/** @file
 * @brief Spelling correction data for a glass database.
 */
/* Copyright (C) 2007,2008,2009,2010,2011,2014,2015,2016,2017,2024 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_GLASS_SPELLING_H
#define XAPIAN_INCLUDED_GLASS_SPELLING_H

#include <xapian/types.h>

#include "glass_lazytable.h"
#include "api/termlist.h"

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

namespace Glass {

class RootInfo;

struct fragment {
    char data[4];

    // Default constructor.
    fragment() { }

    // Allow implicit conversion.
    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] == 'M' ? 4 : 3);
    }

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

}

using Glass::RootInfo;

class GlassSpellingTable : public GlassLazyTable {
    void toggle_word(std::string_view word);
    void toggle_fragment(Glass::fragment frag, std::string_view word);

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

    /** Changes to make to the termlists.
     *
     *  This list is essentially xor-ed with the list on disk, so an entry
     *  here either means a new entry needs to be added on disk, or an
     *  existing entry on disk needs to be removed.  We do it this way so
     *  we don't need to store an additional add/remove flag for every
     *  word.
     */
    std::map<Glass::fragment, std::set<std::string>> termlist_deltas;

    /** Used to track an upper bound on wordfreq. */
    Xapian::termcount wordfreq_upper_bound = 0;

  public:
    /** Create a new GlassSpellingTable object.
     *
     *  This method does not create or open the table on disk - you
     *  must call the create() or open() methods respectively!
     *
     *  @param dbdir            The directory the glass database is stored in.
     *  @param readonly         true if we're opening read-only, else false.
     */
    GlassSpellingTable(const std::string & dbdir, bool readonly)
        : GlassLazyTable("spelling", dbdir + "/spelling.", readonly) { }

    GlassSpellingTable(int fd, off_t offset_, bool readonly)
        : GlassLazyTable("spelling", fd, offset_, readonly) { }

    /** Merge in batched-up changes.
     *
     *  @return Updated upperbound on the word frequency.
     */
    void merge_changes();

    void add_word(std::string_view word, Xapian::termcount freqinc);
    Xapian::termcount remove_word(std::string_view 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;
    }

    /** Override methods of GlassTable.
     *
     *  NB: these aren't virtual, but we always call them on the subclass in
     *  cases where it matters.
     *  @{
     */

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

    /** Returns updated wordfreq upper bound. */
    Xapian::termcount flush_db() {
        merge_changes();
        GlassTable::flush_db();
        return wordfreq_upper_bound;
    }

    void cancel(const RootInfo & root_info, glass_revision_number_t rev) {
        // Discard batched-up changes.
        wordfreq_changes.clear();
        termlist_deltas.clear();

        GlassTable::cancel(root_info, rev);
    }

    // @}
};

/** The list of words containing a particular trigram. */
class GlassSpellingTermList : public TermList {
    /// The encoded data.
    std::string data;

    /// Position in the data.
    unsigned p;

    /// Copying is not allowed.
    GlassSpellingTermList(const GlassSpellingTermList &);

    /// Assignment is not allowed.
    void operator=(const GlassSpellingTermList &);

  public:
    /// Constructor.
    explicit GlassSpellingTermList(const std::string & data_)
        : data(data_), p(0) { }

    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_GLASS_SPELLING_H
