// SOLARGOD rings layer (Stage 3) — Saturn's textured annulus + Uranus's thin
// schematic ring. Sized in true km scaled by the parent's draw scale, tilted with
// the parent's axial tilt, DoubleSide + transparent (brief §7). Texture optional:
// a flat color fallback keeps the ring visible if the PNG is missing.

export default function create(ctx) {
  const { THREE, scene, lib, ui, scale, bodies, toLocal, effectiveE, CONFIG } = ctx;
  const AU_KM = lib.AU_KM;
  const RING_FALLBACK = { saturn: '#c9b98f', uranus: '#8fa3a8' };

  const entries = [];
  for (const id of ['saturn', 'uranus']) {
    const b = bodies[id];
    if (!b.rings) continue;
    const ratio = b.rings.innerKm / b.rings.outerKm;
    const geo = new THREE.RingGeometry(ratio, 1, 128, 1);
    radialUV(geo);                       // remap UV so a radial ring texture maps across width
    const mat = new THREE.MeshBasicMaterial({
      color: new THREE.Color(b.rings.color || RING_FALLBACK[id] || '#bbb'),
      side: THREE.DoubleSide, transparent: true, opacity: id === 'saturn' ? 0.9 : 0.45, depthWrite: false,
    });
    if (b.rings.texture) {
      new THREE.TextureLoader().load(CONFIG.textures.path + b.rings.texture, (tex) => {
        tex.colorSpace = THREE.SRGBColorSpace; mat.map = tex; mat.color.set(0xffffff); mat.needsUpdate = true;
      }, undefined, () => { /* keep flat color */ });
    }
    const group = new THREE.Group();
    group.rotation.z = (b.axialTiltDeg || 0) * lib.DEG; // same tilt as the planet group
    const mesh = new THREE.Mesh(geo, mat);
    mesh.rotation.x = -Math.PI / 2;      // lay flat into the equatorial (XZ) plane
    group.add(mesh);
    scene.add(group);
    entries.push({ id, b, group, mesh });
  }

  let show = true;
  ui.addLayer('rings', 'Rings', true, (on) => { show = on; for (const e of entries) e.group.visible = on; });
  ui.setStatus('rings', 'Saturn · Uranus', 'ok');

  return {
    id: 'rings',
    onClockTick() {
      const K = scale.getK();
      for (const e of entries) {
        const abs = ctx.bodyWorld[e.id];
        if (!abs) continue;
        toLocal(abs, e.group.position);
        const E = effectiveE(e.id);
        e.mesh.scale.setScalar((e.b.rings.outerKm / AU_KM) * K * E); // outer km → view units
      }
    },
  };
}

// Remap RingGeometry UVs so u runs 0→1 across the radius (for a 1-D ring texture).
function radialUV(geo) {
  const pos = geo.attributes.position, uv = geo.attributes.uv;
  const inner = Math.hypot(pos.getX(0), pos.getY(0));
  let outer = inner;
  for (let i = 0; i < pos.count; i++) outer = Math.max(outer, Math.hypot(pos.getX(i), pos.getY(i)));
  for (let i = 0; i < pos.count; i++) {
    const r = Math.hypot(pos.getX(i), pos.getY(i));
    uv.setXY(i, (r - inner) / (outer - inner || 1), 1);
  }
  uv.needsUpdate = true;
}