rocksdb

// Copyright (c) 2018 Benoit Chesneau
//
// This file is provided to you under the Apache License,
// Version 2.0 (the "License"); you may not use this file
// except in compliance with the License.  You may obtain
// a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.


#include <iostream>
#include <string>
#include <memory>
#include <list>
#include <algorithm>
#include <assert.h>

#include "rocksdb/slice.h"
#include "rocksdb/merge_operator.h"

#include "erl_nif.h"
#include "util.h"
#include "bitset_merge_operator.h"

static const std::size_t bits_per_char = 0x08;    // 8 bits in 1 char(unsigned)
static const unsigned char bit_mask[bits_per_char] = {
                                                       0x80,  //10000000
                                                       0x40,  //01000000
                                                       0x20,  //00100000
                                                       0x10,  //00010000
                                                       0x08,  //00001000
                                                       0x04,  //00000100
                                                       0x02,  //00000010
                                                       0x01   //00000001
                                                     };

namespace erocksdb {

    BitsetMergeOperator::BitsetMergeOperator(unsigned int cap)
        :cap_(cap) {
    };

    bool BitsetMergeOperator::Merge(
            const rocksdb::Slice& key,
            const rocksdb::Slice* existing_value,
            const rocksdb::Slice& value,
            std::string* new_value,
            rocksdb::Logger* logger) const {

        size_t size;
        char* data = nullptr;


        if (existing_value == nullptr) {
            size = cap_ / bits_per_char;
            new_value->reserve(size);
            data = new cell_type[size];
            std::fill_n(data, size, 0x00);
        } else {
            data = (char *)existing_value->data();
            size = existing_value->size();
        }

        std::string s = value.ToString();
        if (s.size() < 1) {
            delete[] data;
            return false;
        }

        int pos;
        try {
            pos = std::stoi(s.substr(1));
        } catch(...) {
            delete[] data;
            return false;
        }
        int ofs = pos >> 3;

        if (ofs > size) {
            delete[] data;
            return false;
        }

        //char bytemask = (1 << ((1 << 3)) - (pos & ((1 << 3)))));
        if (value.starts_with(rocksdb::Slice("+"))) {
            //data[(pos >> 3)] |= bytemask;
            data[ofs] |= bit_mask[pos % bits_per_char];
        } else if (value.starts_with(rocksdb::Slice("-"))) {
            //data[(pos >> 3)] &= ~bytemask;
            data[ofs] &= ~bit_mask[pos % bits_per_char];
        } else {
            delete[] data;
            return false;
        }

        new_value->clear();
        new_value->assign(data,size);
        return true;
    }

    const char* BitsetMergeOperator::Name() const  {
        return "BitsetMergeOperator";
    }

    std::shared_ptr<BitsetMergeOperator> CreateBitsetMergeOperator(unsigned int cap) {
        return std::make_shared<BitsetMergeOperator>(cap);
    }
}