using System.Collections.Generic;
using System.Numerics;
using DatReaderWriter.DBObjs;
using DatReaderWriter.Types;

namespace AcDream.Core.Lighting;

/// <summary>
/// Converts a <see cref="Setup"/>'s <c>Lights</c> dictionary (dat-level
/// <see cref="LightInfo"/> records) into runtime <see cref="LightSource"/>
/// instances the <see cref="LightManager"/> can consume.
///
/// <para>
/// Retail <see cref="LightInfo"/> fields (r13 §1):
/// <list type="bullet">
///   <item><description><c>ViewSpaceLocation</c>: local Frame relative to the owning part.</description></item>
///   <item><description><c>Color</c>: packed ARGB. Alpha is ignored; channels go through <c>/255</c>.</description></item>
///   <item><description><c>Intensity</c>: multiplies color for final diffuse.</description></item>
///   <item><description><c>Falloff</c>: world metres — acts as the <see cref="LightSource.Range"/> hard cutoff.</description></item>
///   <item><description><c>ConeAngle</c>: radians; 0 = point, &gt;0 = spot cone.</description></item>
/// </list>
/// </para>
/// </summary>
public static class LightInfoLoader
{
    /// <summary>
    /// Extract all lights from a Setup, positioned in the entity's
    /// world frame (via <paramref name="entityPosition"/> +
    /// <paramref name="entityRotation"/>). The dat's per-light Frame is
    /// treated as a local offset relative to the entity root; acdream
    /// doesn't yet transform through the animated part chain (retail's
    /// hand-held torches), so held lights render at the entity root
    /// until the animation hook layer handles per-part placement.
    /// </summary>
    public static IReadOnlyList<LightSource> Load(
        Setup setup,
        uint ownerId,
        Vector3 entityPosition,
        Quaternion entityRotation)
    {
        var results = new List<LightSource>();
        if (setup?.Lights is null || setup.Lights.Count == 0) return results;

        foreach (var kvp in setup.Lights)
        {
            var info = kvp.Value;
            if (info is null) continue;

            // Local Frame offset into world space.
            Vector3 localOffset = Vector3.Zero;
            Quaternion localRot = Quaternion.Identity;
            if (info.ViewSpaceLocation is not null)
            {
                localOffset = new Vector3(
                    info.ViewSpaceLocation.Origin.X,
                    info.ViewSpaceLocation.Origin.Y,
                    info.ViewSpaceLocation.Origin.Z);
                localRot = new Quaternion(
                    info.ViewSpaceLocation.Orientation.X,
                    info.ViewSpaceLocation.Orientation.Y,
                    info.ViewSpaceLocation.Orientation.Z,
                    info.ViewSpaceLocation.Orientation.W);
            }

            // Transform local offset into world space via the entity's
            // rotation + translation. No per-part chain yet — held
            // torches track the entity's root for now.
            Vector3 worldPos = entityPosition + Vector3.Transform(localOffset, entityRotation);
            Quaternion worldRot = entityRotation * localRot;
            Vector3 forward = Vector3.Transform(Vector3.UnitY, worldRot);

            var light = new LightSource
            {
                Kind = info.ConeAngle > 0f ? LightKind.Spot : LightKind.Point,
                WorldPosition = worldPos,
                WorldForward  = forward,
                ColorLinear   = new Vector3(
                    (info.Color?.Red   ?? 255) / 255f,
                    (info.Color?.Green ?? 255) / 255f,
                    (info.Color?.Blue  ?? 255) / 255f),
                Intensity = info.Intensity,
                Range     = info.Falloff,
                ConeAngle = info.ConeAngle,
                OwnerId   = ownerId,
                IsLit     = true,
            };
            results.Add(light);
        }

        return results;
    }
}