import {
  BufferAttribute,
  BufferGeometry,
  Float32BufferAttribute,
  InstancedBufferAttribute,
  InterleavedBuffer,
  InterleavedBufferAttribute,
  TriangleFanDrawMode,
  TriangleStripDrawMode,
  TrianglesDrawMode,
  Vector3,
} from "three";

/**
 * @module BufferGeometryUtils
 * @three_import import * as BufferGeometryUtils from 'three/addons/utils/BufferGeometryUtils.js';
 */

/**
 * Computes vertex tangents using the MikkTSpace algorithm. MikkTSpace generates the same tangents consistently,
 * and is used in most modelling tools and normal map bakers. Use MikkTSpace for materials with normal maps,
 * because inconsistent tangents may lead to subtle visual issues in the normal map, particularly around mirrored
 * UV seams.
 *
 * In comparison to this method, {@link BufferGeometry#computeTangents} (a custom algorithm) generates tangents that
 * probably will not match the tangents in other software. The custom algorithm is sufficient for general use with a
 * custom material, and may be faster than MikkTSpace.
 *
 * Returns the original BufferGeometry. Indexed geometries will be de-indexed. Requires position, normal, and uv attributes.
 *
 * @param {BufferGeometry} geometry - The geometry to compute tangents for.
 * @param {Object} MikkTSpace - Instance of `examples/jsm/libs/mikktspace.module.js`, or `mikktspace` npm package.
 * Await `MikkTSpace.ready` before use.
 * @param {boolean} [negateSign=true] - Whether to negate the sign component (.w) of each tangent.
 * Required for normal map conventions in some formats, including glTF.
 * @return {BufferGeometry} The updated geometry.
 */
function computeMikkTSpaceTangents(geometry, MikkTSpace, negateSign = true) {
  if (!MikkTSpace || !MikkTSpace.isReady) {
    throw new Error("BufferGeometryUtils: Initialized MikkTSpace library required.");
  }

  if (
    !geometry.hasAttribute("position") ||
    !geometry.hasAttribute("normal") ||
    !geometry.hasAttribute("uv")
  ) {
    throw new Error(
      'BufferGeometryUtils: Tangents require "position", "normal", and "uv" attributes.',
    );
  }

  function getAttributeArray(attribute) {
    if (attribute.normalized || attribute.isInterleavedBufferAttribute) {
      const dstArray = new Float32Array(attribute.count * attribute.itemSize);

      for (let i = 0, j = 0; i < attribute.count; i++) {
        dstArray[j++] = attribute.getX(i);
        dstArray[j++] = attribute.getY(i);

        if (attribute.itemSize > 2) {
          dstArray[j++] = attribute.getZ(i);
        }
      }

      return dstArray;
    }

    if (attribute.array instanceof Float32Array) {
      return attribute.array;
    }

    return new Float32Array(attribute.array);
  }

  // MikkTSpace algorithm requires non-indexed input.

  const _geometry = geometry.index ? geometry.toNonIndexed() : geometry;

  // Compute vertex tangents.

  const tangents = MikkTSpace.generateTangents(
    getAttributeArray(_geometry.attributes.position),
    getAttributeArray(_geometry.attributes.normal),
    getAttributeArray(_geometry.attributes.uv),
  );

  // Texture coordinate convention of glTF differs from the apparent
  // default of the MikkTSpace library; .w component must be flipped.

  if (negateSign) {
    for (let i = 3; i < tangents.length; i += 4) {
      tangents[i] *= -1;
    }
  }

  //

  _geometry.setAttribute("tangent", new BufferAttribute(tangents, 4));

  if (geometry !== _geometry) {
    geometry.copy(_geometry);
  }

  return geometry;
}

/**
 * Merges a set of geometries into a single instance. All geometries must have compatible attributes.
 *
 * @param {Array<BufferGeometry>} geometries - The geometries to merge.
 * @param {boolean} [useGroups=false] - Whether to use groups or not.
 * @return {?BufferGeometry} The merged geometry. Returns `null` if the merge does not succeed.
 */
function mergeGeometries(geometries, useGroups = false) {
  const isIndexed = geometries[0].index !== null;

  const attributesUsed = new Set(Object.keys(geometries[0].attributes));
  const morphAttributesUsed = new Set(Object.keys(geometries[0].morphAttributes));

  const attributes = {};
  const morphAttributes = {};

  const morphTargetsRelative = geometries[0].morphTargetsRelative;

  const mergedGeometry = new BufferGeometry();

  let offset = 0;

  for (let i = 0; i < geometries.length; ++i) {
    const geometry = geometries[i];
    let attributesCount = 0;

    // ensure that all geometries are indexed, or none

    if (isIndexed !== (geometry.index !== null)) {
      console.error(
        "THREE.BufferGeometryUtils: .mergeGeometries() failed with geometry at index " +
          i +
          ". All geometries must have compatible attributes; make sure index attribute exists among all geometries, or in none of them.",
      );
      return null;
    }

    // gather attributes, exit early if they're different

    for (const name in geometry.attributes) {
      if (!attributesUsed.has(name)) {
        console.error(
          "THREE.BufferGeometryUtils: .mergeGeometries() failed with geometry at index " +
            i +
            '. All geometries must have compatible attributes; make sure "' +
            name +
            '" attribute exists among all geometries, or in none of them.',
        );
        return null;
      }

      if (attributes[name] === undefined) attributes[name] = [];

      attributes[name].push(geometry.attributes[name]);

      attributesCount++;
    }

    // ensure geometries have the same number of attributes

    if (attributesCount !== attributesUsed.size) {
      console.error(
        "THREE.BufferGeometryUtils: .mergeGeometries() failed with geometry at index " +
          i +
          ". Make sure all geometries have the same number of attributes.",
      );
      return null;
    }

    // gather morph attributes, exit early if they're different

    if (morphTargetsRelative !== geometry.morphTargetsRelative) {
      console.error(
        "THREE.BufferGeometryUtils: .mergeGeometries() failed with geometry at index " +
          i +
          ". .morphTargetsRelative must be consistent throughout all geometries.",
      );
      return null;
    }

    for (const name in geometry.morphAttributes) {
      if (!morphAttributesUsed.has(name)) {
        console.error(
          "THREE.BufferGeometryUtils: .mergeGeometries() failed with geometry at index " +
            i +
            ".  .morphAttributes must be consistent throughout all geometries.",
        );
        return null;
      }

      if (morphAttributes[name] === undefined) morphAttributes[name] = [];

      morphAttributes[name].push(geometry.morphAttributes[name]);
    }

    if (useGroups) {
      let count;

      if (isIndexed) {
        count = geometry.index.count;
      } else if (geometry.attributes.position !== undefined) {
        count = geometry.attributes.position.count;
      } else {
        console.error(
          "THREE.BufferGeometryUtils: .mergeGeometries() failed with geometry at index " +
            i +
            ". The geometry must have either an index or a position attribute",
        );
        return null;
      }

      mergedGeometry.addGroup(offset, count, i);

      offset += count;
    }
  }

  // merge indices

  if (isIndexed) {
    let indexOffset = 0;
    const mergedIndex = [];

    for (let i = 0; i < geometries.length; ++i) {
      const index = geometries[i].index;

      for (let j = 0; j < index.count; ++j) {
        mergedIndex.push(index.getX(j) + indexOffset);
      }

      indexOffset += geometries[i].attributes.position.count;
    }

    mergedGeometry.setIndex(mergedIndex);
  }

  // merge attributes

  for (const name in attributes) {
    const mergedAttribute = mergeAttributes(attributes[name]);

    if (!mergedAttribute) {
      console.error(
        "THREE.BufferGeometryUtils: .mergeGeometries() failed while trying to merge the " +
          name +
          " attribute.",
      );
      return null;
    }

    mergedGeometry.setAttribute(name, mergedAttribute);
  }

  // merge morph attributes

  for (const name in morphAttributes) {
    const numMorphTargets = morphAttributes[name][0].length;

    if (numMorphTargets === 0) break;

    mergedGeometry.morphAttributes = mergedGeometry.morphAttributes || {};
    mergedGeometry.morphAttributes[name] = [];

    for (let i = 0; i < numMorphTargets; ++i) {
      const morphAttributesToMerge = [];

      for (let j = 0; j < morphAttributes[name].length; ++j) {
        morphAttributesToMerge.push(morphAttributes[name][j][i]);
      }

      const mergedMorphAttribute = mergeAttributes(morphAttributesToMerge);

      if (!mergedMorphAttribute) {
        console.error(
          "THREE.BufferGeometryUtils: .mergeGeometries() failed while trying to merge the " +
            name +
            " morphAttribute.",
        );
        return null;
      }

      mergedGeometry.morphAttributes[name].push(mergedMorphAttribute);
    }
  }

  return mergedGeometry;
}

/**
 * Merges a set of attributes into a single instance. All attributes must have compatible properties and types.
 * Instances of {@link InterleavedBufferAttribute} are not supported.
 *
 * @param {Array<BufferAttribute>} attributes - The attributes to merge.
 * @return {?BufferAttribute} The merged attribute. Returns `null` if the merge does not succeed.
 */
function mergeAttributes(attributes) {
  let TypedArray;
  let itemSize;
  let normalized;
  let gpuType = -1;
  let arrayLength = 0;

  for (let i = 0; i < attributes.length; ++i) {
    const attribute = attributes[i];

    if (TypedArray === undefined) TypedArray = attribute.array.constructor;
    if (TypedArray !== attribute.array.constructor) {
      console.error(
        "THREE.BufferGeometryUtils: .mergeAttributes() failed. BufferAttribute.array must be of consistent array types across matching attributes.",
      );
      return null;
    }

    if (itemSize === undefined) itemSize = attribute.itemSize;
    if (itemSize !== attribute.itemSize) {
      console.error(
        "THREE.BufferGeometryUtils: .mergeAttributes() failed. BufferAttribute.itemSize must be consistent across matching attributes.",
      );
      return null;
    }

    if (normalized === undefined) normalized = attribute.normalized;
    if (normalized !== attribute.normalized) {
      console.error(
        "THREE.BufferGeometryUtils: .mergeAttributes() failed. BufferAttribute.normalized must be consistent across matching attributes.",
      );
      return null;
    }

    if (gpuType === -1) gpuType = attribute.gpuType;
    if (gpuType !== attribute.gpuType) {
      console.error(
        "THREE.BufferGeometryUtils: .mergeAttributes() failed. BufferAttribute.gpuType must be consistent across matching attributes.",
      );
      return null;
    }

    arrayLength += attribute.count * itemSize;
  }

  const array = new TypedArray(arrayLength);
  const result = new BufferAttribute(array, itemSize, normalized);
  let offset = 0;

  for (let i = 0; i < attributes.length; ++i) {
    const attribute = attributes[i];
    if (attribute.isInterleavedBufferAttribute) {
      const tupleOffset = offset / itemSize;
      for (let j = 0, l = attribute.count; j < l; j++) {
        for (let c = 0; c < itemSize; c++) {
          const value = attribute.getComponent(j, c);
          result.setComponent(j + tupleOffset, c, value);
        }
      }
    } else {
      array.set(attribute.array, offset);
    }

    offset += attribute.count * itemSize;
  }

  if (gpuType !== undefined) {
    result.gpuType = gpuType;
  }

  return result;
}

/**
 * Performs a deep clone of the given buffer attribute.
 *
 * @param {BufferAttribute} attribute - The attribute to clone.
 * @return {BufferAttribute} The cloned attribute.
 */
function deepCloneAttribute(attribute) {
  if (attribute.isInstancedInterleavedBufferAttribute || attribute.isInterleavedBufferAttribute) {
    return deinterleaveAttribute(attribute);
  }

  if (attribute.isInstancedBufferAttribute) {
    return new InstancedBufferAttribute().copy(attribute);
  }

  return new BufferAttribute().copy(attribute);
}

/**
 * Interleaves a set of attributes and returns a new array of corresponding attributes that share a
 * single {@link InterleavedBuffer} instance. All attributes must have compatible types.
 *
 * @param {Array<BufferAttribute>} attributes - The attributes to interleave.
 * @return {?Array<InterleavedBufferAttribute>} An array of interleaved attributes. If interleave does not succeed, the method returns `null`.
 */
function interleaveAttributes(attributes) {
  // Interleaves the provided attributes into an InterleavedBuffer and returns
  // a set of InterleavedBufferAttributes for each attribute
  let TypedArray;
  let arrayLength = 0;
  let stride = 0;

  // calculate the length and type of the interleavedBuffer
  for (let i = 0, l = attributes.length; i < l; ++i) {
    const attribute = attributes[i];

    if (TypedArray === undefined) TypedArray = attribute.array.constructor;
    if (TypedArray !== attribute.array.constructor) {
      console.error("AttributeBuffers of different types cannot be interleaved");
      return null;
    }

    arrayLength += attribute.array.length;
    stride += attribute.itemSize;
  }

  // Create the set of buffer attributes
  const interleavedBuffer = new InterleavedBuffer(new TypedArray(arrayLength), stride);
  let offset = 0;
  const res = [];
  const getters = ["getX", "getY", "getZ", "getW"];
  const setters = ["setX", "setY", "setZ", "setW"];

  for (let j = 0, l = attributes.length; j < l; j++) {
    const attribute = attributes[j];
    const itemSize = attribute.itemSize;
    const count = attribute.count;
    const iba = new InterleavedBufferAttribute(
      interleavedBuffer,
      itemSize,
      offset,
      attribute.normalized,
    );
    res.push(iba);

    offset += itemSize;

    // Move the data for each attribute into the new interleavedBuffer
    // at the appropriate offset
    for (let c = 0; c < count; c++) {
      for (let k = 0; k < itemSize; k++) {
        iba[setters[k]](c, attribute[getters[k]](c));
      }
    }
  }

  return res;
}

/**
 * Returns a new, non-interleaved version of the given attribute.
 *
 * @param {InterleavedBufferAttribute} attribute - The interleaved attribute.
 * @return {BufferAttribute} The non-interleaved attribute.
 */
function deinterleaveAttribute(attribute) {
  const cons = attribute.data.array.constructor;
  const count = attribute.count;
  const itemSize = attribute.itemSize;
  const normalized = attribute.normalized;

  const array = new cons(count * itemSize);
  let newAttribute;
  if (attribute.isInstancedInterleavedBufferAttribute) {
    newAttribute = new InstancedBufferAttribute(
      array,
      itemSize,
      normalized,
      attribute.meshPerAttribute,
    );
  } else {
    newAttribute = new BufferAttribute(array, itemSize, normalized);
  }

  for (let i = 0; i < count; i++) {
    newAttribute.setX(i, attribute.getX(i));

    if (itemSize >= 2) {
      newAttribute.setY(i, attribute.getY(i));
    }

    if (itemSize >= 3) {
      newAttribute.setZ(i, attribute.getZ(i));
    }

    if (itemSize >= 4) {
      newAttribute.setW(i, attribute.getW(i));
    }
  }

  return newAttribute;
}

/**
 * Deinterleaves all attributes on the given geometry.
 *
 * @param {BufferGeometry} geometry - The geometry to deinterleave.
 */
function deinterleaveGeometry(geometry) {
  const attributes = geometry.attributes;
  const morphTargets = geometry.morphTargets;
  const attrMap = new Map();

  for (const key in attributes) {
    const attr = attributes[key];
    if (attr.isInterleavedBufferAttribute) {
      if (!attrMap.has(attr)) {
        attrMap.set(attr, deinterleaveAttribute(attr));
      }

      attributes[key] = attrMap.get(attr);
    }
  }

  for (const key in morphTargets) {
    const attr = morphTargets[key];
    if (attr.isInterleavedBufferAttribute) {
      if (!attrMap.has(attr)) {
        attrMap.set(attr, deinterleaveAttribute(attr));
      }

      morphTargets[key] = attrMap.get(attr);
    }
  }
}

/**
 * Returns the amount of bytes used by all attributes to represent the geometry.
 *
 * @param {BufferGeometry} geometry - The geometry.
 * @return {number} The estimate bytes used.
 */
function estimateBytesUsed(geometry) {
  // Return the estimated memory used by this geometry in bytes
  // Calculate using itemSize, count, and BYTES_PER_ELEMENT to account
  // for InterleavedBufferAttributes.
  let mem = 0;
  for (const name in geometry.attributes) {
    const attr = geometry.getAttribute(name);
    mem += attr.count * attr.itemSize * attr.array.BYTES_PER_ELEMENT;
  }

  const indices = geometry.getIndex();
  mem += indices ? indices.count * indices.itemSize * indices.array.BYTES_PER_ELEMENT : 0;
  return mem;
}

/**
 * Returns a new geometry with vertices for which all similar vertex attributes (within tolerance) are merged.
 *
 * @param {BufferGeometry} geometry - The geometry to merge vertices for.
 * @param {number} [tolerance=1e-4] - The tolerance value.
 * @return {BufferGeometry} - The new geometry with merged vertices.
 */
function mergeVertices(geometry, tolerance = 1e-4) {
  tolerance = Math.max(tolerance, Number.EPSILON);

  // Generate an index buffer if the geometry doesn't have one, or optimize it
  // if it's already available.
  const hashToIndex = {};
  const indices = geometry.getIndex();
  const positions = geometry.getAttribute("position");
  const vertexCount = indices ? indices.count : positions.count;

  // next value for triangle indices
  let nextIndex = 0;

  // attributes and new attribute arrays
  const attributeNames = Object.keys(geometry.attributes);
  const tmpAttributes = {};
  const tmpMorphAttributes = {};
  const newIndices = [];
  const getters = ["getX", "getY", "getZ", "getW"];
  const setters = ["setX", "setY", "setZ", "setW"];

  // Initialize the arrays, allocating space conservatively. Extra
  // space will be trimmed in the last step.
  for (let i = 0, l = attributeNames.length; i < l; i++) {
    const name = attributeNames[i];
    const attr = geometry.attributes[name];

    tmpAttributes[name] = new attr.constructor(
      new attr.array.constructor(attr.count * attr.itemSize),
      attr.itemSize,
      attr.normalized,
    );

    const morphAttributes = geometry.morphAttributes[name];
    if (morphAttributes) {
      if (!tmpMorphAttributes[name]) tmpMorphAttributes[name] = [];
      morphAttributes.forEach((morphAttr, i) => {
        const array = new morphAttr.array.constructor(morphAttr.count * morphAttr.itemSize);
        tmpMorphAttributes[name][i] = new morphAttr.constructor(
          array,
          morphAttr.itemSize,
          morphAttr.normalized,
        );
      });
    }
  }

  // convert the error tolerance to an amount of decimal places to truncate to
  const halfTolerance = tolerance * 0.5;
  const exponent = Math.log10(1 / tolerance);
  const hashMultiplier = Math.pow(10, exponent);
  const hashAdditive = halfTolerance * hashMultiplier;
  for (let i = 0; i < vertexCount; i++) {
    const index = indices ? indices.getX(i) : i;

    // Generate a hash for the vertex attributes at the current index 'i'
    let hash = "";
    for (let j = 0, l = attributeNames.length; j < l; j++) {
      const name = attributeNames[j];
      const attribute = geometry.getAttribute(name);
      const itemSize = attribute.itemSize;

      for (let k = 0; k < itemSize; k++) {
        // double tilde truncates the decimal value
        hash += `${~~(attribute[getters[k]](index) * hashMultiplier + hashAdditive)},`;
      }
    }

    // Add another reference to the vertex if it's already
    // used by another index
    if (hash in hashToIndex) {
      newIndices.push(hashToIndex[hash]);
    } else {
      // copy data to the new index in the temporary attributes
      for (let j = 0, l = attributeNames.length; j < l; j++) {
        const name = attributeNames[j];
        const attribute = geometry.getAttribute(name);
        const morphAttributes = geometry.morphAttributes[name];
        const itemSize = attribute.itemSize;
        const newArray = tmpAttributes[name];
        const newMorphArrays = tmpMorphAttributes[name];

        for (let k = 0; k < itemSize; k++) {
          const getterFunc = getters[k];
          const setterFunc = setters[k];
          newArray[setterFunc](nextIndex, attribute[getterFunc](index));

          if (morphAttributes) {
            for (let m = 0, ml = morphAttributes.length; m < ml; m++) {
              newMorphArrays[m][setterFunc](nextIndex, morphAttributes[m][getterFunc](index));
            }
          }
        }
      }

      hashToIndex[hash] = nextIndex;
      newIndices.push(nextIndex);
      nextIndex++;
    }
  }

  // generate result BufferGeometry
  const result = geometry.clone();
  for (const name in geometry.attributes) {
    const tmpAttribute = tmpAttributes[name];

    result.setAttribute(
      name,
      new tmpAttribute.constructor(
        tmpAttribute.array.slice(0, nextIndex * tmpAttribute.itemSize),
        tmpAttribute.itemSize,
        tmpAttribute.normalized,
      ),
    );

    if (!(name in tmpMorphAttributes)) continue;

    for (let j = 0; j < tmpMorphAttributes[name].length; j++) {
      const tmpMorphAttribute = tmpMorphAttributes[name][j];

      result.morphAttributes[name][j] = new tmpMorphAttribute.constructor(
        tmpMorphAttribute.array.slice(0, nextIndex * tmpMorphAttribute.itemSize),
        tmpMorphAttribute.itemSize,
        tmpMorphAttribute.normalized,
      );
    }
  }

  // indices

  result.setIndex(newIndices);

  return result;
}

/**
 * Returns a new indexed geometry based on `TrianglesDrawMode` draw mode.
 * This mode corresponds to the `gl.TRIANGLES` primitive in WebGL.
 *
 * @param {BufferGeometry} geometry - The geometry to convert.
 * @param {number} drawMode - The current draw mode.
 * @return {BufferGeometry} The new geometry using `TrianglesDrawMode`.
 */
function toTrianglesDrawMode(geometry, drawMode) {
  if (drawMode === TrianglesDrawMode) {
    console.warn(
      "THREE.BufferGeometryUtils.toTrianglesDrawMode(): Geometry already defined as triangles.",
    );
    return geometry;
  }

  if (drawMode === TriangleFanDrawMode || drawMode === TriangleStripDrawMode) {
    let index = geometry.getIndex();

    // generate index if not present

    if (index === null) {
      const indices = [];

      const position = geometry.getAttribute("position");

      if (position !== undefined) {
        for (let i = 0; i < position.count; i++) {
          indices.push(i);
        }

        geometry.setIndex(indices);
        index = geometry.getIndex();
      } else {
        console.error(
          "THREE.BufferGeometryUtils.toTrianglesDrawMode(): Undefined position attribute. Processing not possible.",
        );
        return geometry;
      }
    }

    //

    const numberOfTriangles = index.count - 2;
    const newIndices = [];

    if (drawMode === TriangleFanDrawMode) {
      // gl.TRIANGLE_FAN

      for (let i = 1; i <= numberOfTriangles; i++) {
        newIndices.push(index.getX(0));
        newIndices.push(index.getX(i));
        newIndices.push(index.getX(i + 1));
      }
    } else {
      // gl.TRIANGLE_STRIP

      for (let i = 0; i < numberOfTriangles; i++) {
        if (i % 2 === 0) {
          newIndices.push(index.getX(i));
          newIndices.push(index.getX(i + 1));
          newIndices.push(index.getX(i + 2));
        } else {
          newIndices.push(index.getX(i + 2));
          newIndices.push(index.getX(i + 1));
          newIndices.push(index.getX(i));
        }
      }
    }

    if (newIndices.length / 3 !== numberOfTriangles) {
      console.error(
        "THREE.BufferGeometryUtils.toTrianglesDrawMode(): Unable to generate correct amount of triangles.",
      );
    }

    // build final geometry

    const newGeometry = geometry.clone();
    newGeometry.setIndex(newIndices);
    newGeometry.clearGroups();

    return newGeometry;
  } else {
    console.error("THREE.BufferGeometryUtils.toTrianglesDrawMode(): Unknown draw mode:", drawMode);
    return geometry;
  }
}

/**
 * Calculates the morphed attributes of a morphed/skinned BufferGeometry.
 *
 * Helpful for Raytracing or Decals (i.e. a `DecalGeometry` applied to a morphed Object with a `BufferGeometry`
 * will use the original `BufferGeometry`, not the morphed/skinned one, generating an incorrect result.
 * Using this function to create a shadow `Object3`D the `DecalGeometry` can be correctly generated).
 *
 * @param {Mesh|Line|Points} object - The 3D object to compute morph attributes for.
 * @return {Object} An object with original position/normal attributes and morphed ones.
 */
function computeMorphedAttributes(object) {
  const _vA = new Vector3();
  const _vB = new Vector3();
  const _vC = new Vector3();

  const _tempA = new Vector3();
  const _tempB = new Vector3();
  const _tempC = new Vector3();

  const _morphA = new Vector3();
  const _morphB = new Vector3();
  const _morphC = new Vector3();

  function _calculateMorphedAttributeData(
    object,
    attribute,
    morphAttribute,
    morphTargetsRelative,
    a,
    b,
    c,
    modifiedAttributeArray,
  ) {
    _vA.fromBufferAttribute(attribute, a);
    _vB.fromBufferAttribute(attribute, b);
    _vC.fromBufferAttribute(attribute, c);

    const morphInfluences = object.morphTargetInfluences;

    if (morphAttribute && morphInfluences) {
      _morphA.set(0, 0, 0);
      _morphB.set(0, 0, 0);
      _morphC.set(0, 0, 0);

      for (let i = 0, il = morphAttribute.length; i < il; i++) {
        const influence = morphInfluences[i];
        const morph = morphAttribute[i];

        if (influence === 0) continue;

        _tempA.fromBufferAttribute(morph, a);
        _tempB.fromBufferAttribute(morph, b);
        _tempC.fromBufferAttribute(morph, c);

        if (morphTargetsRelative) {
          _morphA.addScaledVector(_tempA, influence);
          _morphB.addScaledVector(_tempB, influence);
          _morphC.addScaledVector(_tempC, influence);
        } else {
          _morphA.addScaledVector(_tempA.sub(_vA), influence);
          _morphB.addScaledVector(_tempB.sub(_vB), influence);
          _morphC.addScaledVector(_tempC.sub(_vC), influence);
        }
      }

      _vA.add(_morphA);
      _vB.add(_morphB);
      _vC.add(_morphC);
    }

    if (object.isSkinnedMesh) {
      object.applyBoneTransform(a, _vA);
      object.applyBoneTransform(b, _vB);
      object.applyBoneTransform(c, _vC);
    }

    modifiedAttributeArray[a * 3 + 0] = _vA.x;
    modifiedAttributeArray[a * 3 + 1] = _vA.y;
    modifiedAttributeArray[a * 3 + 2] = _vA.z;
    modifiedAttributeArray[b * 3 + 0] = _vB.x;
    modifiedAttributeArray[b * 3 + 1] = _vB.y;
    modifiedAttributeArray[b * 3 + 2] = _vB.z;
    modifiedAttributeArray[c * 3 + 0] = _vC.x;
    modifiedAttributeArray[c * 3 + 1] = _vC.y;
    modifiedAttributeArray[c * 3 + 2] = _vC.z;
  }

  const geometry = object.geometry;
  const material = object.material;

  let a, b, c;
  const index = geometry.index;
  const positionAttribute = geometry.attributes.position;
  const morphPosition = geometry.morphAttributes.position;
  const morphTargetsRelative = geometry.morphTargetsRelative;
  const normalAttribute = geometry.attributes.normal;
  const morphNormal = geometry.morphAttributes.position;

  const groups = geometry.groups;
  const drawRange = geometry.drawRange;
  let i, j, il, jl;
  let group;
  let start, end;

  const modifiedPosition = new Float32Array(positionAttribute.count * positionAttribute.itemSize);
  const modifiedNormal = new Float32Array(normalAttribute.count * normalAttribute.itemSize);

  if (index !== null) {
    // indexed buffer geometry

    if (Array.isArray(material)) {
      for (i = 0, il = groups.length; i < il; i++) {
        group = groups[i];

        start = Math.max(group.start, drawRange.start);
        end = Math.min(group.start + group.count, drawRange.start + drawRange.count);

        for (j = start, jl = end; j < jl; j += 3) {
          a = index.getX(j);
          b = index.getX(j + 1);
          c = index.getX(j + 2);

          _calculateMorphedAttributeData(
            object,
            positionAttribute,
            morphPosition,
            morphTargetsRelative,
            a,
            b,
            c,
            modifiedPosition,
          );

          _calculateMorphedAttributeData(
            object,
            normalAttribute,
            morphNormal,
            morphTargetsRelative,
            a,
            b,
            c,
            modifiedNormal,
          );
        }
      }
    } else {
      start = Math.max(0, drawRange.start);
      end = Math.min(index.count, drawRange.start + drawRange.count);

      for (i = start, il = end; i < il; i += 3) {
        a = index.getX(i);
        b = index.getX(i + 1);
        c = index.getX(i + 2);

        _calculateMorphedAttributeData(
          object,
          positionAttribute,
          morphPosition,
          morphTargetsRelative,
          a,
          b,
          c,
          modifiedPosition,
        );

        _calculateMorphedAttributeData(
          object,
          normalAttribute,
          morphNormal,
          morphTargetsRelative,
          a,
          b,
          c,
          modifiedNormal,
        );
      }
    }
  } else {
    // non-indexed buffer geometry

    if (Array.isArray(material)) {
      for (i = 0, il = groups.length; i < il; i++) {
        group = groups[i];

        start = Math.max(group.start, drawRange.start);
        end = Math.min(group.start + group.count, drawRange.start + drawRange.count);

        for (j = start, jl = end; j < jl; j += 3) {
          a = j;
          b = j + 1;
          c = j + 2;

          _calculateMorphedAttributeData(
            object,
            positionAttribute,
            morphPosition,
            morphTargetsRelative,
            a,
            b,
            c,
            modifiedPosition,
          );

          _calculateMorphedAttributeData(
            object,
            normalAttribute,
            morphNormal,
            morphTargetsRelative,
            a,
            b,
            c,
            modifiedNormal,
          );
        }
      }
    } else {
      start = Math.max(0, drawRange.start);
      end = Math.min(positionAttribute.count, drawRange.start + drawRange.count);

      for (i = start, il = end; i < il; i += 3) {
        a = i;
        b = i + 1;
        c = i + 2;

        _calculateMorphedAttributeData(
          object,
          positionAttribute,
          morphPosition,
          morphTargetsRelative,
          a,
          b,
          c,
          modifiedPosition,
        );

        _calculateMorphedAttributeData(
          object,
          normalAttribute,
          morphNormal,
          morphTargetsRelative,
          a,
          b,
          c,
          modifiedNormal,
        );
      }
    }
  }

  const morphedPositionAttribute = new Float32BufferAttribute(modifiedPosition, 3);
  const morphedNormalAttribute = new Float32BufferAttribute(modifiedNormal, 3);

  return {
    positionAttribute: positionAttribute,
    normalAttribute: normalAttribute,
    morphedPositionAttribute: morphedPositionAttribute,
    morphedNormalAttribute: morphedNormalAttribute,
  };
}

/**
 * Merges the {@link BufferGeometry#groups} for the given geometry.
 *
 * @param {BufferGeometry} geometry - The geometry to modify.
 * @return {BufferGeometry} - The updated geometry
 */
function mergeGroups(geometry) {
  if (geometry.groups.length === 0) {
    console.warn(
      "THREE.BufferGeometryUtils.mergeGroups(): No groups are defined. Nothing to merge.",
    );
    return geometry;
  }

  let groups = geometry.groups;

  // sort groups by material index

  groups = groups.sort((a, b) => {
    if (a.materialIndex !== b.materialIndex) return a.materialIndex - b.materialIndex;

    return a.start - b.start;
  });

  // create index for non-indexed geometries

  if (geometry.getIndex() === null) {
    const positionAttribute = geometry.getAttribute("position");
    const indices = [];

    for (let i = 0; i < positionAttribute.count; i += 3) {
      indices.push(i, i + 1, i + 2);
    }

    geometry.setIndex(indices);
  }

  // sort index

  const index = geometry.getIndex();

  const newIndices = [];

  for (let i = 0; i < groups.length; i++) {
    const group = groups[i];

    const groupStart = group.start;
    const groupLength = groupStart + group.count;

    for (let j = groupStart; j < groupLength; j++) {
      newIndices.push(index.getX(j));
    }
  }

  geometry.dispose(); // Required to force buffer recreation
  geometry.setIndex(newIndices);

  // update groups indices

  let start = 0;

  for (let i = 0; i < groups.length; i++) {
    const group = groups[i];

    group.start = start;
    start += group.count;
  }

  // merge groups

  let currentGroup = groups[0];

  geometry.groups = [currentGroup];

  for (let i = 1; i < groups.length; i++) {
    const group = groups[i];

    if (currentGroup.materialIndex === group.materialIndex) {
      currentGroup.count += group.count;
    } else {
      currentGroup = group;
      geometry.groups.push(currentGroup);
    }
  }

  return geometry;
}

/**
 * Modifies the supplied geometry if it is non-indexed, otherwise creates a new,
 * non-indexed geometry. Returns the geometry with smooth normals everywhere except
 * faces that meet at an angle greater than the crease angle.
 *
 * @param {BufferGeometry} geometry - The geometry to modify.
 * @param {number} [creaseAngle=Math.PI/3] - The crease angle in radians.
 * @return {BufferGeometry} - The updated geometry
 */
function toCreasedNormals(geometry, creaseAngle = Math.PI / 3 /* 60 degrees */) {
  const creaseDot = Math.cos(creaseAngle);
  const hashMultiplier = (1 + 1e-10) * 1e2;

  // reusable vectors
  const verts = [new Vector3(), new Vector3(), new Vector3()];
  const tempVec1 = new Vector3();
  const tempVec2 = new Vector3();
  const tempNorm = new Vector3();
  const tempNorm2 = new Vector3();

  // hashes a vector
  function hashVertex(v) {
    const x = ~~(v.x * hashMultiplier);
    const y = ~~(v.y * hashMultiplier);
    const z = ~~(v.z * hashMultiplier);
    return `${x},${y},${z}`;
  }

  // BufferGeometry.toNonIndexed() warns if the geometry is non-indexed
  // and returns the original geometry
  const resultGeometry = geometry.index ? geometry.toNonIndexed() : geometry;
  const posAttr = resultGeometry.attributes.position;
  const vertexMap = {};

  // find all the normals shared by commonly located vertices
  for (let i = 0, l = posAttr.count / 3; i < l; i++) {
    const i3 = 3 * i;
    const a = verts[0].fromBufferAttribute(posAttr, i3 + 0);
    const b = verts[1].fromBufferAttribute(posAttr, i3 + 1);
    const c = verts[2].fromBufferAttribute(posAttr, i3 + 2);

    tempVec1.subVectors(c, b);
    tempVec2.subVectors(a, b);

    // add the normal to the map for all vertices
    const normal = new Vector3().crossVectors(tempVec1, tempVec2).normalize();
    for (let n = 0; n < 3; n++) {
      const vert = verts[n];
      const hash = hashVertex(vert);
      if (!(hash in vertexMap)) {
        vertexMap[hash] = [];
      }

      vertexMap[hash].push(normal);
    }
  }

  // average normals from all vertices that share a common location if they are within the
  // provided crease threshold
  const normalArray = new Float32Array(posAttr.count * 3);
  const normAttr = new BufferAttribute(normalArray, 3, false);
  for (let i = 0, l = posAttr.count / 3; i < l; i++) {
    // get the face normal for this vertex
    const i3 = 3 * i;
    const a = verts[0].fromBufferAttribute(posAttr, i3 + 0);
    const b = verts[1].fromBufferAttribute(posAttr, i3 + 1);
    const c = verts[2].fromBufferAttribute(posAttr, i3 + 2);

    tempVec1.subVectors(c, b);
    tempVec2.subVectors(a, b);

    tempNorm.crossVectors(tempVec1, tempVec2).normalize();

    // average all normals that meet the threshold and set the normal value
    for (let n = 0; n < 3; n++) {
      const vert = verts[n];
      const hash = hashVertex(vert);
      const otherNormals = vertexMap[hash];
      tempNorm2.set(0, 0, 0);

      for (let k = 0, lk = otherNormals.length; k < lk; k++) {
        const otherNorm = otherNormals[k];
        if (tempNorm.dot(otherNorm) > creaseDot) {
          tempNorm2.add(otherNorm);
        }
      }

      tempNorm2.normalize();
      normAttr.setXYZ(i3 + n, tempNorm2.x, tempNorm2.y, tempNorm2.z);
    }
  }

  resultGeometry.setAttribute("normal", normAttr);
  return resultGeometry;
}

export {
  computeMikkTSpaceTangents,
  mergeGeometries,
  mergeAttributes,
  deepCloneAttribute,
  deinterleaveAttribute,
  deinterleaveGeometry,
  interleaveAttributes,
  estimateBytesUsed,
  mergeVertices,
  toTrianglesDrawMode,
  computeMorphedAttributes,
  mergeGroups,
  toCreasedNormals,
};