honey_spelling.h

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/* Copyright (C) 2007-2024 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, see
 * <https://www.gnu.org/licenses/>.
 */
 
#ifndef XAPIAN_INCLUDED_HONEY_SPELLING_H
#define XAPIAN_INCLUDED_HONEY_SPELLING_H
 
#include <xapian/types.h>
 
#include "honey_lazytable.h"
#include "api/termlist.h"
 
#include <map>
#include <set>
#include <string>
#include <string_view>
#include <cstring> // For memcpy() and memcmp().
 
namespace Honey {
 
const unsigned KEY_PREFIX_BOOKEND = 0x00;
const unsigned KEY_PREFIX_HEAD = 0x01;
const unsigned KEY_PREFIX_MIDDLE = 0x02;
const unsigned KEY_PREFIX_TAIL = 0x03;
const unsigned KEY_PREFIX_WORD = 0x04;
 
inline std::string
make_spelling_wordlist_key(std::string_view word)
{
    if (rare(static_cast<unsigned char>(word[0]) <= KEY_PREFIX_WORD))
        return std::string(1, KEY_PREFIX_WORD).append(word);
    return std::string(word);
}
 
struct fragment {
    char data[4];
 
    fragment() { }
 
    explicit fragment(int) { std::memset(data, 0, 4); }
 
    explicit 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] == KEY_PREFIX_MIDDLE ? 4 : 3);
    }
 
    bool operator<(const fragment& b) const {
        return std::memcmp(data, b.data, 4) < 0;
    }
};
 
}
 
class HoneySpellingTable : public HoneyLazyTable {
    void toggle_word(const std::string& word);
    void toggle_fragment(Honey::fragment frag, const std::string& word);
 
    mutable std::map<std::string,
                     Xapian::termcount,
                     std::less<>> wordfreq_changes;
 
    mutable std::map<Honey::fragment, std::set<std::string>> termlist_deltas;
 
    Xapian::termcount wordfreq_upper_bound = 0;
 
  public:
    HoneySpellingTable(const std::string& dbdir, bool readonly)
        : HoneyLazyTable("spelling", dbdir + "/spelling.", readonly) { }
 
    HoneySpellingTable(int fd, off_t offset_, bool readonly)
        : HoneyLazyTable("spelling", fd, offset_, readonly) { }
 
    void merge_changes();
 
    void add_word(const std::string& word, Xapian::termcount freqinc);
    Xapian::termcount remove_word(const std::string& word,
                                  Xapian::termcount freqdec);
 
    TermList* open_termlist(std::string_view word);
 
    Xapian::doccount get_word_frequency(std::string_view word) const;
 
    void set_wordfreq_upper_bound(Xapian::termcount ub) {
        wordfreq_upper_bound = ub;
    }
 
    bool is_modified() const {
        return !wordfreq_changes.empty() || HoneyTable::is_modified();
    }
 
    Xapian::termcount flush_db() {
        merge_changes();
        HoneyTable::flush_db();
        return wordfreq_upper_bound;
    }
 
    void cancel(const Honey::RootInfo& root_info,
                honey_revision_number_t rev) {
        // Discard batched-up changes.
        wordfreq_changes.clear();
        termlist_deltas.clear();
 
        HoneyTable::cancel(root_info, rev);
    }
 
    // @}
};
 
class HoneySpellingTermList : public TermList {
    std::string data;
 
    unsigned p = 0;
 
    int tail = 0;
 
    HoneySpellingTermList(const HoneySpellingTermList&);
 
    void operator=(const HoneySpellingTermList&);
 
  public:
    explicit HoneySpellingTermList(const std::string& data_)
        : data(data_) { }
 
    HoneySpellingTermList(const std::string& data_,
                          const char* key)
        : data(data_) {
        unsigned char first_ch = key[0];
        AssertRel(first_ch, <, Honey::KEY_PREFIX_WORD);
        switch (first_ch) {
            case Honey::KEY_PREFIX_BOOKEND:
                tail = -1;
                break;
            case Honey::KEY_PREFIX_HEAD:
                tail = -2;
                break;
            case Honey::KEY_PREFIX_TAIL:
                tail = 2;
                break;
        }
        if (tail != 0)
            current_term.assign(key + 1, 2);
    }
 
    Xapian::termcount get_approx_size() const;
 
    Xapian::termcount get_wdf() const;
 
    Xapian::doccount get_termfreq() const;
 
    TermList* next();
 
    TermList* skip_to(std::string_view term);
 
    Xapian::termcount positionlist_count() const;
 
    PositionList* positionlist_begin() const;
};
 
#endif // XAPIAN_INCLUDED_HONEY_SPELLING_H