// 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_TABLE_ITERATOR_WRAPPER_H_

#define STORAGE_LEVELDB_TABLE_ITERATOR_WRAPPER_H_

#include "leveldb/iterator.h"

#include "leveldb/slice.h"

namespace leveldb {

// A internal wrapper class with an interface similar to Iterator that

// caches the valid() and key() results for an underlying iterator.

// This can help avoid virtual function calls and also gives better

// cache locality.

class IteratorWrapper {

 public:

  IteratorWrapper() : iter_(nullptr), valid_(false) {}

  explicit IteratorWrapper(Iterator* iter) : iter_(nullptr) { Set(iter); }

  ~IteratorWrapper() { delete iter_; }

  Iterator* iter() const { return iter_; }

  // Takes ownership of "iter" and will delete it when destroyed, or

  // when Set() is invoked again.

  void Set(Iterator* iter) {

    delete iter_;

    iter_ = iter;

    if (iter_ == nullptr) {

      valid_ = false;

    } else {

      Update();

    }

  }

  // Iterator interface methods

  bool Valid() const { return valid_; }

  Slice key() const {

    assert(Valid());

    return key_;

  }

  Slice value() const {

    assert(Valid());

    return iter_->value();

  }

  // Methods below require iter() != nullptr

  Status status() const {

    assert(iter_);

    return iter_->status();

  }

  void Next() {

    assert(iter_);

    iter_->Next();

    Update();

  }

  void Prev() {

    assert(iter_);

    iter_->Prev();

    Update();

  }

  void Seek(const Slice& k) {

    assert(iter_);

    iter_->Seek(k);

    Update();

  }

  void SeekToFirst() {

    assert(iter_);

    iter_->SeekToFirst();

    Update();

  }

  void SeekToLast() {

    assert(iter_);

    iter_->SeekToLast();

    Update();

  }

 private:

  void Update() {

    valid_ = iter_->Valid();

    if (valid_) {

      key_ = iter_->key();

    }

  }

  Iterator* iter_;

  bool valid_;

  Slice key_;

};

}  // namespace leveldb

#endif  // STORAGE_LEVELDB_TABLE_ITERATOR_WRAPPER_H_