/*
 * 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.datasketches.req;

import static org.apache.datasketches.common.Util.LS;
import static org.apache.datasketches.quantilescommon.QuantileSearchCriteria.INCLUSIVE;

import java.lang.foreign.MemorySegment;
import java.util.Arrays;

import org.apache.datasketches.common.positional.PositionalSegment;
import org.apache.datasketches.common.SketchesArgumentException;
import org.apache.datasketches.quantilescommon.InequalitySearch;
import org.apache.datasketches.quantilescommon.QuantileSearchCriteria;

/**
 * A special buffer of floats specifically designed to support the ReqCompactor class.
 *
 * @author Lee Rhodes
 */
class FloatBuffer {
  private float[] arr_;
  private int count_;
  private int capacity_;
  private final int delta_;
  private boolean sorted_;
  private final boolean spaceAtBottom_; //tied to hra

  /**
   * Constructs an new empty FloatBuffer with an initial capacity specified by
   * the <code>capacity</code> argument.
   *
   * @param capacity the initial capacity.
   * @param delta add space in increments of this size
   * @param spaceAtBottom if true, create any extra space at the bottom of the buffer,
   * otherwise, create any extra space at the top of the buffer.
   */
  FloatBuffer(final int capacity, final int delta, final boolean spaceAtBottom) {
    arr_ = new float[capacity];
    count_ = 0;
    capacity_ = capacity;
    delta_ = delta;
    sorted_ = true;
    spaceAtBottom_ = spaceAtBottom;
  }

  /**
   * Copy Constructor
   * @param buf the FloatBuffer to be copied into this one
   */
  FloatBuffer(final FloatBuffer buf) {
    arr_ = buf.arr_.clone();
    count_ = buf.count_;
    capacity_ = buf.capacity_;
    delta_ = buf.delta_;
    sorted_ = buf.sorted_;
    spaceAtBottom_ = buf.spaceAtBottom_;
  }

  /**
   * Exact construction from elements.
   * The active region must be properly positioned in the array.
   * @param arr the array to be used directly as the internal array
   * @param count the number of active elements in the given array
   * @param capacity the initial capacity
   * @param delta add space in increments of this size
   * @param sorted true if already sorted
   * @param spaceAtBottom if true, create any extra space at the bottom of the buffer,
   * otherwise, create any extra space at the top of the buffer.
   */
  private FloatBuffer(final float[] arr, final int count, final int capacity, final int delta,
      final boolean sorted, final boolean spaceAtBottom) {
    arr_ = arr;
    count_ = count;
    capacity_ = capacity;
    delta_ = delta;
    sorted_ = sorted;
    spaceAtBottom_ = spaceAtBottom;
  }

  /**
   * Used by ReqSerDe. The array is only the active region and will be positioned
   * based on capacity, delta, and sab. This copies over the sorted flag.
   * @param arr the active items extracted from the deserialization.
   * @param count the number of active items
   * @param capacity the capacity of the internal array
   * @param delta add space in this increment
   * @param sorted if the incoming array is sorted
   * @param sab equivalent to the HRA flag, e.g., space-at-bottom.
   * @return a new FloatBuffer
   */
  static FloatBuffer reconstruct(
      final float[] arr,
      final int count,
      final int capacity,
      final int delta,
      final boolean sorted,
      final boolean sab //hra
      ) {
    final float[] farr = new float[capacity];
    if (sab) {
      System.arraycopy(arr, 0, farr, capacity - count, count);
    } else {
      System.arraycopy(arr, 0, farr, 0, count);
    }
    return new FloatBuffer(farr, count, capacity, delta, sorted, sab);
  }

  /**
   * Wraps the given array to use as the internal array; thus no copies. For internal use.
   * @param arr the given array
   * @param isSorted set true, if incoming array is already sorted.
   * @param spaceAtBottom if true, create any extra space at the bottom of the buffer,
   * otherwise, create any extra space at the top of the buffer.
   * @return this, which will be sorted, if necessary.
   */
  static FloatBuffer wrap(final float[] arr, final boolean isSorted, final boolean spaceAtBottom) {
    final FloatBuffer buf = new FloatBuffer(arr, arr.length, arr.length, 0, isSorted, spaceAtBottom);
    buf.sort();
    return buf;
  }

  /**
   * Appends the given item to the active array and increments the active count.
   * This will expand the array if necessary.
   * @param item the given item
   * @return this
   */
  FloatBuffer append(final float item) {
    ensureSpace(1);
    final int index = spaceAtBottom_ ? capacity_ - count_ - 1 : count_;
    arr_[index] = item;
    count_++;
    sorted_ = false;
    return this;
  }

  /**
   * Ensures that the capacity of this FloatBuffer is at least newCapacity.
   * If newCapacity &lt; capacity(), no action is taken.
   * @param newCapacity the new desired capacity
   * @return this
   */
  FloatBuffer ensureCapacity(final int newCapacity) {
    if (newCapacity > capacity_) {
      final float[] out = new float[newCapacity];
      final int srcPos = spaceAtBottom_ ? capacity_ - count_ : 0;
      final int destPos = spaceAtBottom_ ? newCapacity - count_ : 0;
      System.arraycopy(arr_, srcPos, out, destPos, count_);
      arr_ = out;
      capacity_ = newCapacity;
    }
    return this;
  }

  /**
   * Ensures that the space remaining (capacity() - getCount()) is at least the given space.
   * @param space the requested space remaining
   * @return this
   */
  private FloatBuffer ensureSpace(final int space) {
    if ((count_ + space) > capacity_) {
      final int newCap = count_ + space + delta_;
      ensureCapacity(newCap);
    }
    return this;
  }

  /**
   * Returns a reference to the internal quantiles array. Be careful and don't modify this array!
   * @return the internal quantiles array.
   */
  float[] getArray() {
    return arr_;
  }

  /**
   * Gets the current capacity of this FloatBuffer. The capacity is the total amount of storage
   * currently available without expanding the array.
   *
   * @return the current capacity
   */
  int getCapacity() {
    return capacity_;
  }

  /**
   * Returns the count of items based on the given criteria.
   * Also used in test.
   * @param item the given item
   * @param searchCrit the chosen criterion: LT, LT Strict, or LE
   * @return count of items based on the given criterion.
   */
  int getCountWithCriterion(final float item, final QuantileSearchCriteria searchCrit) {
    assert !Float.isNaN(item) : "Float items must not be NaN.";
    if (!sorted_) { sort(); } //we must be sorted!
    int low = 0;    //Initialized to space at top
    int high = count_ - 1;
    if (spaceAtBottom_) {
      low = capacity_ - count_;
      high = capacity_ - 1;
    }
    final InequalitySearch crit = (searchCrit == INCLUSIVE) ? InequalitySearch.LE : InequalitySearch.LT;
    final int index = InequalitySearch.find(arr_, low, high, item, crit);
    return index == -1 ? 0 : (index - low) + 1;
  }

  /**
   * Returns a sorted FloatBuffer of the odd or even offsets from the range startOffset (inclusive)
   * to endOffset (exclusive). The size of the range must be of even size.
   * The offsets are with respect to the start of the active region and independent of the
   * location of the active region within the overall buffer. The requested region will be sorted
   * first.
   * @param startOffset the starting offset within the active region
   * @param endOffset the end offset within the active region, exclusive
   * @param odds if true, return the odds, otherwise return the evens.
   * @return the selected odds from the range
   */
  FloatBuffer getEvensOrOdds(final int startOffset, final int endOffset, final boolean odds) {
    final int start = spaceAtBottom_ ? (capacity_ - count_) + startOffset : startOffset;
    final int end = spaceAtBottom_ ? (capacity_ - count_) + endOffset : endOffset;
    sort();
    final int range = endOffset - startOffset;
    if ((range & 1) == 1) {
      throw new SketchesArgumentException("Input range size must be even");
    }
    final int odd = odds ? 1 : 0;
    final float[] out = new float[range / 2];
    for (int i = start + odd, j = 0; i < end; i += 2, j++) {
      out[j] = arr_[i];
    }
    return wrap(out, true, spaceAtBottom_);
  }

  /**
   * Gets an item from the backing array given its index.
   * Only used in test or debug.
   * @param index the given index
   * @return an item given its backing array index
   */
  float getItemFromIndex(final int index) {
    return arr_[index];
  }

  /**
   * Gets an item given its offset in the active region
   * @param offset the given offset in the active region
   * @return an item given its offset
   */
  float getItem(final int offset) {
    final int index = spaceAtBottom_ ? (capacity_ - count_) + offset : offset;
    return arr_[index];
  }

  /**
   * Returns the delta margin
   * @return the delta margin
   */
  int getDelta() {
    return delta_;
  }

  /**
   * Returns the active item count.
   *
   * @return the active item count of this buffer.
   */
  int getCount() {
    return count_;
  }

  /**
   * Gets available space, which is getCapacity() - getCount().
   * When spaceAtBottom is true this is the start position for active data, otherwise it is zero.
   * @return available space
   */
  int getSpace() {
    return capacity_ - count_;
  }

  /**
   * Returns the space at bottom flag
   * @return the space at bottom flag
   */
  boolean isSpaceAtBottom() {
    return spaceAtBottom_;
  }

  /**
   * Returns true if getCount() == 0.
   * @return true if getCount() == 0.
   */
  boolean isEmpty() {
    return count_ == 0;
  }

  /**
   * Returns true iff this is exactly equal to that FloatBuffer.
   * @param that the other buffer
   * @return true iff this is exactly equal to that FloatBuffer.
   */
  boolean isEqualTo(final FloatBuffer that) {
    if ((capacity_ != that.capacity_)
        || (count_ != that.count_)
        || (delta_ != that.delta_)
        || (sorted_ != that.sorted_)
        || (spaceAtBottom_ != that.spaceAtBottom_)) { return false; }
    for (int i = 0; i < capacity_; i++) {
      if (arr_[i] != that.arr_[i]) { return false; }
    }
    return true;
  }

  /**
   * Returns true if this FloatBuffer is sorted.
   * @return true if sorted
   */
  boolean isSorted() {
    return sorted_;
  }

  /**
   * Merges the incoming sorted buffer into this sorted buffer.
   * @param bufIn sorted buffer in
   * @return this
   */
  FloatBuffer mergeSortIn(final FloatBuffer bufIn) {
    if (!sorted_ || !bufIn.isSorted()) {
      throw new SketchesArgumentException("Both buffers must be sorted.");
    }
    final float[] arrIn = bufIn.getArray(); //may be larger than its item count.
    final int bufInLen = bufIn.getCount();
    ensureSpace(bufInLen);
    final int totLen = count_ + bufInLen;
    if (spaceAtBottom_) { //scan up, insert at bottom
      final int tgtStart = capacity_ - totLen;
      int i = capacity_ - count_;
      int j = bufIn.capacity_ - bufIn.count_;
      for (int k = tgtStart; k < capacity_; k++) {
        if ((i < capacity_) && (j < bufIn.capacity_)) { //both valid
          arr_[k] = arr_[i] <= arrIn[j] ? arr_[i++] : arrIn[j++];
        } else if (i < capacity_) { //i is valid
          arr_[k] = arr_[i++];
        } else if (j <  bufIn.capacity_) { //j is valid
          arr_[k] = arrIn[j++];
        } else {
          break;
        }
      }
    } else { //scan down, insert at top
      int i = count_ - 1;
      int j = bufInLen - 1;
      for (int k = totLen; k-- > 0; ) {
        if ((i >= 0) && (j >= 0)) { //both valid
          arr_[k] = arr_[i] >= arrIn[j] ? arr_[i--] : arrIn[j--];
        } else if (i >= 0) { //i is valid
          arr_[k] = arr_[i--];
        } else if (j >= 0) { //j is valid
          arr_[k] = arrIn[j--];
        } else {
          break;
        }
      }
    }
    count_ += bufInLen;
    sorted_ = true;
    return this;
  }

  /**
   * Sorts the active region;
   * @return this
   */
  FloatBuffer sort() {
    if (sorted_) { return this; }
    final int start = spaceAtBottom_ ? capacity_ - count_ : 0;
    final int end = spaceAtBottom_ ? capacity_ : count_;
    Arrays.sort(arr_, start, end);
    sorted_ = true;
    return this;
  }

  // This only serializes count * floats
  byte[] floatsToBytes() {
    final int bytes = Float.BYTES * count_;
    final byte[] arr = new byte[bytes];
    final PositionalSegment posSeg = PositionalSegment.wrap(MemorySegment.ofArray(arr));
    if (spaceAtBottom_) {
      posSeg.setFloatArray(arr_, capacity_ - count_, count_);
    } else {
      posSeg.setFloatArray(arr_, 0, count_);
    }
    assert posSeg.getPosition() == bytes;
    return arr;
  }

  /**
   * Returns a printable formatted string of the items of this FloatBuffer separated by a single space.
   * @param fmt The format for each printed item.
   * @param width the number of items to print per line
   * @return a printable, formatted string of the items of this buffer.
   */
  String toHorizList(final String fmt, final int width) {
    final StringBuilder sb = new StringBuilder();
    final String spaces = "  ";
    final int start = spaceAtBottom_ ? capacity_ - count_ : 0;
    final int end   = spaceAtBottom_ ? capacity_ : count_;
    int cnt = 0;
    sb.append(spaces);
    for (int i = start; i < end; i++) {
      final float v = arr_[i];
      final String str = String.format(fmt, v);
      if ((i > start) && ((++cnt % width) == 0)) { sb.append(LS).append(spaces); }
      sb.append(str);
    }
    return sb.toString();
  }

  /**
   * Trims the capacity of this FloatBuffer to the active count.
   * @return this
   */
  FloatBuffer trimCapacity() {
    if (count_ < capacity_) {
      final float[] out = new float[count_];
      final int start = spaceAtBottom_ ? capacity_ - count_ : 0;
      System.arraycopy(arr_, start, out, 0, count_);
      capacity_ = count_;
      arr_ = out;
    }
    return this;
  }

  /**
   * Trims the count_ to newCount. If newCount &gt; count_ this does nothing and returns.
   * Otherwise, the internal count_ is reduced to the given newCount. There is no clearing of
   * the remainder of the capacity. Any items there are considered garbage.
   *
   * @param newCount the new active count
   * @return this
   */
  FloatBuffer trimCount(final int newCount) {
    if (newCount < count_) {
      count_ = newCount;
    }
    return this;
  }
}
