backends/chert/chert_spelling.h

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/* Copyright (C) 2007,2008,2009,2010,2011 Olly Betts
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
 */

#ifndef XAPIAN_INCLUDED_CHERT_SPELLING_H
#define XAPIAN_INCLUDED_CHERT_SPELLING_H

#include <xapian/types.h>

#include "chert_lazytable.h"
#include "termlist.h"

#include <map>
#include <set>
#include <string>
#include <cstring> // For memcpy() and memcmp().

struct fragment {
    char data[4];

    // Default constructor.
    fragment() { }

    // Allow implicit conversion.
    fragment(char data_[4]) { std::memcpy(data, data_, 4); }

    char & operator[] (unsigned i) { return data[i]; }
    const char & operator[] (unsigned i) const { return data[i]; }

    operator std::string () const {
        return std::string(data, data[0] == 'M' ? 4 : 3);
    }
};

inline bool operator<(const fragment &a, const fragment &b) {
    return std::memcmp(a.data, b.data, 4) < 0;
}

class ChertSpellingTable : public ChertLazyTable {
    void toggle_word(const std::string & word);
    void toggle_fragment(fragment frag, const std::string & word);

    std::map<std::string, Xapian::termcount> wordfreq_changes;

    std::map<fragment, std::set<std::string> > termlist_deltas;

  public:
    ChertSpellingTable(const std::string & dbdir, bool readonly)
        : ChertLazyTable("spelling", dbdir + "/spelling.", readonly,
                         Z_DEFAULT_STRATEGY) { }

    // Merge in batched-up changes.
    void merge_changes();

    void add_word(const std::string & word, Xapian::termcount freqinc);
    void remove_word(const std::string & word, Xapian::termcount freqdec);

    TermList * open_termlist(const std::string & word);

    Xapian::doccount get_word_frequency(const std::string & word) const;

    bool is_modified() const {
        return !wordfreq_changes.empty() || ChertTable::is_modified();
    }

    void flush_db() {
        merge_changes();
        ChertTable::flush_db();
    }

    void cancel() {
        // Discard batched-up changes.
        wordfreq_changes.clear();
        termlist_deltas.clear();

        ChertTable::cancel();
    }

    // @}
};

class ChertSpellingTermList : public TermList {
    std::string data;

    unsigned p;

    std::string current_term;

    ChertSpellingTermList(const ChertSpellingTermList &);

    void operator=(const ChertSpellingTermList &);

  public:
    ChertSpellingTermList(const std::string & data_)
        : data(data_), p(0) { }

    Xapian::termcount get_approx_size() const;

    std::string get_termname() const;

    Xapian::termcount get_wdf() const;

    Xapian::doccount get_termfreq() const;

    Xapian::termcount get_collection_freq() const;

    TermList * next();

    TermList * skip_to(const std::string & term);

    bool at_end() const;

    Xapian::termcount positionlist_count() const;

    Xapian::PositionIterator positionlist_begin() const;
};

#endif // XAPIAN_INCLUDED_CHERT_SPELLING_H

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