/*
 * 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.lucene.util.bkd;

import org.apache.lucene.codecs.MutablePointValues;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.FutureArrays;
import org.apache.lucene.util.IntroSelector;
import org.apache.lucene.util.IntroSorter;
import org.apache.lucene.util.MSBRadixSorter;
import org.apache.lucene.util.RadixSelector;
import org.apache.lucene.util.Selector;
import org.apache.lucene.util.packed.PackedInts;

Utility APIs for sorting and partitioning buffered points.
@lucene.internal
/** Utility APIs for sorting and partitioning buffered points.
 *
 * @lucene.internal */
public final class MutablePointsReaderUtils {

  MutablePointsReaderUtils() {}

  
Sort the given MutablePointValues based on its packed value then doc ID. /** Sort the given {@link MutablePointValues} based on its packed value then doc ID. */
  public static void sort(int maxDoc, int packedBytesLength,
                          MutablePointValues reader, int from, int to) {
    final int bitsPerDocId = PackedInts.bitsRequired(maxDoc - 1);
    new MSBRadixSorter(packedBytesLength + (bitsPerDocId + 7) / 8) {

      @Override
      protected void swap(int i, int j) {
        reader.swap(i, j);
      }

      @Override
      protected int byteAt(int i, int k) {
        if (k < packedBytesLength) {
          return Byte.toUnsignedInt(reader.getByteAt(i, k));
        } else {
          final int shift = bitsPerDocId - ((k - packedBytesLength + 1) << 3);
          return (reader.getDocID(i) >>> Math.max(0, shift)) & 0xff;
        }
      }

      @Override
      protected org.apache.lucene.util.Sorter getFallbackSorter(int k) {
        return new IntroSorter() {

          final BytesRef pivot = new BytesRef();
          final BytesRef scratch = new BytesRef();
          int pivotDoc;

          @Override
          protected void swap(int i, int j) {
            reader.swap(i, j);
          }

          @Override
          protected void setPivot(int i) {
            reader.getValue(i, pivot);
            pivotDoc = reader.getDocID(i);
          }

          @Override
          protected int comparePivot(int j) {
            if (k < packedBytesLength) {
              reader.getValue(j, scratch);
              int cmp = FutureArrays.compareUnsigned(pivot.bytes, pivot.offset + k, pivot.offset + k + packedBytesLength - k,
                  scratch.bytes, scratch.offset + k, scratch.offset + k + packedBytesLength - k);
              if (cmp != 0) {
                return cmp;
              }
            }
            return pivotDoc - reader.getDocID(j);
          }
        };
      }

    }.sort(from, to);
  }

  
Sort points on the given dimension. /** Sort points on the given dimension. */
  public static void sortByDim(int numDataDim, int numIndexDim, int sortedDim, int bytesPerDim, int[] commonPrefixLengths,
                               MutablePointValues reader, int from, int to,
                               BytesRef scratch1, BytesRef scratch2) {

    final int start = sortedDim * bytesPerDim + commonPrefixLengths[sortedDim];
    final int dimEnd =  sortedDim * bytesPerDim + bytesPerDim;
    final int dataStart = numIndexDim * bytesPerDim;
    final int dataEnd = dataStart + (numDataDim - numIndexDim) * bytesPerDim;
    // No need for a fancy radix sort here, this is called on the leaves only so
    // there are not many values to sort
    new IntroSorter() {

      final BytesRef pivot = scratch1;
      int pivotDoc = -1;

      @Override
      protected void swap(int i, int j) {
        reader.swap(i, j);
      }

      @Override
      protected void setPivot(int i) {
        reader.getValue(i, pivot);
        pivotDoc = reader.getDocID(i);
      }

      @Override
      protected int comparePivot(int j) {
        reader.getValue(j, scratch2);
        int cmp = FutureArrays.compareUnsigned(pivot.bytes, pivot.offset + start, pivot.offset + dimEnd, scratch2.bytes,
            scratch2.offset + start, scratch2.offset + dimEnd);
        if (cmp == 0) {
          cmp = FutureArrays.compareUnsigned(pivot.bytes, pivot.offset + dataStart, pivot.offset + dataEnd,
              scratch2.bytes, scratch2.offset + dataStart, scratch2.offset + dataEnd);
          if (cmp == 0) {
            cmp = pivotDoc - reader.getDocID(j);
          }
        }
        return cmp;
      }
    }.sort(from, to);
  }

  
Partition points around mid. All values on the left must be less than or equal to it and all values on the right must be greater than or equal to it. /** Partition points around {@code mid}. All values on the left must be less
   *  than or equal to it and all values on the right must be greater than or
   *  equal to it. */
  public static void partition(int numDataDim, int numIndexDim, int maxDoc, int splitDim, int bytesPerDim, int commonPrefixLen,
                               MutablePointValues reader, int from, int to, int mid,
                               BytesRef scratch1, BytesRef scratch2) {
    final int dimOffset = splitDim * bytesPerDim + commonPrefixLen;
    final int dimCmpBytes = bytesPerDim - commonPrefixLen;
    final int dataOffset = numIndexDim * bytesPerDim;
    final int dataCmpBytes = (numDataDim - numIndexDim) * bytesPerDim + dimCmpBytes;
    final int bitsPerDocId = PackedInts.bitsRequired(maxDoc - 1);
    new RadixSelector(dataCmpBytes + (bitsPerDocId + 7) / 8) {

      @Override
      protected Selector getFallbackSelector(int k) {
        final int dataStart = (k < dimCmpBytes) ? dataOffset : dataOffset + k - dimCmpBytes;
        final int dataEnd = numDataDim * bytesPerDim;
        return new IntroSelector() {

          final BytesRef pivot = scratch1;
          int pivotDoc;

          @Override
          protected void swap(int i, int j) {
            reader.swap(i, j);
          }

          @Override
          protected void setPivot(int i) {
            reader.getValue(i, pivot);
            pivotDoc = reader.getDocID(i);
          }

          @Override
          protected int comparePivot(int j) {
            if (k < dimCmpBytes) {
              reader.getValue(j, scratch2);
              int cmp = FutureArrays.compareUnsigned(pivot.bytes, pivot.offset + dimOffset + k, pivot.offset + dimOffset + dimCmpBytes,
                  scratch2.bytes, scratch2.offset + dimOffset + k, scratch2.offset + dimOffset + dimCmpBytes);
              if (cmp != 0) {
                return cmp;
              }
            }
            if (k < dataCmpBytes) {
              reader.getValue(j, scratch2);
              int cmp = FutureArrays.compareUnsigned(pivot.bytes, pivot.offset + dataStart, pivot.offset + dataEnd,
                  scratch2.bytes, scratch2.offset + dataStart, scratch2.offset + dataEnd);
              if (cmp != 0) {
                return cmp;
              }
            }
            return pivotDoc - reader.getDocID(j);
          }
        };
      }

      @Override
      protected void swap(int i, int j) {
        reader.swap(i, j);
      }

      @Override
      protected int byteAt(int i, int k) {
        if (k < dimCmpBytes) {
          return Byte.toUnsignedInt(reader.getByteAt(i, dimOffset + k));
        } else if (k < dataCmpBytes) {
          return Byte.toUnsignedInt(reader.getByteAt(i, dataOffset + k - dimCmpBytes));
        } else {
          final int shift = bitsPerDocId - ((k - dataCmpBytes + 1) << 3);
          return (reader.getDocID(i) >>> Math.max(0, shift)) & 0xff;
        }
      }
    }.select(from, to, mid);
  }
}