/** @file
 * @brief stemming algorithms
 */
/* Copyright (C) 2005-2026 Olly Betts
 * Copyright (C) 2010 Evgeny Sizikov
 *
 * 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_STEM_H
#define XAPIAN_INCLUDED_STEM_H

#if !defined XAPIAN_IN_XAPIAN_H && !defined XAPIAN_LIB_BUILD
# error Never use <xapian/stem.h> directly; include <xapian.h> instead.
#endif

#include <xapian/constinfo.h>
#include <xapian/intrusive_ptr.h>
#include <xapian/visibility.h>

#include <string>
#include <string_view>

namespace Xapian {

/// Class representing a stemming algorithm implementation.
class XAPIAN_VISIBILITY_DEFAULT StemImplementation
    : public Xapian::Internal::intrusive_base
{
    /// Don't allow assignment.
    void operator=(const StemImplementation &) = delete;

    /// Don't allow copying.
    StemImplementation(const StemImplementation &) = delete;

  public:
    /// Default constructor.
    StemImplementation() { }

    /// Virtual destructor.
    virtual ~StemImplementation();

    /// Stem the specified word.
    virtual std::string operator()(const std::string & word) = 0;

    /** Should QueryParser suppress stemming for capitalised words?
     *
     *  See QueryParser::feature_flag value FLAG_NO_PROPER_NOUN_HEURISTIC
     *  for details.
     *
     *  The default implementation of this method returns false.
     *
     *  @since Xapian 2.0.0.
     */
    virtual bool use_proper_noun_heuristic() const;

    /// Return a string describing this object.
    virtual std::string get_description() const = 0;
};

/// Class representing a stemming algorithm.
class XAPIAN_VISIBILITY_DEFAULT Stem {
  public:
    /// @private @internal Reference counted internals.
    Xapian::Internal::intrusive_ptr<StemImplementation> internal;

    /// Copy constructor.
    Stem(const Stem& o) : internal(o.internal) { }

    /// Assignment.
    Stem& operator=(const Stem& o) {
        internal = o.internal;
        return *this;
    }

    /// Move constructor.
    Stem(Stem&&) = default;

    /// Move assignment operator.
    Stem& operator=(Stem&&) = default;

    /** Construct a Xapian::Stem object which doesn't change terms.
     *
     *  Equivalent to Stem("none").
     */
    Stem() { }

    /** Construct a Xapian::Stem object for a particular language.
     *
     *  @param language Either the English name for the language
     *                  or the two letter ISO639 code.
     *
     *  The following language names are understood (aliases follow the
     *  name):
     *
     *  - none - don't stem terms
     *  - arabic (ar) - Since Xapian 1.3.5
     *  - armenian (hy) - Since Xapian 1.3.0
     *  - basque (eu) - Since Xapian 1.3.0
     *  - catalan (ca) - Since Xapian 1.3.0
     *  - czech (cs) - Since Xapian 2.1.0
     *  - danish (da)
     *  - dutch (nl, kraaij_pohlmann) - Before Xapian 2.0.0, "dutch" was
     *    Martin Porter's Dutch stemmer, and a stemmer which approximately
     *    implemented the Kraaij-Pohlmann Dutch stemmer was available
     *    separately as "kraaij_pohlmann".
     *  - dutch_porter - This was the "dutch" stemmer before Xapian 2.0.0.
     *    In 1.4.x for x >= 28, "dutch_porter" was an alias for dutch to
     *    provide forward compatibility to Xapian 2.
     *  - english (en) - Martin Porter's 2002 revision of his stemmer
     *  - earlyenglish (earlymodernenglish) - English stemmer with additional
     *    rules to improve handling of Early Modern English (e.g. Shakespeare,
     *    Pepys, the King James Bible) but these overstem some words in
     *    contemporary English (since Xapian 1.3.2; originally this was based
     *    on "porter", since Xapian 2.0.0 this is based on "english"; the
     *    "earlymodernenglish" alias was added in Xapian 2.1.0).
     *  - lovins - Lovin's English stemmer
     *  - porter - Porter's English stemmer exactly matching his 1980 paper
     *  - esperanto (eo) - Since Xapian 2.0.0
     *  - estonian (et) - Since Xapian 2.0.0
     *  - finnish (fi)
     *  - french (fr)
     *  - german (de, german2) - Before Xapian 2.0.0, german2 was a separate
     *    variant of the german stemmer which normalised umlauts (e.g. ä and
     *    ae).  The two variants have now been merged into one.
     *  - greek (el) - Since Xapian 2.0.0
     *  - hindi (hi) - Since Xapian 2.0.0
     *  - hungarian (hu)
     *  - indonesian (id) - Since Xapian 1.4.6
     *  - irish (ga) - Since Xapian 1.4.7
     *  - italian (it)
     *  - lithuanian (lt) - Since Xapian 1.4.7
     *  - nepali (ne) - Since Xapian 1.4.7
     *  - norwegian (nb, nn, no)
     *  - persian (fa) - Since Xapian 2.1.0
     *  - polish (pl) - Since Xapian 2.0.0
     *  - portuguese (pt)
     *  - romanian (ro)
     *  - russian (ru)
     *  - serbian (sr) - Since Xapian 2.0.0
     *  - sesotho (st) - Since Xapian 2.1.0
     *  - spanish (es)
     *  - swedish (sv)
     *  - tamil (ta) - Since Xapian 1.4.7
     *  - turkish (tr)
     *  - yiddish (yi) - Since Xapian 2.0.0
     *
     *  @param fallback If true then treat unknown @a language as "none",
     *                  otherwise an exception is thrown (default: false).
     *                  Parameter added in Xapian 1.4.14 - older versions
     *                  always threw an exception.
     *
     *  @exception      Xapian::InvalidArgumentError is thrown if
     *                  @a language isn't recognised and @a fallback is false.
     */
    Stem(std::string_view language, bool fallback = false);

    /** Construct a Xapian::Stem object with a user-provided stemming algorithm.
     *
     *  You can subclass Xapian::StemImplementation to implement your own
     *  stemming algorithm (or to wrap a third-party algorithm) and then wrap
     *  your implementation in a Xapian::Stem object to pass to the Xapian API.
     *
     *  @param p        The user-subclassed StemImplementation object.  This
     *                  is reference counted, and so will be automatically
     *                  deleted by the Xapian::Stem wrapper when no longer
     *                  required.
     */
    explicit Stem(StemImplementation* p) : internal(p) { }

    /// Destructor.
    ~Stem() { }

    /** Stem a word.
     *
     *  @param word     a word to stem.
     *  @return         the stem
     */
    std::string operator()(const std::string& word) const {
        if (!internal || word.empty()) return word;
        return internal->operator()(word);
    }

    /// Return true if this is a no-op stemmer.
    bool is_none() const { return !internal; }

    /// Return a string describing this object.
    std::string get_description() const;

    /** Return a list of available languages.
     *
     *  Each stemmer is only included once in the list (not once for
     *  each alias).  The name included is the English name of the
     *  language.
     *
     *  The list is returned as a string, with language names separated by
     *  spaces.  This is a static method, so a Xapian::Stem object is not
     *  required for this operation.
     */
    static std::string get_available_languages() {
        const struct Xapian::Internal::constinfo * info =
            Xapian::Internal::get_constinfo_();
        return std::string(info->stemmer_data, info->stemmer_name_len);
    }
};

}

#endif // XAPIAN_INCLUDED_STEM_H