//  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).
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.

#include "table/cuckoo/cuckoo_table_reader.h"

#include <algorithm>
#include <limits>
#include <string>
#include <utility>
#include <vector>

#include "memory/arena.h"
#include "options/cf_options.h"
#include "rocksdb/iterator.h"
#include "rocksdb/table.h"
#include "table/cuckoo/cuckoo_table_factory.h"
#include "table/get_context.h"
#include "table/internal_iterator.h"
#include "table/meta_blocks.h"
#include "util/coding.h"

namespace ROCKSDB_NAMESPACE {
namespace {
const uint64_t CACHE_LINE_MASK = ~((uint64_t)CACHE_LINE_SIZE - 1);
const uint32_t kInvalidIndex = std::numeric_limits<uint32_t>::max();
}  // namespace

extern const uint64_t kCuckooTableMagicNumber;

CuckooTableReader::CuckooTableReader(
    const ImmutableOptions& ioptions,
    std::unique_ptr<RandomAccessFileReader>&& file, uint64_t file_size,
    const Comparator* comparator,
    uint64_t (*get_slice_hash)(const Slice&, uint32_t, uint64_t))
    : file_(std::move(file)),
      is_last_level_(false),
      identity_as_first_hash_(false),
      use_module_hash_(false),
      num_hash_func_(0),

      key_length_(0),
      user_key_length_(0),
      value_length_(0),
      bucket_length_(0),
      cuckoo_block_size_(0),
      cuckoo_block_bytes_minus_one_(0),
      table_size_(0),
      ucomp_(comparator),
      get_slice_hash_(get_slice_hash) {
  if (!ioptions.allow_mmap_reads) {
    status_ = Status::InvalidArgument("File is not mmaped");
    return;
  }
  {
    std::unique_ptr<TableProperties> props;
    // TODO: plumb Env::IOActivity, Env::IOPriority
    const ReadOptions read_options;
    status_ =
        ReadTableProperties(file_.get(), file_size, kCuckooTableMagicNumber,
                            ioptions, read_options, &props);
    if (!status_.ok()) {
      return;
    }
    table_props_ = std::move(props);
  }
  auto& user_props = table_props_->user_collected_properties;
  auto hash_funs = user_props.find(CuckooTablePropertyNames::kNumHashFunc);
  if (hash_funs == user_props.end()) {
    status_ = Status::Corruption("Number of hash functions not found");
    return;
  }
  num_hash_func_ = *reinterpret_cast<const uint32_t*>(hash_funs->second.data());
  auto unused_key = user_props.find(CuckooTablePropertyNames::kEmptyKey);
  if (unused_key == user_props.end()) {
    status_ = Status::Corruption("Empty bucket value not found");
    return;
  }
  unused_key_ = unused_key->second;

  key_length_ = static_cast<uint32_t>(table_props_->fixed_key_len);
  auto user_key_len = user_props.find(CuckooTablePropertyNames::kUserKeyLength);
  if (user_key_len == user_props.end()) {
    status_ = Status::Corruption("User key length not found");
    return;
  }
  user_key_length_ =
      *reinterpret_cast<const uint32_t*>(user_key_len->second.data());

  auto value_length = user_props.find(CuckooTablePropertyNames::kValueLength);
  if (value_length == user_props.end()) {
    status_ = Status::Corruption("Value length not found");
    return;
  }
  value_length_ =
      *reinterpret_cast<const uint32_t*>(value_length->second.data());
  bucket_length_ = key_length_ + value_length_;

  auto hash_table_size =
      user_props.find(CuckooTablePropertyNames::kHashTableSize);
  if (hash_table_size == user_props.end()) {
    status_ = Status::Corruption("Hash table size not found");
    return;
  }
  table_size_ =
      *reinterpret_cast<const uint64_t*>(hash_table_size->second.data());

  auto is_last_level = user_props.find(CuckooTablePropertyNames::kIsLastLevel);
  if (is_last_level == user_props.end()) {
    status_ = Status::Corruption("Is last level not found");
    return;
  }
  is_last_level_ = *reinterpret_cast<const bool*>(is_last_level->second.data());

  auto identity_as_first_hash =
      user_props.find(CuckooTablePropertyNames::kIdentityAsFirstHash);
  if (identity_as_first_hash == user_props.end()) {
    status_ = Status::Corruption("identity as first hash not found");
    return;
  }
  identity_as_first_hash_ =
      *reinterpret_cast<const bool*>(identity_as_first_hash->second.data());

  auto use_module_hash =
      user_props.find(CuckooTablePropertyNames::kUseModuleHash);
  if (use_module_hash == user_props.end()) {
    status_ = Status::Corruption("hash type is not found");
    return;
  }
  use_module_hash_ =
      *reinterpret_cast<const bool*>(use_module_hash->second.data());
  auto cuckoo_block_size =
      user_props.find(CuckooTablePropertyNames::kCuckooBlockSize);
  if (cuckoo_block_size == user_props.end()) {
    status_ = Status::Corruption("Cuckoo block size not found");
    return;
  }
  cuckoo_block_size_ =
      *reinterpret_cast<const uint32_t*>(cuckoo_block_size->second.data());
  cuckoo_block_bytes_minus_one_ = cuckoo_block_size_ * bucket_length_ - 1;
  // TODO: rate limit reads of whole cuckoo tables.
  status_ = file_->Read(IOOptions(), 0, static_cast<size_t>(file_size),
                        &file_data_, nullptr, nullptr);
}

Status CuckooTableReader::Get(const ReadOptions& /*readOptions*/,
                              const Slice& key, GetContext* get_context,
                              const SliceTransform* /* prefix_extractor */,
                              bool /*skip_filters*/) {
  assert(key.size() == key_length_ + (is_last_level_ ? 8 : 0));
  Slice user_key = ExtractUserKey(key);
  for (uint32_t hash_cnt = 0; hash_cnt < num_hash_func_; ++hash_cnt) {
    uint64_t offset =
        bucket_length_ * CuckooHash(user_key, hash_cnt, use_module_hash_,
                                    table_size_, identity_as_first_hash_,
                                    get_slice_hash_);
    const char* bucket = &file_data_.data()[offset];
    for (uint32_t block_idx = 0; block_idx < cuckoo_block_size_;
         ++block_idx, bucket += bucket_length_) {
      if (ucomp_->Equal(Slice(unused_key_.data(), user_key.size()),
                        Slice(bucket, user_key.size()))) {
        return Status::OK();
      }
      // Here, we compare only the user key part as we support only one entry
      // per user key and we don't support snapshot.
      if (ucomp_->Equal(user_key, Slice(bucket, user_key.size()))) {
        Slice value(bucket + key_length_, value_length_);
        if (is_last_level_) {
          // Sequence number is not stored at the last level, so we will use
          // kMaxSequenceNumber since it is unknown.  This could cause some
          // transactions to fail to lock a key due to known sequence number.
          // However, it is expected for anyone to use a CuckooTable in a
          // TransactionDB.
          get_context->SaveValue(value, kMaxSequenceNumber);
        } else {
          Slice full_key(bucket, key_length_);
          ParsedInternalKey found_ikey;
          Status s = ParseInternalKey(full_key, &found_ikey,
                                      false /* log_err_key */);  // TODO
          if (!s.ok()) {
            return s;
          }
          bool dont_care __attribute__((__unused__));
          get_context->SaveValue(found_ikey, value, &dont_care);
        }
        // We don't support merge operations. So, we return here.
        return Status::OK();
      }
    }
  }
  return Status::OK();
}

void CuckooTableReader::Prepare(const Slice& key) {
  // Prefetch the first Cuckoo Block.
  Slice user_key = ExtractUserKey(key);
  uint64_t addr =
      reinterpret_cast<uint64_t>(file_data_.data()) +
      bucket_length_ * CuckooHash(user_key, 0, use_module_hash_, table_size_,
                                  identity_as_first_hash_, nullptr);
  uint64_t end_addr = addr + cuckoo_block_bytes_minus_one_;
  for (addr &= CACHE_LINE_MASK; addr < end_addr; addr += CACHE_LINE_SIZE) {
    PREFETCH(reinterpret_cast<const char*>(addr), 0, 3);
  }
}

class CuckooTableIterator : public InternalIterator {
 public:
  explicit CuckooTableIterator(CuckooTableReader* reader);
  // No copying allowed
  CuckooTableIterator(const CuckooTableIterator&) = delete;
  void operator=(const Iterator&) = delete;
  ~CuckooTableIterator() override = default;
  bool Valid() const override;
  void SeekToFirst() override;
  void SeekToLast() override;
  void Seek(const Slice& target) override;
  void SeekForPrev(const Slice& target) override;
  void Next() override;
  void Prev() override;
  Slice key() const override;
  Slice value() const override;
  Status status() const override { return Status::OK(); }
  void InitIfNeeded();

 private:
  struct BucketComparator {
    BucketComparator(const Slice& file_data, const Comparator* ucomp,
                     uint32_t bucket_len, uint32_t user_key_len,
                     const Slice& target = Slice())
        : file_data_(file_data),
          ucomp_(ucomp),
          bucket_len_(bucket_len),
          user_key_len_(user_key_len),
          target_(target) {}
    bool operator()(const uint32_t first, const uint32_t second) const {
      const char* first_bucket = (first == kInvalidIndex)
                                     ? target_.data()
                                     : &file_data_.data()[first * bucket_len_];
      const char* second_bucket =
          (second == kInvalidIndex) ? target_.data()
                                    : &file_data_.data()[second * bucket_len_];
      return ucomp_->Compare(Slice(first_bucket, user_key_len_),
                             Slice(second_bucket, user_key_len_)) < 0;
    }

   private:
    const Slice file_data_;
    const Comparator* ucomp_;
    const uint32_t bucket_len_;
    const uint32_t user_key_len_;
    const Slice target_;
  };

  const BucketComparator bucket_comparator_;
  void PrepareKVAtCurrIdx();
  CuckooTableReader* reader_;
  bool initialized_;
  // Contains a map of keys to bucket_id sorted in key order.
  std::vector<uint32_t> sorted_bucket_ids_;
  // We assume that the number of items can be stored in uint32 (4 Billion).
  uint32_t curr_key_idx_;
  Slice curr_value_;
  IterKey curr_key_;
};

CuckooTableIterator::CuckooTableIterator(CuckooTableReader* reader)
    : bucket_comparator_(reader->file_data_, reader->ucomp_,
                         reader->bucket_length_, reader->user_key_length_),
      reader_(reader),
      initialized_(false),
      curr_key_idx_(kInvalidIndex) {
  sorted_bucket_ids_.clear();
  curr_value_.clear();
  curr_key_.Clear();
}

void CuckooTableIterator::InitIfNeeded() {
  if (initialized_) {
    return;
  }
  sorted_bucket_ids_.reserve(
      static_cast<size_t>(reader_->GetTableProperties()->num_entries));
  uint64_t num_buckets = reader_->table_size_ + reader_->cuckoo_block_size_ - 1;
  assert(num_buckets < kInvalidIndex);
  const char* bucket = reader_->file_data_.data();
  for (uint32_t bucket_id = 0; bucket_id < num_buckets; ++bucket_id) {
    if (Slice(bucket, reader_->key_length_) != Slice(reader_->unused_key_)) {
      sorted_bucket_ids_.push_back(bucket_id);
    }
    bucket += reader_->bucket_length_;
  }
  assert(sorted_bucket_ids_.size() ==
         reader_->GetTableProperties()->num_entries);
  std::sort(sorted_bucket_ids_.begin(), sorted_bucket_ids_.end(),
            bucket_comparator_);
  curr_key_idx_ = kInvalidIndex;
  initialized_ = true;
}

void CuckooTableIterator::SeekToFirst() {
  InitIfNeeded();
  curr_key_idx_ = 0;
  PrepareKVAtCurrIdx();
}

void CuckooTableIterator::SeekToLast() {
  InitIfNeeded();
  curr_key_idx_ = static_cast<uint32_t>(sorted_bucket_ids_.size()) - 1;
  PrepareKVAtCurrIdx();
}

void CuckooTableIterator::Seek(const Slice& target) {
  InitIfNeeded();
  const BucketComparator seek_comparator(
      reader_->file_data_, reader_->ucomp_, reader_->bucket_length_,
      reader_->user_key_length_, ExtractUserKey(target));
  auto seek_it =
      std::lower_bound(sorted_bucket_ids_.begin(), sorted_bucket_ids_.end(),
                       kInvalidIndex, seek_comparator);
  curr_key_idx_ =
      static_cast<uint32_t>(std::distance(sorted_bucket_ids_.begin(), seek_it));
  PrepareKVAtCurrIdx();
}

void CuckooTableIterator::SeekForPrev(const Slice& /*target*/) {
  // Not supported
  assert(false);
}

bool CuckooTableIterator::Valid() const {
  return curr_key_idx_ < sorted_bucket_ids_.size();
}

void CuckooTableIterator::PrepareKVAtCurrIdx() {
  if (!Valid()) {
    curr_value_.clear();
    curr_key_.Clear();
    return;
  }
  uint32_t id = sorted_bucket_ids_[curr_key_idx_];
  const char* offset =
      reader_->file_data_.data() + id * reader_->bucket_length_;
  if (reader_->is_last_level_) {
    // Always return internal key.
    curr_key_.SetInternalKey(Slice(offset, reader_->user_key_length_), 0,
                             kTypeValue);
  } else {
    curr_key_.SetInternalKey(Slice(offset, reader_->key_length_));
  }
  curr_value_ = Slice(offset + reader_->key_length_, reader_->value_length_);
}

void CuckooTableIterator::Next() {
  if (!Valid()) {
    curr_value_.clear();
    curr_key_.Clear();
    return;
  }
  ++curr_key_idx_;
  PrepareKVAtCurrIdx();
}

void CuckooTableIterator::Prev() {
  if (curr_key_idx_ == 0) {
    curr_key_idx_ = static_cast<uint32_t>(sorted_bucket_ids_.size());
  }
  if (!Valid()) {
    curr_value_.clear();
    curr_key_.Clear();
    return;
  }
  --curr_key_idx_;
  PrepareKVAtCurrIdx();
}

Slice CuckooTableIterator::key() const {
  assert(Valid());
  return curr_key_.GetInternalKey();
}

Slice CuckooTableIterator::value() const {
  assert(Valid());
  return curr_value_;
}

InternalIterator* CuckooTableReader::NewIterator(
    const ReadOptions& /*read_options*/,
    const SliceTransform* /* prefix_extractor */, Arena* arena,
    bool /*skip_filters*/, TableReaderCaller /*caller*/,
    size_t /*compaction_readahead_size*/, bool /* allow_unprepared_value */) {
  if (!status().ok()) {
    return NewErrorInternalIterator<Slice>(
        Status::Corruption("CuckooTableReader status is not okay."), arena);
  }
  CuckooTableIterator* iter;
  if (arena == nullptr) {
    iter = new CuckooTableIterator(this);
  } else {
    auto iter_mem = arena->AllocateAligned(sizeof(CuckooTableIterator));
    iter = new (iter_mem) CuckooTableIterator(this);
  }
  return iter;
}

size_t CuckooTableReader::ApproximateMemoryUsage() const { return 0; }

}  // namespace ROCKSDB_NAMESPACE
