// fts_element_iterator.h

/**
*    Copyright (C) 2014 MongoDB Inc.
*
*    This program is free software: you can redistribute it and/or  modify
*    it under the terms of the GNU Affero General Public License, version 3,
*    as published by the Free Software Foundation.
*
*    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 Affero General Public License for more details.
*
*    You should have received a copy of the GNU Affero General Public License
*    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*
*    As a special exception, the copyright holders give permission to link the
*    code of portions of this program with the OpenSSL library under certain
*    conditions as described in each individual source file and distribute
*    linked combinations including the program with the OpenSSL library. You
*    must comply with the GNU Affero General Public License in all respects for
*    all of the code used other than as permitted herein. If you modify file(s)
*    with this exception, you may extend this exception to your version of the
*    file(s), but you are not obligated to do so. If you do not wish to do so,
*    delete this exception statement from your version. If you delete this
*    exception statement from all source files in the program, then also delete
*    it in the license file.
*/

#pragma once

#include "mongo/bson/bsonobj.h"
#include "mongo/bson/bsonobjiterator.h"
#include "mongo/db/fts/fts_language.h"
#include "mongo/db/fts/fts_spec.h"

#include <map>
#include <stack>
#include <string>

namespace mongo {

    namespace fts {
   
        /**
         *  Encapsulates data fields returned by FTSElementIterator
         */
        struct FTSIteratorValue {

            FTSIteratorValue( const char* text,
                              const FTSLanguage* language,
                              double weight )
            : _text(text),
              _language(language),
              _weight(weight),
              _valid(true)
            {}

            FTSIteratorValue()
            : _text(NULL),
              _language(),
              _weight(0.0),
              _valid(false)
            {}

            bool valid() const { return _valid; }
            
            const char* _text;
            const FTSLanguage* _language;
            double _weight;
            bool _valid;
        };

        /**
         *  Iterator pattern for walking through text-indexed fields of a
         *  BSON document.
         *
         *  Example usage:
         *      FTSSpec spec( FTSSpec::fixSpec( indexSpec ) );
         *      FTSElementIterator it( spec, obj );
         *      while ( it.more() ) {
         *          FTSIteratorValue val = it.next();
         *          std::cout << val._text << '[' << val._language.str()
         *                                 << ',' << val._weight << ']' << std::endl;
         *      }
         *
         */
        class FTSElementIterator {
        public:
            /**
             *  Iterator constructor 
             *
             *  Note: Caller must ensure that the constructed FTSElementIterator
             *          does >not< outlive either spec or obj.
             *
             *  @arg spec  text index specifier
             *  @arg obj   document that the iterator will traverse
             */
            FTSElementIterator( const FTSSpec& spec, const BSONObj& obj);

            /**
             *  Iterator interface: returns false iff there are no further text-indexable fields.
             */
            bool more();

            /**
             *  Iterator interface: advances to the next text-indexable field.
             */
            FTSIteratorValue next();

            /**
             *  Iterator frame needed for iterative implementation of
             *  recursive sub-documents.
             */
            struct FTSIteratorFrame {
                FTSIteratorFrame( const BSONObj& obj,
                                  const FTSSpec& spec,
                                  const FTSLanguage* parentLanguage,
                                  const std::string& parentPath,
                                  bool isArray )
                : _it( obj ),
                  _language( spec._getLanguageToUseV2( obj, parentLanguage ) ),
                  _parentPath( parentPath ),
                  _isArray( isArray )
                {}
    
                friend std::ostream& operator<<(std::ostream&, FTSIteratorFrame&);
    
                BSONObjIterator _it;
                const FTSLanguage* _language;
                std::string _parentPath;
                bool _isArray;
            };
    
        private:
            /**
             *  Helper method:
             *      returns false iff all FTSIteratorFrames on _frameStack are exhausted.
             */
            bool moreFrames();

            /**
             *  Helper method:
             *      advances to the next text-indexable field, possibly pushing frames as
             *      needed for recursive sub-documents.
             */
            FTSIteratorValue advance();
            
            /**
             *  Stack used by iterative implementation of recursive sub-document traversal.
             */
            std::stack<FTSIteratorFrame> _frameStack;

            /**
             *  Current frame, not yet pushed to stack.
             */
            FTSIteratorFrame _frame;

            /**
             *  Constructor input parameter: text index specification.
             */
            const FTSSpec& _spec;

            /**
             *  Current iterator return value, computed by 'more()', returned by 'next()'.
             */
            FTSIteratorValue _currentValue;
        };

    }   // namespace fts
}   // namespace mongo

