import { Document, NodeIO } from "@gltf-transform/core";
import { Matrix4, Vector3 } from "three";
import path from "node:path";
import { mkdir } from "node:fs/promises";

/** Preserve world-space source triangles while bounding each physical GLB. */
export async function writeBoundedCollisionGlbs(sourceFile, outputDirectory, slug, {
  maximumTriangles = 90_000,
  sourceSha256,
} = {}) {
  if (!Number.isSafeInteger(maximumTriangles) || maximumTriangles < 1) {
    throw new Error("Collision chunk limit must be a positive integer.");
  }
  const io = new NodeIO();
  const source = await io.read(sourceFile);
  const scene = source.getRoot().getDefaultScene() ?? source.getRoot().listScenes()[0];
  if (!scene) throw new Error("Native collision source has no scene.");
  const positions = [];
  scene.traverse((node) => {
    const mesh = node.getMesh();
    if (!mesh) return;
    const matrix = new Matrix4().fromArray(node.getWorldMatrix());
    const reverse = matrix.determinant() < 0;
    for (const primitive of mesh.listPrimitives()) {
      if (primitive.getMode() !== 4) throw new Error("Collision must contain triangle primitives.");
      const position = primitive.getAttribute("POSITION");
      const index = primitive.getIndices();
      const count = index?.getCount() ?? position?.getCount() ?? 0;
      if (!position || count % 3) throw new Error("Invalid collision triangle positions.");
      for (let triangle = 0; triangle < count; triangle += 3) {
        for (const corner of reverse ? [0, 2, 1] : [0, 1, 2]) {
          const vertex = index ? index.getScalar(triangle + corner) : triangle + corner;
          const point = new Vector3(...position.getElement(vertex, [])).applyMatrix4(matrix);
          if (!point.toArray().every(Number.isFinite)) throw new Error("Non-finite collision coordinate.");
          positions.push(...point.toArray());
        }
      }
    }
  });
  if (!positions.length) throw new Error("Native collision source is empty.");
  await mkdir(outputDirectory, { recursive: true });
  const records = [];
  for (let begin = 0; begin < positions.length; begin += maximumTriangles * 9) {
    const document = new Document();
    const buffer = document.createBuffer();
    const targetScene = document.createScene("native-options-and-source-supports");
    document.getRoot().setDefaultScene(targetScene);
    const array = new Float32Array(positions.slice(begin, begin + maximumTriangles * 9));
    const primitive = document.createPrimitive().setAttribute("POSITION", document.createAccessor("collision-positions", buffer).setType("VEC3").setArray(array));
    targetScene.addChild(document.createNode("collision").setMesh(document.createMesh().addPrimitive(primitive)));
    document.getRoot().setExtras({
      collisionMode: "respect-options", sourceCandidateSha256: sourceSha256 ?? null,
      triangleRange: [begin / 9, begin / 9 + array.length / 9],
    });
    const file = `${slug}-collision-${String(records.length).padStart(3, "0")}.glb`;
    await io.write(path.join(outputDirectory, file), document);
    records.push({ file, triangles: array.length / 9, nativeSerializedCollision: true, derivedSourceAnchorSupport: true });
  }
  return records;
}