text: /* brass_postlist.h: Postlists in brass databases
   *
   * Copyright 1999,2000,2001 BrightStation PLC
   * Copyright 2002 Ananova Ltd
   * Copyright 2002,2003,2004,2005,2007,2008,2009,2011 Olly Betts
   * Copyright 2007,2009 Lemur Consulting Ltd
   *
   * 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 OM_HGUARD_BRASS_POSTLIST_H
  #define OM_HGUARD_BRASS_POSTLIST_H
  
  #include <xapian/database.h>
  
  #include "brass_inverter.h"
  #include "brass_types.h"
  #include "brass_positionlist.h"
  #include "leafpostlist.h"
  #include "omassert.h"
  
  #include "autoptr.h"
  #include <map>
  #include <string>
  
  using namespace std;
  
  class BrassCursor;
  class BrassDatabase;
  
  namespace Brass {
      class PostlistChunkReader;
      class PostlistChunkWriter;
  }
  
  class BrassPostList;
  
  class BrassPostListTable : public BrassTable {
  	/// PostList for looking up document lengths.
  	mutable AutoPtr<BrassPostList> doclen_pl;
  
      public:
  	/** Create a new table object.
  	 *
  	 *  This does not create the table on disk - the create() method must
  	 *  be called before the table is created on disk
  	 *
  	 *  This also does not open the table - the open() method must be
  	 *  called before use is made of the table.
  	 *
  	 *  @param path_          - Path at which the table is stored.
  	 *  @param readonly_      - whether to open the table for read only
  	 *                          access.
  	 */
  	BrassPostListTable(const string & path_, bool readonly_)
  	    : BrassTable("postlist", path_ + "/postlist.", readonly_),
  	      doclen_pl()
  	{ }
  
  	bool open(brass_revision_number_t revno) {
  	    doclen_pl.reset(0);
  	    return BrassTable::open(revno);
  	}
  
  	/// Merge changes for a term.
  	void merge_changes(const string &term, const Inverter::PostingChanges & changes);
  
  	/// Merge document length changes.
  	void merge_doclen_changes(const map<Xapian::docid, Xapian::termcount> & doclens);
  
  	Xapian::docid get_chunk(const string &tname,
  		Xapian::docid did, bool adding,
  		Brass::PostlistChunkReader ** from,
  		Brass::PostlistChunkWriter **to);
  
  	/// Compose a key from a termname and docid.
  	static string make_key(const string & term, Xapian::docid did) {
  	    return pack_brass_postlist_key(term, did);
  	}
  
  	/// Compose a key from a termname.
  	static string make_key(const string & term) {
  	    return pack_brass_postlist_key(term);
  	}
  
  	bool term_exists(const string & term) const {
  	    return key_exists(make_key(term));
  	}
  
  	/** Returns number of docs indexed by @a term.
  	 *
  	 *  This is the length of the postlist.
  	 */
  	Xapian::doccount get_termfreq(const std::string & term) const;
  
  	/** Returns the number of occurrences of @a term in the database.
  	 *
  	 *  This is the sum of the wdfs in the postlist.
  	 */
  	Xapian::termcount get_collection_freq(const std::string & term) const;
  
  	/** Returns the length of document @a did. */
  	Xapian::termcount get_doclength(Xapian::docid did,
  					Xapian::Internal::RefCntPtr<const BrassDatabase> db) const;
  
  	/** Check if document @a did exists. */
  	bool document_exists(Xapian::docid did,
  			     Xapian::Internal::RefCntPtr<const BrassDatabase> db) const;
  };
  
  /** A postlist in a brass database.
   */
  class BrassPostList : public LeafPostList {
      protected: // BrassModifiedPostList needs to access these.
  	/** The database we are searching.  This pointer is held so that the
  	 *  database doesn't get deleted before us, and also to give us access
  	 *  to the position_table.
  	 */
  	Xapian::Internal::RefCntPtr<const BrassDatabase> this_db;
  
  	/// The position list object for this posting list.
  	BrassPositionList positionlist;
  
  	/// Whether we've started reading the list yet.
  	bool have_started;
  
      private:
  	/// True if this is the last chunk.
  	bool is_last_chunk;
  
  	/// Whether we've run off the end of the list yet.
  	bool is_at_end;
  
  	/// Cursor pointing to current chunk of postlist.
  	AutoPtr<BrassCursor> cursor;
  
  	/// The first document id in this chunk.
  	Xapian::docid first_did_in_chunk;
  
  	/// The last document id in this chunk.
  	Xapian::docid last_did_in_chunk;
  
  	/// Position of iteration through current chunk.
  	const char * pos;
  
  	/// Pointer to byte after end of current chunk.
  	const char * end;
  
  	/// Document id we're currently at.
  	Xapian::docid did;
  
  	/// The wdf of the current document.
  	Xapian::termcount wdf;
  
  	/// The number of entries in the posting list.
  	Xapian::doccount number_of_entries;
  
  	/// Copying is not allowed.
  	BrassPostList(const BrassPostList &);
  
  	/// Assignment is not allowed.
  	void operator=(const BrassPostList &);
  
  	/** Move to the next item in the chunk, if possible.
  	 *  If already at the end of the chunk, returns false.
  	 */
  	bool next_in_chunk();
  
  	/** Move to the next chunk.
  	 *
  	 *  If there are no more chunks in this postlist, this will set
  	 *  is_at_end to true.
  	 */
  	void next_chunk();
  
  	/** Return true if the given document ID lies in the range covered
  	 *  by the current chunk.  This does not say whether the document ID
  	 *  is actually present.  It will return false if the document ID
  	 *  is greater than the last document ID in the chunk, even if it is
  	 *  less than the first document ID in the next chunk: it is possible
  	 *  for no chunk to contain a particular document ID.
  	 */
  	bool current_chunk_contains(Xapian::docid desired_did);
  
  	/** Move to chunk containing the specified document ID.
  	 *
  	 *  This moves to the chunk whose starting document ID is
  	 *  <= desired_did, but such that the next chunk's starting
  	 *  document ID is > desired_did.
  	 *
  	 *  It is thus possible that current_chunk_contains(desired_did)
  	 *  will return false after this call, since the document ID
  	 *  might lie after the end of this chunk, but before the start
  	 *  of the next chunk.
  	 */
  	void move_to_chunk_containing(Xapian::docid desired_did);
  
  	/** Scan forward in the current chunk for the specified document ID.
  	 *
  	 *  This is particularly efficient if the desired document ID is
  	 *  greater than the last in the chunk - it then skips straight
  	 *  to the end.
  	 *
  	 *  @return true if we moved to a valid document,
  	 *	    false if we reached the end of the chunk.
  	 */
  	bool move_forward_in_chunk_to_at_least(Xapian::docid desired_did);
  
      public:
  	/// Default constructor.
  	BrassPostList(Xapian::Internal::RefCntPtr<const BrassDatabase> this_db_,
  		      const string & term,
  		      bool keep_reference);
  
  	/// Destructor.
  	~BrassPostList();
  
  	/** Used for looking up doclens.
  	 *
  	 *  @return true if docid @a desired_did has a document length.
  	 */
  	bool jump_to(Xapian::docid desired_did);
  
  	/** Returns number of docs indexed by this term.
  	 *
  	 *  This is the length of the postlist.
  	 */
  	Xapian::doccount get_termfreq() const { return number_of_entries; }
  
  	/// Returns the current docid.
  	Xapian::docid get_docid() const { Assert(have_started); return did; }
  
  	/// Returns the length of current document.
  	Xapian::termcount get_doclength() const;
  
  	/** Returns the Within Document Frequency of the term in the current
  	 *  document.
  	 */
  	Xapian::termcount get_wdf() const { Assert(have_started); return wdf; }
  
  	/** Get the list of positions of the term in the current document.
  	 */
  	PositionList *read_position_list();
  
  	/** Get the list of positions of the term in the current document.
  	 */
  	PositionList * open_position_list() const;
  
  	/// Move to the next document.
  	PostList * next(Xapian::weight w_min);
  
  	/// Skip to next document with docid >= docid.
  	PostList * skip_to(Xapian::docid desired_did, Xapian::weight w_min);
  
  	/// Return true if and only if we're off the end of the list.
  	bool at_end() const { return is_at_end; }
  
  	/// Get a description of the document.
  	std::string get_description() const;
  
  	/// Read the number of entries and the collection frequency.
  	static void read_number_of_entries(const char ** posptr,
  					   const char * end,
  					   Xapian::doccount * number_of_entries_ptr,
  					   Xapian::termcount * collection_freq_ptr);
  };
  
  #endif /* OM_HGUARD_BRASS_POSTLIST_H */
  