block_freq_index.hpp

#pragma once

#include <succinct/mappable_vector.hpp>
#include <succinct/bit_vector.hpp>

#include "compact_elias_fano.hpp"
#include "block_posting_list.hpp"

namespace quasi_succinct {

    template <typename BlockCodec>
    class block_freq_index {
    public:
        block_freq_index()
            : m_size(0)
        {}

        class builder {
        public:
            builder(uint64_t num_docs, global_parameters const& params)
                : m_params(params)
            {
                m_num_docs = num_docs;
                m_endpoints.push_back(0);
            }
            template <typename DocsIterator, typename FreqsIterator>
            void add_posting_list(uint64_t n, DocsIterator docs_begin,
                                  FreqsIterator freqs_begin, uint64_t /* occurrences */)
            {
                if (!n) throw std::invalid_argument("List must be nonempty");
                block_posting_list<BlockCodec>::write(m_lists, n,
                                                      docs_begin, freqs_begin);
                m_endpoints.push_back(m_lists.size());
            }

            void build(block_freq_index& sq)
            {
                sq.m_params = m_params;
                sq.m_size = m_endpoints.size() - 1;
                sq.m_num_docs = m_num_docs;
                sq.m_lists.steal(m_lists);

                succinct::bit_vector_builder bvb;
                compact_elias_fano::write(bvb, m_endpoints.begin(),
                                          sq.m_lists.size(), sq.m_size,
                                          m_params); // XXX
                succinct::bit_vector(&bvb).swap(sq.m_endpoints);
            }

        private:
            global_parameters m_params;
            size_t m_num_docs;
            std::vector<uint64_t> m_endpoints;
            std::vector<uint8_t> m_lists;
        };

        size_t size() const
        {
            return m_size;
        }

        uint64_t num_docs() const
        {
            return m_num_docs;
        }

        typedef typename block_posting_list<BlockCodec>::document_enumerator document_enumerator;

        document_enumerator operator[](size_t i) const
        {
            assert(i < size());
            compact_elias_fano::enumerator endpoints(m_endpoints, 0,
                                                     m_lists.size(), m_size,
                                                     m_params);

            auto endpoint = endpoints.move(i).second;
            return document_enumerator(m_lists.data() + endpoint, num_docs());
        }

        void swap(block_freq_index& other)
        {
            std::swap(m_params, other.m_params);
            std::swap(m_size, other.m_size);
            m_endpoints.swap(other.m_endpoints);
            m_lists.swap(other.m_lists);
        }

        template <typename Visitor>
        void map(Visitor& visit)
        {
            visit
                (m_params, "m_params")
                (m_size, "m_size")
                (m_num_docs, "m_num_docs")
                (m_endpoints, "m_endpoints")
                (m_lists, "m_lists")
                ;
        }

    private:
        global_parameters m_params;
        size_t m_size;
        size_t m_num_docs;
        succinct::bit_vector m_endpoints;
        succinct::mapper::mappable_vector<uint8_t> m_lists;
    };
}