/*
 * 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.hadoop.hbase.filter;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Objects;
import org.apache.hadoop.hbase.Cell;
import org.apache.hadoop.hbase.CellUtil;
import org.apache.hadoop.hbase.PrivateCellUtil;
import org.apache.hadoop.hbase.exceptions.DeserializationException;
import org.apache.hadoop.hbase.util.Bytes;
import org.apache.yetus.audience.InterfaceAudience;

import org.apache.hbase.thirdparty.com.google.common.base.Preconditions;
import org.apache.hbase.thirdparty.com.google.protobuf.InvalidProtocolBufferException;
import org.apache.hbase.thirdparty.com.google.protobuf.UnsafeByteOperations;

import org.apache.hadoop.hbase.shaded.protobuf.generated.FilterProtos;

/**
 * A filter, based on the ColumnCountGetFilter, takes two arguments: limit and offset. This filter
 * can be used for row-based indexing, where references to other tables are stored across many
 * columns, in order to efficient lookups and paginated results for end users. Only most recent
 * versions are considered for pagination.
 * @apiNote This filter is in awkward place, as even though it can return SEEK_NEXT_USING_HINT, it
 *          also maintains an internal row state, so it is not marked as HintingFilter. Hinted seek
 *          information may be lost when used in a MUST_PASS_ALL FilterList, which can result in
 *          suboptimal performance.
 */
@InterfaceAudience.Public
public class ColumnPaginationFilter extends FilterBase {

  private int limit = 0;
  private int offset = -1;
  private byte[] columnOffset = null;
  private int count = 0;

  /**
   * Initializes filter with an integer offset and limit. The offset is arrived at scanning
   * sequentially and skipping entries. @limit number of columns are then retrieved. If multiple
   * column families are involved, the columns may be spread across them.
   * @param limit  Max number of columns to return.
   * @param offset The integer offset where to start pagination.
   */
  public ColumnPaginationFilter(final int limit, final int offset) {
    Preconditions.checkArgument(limit >= 0, "limit must be positive %s", limit);
    Preconditions.checkArgument(offset >= 0, "offset must be positive %s", offset);
    this.limit = limit;
    this.offset = offset;
  }

  /**
   * Initializes filter with a string/bookmark based offset and limit. The offset is arrived at, by
   * seeking to it using scanner hints. If multiple column families are involved, pagination starts
   * at the first column family which contains @columnOffset. Columns are then retrieved
   * sequentially upto @limit number of columns which maybe spread across multiple column families,
   * depending on how the scan is setup.
   * @param limit        Max number of columns to return.
   * @param columnOffset The string/bookmark offset on where to start pagination.
   */
  public ColumnPaginationFilter(final int limit, final byte[] columnOffset) {
    Preconditions.checkArgument(limit >= 0, "limit must be positive %s", limit);
    Preconditions.checkArgument(columnOffset != null, "columnOffset must be non-null %s",
      columnOffset);
    this.limit = limit;
    this.columnOffset = columnOffset;
  }

  public int getLimit() {
    return limit;
  }

  public int getOffset() {
    return offset;
  }

  public byte[] getColumnOffset() {
    return columnOffset;
  }

  @Override
  public boolean filterRowKey(Cell cell) throws IOException {
    // Impl in FilterBase might do unnecessary copy for Off heap backed Cells.
    return false;
  }

  @Override
  public ReturnCode filterCell(final Cell c) {
    if (columnOffset != null) {
      if (count >= limit) {
        return ReturnCode.NEXT_ROW;
      }
      int cmp = 0;
      // Only compare if no KV's have been seen so far.
      if (count == 0) {
        cmp = CellUtil.compareQualifiers(c, this.columnOffset, 0, this.columnOffset.length);
      }
      if (cmp < 0) {
        return ReturnCode.SEEK_NEXT_USING_HINT;
      } else {
        count++;
        return ReturnCode.INCLUDE_AND_NEXT_COL;
      }
    } else {
      if (count >= offset + limit) {
        return ReturnCode.NEXT_ROW;
      }

      ReturnCode code = count < offset ? ReturnCode.NEXT_COL : ReturnCode.INCLUDE_AND_NEXT_COL;
      count++;
      return code;
    }
  }

  @Override
  public Cell getNextCellHint(Cell cell) {
    return PrivateCellUtil.createFirstOnRowCol(cell, columnOffset, 0, columnOffset.length);
  }

  @Override
  public void reset() {
    this.count = 0;
  }

  public static Filter createFilterFromArguments(ArrayList<byte[]> filterArguments) {
    Preconditions.checkArgument(filterArguments.size() == 2, "Expected 2 but got: %s",
      filterArguments.size());
    int limit = ParseFilter.convertByteArrayToInt(filterArguments.get(0));
    int offset = ParseFilter.convertByteArrayToInt(filterArguments.get(1));
    return new ColumnPaginationFilter(limit, offset);
  }

  /** Returns The filter serialized using pb */
  @Override
  public byte[] toByteArray() {
    FilterProtos.ColumnPaginationFilter.Builder builder =
      FilterProtos.ColumnPaginationFilter.newBuilder();
    builder.setLimit(this.limit);
    if (this.offset >= 0) {
      builder.setOffset(this.offset);
    }
    if (this.columnOffset != null) {
      builder.setColumnOffset(UnsafeByteOperations.unsafeWrap(this.columnOffset));
    }
    return builder.build().toByteArray();
  }

  /**
   * Parse a serialized representation of {@link ColumnPaginationFilter}
   * @param pbBytes A pb serialized {@link ColumnPaginationFilter} instance
   * @return An instance of {@link ColumnPaginationFilter} made from <code>bytes</code>
   * @throws DeserializationException if an error occurred
   * @see #toByteArray
   */
  public static ColumnPaginationFilter parseFrom(final byte[] pbBytes)
    throws DeserializationException {
    FilterProtos.ColumnPaginationFilter proto;
    try {
      proto = FilterProtos.ColumnPaginationFilter.parseFrom(pbBytes);
    } catch (InvalidProtocolBufferException e) {
      throw new DeserializationException(e);
    }
    if (proto.hasColumnOffset()) {
      return new ColumnPaginationFilter(proto.getLimit(), proto.getColumnOffset().toByteArray());
    }
    return new ColumnPaginationFilter(proto.getLimit(), proto.getOffset());
  }

  /**
   * Returns true if and only if the fields of the filter that are serialized are equal to the
   * corresponding fields in other. Used for testing.
   */
  @Override
  boolean areSerializedFieldsEqual(Filter o) {
    if (o == this) {
      return true;
    }
    if (!(o instanceof ColumnPaginationFilter)) {
      return false;
    }
    ColumnPaginationFilter other = (ColumnPaginationFilter) o;
    if (this.columnOffset != null) {
      return this.getLimit() == other.getLimit()
        && Bytes.equals(this.getColumnOffset(), other.getColumnOffset());
    }
    return this.getLimit() == other.getLimit() && this.getOffset() == other.getOffset();
  }

  @Override
  public String toString() {
    if (this.columnOffset != null) {
      return (this.getClass().getSimpleName() + "(" + this.limit + ", "
        + Bytes.toStringBinary(this.columnOffset) + ")");
    }
    return String.format("%s (%d, %d)", this.getClass().getSimpleName(), this.limit, this.offset);
  }

  @Override
  public boolean equals(Object obj) {
    return obj instanceof Filter && areSerializedFieldsEqual((Filter) obj);
  }

  @Override
  public int hashCode() {
    return columnOffset == null
      ? Objects.hash(this.limit, this.offset)
      : Objects.hash(this.limit, Bytes.hashCode(this.columnOffset));
  }
}