using System;
using System.Collections.Generic;
using System.Numerics;
using AcDream.Core.Vfx;
using AcDream.Core.World;

namespace AcDream.App.Rendering.Vfx;

/// <summary>
/// What the activator's resolver returns when an entity's Setup carries
/// a <c>DefaultScript</c>. Bundles the script id with the per-part
/// transforms baked from <c>Setup.PlacementFrames</c> so a single dat
/// lookup yields both pieces of state. The activator pushes the part
/// transforms into <see cref="ParticleHookSink.SetEntityPartTransforms"/>
/// before calling <see cref="PhysicsScriptRunner.Play"/>, which closes
/// the part-anchor pipeline introduced for issue #56.
/// </summary>
public sealed record ScriptActivationInfo(
    uint ScriptId,
    IReadOnlyList<Matrix4x4> PartTransforms);

/// <summary>
/// Fires <c>Setup.DefaultScript</c> through <see cref="PhysicsScriptRunner"/>
/// when a <see cref="WorldEntity"/> enters the world, so static objects
/// (portals, chimneys, fireplaces, EnvCell decorations, building details)
/// emit their retail-faithful persistent particle effects automatically.
/// Stops the scripts and live emitters when the entity despawns.
///
/// <para>
/// Handles both server-spawned entities (<c>ServerGuid != 0</c>, keyed by
/// ServerGuid) and dat-hydrated entities (<c>ServerGuid == 0</c>, keyed by
/// <c>entity.Id</c>). The C.1.5a guard that early-returned for
/// <c>ServerGuid == 0</c> was relaxed in C.1.5b so EnvCell static objects
/// (which have no server guid because they come from the dat file, not
/// the network) also fire their DefaultScript.
/// </para>
///
/// <para>
/// Wires alongside <c>EntitySpawnAdapter</c> in <c>GpuWorldState</c>: the
/// adapter handles meshes + animation state, the activator handles scripts
/// + particles. Both are render-thread-only. The activator is invoked from
/// four GpuWorldState fire-sites (AppendLiveEntity, AddLandblock,
/// AddEntitiesToExistingLandblock, plus the matching remove paths).
/// </para>
///
/// <para>
/// Retail oracle: <c>play_script_internal(setup.DefaultScript)</c> is what
/// retail's <c>CPhysicsObj</c> invokes at object load (see Phase C.1 plan
/// §C.1 and <c>memory/project_sky_pes_port.md</c>). C.1 already shipped the
/// runner; this class adds the missing fire-on-spawn call site.
/// </para>
/// </summary>
public sealed class EntityScriptActivator
{
    private readonly PhysicsScriptRunner _scriptRunner;
    private readonly ParticleHookSink _particleSink;
    private readonly Func<WorldEntity, ScriptActivationInfo?> _resolver;

    /// <param name="scriptRunner">Already-shipped runner from C.1. Owns the
    /// (scriptId, entityId) instance table and schedules hooks at their
    /// <c>StartTime</c> offsets.</param>
    /// <param name="particleSink">Already-shipped hook sink from C.1. The
    /// activator pushes per-entity rotation + part transforms here, and
    /// calls <see cref="ParticleHookSink.StopAllForEntity"/> to drop
    /// per-entity emitter handles on despawn.</param>
    /// <param name="resolver">Returns
    /// <see cref="ScriptActivationInfo"/> with the entity's
    /// <c>Setup.DefaultScript.DataId</c> and per-part transforms (via
    /// <c>SetupPartTransforms.Compute</c>), or <c>null</c> on dat miss /
    /// throw / missing DefaultScript. Production lambda hits
    /// <c>DatCollection</c>; tests pass a hand-rolled stub.</param>
    public EntityScriptActivator(
        PhysicsScriptRunner scriptRunner,
        ParticleHookSink particleSink,
        Func<WorldEntity, ScriptActivationInfo?> resolver)
    {
        ArgumentNullException.ThrowIfNull(scriptRunner);
        ArgumentNullException.ThrowIfNull(particleSink);
        ArgumentNullException.ThrowIfNull(resolver);
        _scriptRunner = scriptRunner;
        _particleSink = particleSink;
        _resolver = resolver;
    }

    /// <summary>
    /// Resolve the entity's <c>Setup.DefaultScript</c> and fire it through
    /// the script runner. Keys by <c>entity.ServerGuid</c> when non-zero,
    /// otherwise by <c>entity.Id</c> (the latter handles dat-hydrated
    /// EnvCell statics + exterior stabs whose <c>entity.Id</c> lives in
    /// the <c>0x40xxxxxx</c> range — collision-free with server guids).
    /// No-op if the entity has no DefaultScript (resolver returns null
    /// or zero-script).
    /// </summary>
    public void OnCreate(WorldEntity entity)
    {
        ArgumentNullException.ThrowIfNull(entity);
        uint key = entity.ServerGuid != 0 ? entity.ServerGuid : entity.Id;
        if (key == 0) return;  // malformed entity

        var info = _resolver(entity);
        if (info is null || info.ScriptId == 0) return;

        // Seed the sink's per-entity rotation so CreateParticleHook.Offset.Origin
        // (in entity-local frame) transforms correctly to world space when the
        // hook fires. C.1.5a fix: without this, the sink falls through to
        // Quaternion.Identity and the offset gets applied in world axes —
        // visual symptom for portals: swirl oriented along world XYZ instead
        // of the portal's facing, partially buried.
        _particleSink.SetEntityRotation(key, entity.Rotation);

        // C.1.5b #56: seed the sink's per-entity part transforms so
        // CreateParticleHook.PartIndex routes the hook offset through the
        // right mesh part's resting transform. Without this, every emitter
        // in a multi-part Setup collapses to the entity root.
        _particleSink.SetEntityPartTransforms(key, info.PartTransforms);

        _scriptRunner.Play(info.ScriptId, key, entity.Position);
    }

    /// <summary>
    /// Stop every script instance the runner is tracking for this key, and
    /// kill every live emitter the sink has attributed to it. Caller picks
    /// the key (the matching ServerGuid for live entities, or
    /// <c>entity.Id</c> for dat-hydrated entities — mirror whatever was
    /// used at <see cref="OnCreate"/>). Idempotent for unknown keys.
    /// </summary>
    public void OnRemove(uint key)
    {
        if (key == 0) return;
        _scriptRunner.StopAllForEntity(key);
        _particleSink.StopAllForEntity(key, fadeOut: false);
    }
}