/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You under the Apache License, Version 2.0
    * (the "License"); you may not use this file except in compliance with
    * the License.  You may obtain a copy of the License at
    *
    *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.commons.geometry.euclidean.threed.mesh;
  
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Comparator;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Map;
  import java.util.NoSuchElementException;
  import java.util.Objects;
  import java.util.TreeMap;
  import java.util.function.Function;
  import java.util.stream.Stream;
  import java.util.stream.StreamSupport;
  
  import org.apache.commons.geometry.core.Transform;
  import org.apache.commons.geometry.core.precision.DoublePrecisionContext;
  import org.apache.commons.geometry.euclidean.threed.BoundarySource3D;
  import org.apache.commons.geometry.euclidean.threed.Bounds3D;
  import org.apache.commons.geometry.euclidean.threed.PlaneConvexSubset;
  import org.apache.commons.geometry.euclidean.threed.Planes;
  import org.apache.commons.geometry.euclidean.threed.Triangle3D;
  import org.apache.commons.geometry.euclidean.threed.Vector3D;
  
  /** A simple implementation of the {@link TriangleMesh} interface. This class ensures that
   * faces always contain 3 valid references into the vertex list but does not enforce that
   * the referenced vertices are unique or that they define a triangle with non-zero size. For
   * example, a mesh could contain a face with 3 vertices that are considered equivalent by the
   * configured precision context. Attempting to call the {@link TriangleMesh.Face#getPolygon()}
   * method on such a face results in an exception. The
   * {@link TriangleMesh.Face#definesPolygon()} method can be used to determine if a face defines
   * a valid triangle.
   *
   * <p>Instances of this class are guaranteed to be immutable.</p>
   */
  public final class SimpleTriangleMesh implements TriangleMesh {
  
      /** Vertices in the mesh. */
      private final List<Vector3D> vertices;
  
      /** Faces in the mesh. */
      private final List<int[]> faces;
  
      /** The bounds of the mesh. */
      private final Bounds3D bounds;
  
      /** Object used for floating point comparisons. */
      private final DoublePrecisionContext precision;
  
      /** Construct a new instance from a vertex list and set of faces. No validation is
       * performed on the input.
       * @param vertices vertex list
       * @param faces face indices list
       * @param bounds mesh bounds
       * @param precision precision context used when creating face polygons
       */
      private SimpleTriangleMesh(final List<Vector3D> vertices, final List<int[]> faces, final Bounds3D bounds,
              final DoublePrecisionContext precision) {
          this.vertices = Collections.unmodifiableList(vertices);
          this.faces = Collections.unmodifiableList(faces);
          this.bounds = bounds;
          this.precision = precision;
      }
  
      /** {@inheritDoc} */
      @Override
      public Iterable<Vector3D> vertices() {
          return getVertices();
      }
  
      /** {@inheritDoc} */
      @Override
      public List<Vector3D> getVertices() {
          return vertices;
      }
  
      /** {@inheritDoc} */
      @Override
      public int getVertexCount() {
          return vertices.size();
      }
 
     /** {@inheritDoc} */
     @Override
     public Iterable<TriangleMesh.Face> faces() {
         return () -> new FaceIterator<>(Function.identity());
     }
 
     /** {@inheritDoc} */
     @Override
     public List<TriangleMesh.Face> getFaces() {
         final int count = getFaceCount();
 
         final List<Face> faceList = new ArrayList<>(count);
         for (int i = 0; i < count; ++i) {
             faceList.add(getFace(i));
         }
 
         return faceList;
     }
 
     /** {@inheritDoc} */
     @Override
     public int getFaceCount() {
         return faces.size();
     }
 
     /** {@inheritDoc} */
     @Override
     public TriangleMesh.Face getFace(final int index) {
         return new SimpleTriangleFace(index, faces.get(index));
     }
 
     /** {@inheritDoc} */
     @Override
     public Bounds3D getBounds() {
         return bounds;
     }
 
     /** Get the precision context for the mesh. This context is used during construction of
      * face {@link Triangle3D} instances.
      * @return the precision context for the mesh
      */
     public DoublePrecisionContext getPrecision() {
         return precision;
     }
 
     /** {@inheritDoc} */
     @Override
     public Stream<PlaneConvexSubset> boundaryStream() {
         return createFaceStream(Face::getPolygon);
     }
 
     /** {@inheritDoc} */
     @Override
     public Stream<Triangle3D> triangleStream() {
         return createFaceStream(Face::getPolygon);
     }
 
     /** {@inheritDoc} */
     @Override
     public SimpleTriangleMesh transform(final Transform<Vector3D> transform) {
         // only the vertices and bounds are modified; the faces are the same
         final Bounds3D.Builder boundsBuilder = Bounds3D.builder();
         final List<Vector3D> tVertices = new ArrayList<>(vertices.size());
 
         Vector3D tVertex;
         for (final Vector3D vertex : vertices) {
             tVertex = transform.apply(vertex);
 
             boundsBuilder.add(tVertex);
             tVertices.add(tVertex);
         }
 
         final Bounds3D tBounds = boundsBuilder.hasBounds() ?
                 boundsBuilder.build() :
                 null;
 
         return new SimpleTriangleMesh(tVertices, faces, tBounds, precision);
     }
 
     /** Return this instance if the given precision context is equal to the current precision context.
      * Otherwise, create a new mesh with the given precision context but the same vertices, faces, and
      * bounds.
      * @param meshPrecision precision context to use when generating face polygons
      * @return a mesh instance with the given precision context and the same mesh structure as the current
      *      instance
      */
     @Override
     public SimpleTriangleMesh toTriangleMesh(final DoublePrecisionContext meshPrecision) {
         if (this.precision.equals(meshPrecision)) {
             return this;
         }
 
         return new SimpleTriangleMesh(vertices, faces, bounds, meshPrecision);
     }
 
     /** {@inheritDoc} */
     @Override
     public String toString() {
         final StringBuilder sb = new StringBuilder();
         sb.append(getClass().getSimpleName())
             .append("[vertexCount= ")
             .append(getVertexCount())
             .append(", faceCount= ")
             .append(getFaceCount())
             .append(", bounds= ")
             .append(getBounds())
             .append(']');
 
         return sb.toString();
     }
 
     /** Create a stream containing the results of applying {@code fn} to each face in
      * the mesh.
      * @param <T> Stream element type
      * @param fn function used to extract the stream values from each face
      * @return a stream containing the results of applying {@code fn} to each face in
      *      the mesh
      */
     private <T> Stream<T> createFaceStream(final Function<TriangleMesh.Face, T> fn) {
         final Iterable<T> iterable = () -> new FaceIterator<>(fn);
         return StreamSupport.stream(iterable.spliterator(), false);
     }
 
     /** Return a builder for creating new triangle mesh objects.
      * @param precision precision object used for floating point comparisons
      * @return a builder for creating new triangle mesh objects
      */
     public static Builder builder(final DoublePrecisionContext precision) {
         return new Builder(precision);
     }
 
     /** Construct a new triangle mesh from the given vertices and face indices.
      * @param vertices vertices for the mesh
      * @param faces face indices for the mesh
      * @param precision precision context used for floating point comparisons
      * @return a new triangle mesh instance
      * @throws IllegalArgumentException if any of the face index arrays does not have exactly 3 elements or
      *       if any index is not a valid index into the vertex list
      */
     public static SimpleTriangleMesh from(final Vector3D[] vertices, final int[][] faces,
                                           final DoublePrecisionContext precision) {
         return from(Arrays.asList(vertices), Arrays.asList(faces), precision);
     }
 
     /** Construct a new triangle mesh from the given vertices and face indices.
      * @param vertices vertices for the mesh
      * @param faces face indices for the mesh
      * @param precision precision context used for floating point comparisons
      * @return a new triangle mesh instance
      * @throws IllegalArgumentException if any of the face index arrays does not have exactly 3 elements or
      *       if any index is not a valid index into the vertex list
      */
     public static SimpleTriangleMesh from(final Collection<Vector3D> vertices, final Collection<int[]> faces,
                                           final DoublePrecisionContext precision) {
         final Builder builder = builder(precision);
 
         return builder.addVertices(vertices)
                 .addFaces(faces)
                 .build();
     }
 
     /** Construct a new mesh instance containing all triangles from the given boundary
      * source. Equivalent vertices are reused wherever possible.
      * @param boundarySrc boundary source to construct a mesh from
      * @param precision precision context used for floating point comparisons
      * @return new mesh instance containing all triangles from the given boundary
      *      source
      * @throws IllegalStateException if any boundary in the boundary source has infinite size and cannot
      *      be converted to triangles
      */
     public static SimpleTriangleMesh from(final BoundarySource3D boundarySrc, final DoublePrecisionContext precision) {
         final Builder builder = builder(precision);
         try (Stream<Triangle3D> stream = boundarySrc.triangleStream()) {
             stream.forEach(tri -> builder.addFaceUsingVertices(
                 tri.getPoint1(),
                 tri.getPoint2(),
                 tri.getPoint3()));
         }
 
         return builder.build();
     }
 
     /** Internal implementation of {@link TriangleMesh.Face}.
      */
     private final class SimpleTriangleFace implements TriangleMesh.Face {
 
         /** The index of the face in the mesh. */
         private final int index;
 
         /** Vertex indices for the face. */
         private final int[] vertexIndices;
 
         SimpleTriangleFace(final int index, final int[] vertexIndices) {
             this.index = index;
             this.vertexIndices = vertexIndices;
         }
 
         /** {@inheritDoc} */
         @Override
         public int getIndex() {
             return index;
         }
 
         /** {@inheritDoc} */
         @Override
         public int[] getVertexIndices() {
             return vertexIndices.clone();
         }
 
         /** {@inheritDoc} */
         @Override
         public List<Vector3D> getVertices() {
             return Arrays.asList(
                     getPoint1(),
                     getPoint2(),
                     getPoint3());
         }
 
         /** {@inheritDoc} */
         @Override
         public Vector3D getPoint1() {
             return vertices.get(vertexIndices[0]);
         }
 
         /** {@inheritDoc} */
         @Override
         public Vector3D getPoint2() {
             return vertices.get(vertexIndices[1]);
         }
 
         /** {@inheritDoc} */
         @Override
         public Vector3D getPoint3() {
             return vertices.get(vertexIndices[2]);
         }
 
         /** {@inheritDoc} */
         @Override
         public boolean definesPolygon() {
             final Vector3D p1 = getPoint1();
             final Vector3D v1 = p1.vectorTo(getPoint2());
             final Vector3D v2 = p1.vectorTo(getPoint3());
 
             return !precision.eqZero(v1.cross(v2).norm());
         }
 
         /** {@inheritDoc} */
         @Override
         public Triangle3D getPolygon() {
             return Planes.triangleFromVertices(
                     getPoint1(),
                     getPoint2(),
                     getPoint3(),
                     precision);
         }
 
         /** {@inheritDoc} */
         @Override
         public String toString() {
             final StringBuilder sb = new StringBuilder();
             sb.append(getClass().getSimpleName())
                 .append("[index= ")
                 .append(getIndex())
                 .append(", vertexIndices= ")
                 .append(Arrays.toString(getVertexIndices()))
                 .append(", vertices= ")
                 .append(getVertices())
                 .append(']');
 
             return sb.toString();
         }
     }
 
     /** Internal class for iterating through the mesh faces and extracting a value from each.
      * @param <T> Type returned by the iterator
      */
     private final class FaceIterator<T> implements Iterator<T> {
 
         /** The current index of the iterator. */
         private int index = 0;
 
         /** Function to apply to each face in the mesh. */
         private final Function<TriangleMesh.Face, T> fn;
 
         /** Construct a new instance for iterating through the mesh faces and extracting
          * a value from each.
          * @param fn function to apply to each face in order to obtain the iterated value
          */
         FaceIterator(final Function<TriangleMesh.Face, T> fn) {
             this.fn = fn;
         }
 
         /** {@inheritDoc} */
         @Override
         public boolean hasNext() {
             return index < faces.size();
         }
 
         /** {@inheritDoc} */
         @Override
         public T next() {
             if (hasNext()) {
                 final Face face = getFace(index++);
                 return fn.apply(face);
             }
             throw new NoSuchElementException();
         }
     }
 
     /** Builder class for creating mesh instances.
      */
     public static final class Builder {
 
         /** List of vertices. */
         private final ArrayList<Vector3D> vertices = new ArrayList<>();
 
         /** Map of vertices to their first occurrence in the vertex list. */
         private Map<Vector3D, Integer> vertexIndexMap;
 
         /** List of face vertex indices. */
         private final ArrayList<int[]> faces = new ArrayList<>();
 
         /** Object used to construct the 3D bounds of the vertex list. */
         private final Bounds3D.Builder boundsBuilder = Bounds3D.builder();
 
         /** Precision context used for floating point comparisons; this value may be null
          * if vertices are not to be combined in this builder.
          */
         private final DoublePrecisionContext precision;
 
         /** Flag set to true once a mesh is constructed from this builder. */
         private boolean built = false;
 
         /** Construct a new builder.
          * @param precision precision context used for floating point comparisons; may
          *      be null if vertices are not to be combined in this builder.
          */
         private Builder(final DoublePrecisionContext precision) {
             Objects.requireNonNull(precision, "Precision context must not be null");
 
             this.precision = precision;
         }
 
         /** Use a vertex in the constructed mesh. If an equivalent vertex already exist, as determined
          * by the configured {@link DoublePrecisionContext}, then the index of the previously added
          * vertex is returned. Otherwise, the given vertex is added to the vertex list and the index
          * of the new entry is returned. This is in contrast with the {@link #addVertex(Vector3D)},
          * which always adds a new entry to the vertex list.
          * @param vertex vertex to use
          * @return the index of the added vertex or an equivalent vertex that was added previously
          * @see #addVertex(Vector3D)
          */
         public int useVertex(final Vector3D vertex) {
             final int nextIdx = vertices.size();
             final int actualIdx = addToVertexIndexMap(vertex, nextIdx, getVertexIndexMap());
 
             // add to the vertex list if not already present
             if (actualIdx == nextIdx) {
                 addToVertexList(vertex);
             }
 
             return actualIdx;
         }
 
         /** Add a vertex directly to the vertex list, returning the index of the added vertex.
          * The vertex is added regardless of whether or not an equivalent vertex already
          * exists in the list. This is in contrast with the {@link #useVertex(Vector3D)} method,
          * which only adds a new entry to the vertex list if an equivalent one does not
          * already exist.
          * @param vertex the vertex to append
          * @return the index of the appended vertex in the vertex list
          */
         public int addVertex(final Vector3D vertex) {
             final int idx = addToVertexList(vertex);
 
             if (vertexIndexMap != null) {
                 // add to the map in order to keep it in sync
                 addToVertexIndexMap(vertex, idx, vertexIndexMap);
             }
 
             return idx;
         }
 
         /** Add a group of vertices directly to the vertex list. No equivalent vertices are reused.
          * @param newVertices vertices to append
          * @return this instance
          * @see #addVertex(Vector3D)
          */
         public Builder addVertices(final Vector3D[] newVertices) {
             return addVertices(Arrays.asList(newVertices));
         }
 
         /** Add a group of vertices directly to the vertex list. No equivalent vertices are reused.
          * @param newVertices vertices to append
          * @return this instance
          * @see #addVertex(Vector3D)
          */
         public Builder addVertices(final Collection<Vector3D> newVertices) {
             final int newSize = vertices.size() + newVertices.size();
             ensureVertexCapacity(newSize);
 
             for (final Vector3D vertex : newVertices) {
                 addVertex(vertex);
             }
 
             return this;
         }
 
         /** Ensure that this instance has enough capacity to store at least {@code numVertices}
          * number of vertices without reallocating space. This can be used to help improve performance
          * and memory usage when creating meshes with large numbers of vertices.
          * @param numVertices the number of vertices to ensure that this instance can contain
          * @return this instance
          */
         public Builder ensureVertexCapacity(final int numVertices) {
             vertices.ensureCapacity(numVertices);
             return this;
         }
 
         /** Get the current number of vertices in this mesh.
          * @return the current number of vertices in this mesh
          */
         public int getVertexCount() {
             return vertices.size();
         }
 
         /** Append a face to this mesh.
          * @param index1 index of the first vertex in the face
          * @param index2 index of the second vertex in the face
          * @param index3 index of the third vertex in the face
          * @return this instance
          * @throws IllegalArgumentException if any of the arguments is not a valid index into
          *      the current vertex list
          */
         public Builder addFace(final int index1, final int index2, final int index3) {
             validateCanModify();
 
             final int[] indices = {
                 validateVertexIndex(index1),
                 validateVertexIndex(index2),
                 validateVertexIndex(index3)
             };
 
             faces.add(indices);
 
             return this;
         }
 
         /** Append a group of faces to this mesh.
          * @param faceIndices faces to append
          * @return this instance
          * @throws IllegalArgumentException if any of the face index arrays does not have exactly 3 elements or
          *       if any index is not a valid index into the current vertex list
          */
         public Builder addFaces(final int[][] faceIndices) {
             return addFaces(Arrays.asList(faceIndices));
         }
 
         /** Append a group of faces to this mesh.
          * @param faceIndices faces to append
          * @return this instance
          * @throws IllegalArgumentException if any of the face index arrays does not have exactly 3 elements or
          *       if any index is not a valid index into the current vertex list
          */
         public Builder addFaces(final Collection<int[]> faceIndices) {
             final int newSize = faces.size() + faceIndices.size();
             ensureFaceCapacity(newSize);
 
             for (final int[] face : faceIndices) {
                 if (face.length != 3) {
                     throw new IllegalArgumentException("Face must contain 3 vertex indices; found " + face.length);
                 }
 
                 addFace(face[0], face[1], face[2]);
             }
 
             return this;
         }
 
         /** Add a face to this mesh, only adding vertices to the vertex list if equivalent vertices are
          * not found.
          * @param p1 first face vertex
          * @param p2 second face vertex
          * @param p3 third face vertex
          * @return this instance
          * @see #useVertex(Vector3D)
          */
         public Builder addFaceUsingVertices(final Vector3D p1, final Vector3D p2, final Vector3D p3) {
             return addFace(
                         useVertex(p1),
                         useVertex(p2),
                         useVertex(p3)
                     );
         }
 
         /** Add a face and its vertices to this mesh. The vertices are always added to the vertex list,
          * regardless of whether or not equivalent vertices exist in the vertex list.
          * @param p1 first face vertex
          * @param p2 second face vertex
          * @param p3 third face vertex
          * @return this instance
          * @see #addVertex(Vector3D)
          */
         public Builder addFaceAndVertices(final Vector3D p1, final Vector3D p2, final Vector3D p3) {
             return addFace(
                         addVertex(p1),
                         addVertex(p2),
                         addVertex(p3)
                     );
         }
 
         /** Ensure that this instance has enough capacity to store at least {@code numFaces}
          * number of faces without reallocating space. This can be used to help improve performance
          * and memory usage when creating meshes with large numbers of faces.
          * @param numFaces the number of faces to ensure that this instance can contain
          * @return this instance
          */
         public Builder ensureFaceCapacity(final int numFaces) {
             faces.ensureCapacity(numFaces);
             return this;
         }
 
         /** Get the current number of faces in this mesh.
          * @return the current number of faces in this meshr
          */
         public int getFaceCount() {
             return faces.size();
         }
 
         /** Build a triangle mesh containing the vertices and faces in this builder.
          * @return a triangle mesh containing the vertices and faces in this builder
          */
         public SimpleTriangleMesh build() {
             built = true;
 
             final Bounds3D bounds = boundsBuilder.hasBounds() ?
                     boundsBuilder.build() :
                     null;
 
             vertices.trimToSize();
             faces.trimToSize();
 
             return new SimpleTriangleMesh(
                     vertices,
                     faces,
                     bounds,
                     precision);
         }
 
         /** Get the vertex index map, creating and initializing it if needed.
          * @return the vertex index map
          */
         private Map<Vector3D, Integer> getVertexIndexMap() {
             if (vertexIndexMap == null) {
                 vertexIndexMap = new TreeMap<>(new FuzzyVectorComparator(precision));
 
                 // populate the index map
                 final int size = vertices.size();
                 for (int i = 0; i < size; ++i) {
                     addToVertexIndexMap(vertices.get(i), i, vertexIndexMap);
                 }
             }
             return vertexIndexMap;
         }
 
         /** Add a vertex to the given vertex index map. The vertex is inserted and mapped to {@code targetidx}
          *  if an equivalent vertex does not already exist. The index now associated with the given vertex
          *  or its equivalent is returned.
          * @param vertex vertex to add
          * @param targetIdx the index to associate with the vertex if no equivalent vertex has already been
          *      mapped
          * @param map vertex index map
          * @return the index now associated with the given vertex or its equivalent
          */
         private int addToVertexIndexMap(final Vector3D vertex, final int targetIdx, final Map<Vector3D, Integer> map) {
             validateCanModify();
 
             final Integer actualIdx = map.putIfAbsent(vertex, targetIdx);
 
             return actualIdx != null ?
                     actualIdx.intValue() :
                     targetIdx;
         }
 
         /** Append the given vertex to the end of the vertex list. The index of the vertex is returned.
          * @param vertex the vertex to append
          * @return the index of the appended vertex
          */
         private int addToVertexList(final Vector3D vertex) {
             validateCanModify();
 
             boundsBuilder.add(vertex);
 
             final int idx = vertices.size();
             vertices.add(vertex);
 
             return idx;
         }
 
         /** Throw an exception if the given vertex index is not valid.
          * @param idx vertex index to validate
          * @return the validated index
          * @throws IllegalArgumentException if the given index is not a valid index into
          *      the vertices list
          */
         private int validateVertexIndex(final int idx) {
             if (idx < 0 || idx >= vertices.size()) {
                 throw new IllegalArgumentException("Invalid vertex index: " + idx);
             }
 
             return idx;
         }
 
         /** Throw an exception if the builder has been used to construct a mesh instance
          * and can no longer be modified.
          */
         private void validateCanModify() {
             if (built) {
                 throw new IllegalStateException("Builder instance cannot be modified: mesh construction is complete");
             }
         }
     }
 
     /** Comparator used to sort vectors using non-strict ("fuzzy") comparisons.
      * Vectors are considered equal if their values in all coordinate dimensions
      * are equivalent as evaluated by the precision context.
      */
     private static final class FuzzyVectorComparator implements Comparator<Vector3D> {
         /** Precision context to determine floating-point equality. */
         private final DoublePrecisionContext precision;
 
         /** Construct a new instance that uses the given precision context for
          * floating point comparisons.
          * @param precision precision context used for floating point comparisons
          */
         FuzzyVectorComparator(final DoublePrecisionContext precision) {
             this.precision = precision;
         }
 
         /** {@inheritDoc} */
         @Override
         public int compare(final Vector3D a, final Vector3D b) {
             int result = precision.compare(a.getX(), b.getX());
             if (result == 0) {
                 result = precision.compare(a.getY(), b.getY());
                 if (result == 0) {
                     result = precision.compare(a.getZ(), b.getZ());
                 }
             }
 
             return result;
         }
     }
 }