/**
 * @license
 * SPDX-License-Identifier: Apache-2.0
 *
 * ContactMarkers — instanced sphere visualization of MuJoCo contacts (spec 6.2)
 *
 * Fixed from original: reads data.ncon first, accesses contact via .get(i),
 * limits to maxContacts to avoid WASM heap OOM.
 */

import { useRef } from 'react';
import { useFrame } from '@react-three/fiber';
import type { ThreeElements } from '@react-three/fiber';
import * as THREE from 'three';
import { useMujocoContext } from '../core/MujocoSimProvider';
import { CAPTURE_EXCLUDE_KEY } from '../rendering/cameraFrameCapture';
import { getContact, withContacts } from '../types';

const _dummy = new THREE.Object3D();

interface ContactMarkersProps {
  /** Maximum contacts to render. Default: 100. */
  maxContacts?: number;
  /** Sphere radius. Default: 0.008. */
  radius?: number;
  /** Color. Default: '#22d3ee'. */
  color?: string;
  /** Show markers. Default: true. */
  visible?: boolean;
}

export function ContactMarkers({
  maxContacts = 100,
  radius = 0.008,
  color = '#22d3ee',
  visible = true,
  ...groupProps
}: ContactMarkersProps & Omit<ThreeElements['group'], 'ref' | 'visible'> = {}) {
  const { mjDataRef, status } = useMujocoContext();
  const meshRef = useRef<THREE.InstancedMesh>(null);

  useFrame(() => {
    const mesh = meshRef.current;
    const data = mjDataRef.current;
    if (!mesh || !data || !visible) {
      if (mesh) mesh.count = 0;
      return;
    }

    const ncon = data.ncon;
    const count = Math.min(ncon, maxContacts);

    let resolvedCount = count;
    withContacts(data, (contactArray) => {
      for (let i = 0; i < count; i++) {
        const c = getContact(contactArray, i);
        if (!c) {
          resolvedCount = i;
          return;
        }
        _dummy.position.set(c.pos[0], c.pos[1], c.pos[2]);
        _dummy.updateMatrix();
        mesh.setMatrixAt(i, _dummy.matrix);
      }
    });

    mesh.count = resolvedCount;
    mesh.instanceMatrix.needsUpdate = true;
  });

  if (status !== 'ready') return null;

  return (
    <group
      {...groupProps}
      userData={{
        ...groupProps.userData,
        [CAPTURE_EXCLUDE_KEY]: true,
      }}
    >
      <instancedMesh ref={meshRef} args={[undefined, undefined, maxContacts]} frustumCulled={false} renderOrder={999}>
        <sphereGeometry args={[radius, 8, 8]} />
        <meshBasicMaterial color={color} depthTest={false} />
      </instancedMesh>
    </group>
  );
}