// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.

//  This source code is licensed under both the GPLv2 (found in the

//  COPYING file in the root directory) and Apache 2.0 License

//  (found in the LICENSE.Apache file in the root directory).

#pragma once

#include <stdint.h>

#include "db/dbformat.h"

#include "rocksdb/status.h"

namespace ROCKSDB_NAMESPACE {

class Comparator;

class Iterator;

class Slice;

class SliceTransform;

// Build a hash-based index to speed up the lookup for "index block".

// BlockHashIndex accepts a key and, if found, returns its restart index within

// that index block.

class BlockPrefixIndex {

 public:

  // Maps a key to a list of data blocks that could potentially contain

  // the key, based on the prefix.

  // Returns the total number of relevant blocks, 0 means the key does

  // not exist.

  uint32_t GetBlocks(const Slice& key, uint32_t** blocks);

  size_t ApproximateMemoryUsage() const {

    return sizeof(BlockPrefixIndex) +

           (num_block_array_buffer_entries_ + num_buckets_) * sizeof(uint32_t);

  }

  // Create hash index by reading from the metadata blocks.

  // Note: table reader (caller) is responsible for keeping shared_ptr to

  // underlying prefix extractor

  // @params prefixes: a sequence of prefixes.

  // @params prefix_meta: contains the "metadata" to of the prefixes.

  static Status Create(const SliceTransform* hash_key_extractor,

                       const Slice& prefixes, const Slice& prefix_meta,

                       BlockPrefixIndex** prefix_index);

  ~BlockPrefixIndex() {

    delete[] buckets_;

    delete[] block_array_buffer_;

  }

 private:

  class Builder;

  friend Builder;

  BlockPrefixIndex(const SliceTransform* prefix_extractor, uint32_t num_buckets,

                   uint32_t* buckets, uint32_t num_block_array_buffer_entries,

                   uint32_t* block_array_buffer)

      : internal_prefix_extractor_(prefix_extractor),

        num_buckets_(num_buckets),

        num_block_array_buffer_entries_(num_block_array_buffer_entries),

        buckets_(buckets),

        block_array_buffer_(block_array_buffer) {}

  InternalKeySliceTransform internal_prefix_extractor_;

  uint32_t num_buckets_;

  uint32_t num_block_array_buffer_entries_;

  uint32_t* buckets_;

  uint32_t* block_array_buffer_;

};

}  // namespace ROCKSDB_NAMESPACE