// 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.

#ifndef STORAGE_LEVELDB_DB_DBFORMAT_H_

#define STORAGE_LEVELDB_DB_DBFORMAT_H_

#include <cstddef>

#include <cstdint>

#include <string>

#include "leveldb/comparator.h"

#include "leveldb/db.h"

#include "leveldb/filter_policy.h"

#include "leveldb/slice.h"

#include "leveldb/table_builder.h"

#include "util/coding.h"

#include "util/logging.h"

namespace leveldb {

// Grouping of constants.  We may want to make some of these

// parameters set via options.

namespace config {

static const int kNumLevels = 7;

// Level-0 compaction is started when we hit this many files.

static const int kL0_CompactionTrigger = 4;

// Soft limit on number of level-0 files.  We slow down writes at this point.

static const int kL0_SlowdownWritesTrigger = 8;

// Maximum number of level-0 files.  We stop writes at this point.

static const int kL0_StopWritesTrigger = 12;

// Maximum level to which a new compacted memtable is pushed if it

// does not create overlap.  We try to push to level 2 to avoid the

// relatively expensive level 0=>1 compactions and to avoid some

// expensive manifest file operations.  We do not push all the way to

// the largest level since that can generate a lot of wasted disk

// space if the same key space is being repeatedly overwritten.

static const int kMaxMemCompactLevel = 2;

// Approximate gap in bytes between samples of data read during iteration.

static const int kReadBytesPeriod = 1048576;

}  // namespace config

class InternalKey;

// Value types encoded as the last component of internal keys.

// DO NOT CHANGE THESE ENUM VALUES: they are embedded in the on-disk

// data structures.

enum ValueType { kTypeDeletion = 0x0, kTypeValue = 0x1 };

// kValueTypeForSeek defines the ValueType that should be passed when

// constructing a ParsedInternalKey object for seeking to a particular

// sequence number (since we sort sequence numbers in decreasing order

// and the value type is embedded as the low 8 bits in the sequence

// number in internal keys, we need to use the highest-numbered

// ValueType, not the lowest).

static const ValueType kValueTypeForSeek = kTypeValue;

typedef uint64_t SequenceNumber;

// We leave eight bits empty at the bottom so a type and sequence#

// can be packed together into 64-bits.

static const SequenceNumber kMaxSequenceNumber = ((0x1ull << 56) - 1);

struct ParsedInternalKey {

  Slice user_key;

  SequenceNumber sequence;

  ValueType type;

  ParsedInternalKey() {}  // Intentionally left uninitialized (for speed)

  ParsedInternalKey(const Slice& u, const SequenceNumber& seq, ValueType t)

      : user_key(u), sequence(seq), type(t) {}

  std::string DebugString() const;

};

// Return the length of the encoding of "key".

inline size_t InternalKeyEncodingLength(const ParsedInternalKey& key) {

  return key.user_key.size() + 8;

}

// Append the serialization of "key" to *result.

void AppendInternalKey(std::string* result, const ParsedInternalKey& key);

// Attempt to parse an internal key from "internal_key".  On success,

// stores the parsed data in "*result", and returns true.

//

// On error, returns false, leaves "*result" in an undefined state.

bool ParseInternalKey(const Slice& internal_key, ParsedInternalKey* result);

// Returns the user key portion of an internal key.

inline Slice ExtractUserKey(const Slice& internal_key) {

  assert(internal_key.size() >= 8);

  return Slice(internal_key.data(), internal_key.size() - 8);

}

// A comparator for internal keys that uses a specified comparator for

// the user key portion and breaks ties by decreasing sequence number.

class InternalKeyComparator : public Comparator {

 private:

  const Comparator* user_comparator_;

 public:

  explicit InternalKeyComparator(const Comparator* c) : user_comparator_(c) {}

  const char* Name() const override;

  int Compare(const Slice& a, const Slice& b) const override;

  void FindShortestSeparator(std::string* start,

                             const Slice& limit) const override;

  void FindShortSuccessor(std::string* key) const override;

  const Comparator* user_comparator() const { return user_comparator_; }

  int Compare(const InternalKey& a, const InternalKey& b) const;

};

// Filter policy wrapper that converts from internal keys to user keys

class InternalFilterPolicy : public FilterPolicy {

 private:

  const FilterPolicy* const user_policy_;

 public:

  explicit InternalFilterPolicy(const FilterPolicy* p) : user_policy_(p) {}

  const char* Name() const override;

  void CreateFilter(const Slice* keys, int n, std::string* dst) const override;

  bool KeyMayMatch(const Slice& key, const Slice& filter) const override;

};

// Modules in this directory should keep internal keys wrapped inside

// the following class instead of plain strings so that we do not

// incorrectly use string comparisons instead of an InternalKeyComparator.

class InternalKey {

 private:

  std::string rep_;

 public:

  InternalKey() {}  // Leave rep_ as empty to indicate it is invalid

  InternalKey(const Slice& user_key, SequenceNumber s, ValueType t) {

    AppendInternalKey(&rep_, ParsedInternalKey(user_key, s, t));

  }

  bool DecodeFrom(const Slice& s) {

    rep_.assign(s.data(), s.size());

    return !rep_.empty();

  }

  Slice Encode() const {

    assert(!rep_.empty());

    return rep_;

  }

  Slice user_key() const { return ExtractUserKey(rep_); }

  void SetFrom(const ParsedInternalKey& p) {

    rep_.clear();

    AppendInternalKey(&rep_, p);

  }

  void Clear() { rep_.clear(); }

  std::string DebugString() const;

};

inline int InternalKeyComparator::Compare(const InternalKey& a,

                                          const InternalKey& b) const {

  return Compare(a.Encode(), b.Encode());

}

inline bool ParseInternalKey(const Slice& internal_key,

                             ParsedInternalKey* result) {

  const size_t n = internal_key.size();

  if (n < 8) return false;

  uint64_t num = DecodeFixed64(internal_key.data() + n - 8);

  uint8_t c = num & 0xff;

  result->sequence = num >> 8;

  result->type = static_cast<ValueType>(c);

  result->user_key = Slice(internal_key.data(), n - 8);

  return (c <= static_cast<uint8_t>(kTypeValue));

}

// A helper class useful for DBImpl::Get()

class LookupKey {

 public:

  // Initialize *this for looking up user_key at a snapshot with

  // the specified sequence number.

  LookupKey(const Slice& user_key, SequenceNumber sequence);

  LookupKey(const LookupKey&) = delete;

  LookupKey& operator=(const LookupKey&) = delete;

  ~LookupKey();

  // Return a key suitable for lookup in a MemTable.

  Slice memtable_key() const { return Slice(start_, end_ - start_); }

  // Return an internal key (suitable for passing to an internal iterator)

  Slice internal_key() const { return Slice(kstart_, end_ - kstart_); }

  // Return the user key

  Slice user_key() const { return Slice(kstart_, end_ - kstart_ - 8); }

 private:

  // We construct a char array of the form:

  //    klength  varint32               <-- start_

  //    userkey  char[klength]          <-- kstart_

  //    tag      uint64

  //                                    <-- end_

  // The array is a suitable MemTable key.

  // The suffix starting with "userkey" can be used as an InternalKey.

  const char* start_;

  const char* kstart_;

  const char* end_;

  char space_[200];  // Avoid allocation for short keys

};

inline LookupKey::~LookupKey() {

  if (start_ != space_) delete[] start_;

}

}  // namespace leveldb

#endif  // STORAGE_LEVELDB_DB_DBFORMAT_H_