of
/// Chorizite.DatReaderWriter (v2.1.7) doesn't yet ship a
/// <c>ParticleEmitterInfo</c> DBObj class, so we maintain a small
/// registry of synthesized descriptors for the handful of emitters
/// acdream actually needs (portal swirl, chimney smoke, fireplace
/// flames, footstep dust, spell auras, weapon trails) and fall back to
/// a generic "puff" for unknown ids. When a future DRW release adds
/// the dat-type, this class will additionally load + cache from dats.
///
/// <para>
/// Field mapping once the dat-type arrives (docs/research/deepdives/
/// r04-vfx-particles.md §1 + references/DatReaderWriter's own generated
/// <c>ParticleEmitterInfo.generated.cs</c>):
/// <list type="bullet">
///   <item><description>
///     <c>Birthrate</c> → <c>1 / EmitRate</c> (retail stores the avg
///     time between spawns, not the rate).
///   </description></item>
///   <item><description>
///     <c>Lifespan ± LifespanRand</c> → <c>LifetimeMin / LifetimeMax</c>
///     range.
///   </description></item>
///   <item><description>
///     <c>A, MinA, MaxA</c> → primary initial velocity with magnitude
///     jitter; <c>B</c> / <c>C</c> are secondary spread components.
///   </description></item>
///   <item><description>
///     <c>StartScale, FinalScale</c> / <c>StartTrans, FinalTrans</c>
///     interpolate linearly over life.
///   </description></item>
/// </list>
/// </para>
/// </summary>
public sealed class EmitterDescRegistry
{
    private readonly ConcurrentDictionary<uint, EmitterDesc> _byId = new();

    public EmitterDescRegistry()
    {
        // Seed with a handful of well-known AC emitter ids plus a
        // fallback. Ids here come from empirical ACViewer dat dumps —
        // see r04 §5.2 for the more complete inventory.
        Register(new EmitterDesc
        {
            DatId            = 0xFFFFFFFFu, // "default" sentinel
            Type             = ParticleType.LocalVelocity,
            Flags            = EmitterFlags.Billboard | EmitterFlags.FaceCamera,
            EmitRate         = 10f,
            MaxParticles     = 32,
            LifetimeMin      = 0.6f,
            LifetimeMax      = 1.2f,
            OffsetDir        = new Vector3(0, 0, 1),
            MinOffset        = 0f,
            MaxOffset        = 0.1f,
            SpawnDiskRadius  = 0.1f,
            InitialVelocity  = new Vector3(0, 0, 0.5f),
            VelocityJitter   = 0.3f,
            StartSize        = 0.25f,
            EndSize          = 0.6f,
            StartAlpha       = 0.85f,
            EndAlpha         = 0f,
        });
    }

    public void Register(EmitterDesc desc)
    {
        ArgumentNullException.ThrowIfNull(desc);
        _byId[desc.DatId] = desc;
    }

    public EmitterDesc Get(uint emitterId)
    {
        if (_byId.TryGetValue(emitterId, out var desc)) return desc;
        if (_byId.TryGetValue(0xFFFFFFFFu, out var fallback)) return fallback;
        throw new InvalidOperationException("No default emitter registered in registry.");
    }

    public int Count => _byId.Count;
}