// 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.

//

// Slice is a simple structure containing a pointer into some external

// storage and a size.  The user of a Slice must ensure that the slice

// is not used after the corresponding external storage has been

// deallocated.

//

// Multiple threads can invoke const methods on a Slice without

// external synchronization, but if any of the threads may call a

// non-const method, all threads accessing the same Slice must use

// external synchronization.

#ifndef STORAGE_LEVELDB_INCLUDE_SLICE_H_

#define STORAGE_LEVELDB_INCLUDE_SLICE_H_

#include <cassert>

#include <cstddef>

#include <cstring>

#include <string>

#include "leveldb/export.h"

namespace leveldb {

class LEVELDB_EXPORT Slice {

 public:

  // Create an empty slice.

  Slice() : data_(""), size_(0) {}

  // Create a slice that refers to d[0,n-1].

  Slice(const char* d, size_t n) : data_(d), size_(n) {}

  // Create a slice that refers to the contents of "s"

  Slice(const std::string& s) : data_(s.data()), size_(s.size()) {}

  // Create a slice that refers to s[0,strlen(s)-1]

  Slice(const char* s) : data_(s), size_(strlen(s)) {}

  // Intentionally copyable.

  Slice(const Slice&) = default;

  Slice& operator=(const Slice&) = default;

  // Return a pointer to the beginning of the referenced data

  const char* data() const { return data_; }

  // Return the length (in bytes) of the referenced data

  size_t size() const { return size_; }

  // Return true iff the length of the referenced data is zero

  bool empty() const { return size_ == 0; }

  const char* begin() const { return data(); }

  const char* end() const { return data() + size(); }

  // Return the ith byte in the referenced data.

  // REQUIRES: n < size()

  char operator[](size_t n) const {

    assert(n < size());

    return data_[n];

  }

  // Change this slice to refer to an empty array

  void clear() {

    data_ = "";

    size_ = 0;

  }

  // Drop the first "n" bytes from this slice.

  void remove_prefix(size_t n) {

    assert(n <= size());

    data_ += n;

    size_ -= n;

  }

  // Return a string that contains the copy of the referenced data.

  std::string ToString() const { return std::string(data_, size_); }

  // Three-way comparison.  Returns value:

  //   <  0 iff "*this" <  "b",

  //   == 0 iff "*this" == "b",

  //   >  0 iff "*this" >  "b"

  int compare(const Slice& b) const;

  // Return true iff "x" is a prefix of "*this"

  bool starts_with(const Slice& x) const {

    return ((size_ >= x.size_) && (memcmp(data_, x.data_, x.size_) == 0));

  }

 private:

  const char* data_;

  size_t size_;

};

inline bool operator==(const Slice& x, const Slice& y) {

  return ((x.size() == y.size()) &&

          (memcmp(x.data(), y.data(), x.size()) == 0));

}

inline bool operator!=(const Slice& x, const Slice& y) { return !(x == y); }

inline int Slice::compare(const Slice& b) const {

  const size_t min_len = (size_ < b.size_) ? size_ : b.size_;

  int r = memcmp(data_, b.data_, min_len);

  if (r == 0) {

    if (size_ < b.size_)

      r = -1;

    else if (size_ > b.size_)

      r = +1;

  }

  return r;

}

}  // namespace leveldb

#endif  // STORAGE_LEVELDB_INCLUDE_SLICE_H_