/** \file  queryparser.h
 *  \brief parsing a user query string to build a Xapian::Query object
 */
/* Copyright (C) 2005,2006,2007,2008,2009,2010,2011,2014 Olly Betts
 * Copyright (C) 2010 Adam Sjøgren
 *
 * 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_QUERYPARSER_H
#define XAPIAN_INCLUDED_QUERYPARSER_H

#include <xapian/base.h>
#include <xapian/query.h>
#include <xapian/termiterator.h>
#include <xapian/visibility.h>

#include <set>
#include <string>

namespace Xapian {

class Database;
class Stem;

/// Base class for stop-word decision functor.
class XAPIAN_VISIBILITY_DEFAULT Stopper {
  public:
    /** Is term a stop-word?
     *
     *  @param term	The term to test.
     */
    virtual bool operator()(const std::string & term) const = 0;

    /// Class has virtual methods, so provide a virtual destructor.
    virtual ~Stopper() { }

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

/// Simple implementation of Stopper class - this will suit most users.
class XAPIAN_VISIBILITY_DEFAULT SimpleStopper : public Stopper {
    std::set<std::string> stop_words;

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

    /** Initialise from a pair of iterators.
     *
     * Xapian includes stop list files for many languages. You can initialise from a file like that:
     * @code
     * ifstream inFile ("stopwords/english/stop.txt");
     * Xapian::SimplerStopper stopper(istream_iterator<string>(inFile), istream_iterator<string>());
     * @endcode
     *
     */
#if ! defined __SUNPRO_CC || __SUNPRO_CC - 0 >= 0x580
    template <class Iterator>
    SimpleStopper(Iterator begin, Iterator end) : stop_words(begin, end) { }
#else
    // Older versions of Sun's C++ compiler don't cope with the Iterator
    // pointing to const char *.
    template <class Iterator>
    SimpleStopper(Iterator begin, Iterator end) {
	while (begin != end) stop_words.insert(*begin++);
    }
#endif

    /// Add a single stop word.
    void add(const std::string & word) { stop_words.insert(word); }

    virtual bool operator()(const std::string & term) const {
	return stop_words.find(term) != stop_words.end();
    }

    virtual std::string get_description() const;
};

/// Base class for value range processors.
struct XAPIAN_VISIBILITY_DEFAULT ValueRangeProcessor {
    /// Destructor.
    virtual ~ValueRangeProcessor();

    /** Check for a valid range of this type.
     *
     *  @param[in,out] begin	The start of the range as specified in the query
     *				string by the user.  This parameter is a
     *				non-const reference so the ValueRangeProcessor
     *				can modify it to return the value to start the
     *				range with.
     *  @param[in,out] end	The end of the range.  This is also a non-const
     *				reference so it can be modified.
     *
     *  @return	If this ValueRangeProcessor recognises the range BEGIN..END it
     *		returns the value slot number to range filter on.  Otherwise it
     *		returns Xapian::BAD_VALUENO.
     */
    virtual Xapian::valueno operator()(std::string &begin, std::string &end) = 0;
};

/** Handle a string range.
 *
 *  The end points can be any strings.
 */
class XAPIAN_VISIBILITY_DEFAULT StringValueRangeProcessor : public ValueRangeProcessor {
  protected:
    Xapian::valueno valno;

  private:
    bool prefix;
    std::string str;

  public:
    /** Constructor.
     *
     *  @param slot_	The value number to return from operator().
     */
    explicit StringValueRangeProcessor(Xapian::valueno slot_)
	: valno(slot_), str() { }

    /** Constructor.
     *
     *  @param slot_	The value number to return from operator().
     *  @param str_     A string to look for to recognise values as belonging
     *                  to this range.
     *  @param prefix_	Flag specifying whether to check for str_ as a prefix
     *			or a suffix.
     */
    StringValueRangeProcessor(Xapian::valueno slot_, const std::string &str_,
			      bool prefix_ = true)
	: valno(slot_), prefix(prefix_), str(str_) { }

    /** Check for a valid string range.
     *
     *  @param[in,out] begin	The start of the range as specified in the
     *				query string by the user.  This parameter is a
     *				non-const reference so the ValueRangeProcessor
     *				can modify it to return the value to start the
     *				range with.
     *  @param[in,out] end	The end of the range.  This is also a non-const
     *				reference so it can be modified.
     *
     *  @return	A StringValueRangeProcessor always accepts a range it is
     *		offered, and returns the value of slot_ passed at construction
     *		time.  It doesn't modify @a begin or @a end.
     */
    Xapian::valueno operator()(std::string &begin, std::string &end);
};

/** Handle a date range.
 *
 *  Begin and end must be dates in a recognised format.
 */
class XAPIAN_VISIBILITY_DEFAULT DateValueRangeProcessor : public StringValueRangeProcessor {
    bool prefer_mdy;
    int epoch_year;

  public:
    /** Constructor.
     *
     *  @param slot_	    The value number to return from operator().
     *  @param prefer_mdy_  Should ambiguous dates be interpreted as
     *			    month/day/year rather than day/month/year?
     *			    (default: false)
     *  @param epoch_year_  Year to use as the epoch for dates with 2 digit
     *			    years (default: 1970, so 1/1/69 is 2069 while
     *			    1/1/70 is 1970).
     */
    DateValueRangeProcessor(Xapian::valueno slot_, bool prefer_mdy_ = false,
			    int epoch_year_ = 1970)
	: StringValueRangeProcessor(slot_),
	  prefer_mdy(prefer_mdy_), epoch_year(epoch_year_) { }

    /** Constructor.
     *
     *  @param slot_	    The value number to return from operator().
     *
     *  @param str_     A string to look for to recognise values as belonging
     *                  to this date range.
     *
     *  @param prefix_  Whether to look for the string at the start or end of
     *                  the values.  If true, the string is a prefix; if
     *                  false, the string is a suffix (default: true).
     *
     *  @param prefer_mdy_  Should ambiguous dates be interpreted as
     *			    month/day/year rather than day/month/year?
     *			    (default: false)
     *
     *  @param epoch_year_  Year to use as the epoch for dates with 2 digit
     *			    years (default: 1970, so 1/1/69 is 2069 while
     *			    1/1/70 is 1970).
     *
     *  The string supplied in str_ is used by @a operator() to decide whether
     *  the pair of strings supplied to it constitute a valid range.  If
     *  prefix_ is true, the first value in a range must begin with str_ (and
     *  the second value may optionally begin with str_);
     *  if prefix_ is false, the second value in a range must end with str_
     *  (and the first value may optionally end with str_).
     *
     *  If str_ is empty, the setting of prefix_ is irrelevant, and no special
     *  strings are required at the start or end of the strings defining the
     *  range.
     *
     *  The remainder of both strings defining the endpoints must be valid
     *  dates.
     *
     *  For example, if str_ is "created:" and prefix_ is true, and the range
     *  processor has been added to the queryparser, the queryparser will
     *  accept "created:1/1/2000..31/12/2001".
     */
    DateValueRangeProcessor(Xapian::valueno slot_, const std::string &str_,
			    bool prefix_ = true,
			    bool prefer_mdy_ = false, int epoch_year_ = 1970)
	: StringValueRangeProcessor(slot_, str_, prefix_),
	  prefer_mdy(prefer_mdy_), epoch_year(epoch_year_) { }

#ifndef SWIG
    /** Constructor.
     *
     *  This is like the previous version, but with const char * instead of
     *  std::string - we need this overload as otherwise
     *  DateValueRangeProcessor(1, "date:") quietly interprets the second
     *  argument as a boolean in preference to std::string.  If you want to
     *  be compatible with 1.2.12 and earlier, then explicitly convert to
     *  std::string, i.e.: DateValueRangeProcessor(1, std::string("date:"))
     *
     *  @param slot_	    The value number to return from operator().
     *
     *  @param str_     A string to look for to recognise values as belonging
     *                  to this date range.
     *
     *  @param prefix_  Whether to look for the string at the start or end of
     *                  the values.  If true, the string is a prefix; if
     *                  false, the string is a suffix (default: true).
     *
     *  @param prefer_mdy_  Should ambiguous dates be interpreted as
     *			    month/day/year rather than day/month/year?
     *			    (default: false)
     *
     *  @param epoch_year_  Year to use as the epoch for dates with 2 digit
     *			    years (default: 1970, so 1/1/69 is 2069 while
     *			    1/1/70 is 1970).
     *
     *  The string supplied in str_ is used by @a operator() to decide whether
     *  the pair of strings supplied to it constitute a valid range.  If
     *  prefix_ is true, the first value in a range must begin with str_ (and
     *  the second value may optionally begin with str_);
     *  if prefix_ is false, the second value in a range must end with str_
     *  (and the first value may optionally end with str_).
     *
     *  If str_ is empty, the setting of prefix_ is irrelevant, and no special
     *  strings are required at the start or end of the strings defining the
     *  range.
     *
     *  The remainder of both strings defining the endpoints must be valid
     *  dates.
     *
     *  For example, if str_ is "created:" and prefix_ is true, and the range
     *  processor has been added to the queryparser, the queryparser will
     *  accept "created:1/1/2000..31/12/2001".
     */
    DateValueRangeProcessor(Xapian::valueno slot_, const char * str_,
			    bool prefix_ = true,
			    bool prefer_mdy_ = false, int epoch_year_ = 1970)
	: StringValueRangeProcessor(slot_, str_, prefix_),
	  prefer_mdy(prefer_mdy_), epoch_year(epoch_year_) { }
#endif

    /** Check for a valid date range.
     *
     *  @param[in,out] begin	The start of the range as specified in the
     *				query string by the user.  This parameter is a
     *				non-const reference so the ValueRangeProcessor
     *				can modify it to return the value to start the
     *				range with.
     *  @param[in,out] end	The end of the range.  This is also a non-const
     *				reference so it can be modified.
     *
     *  @return	If BEGIN..END is a sensible date range, this method modifies
     *		them into the format YYYYMMDD and returns the value of slot_
     *		passed at construction time.  Otherwise it returns
     *		Xapian::BAD_VALUENO.
     */
    Xapian::valueno operator()(std::string &begin, std::string &end);
};

/** Handle a number range.
 *
 *  This class must be used on values which have been encoded using
 *  Xapian::sortable_serialise() which turns numbers into strings which
 *  will sort in the same order as the numbers (the same values can be
 *  used to implement a numeric sort).
 */
class XAPIAN_VISIBILITY_DEFAULT NumberValueRangeProcessor : public StringValueRangeProcessor {
  public:
    /** Constructor.
     *
     *  @param slot_   The value number to return from operator().
     */
    explicit NumberValueRangeProcessor(Xapian::valueno slot_)
	: StringValueRangeProcessor(slot_) { }

    /** Constructor.
     *
     *  @param slot_    The value number to return from operator().
     *
     *  @param str_     A string to look for to recognise values as belonging
     *                  to this numeric range.
     *
     *  @param prefix_  Whether to look for the string at the start or end of
     *                  the values.  If true, the string is a prefix; if
     *                  false, the string is a suffix (default: true).
     *
     *  The string supplied in str_ is used by @a operator() to decide whether
     *  the pair of strings supplied to it constitute a valid range.  If
     *  prefix_ is true, the first value in a range must begin with str_ (and
     *  the second value may optionally begin with str_);
     *  if prefix_ is false, the second value in a range must end with str_
     *  (and the first value may optionally end with str_).
     *
     *  If str_ is empty, the setting of prefix_ is irrelevant, and no special
     *  strings are required at the start or end of the strings defining the
     *  range.
     *
     *  The remainder of both strings defining the endpoints must be valid
     *  floating point numbers. (FIXME: define format recognised).
     *
     *  For example, if str_ is "$" and prefix_ is true, and the range
     *  processor has been added to the queryparser, the queryparser will
     *  accept "$10..50" or "$10..$50", but not "10..50" or "10..$50" as valid
     *  ranges.  If str_ is "kg" and prefix_ is false, the queryparser will
     *  accept "10..50kg" or "10kg..50kg", but not "10..50" or "10kg..50" as
     *  valid ranges.
     */
    NumberValueRangeProcessor(Xapian::valueno slot_, const std::string &str_,
			      bool prefix_ = true)
	: StringValueRangeProcessor(slot_, str_, prefix_) { }

    /** Check for a valid numeric range.
     *
     *  @param[in,out] begin	The start of the range as specified in the
     *				query string by the user.  This parameter is a
     *				non-const reference so the ValueRangeProcessor
     *				can modify it to return the value to start the
     *				range with.
     *  @param[in,out] end	The end of the range.  This is also a non-const
     *				reference so it can be modified.
     *
     *  @return	If BEGIN..END is a valid numeric range with the specified
     *		prefix/suffix (if one was specified), this method modifies
     *		them by removing the prefix/suffix, converting to a number,
     *		and encoding with Xapian::sortable_serialise(), and returns the
     *		value of slot_ passed at construction time.  Otherwise it
     *		returns Xapian::BAD_VALUENO.
     */
    Xapian::valueno operator()(std::string &begin, std::string &end);
};

/// Build a Xapian::Query object from a user query string.
class XAPIAN_VISIBILITY_DEFAULT QueryParser {
  public:
    /// Class representing the queryparser internals.
    class Internal;
    /// @private @internal Reference counted internals.
    Xapian::Internal::RefCntPtr<Internal> internal;

    /// Enum of feature flags.
    typedef enum {
	/// Support AND, OR, etc and bracketed subexpressions.
	FLAG_BOOLEAN = 1,
	/// Support quoted phrases.
	FLAG_PHRASE = 2,
	/// Support + and -.
	FLAG_LOVEHATE = 4,
	/// Support AND, OR, etc even if they aren't in ALLCAPS.
	FLAG_BOOLEAN_ANY_CASE = 8,
	/** Support wildcards.
	 *
	 *  At present only right truncation (e.g. Xap*) is supported.
	 *
	 *  Currently you can't use wildcards with boolean filter prefixes,
	 *  or in a phrase (either an explicitly quoted one, or one implicitly
	 *  generated by hyphens or other punctuation).
	 *
	 *  NB: You need to tell the QueryParser object which database to
	 *  expand wildcards from by calling set_database.
	 */
	FLAG_WILDCARD = 16,
	/** Allow queries such as 'NOT apples'.
	 *
	 *  These require the use of a list of all documents in the database
	 *  which is potentially expensive, so this feature isn't enabled by
	 *  default.
	 */
	FLAG_PURE_NOT = 32,
	/** Enable partial matching.
	 *
	 *  Partial matching causes the parser to treat the query as a
	 *  "partially entered" search.  This will automatically treat the
	 *  final word as a wildcarded match, unless it is followed by
	 *  whitespace, to produce more stable results from interactive
	 *  searches.
	 *
	 *  Currently FLAG_PARTIAL doesn't do anything if the final word
	 *  in the query has a boolean filter prefix, or if it is in a phrase
	 *  (either an explicitly quoted one, or one implicitly generated by
	 *  hyphens or other punctuation).  It also doesn't do anything if
	 *  if the final word is part of a value range.
	 *
	 *  NB: You need to tell the QueryParser object which database to
	 *  expand wildcards from by calling set_database.
	 */
	FLAG_PARTIAL = 64,

	/** Enable spelling correction.
	 *
	 *  For each word in the query which doesn't exist as a term in the
	 *  database, Database::get_spelling_suggestion() will be called and if
	 *  a suggestion is returned, a corrected version of the query string
	 *  will be built up which can be read using
	 *  QueryParser::get_corrected_query_string().  The query returned is
	 *  based on the uncorrected query string however - if you want a
	 *  parsed query based on the corrected query string, you must call
	 *  QueryParser::parse_query() again.
	 *
	 *  NB: You must also call set_database() for this to work.
	 */
	FLAG_SPELLING_CORRECTION = 128,

	/** Enable synonym operator '~'.
	 *
	 *  NB: You must also call set_database() for this to work.
	 */
	FLAG_SYNONYM = 256,

	/** Enable automatic use of synonyms for single terms.
	 *
	 *  NB: You must also call set_database() for this to work.
	 */
	FLAG_AUTO_SYNONYMS = 512,

	/** Enable automatic use of synonyms for single terms and groups of
	 *  terms.
	 *
	 *  NB: You must also call set_database() for this to work.
	 */
	FLAG_AUTO_MULTIWORD_SYNONYMS = 1024 | FLAG_AUTO_SYNONYMS,

	/** Enable generation of n-grams from CJK text.
	 *
	 *  With this enabled, spans of CJK characters are split into unigrams
	 *  and bigrams, with the unigrams carrying positional information.
	 *  Non-CJK characters are split into words as normal.
	 *
	 *  The corresponding option needs to have been used at index time.
	 *
	 *  Flag added in Xapian 1.3.4 and 1.2.22, but this mode can be
	 *  enabled in 1.2.8 and later by setting environment variable
	 *  XAPIAN_CJK_NGRAM.
	 */
	FLAG_CJK_NGRAM = 2048,

	/** The default flags.
	 *
	 *  Used if you don't explicitly pass any to @a parse_query().
	 *  The default flags are FLAG_PHRASE|FLAG_BOOLEAN|FLAG_LOVEHATE.
	 *
	 *  Added in Xapian 1.0.11.
	 */
	FLAG_DEFAULT = FLAG_PHRASE|FLAG_BOOLEAN|FLAG_LOVEHATE
    } feature_flag;

    /// Stemming strategies, for use with set_stemming_strategy().
    typedef enum { STEM_NONE, STEM_SOME, STEM_ALL, STEM_ALL_Z } stem_strategy;

    /// Copy constructor.
    QueryParser(const QueryParser & o);

    /// Assignment.
    QueryParser & operator=(const QueryParser & o);

    /// Default constructor.
    QueryParser();

    /// Destructor.
    ~QueryParser();

    /** Set the stemmer.
     *
     *  This sets the stemming algorithm which will be used by the query
     *  parser.  Note that the stemming algorithm will only be used according
     *  to the stemming strategy set by set_stemming_strategy(), which defaults
     *  to STEM_NONE.  Therefore, to use a stemming algorithm, you will also
     *  need to call set_stemming_strategy() with a value other than STEM_NONE.
     *
     *  @param stemmer	The Xapian::Stem object to set.
     */
    void set_stemmer(const Xapian::Stem & stemmer);

    /** Set the stemming strategy.
     *
     *  This controls how the query parser will apply the stemming algorithm.
     *  Note that the stemming algorithm is only applied to words in
     *  probabilistic fields - boolean filter terms are never stemmed.
     *
     *  @param strategy	The strategy to use - possible values are:
     *   - STEM_NONE:	Don't perform any stemming.  (default in Xapian <=
     *			1.3.0)
     *   - STEM_SOME:	Stem all terms except for those which start with a
     *			capital letter, or are followed by certain characters
     *			(currently: <code>(/\@<>=*[{"</code> ), or are used
     *			with operators which need positional information.
     *			Stemmed terms are prefixed with 'Z'.  (default in
     *			Xapian >= 1.3.1)
     *   - STEM_ALL:	Stem all terms (note: no 'Z' prefix is added).
     *   - STEM_ALL_Z:	Stem all terms (note: 'Z' prefix is added).  (new in
     *			Xapian 1.2.11 and 1.3.1)
     */
    void set_stemming_strategy(stem_strategy strategy);

    /** Set the stopper.
     *
     *  @param stop	The Stopper object to set (default NULL, which means no
     *			stopwords).
     */
    void set_stopper(const Stopper *stop = NULL);

    /** Set the default operator.
     *
     *  @param default_op	The operator to use to combine non-filter
     *				query items when no explicit operator is used.
     *
     *				The most useful values for this are OP_OR (the
     *				default) and OP_AND.  OP_NEAR and OP_PHRASE can
     *				also be useful.
     *
     *				So for example, 'weather forecast' is parsed as
     *				if it were 'weather OR forecast' by default.
     */
    void set_default_op(Query::op default_op);

    /** Get the current default operator. */
    Query::op get_default_op() const;

    /** Specify the database being searched.
     *
     *  @param db	The database to use for wildcard expansion
     *			(FLAG_WILDCARD and FLAG_PARTIAL), spelling correction
     *			(FLAG_SPELLING_CORRECTION), and synonyms (FLAG_SYNONYM,
     *			FLAG_AUTO_SYNONYMS, and FLAG_AUTO_MULTIWORD_SYNONYMS).
     */
    void set_database(const Database &db);

    /** Specify the maximum expansion of a wildcard term.
     *
     *  Note: you must also set FLAG_WILDCARD for wildcard expansion to happen.
     *
     *  @param limit	The maximum number of terms each wildcard in the query
     *			can expand to, or 0 for no limit (which is the default).
     */
    void set_max_wildcard_expansion(Xapian::termcount limit);

    /** Parse a query.
     *
     *  @param query_string  A free-text query as entered by a user
     *  @param flags         Zero or more Query::feature_flag specifying
     *		what features the QueryParser should support.  Combine
     *		multiple values with bitwise-or (|) (default FLAG_DEFAULT).
     *	@param default_prefix  The default term prefix to use (default none).
     *		For example, you can pass "A" when parsing an "Author" field.
     *
     *  @exception If the query string can't be parsed, then
     *		   Xapian::QueryParserError is thrown.  You can get an English
     *		   error message to report to the user by catching it and
     *		   calling get_msg() on the caught exception.  The current
     *		   possible values (in case you want to translate them) are:
     *
     *		   @li Unknown range operation
     *		   @li parse error
     *		   @li Syntax: &lt;expression&gt; AND &lt;expression&gt;
     *		   @li Syntax: &lt;expression&gt; AND NOT &lt;expression&gt;
     *		   @li Syntax: &lt;expression&gt; NOT &lt;expression&gt;
     *		   @li Syntax: &lt;expression&gt; OR &lt;expression&gt;
     *		   @li Syntax: &lt;expression&gt; XOR &lt;expression&gt;
     */
    Query parse_query(const std::string &query_string,
		      unsigned flags = FLAG_DEFAULT,
		      const std::string &default_prefix = std::string());

    /** Add a probabilistic term prefix.
     *
     *  For example:
     *
     *  @code
     *  qp.add_prefix("author", "A");
     *  @endcode
     *
     *  This allows the user to search for author:Orwell which will be
     *  converted to a search for the term "Aorwell".
     *
     *  Multiple fields can be mapped to the same prefix.  For example, you
     *  can make title: and subject: aliases for each other.
     *
     *  As of 1.0.4, you can call this method multiple times with the same
     *  value of field to allow a single field to be mapped to multiple
     *  prefixes.  Multiple terms being generated for such a field, and
     *  combined with @c Xapian::Query::OP_OR.
     *
     *  If any prefixes are specified for the empty field name (i.e. you
     *  call this method with an empty string as the first parameter)
     *  these prefixes will be used for terms without a field specifier.
     *  If you do this and also specify the @c default_prefix parameter to @c
     *  parse_query(), then the @c default_prefix parameter will override.
     *
     *  If the prefix parameter is empty, then "field:word" will produce the
     *  term "word" (and this can be one of several prefixes for a particular
     *  field, or for terms without a field specifier).
     *
     *  If you call @c add_prefix() and @c add_boolean_prefix() for the
     *  same value of @a field, a @c Xapian::InvalidOperationError exception
     *  will be thrown.
     *
     *  In 1.0.3 and earlier, subsequent calls to this method with the same
     *  value of @a field had no effect.
     *
     *  @param field   The user visible field name
     *  @param prefix  The term prefix to map this to
     */
    void add_prefix(const std::string &field, const std::string &prefix);

    /** Add a boolean term prefix allowing the user to restrict a
     *  search with a boolean filter specified in the free text query.
     *
     *  For example:
     *
     *  @code
     *  qp.add_boolean_prefix("site", "H");
     *  @endcode
     *
     *  This allows the user to restrict a search with site:xapian.org which
     *  will be converted to Hxapian.org combined with any probabilistic
     *  query with @c Xapian::Query::OP_FILTER.
     *
     *  If multiple boolean filters are specified in a query for the same
     *  prefix, they will be combined with the @c Xapian::Query::OP_OR
     *  operator.  Then, if there are boolean filters for different prefixes,
     *  they will be combined with the @c Xapian::Query::OP_AND operator.
     *
     *  Multiple fields can be mapped to the same prefix (so for example
     *  you can make site: and domain: aliases for each other).  Instances of
     *  fields with different aliases but the same prefix will still be
     *  combined with the OR operator.
     *
     *  For example, if "site" and "domain" map to "H", but author maps to "A",
     *  a search for "site:foo domain:bar author:Fred" will map to
     *  "(Hfoo OR Hbar) AND Afred".
     *
     *  As of 1.0.4, you can call this method multiple times with the same
     *  value of field to allow a single field to be mapped to multiple
     *  prefixes.  Multiple terms being generated for such a field, and
     *  combined with @c Xapian::Query::OP_OR.
     *
     *  Calling this method with an empty string for @a field will cause
     *  a @c Xapian::InvalidArgumentError.
     *
     *  If you call @c add_prefix() and @c add_boolean_prefix() for the
     *  same value of @a field, a @c Xapian::InvalidOperationError exception
     *  will be thrown.
     *
     *  In 1.0.3 and earlier, subsequent calls to this method with the same
     *  value of @a field had no effect.
     *
     *  @param field   The user visible field name
     *  @param prefix  The term prefix to map this to
     *  @param exclusive If true, each document can have at most one term with
     *			 this prefix, so multiple filters with this prefix
     *			 should be combined with OP_OR.  If false, each
     *			 document can have multiple terms with this prefix, so
     *			 multiple filters should be combined with OP_AND, like
     *			 happens with filters with different prefixes.
     *			 [default: true]
     */
    void add_boolean_prefix(const std::string &field, const std::string &prefix,
			    bool exclusive);

    /* FIXME:1.3: Merge two versions into one with optional parameter
     * "exclusive", default true. */
    void add_boolean_prefix(const std::string &field, const std::string &prefix);

    /// Iterate over terms omitted from the query as stopwords.
    TermIterator stoplist_begin() const;
    TermIterator stoplist_end() const {
	return TermIterator();
    }

    /// Iterate over unstemmed forms of the given (stemmed) term used in the query.
    TermIterator unstem_begin(const std::string &term) const;
    TermIterator unstem_end(const std::string &) const {
	return TermIterator();
    }

    /// Register a ValueRangeProcessor.
    void add_valuerangeprocessor(Xapian::ValueRangeProcessor * vrproc);

    /** Get the spelling-corrected query string.
     *
     *  This will only be set if FLAG_SPELLING_CORRECTION is specified when
     *  QueryParser::parse_query() was last called.
     *
     *  If there were no corrections, an empty string is returned.
     */
    std::string get_corrected_query_string() const;

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

/** Convert a floating point number to a string, preserving sort order.
 *
 *  This method converts a floating point number to a string, suitable for
 *  using as a value for numeric range restriction, or for use as a sort
 *  key.
 *
 *  The conversion is platform independent.
 *
 *  The conversion attempts to ensure that, for any pair of values supplied
 *  to the conversion algorithm, the result of comparing the original
 *  values (with a numeric comparison operator) will be the same as the
 *  result of comparing the resulting values (with a string comparison
 *  operator).  On platforms which represent doubles with the precisions
 *  specified by IEEE_754, this will be the case: if the representation of
 *  doubles is more precise, it is possible that two very close doubles
 *  will be mapped to the same string, so will compare equal.
 *
 *  Note also that both zero and -zero will be converted to the same
 *  representation: since these compare equal, this satisfies the
 *  comparison constraint, but it's worth knowing this if you wish to use
 *  the encoding in some situation where this distinction matters.
 *
 *  Handling of NaN isn't (currently) guaranteed to be sensible.
 *
 *  @param value	The number to serialise.
 */
XAPIAN_VISIBILITY_DEFAULT
std::string sortable_serialise(double value);

/** Convert a string encoded using @a sortable_serialise back to a floating
 *  point number.
 *
 *  This expects the input to be a string produced by @a sortable_serialise().
 *  If the input is not such a string, the value returned is undefined (but
 *  no error will be thrown).
 *
 *  The result of the conversion will be exactly the value which was
 *  supplied to @a sortable_serialise() when making the string on platforms
 *  which represent doubles with the precisions specified by IEEE_754, but
 *  may be a different (nearby) value on other platforms.
 *
 *  @param value	The serialised string to decode.
 */
XAPIAN_VISIBILITY_DEFAULT
double sortable_unserialise(const std::string & value);

}

#endif // XAPIAN_INCLUDED_QUERYPARSER_H
