bleve/search/searcher/search_phrase.go

//  Copyright (c) 2014 Couchbase, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 		http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package searcher

import (
	"math"

	"github.com/blevesearch/bleve/index"
	"github.com/blevesearch/bleve/search"
)

type PhraseSearcher struct {
	indexReader  index.IndexReader
	mustSearcher *ConjunctionSearcher
	queryNorm    float64
	currMust     *search.DocumentMatch
	slop         int
	terms        []string
	initialized  bool
}

func NewPhraseSearcher(indexReader index.IndexReader, mustSearcher *ConjunctionSearcher, terms []string) (*PhraseSearcher, error) {
	// build our searcher
	rv := PhraseSearcher{
		indexReader:  indexReader,
		mustSearcher: mustSearcher,
		terms:        terms,
	}
	rv.computeQueryNorm()
	return &rv, nil
}

func (s *PhraseSearcher) computeQueryNorm() {
	// first calculate sum of squared weights
	sumOfSquaredWeights := 0.0
	if s.mustSearcher != nil {
		sumOfSquaredWeights += s.mustSearcher.Weight()
	}

	// now compute query norm from this
	s.queryNorm = 1.0 / math.Sqrt(sumOfSquaredWeights)
	// finally tell all the downstream searchers the norm
	if s.mustSearcher != nil {
		s.mustSearcher.SetQueryNorm(s.queryNorm)
	}
}

func (s *PhraseSearcher) initSearchers(ctx *search.SearchContext) error {
	err := s.advanceNextMust(ctx)
	if err != nil {
		return err
	}

	s.initialized = true
	return nil
}

func (s *PhraseSearcher) advanceNextMust(ctx *search.SearchContext) error {
	var err error

	if s.mustSearcher != nil {
		s.currMust, err = s.mustSearcher.Next(ctx)
		if err != nil {
			return err
		}
	}

	return nil
}

func (s *PhraseSearcher) Weight() float64 {
	return s.mustSearcher.Weight()
}

func (s *PhraseSearcher) SetQueryNorm(qnorm float64) {
	s.mustSearcher.SetQueryNorm(qnorm)
}

func (s *PhraseSearcher) Next(ctx *search.SearchContext) (*search.DocumentMatch, error) {
	if !s.initialized {
		err := s.initSearchers(ctx)
		if err != nil {
			return nil, err
		}
	}

	for s.currMust != nil {
		// check this match against phrase constraints
		rv := s.checkCurrMustMatch(ctx)

		// prepare for next iteration (either loop or subsequent call to Next())
		err := s.advanceNextMust(ctx)
		if err != nil {
			return nil, err
		}

		// if match satisfied phrase constraints return it as a hit
		if rv != nil {
			return rv, nil
		}
	}

	return nil, nil
}

// checkCurrMustMatch is soley concerned with determining if the DocumentMatch
// pointed to by s.currMust (which satisifies the pre-condition searcher)
// also satisfies the phase constraints.  if so, it returns a DocumentMatch
// for this document, otherwise nil
func (s *PhraseSearcher) checkCurrMustMatch(ctx *search.SearchContext) *search.DocumentMatch {
	rvftlm := make(search.FieldTermLocationMap, 0)
	freq := 0
	// typically we would expect there to only actually be results in
	// one field, but we allow for this to not be the case
	// but, we note that phrase constraints can only be satisfied within
	// a single field, so we can check them each independently
	for field := range s.currMust.Locations {

		f, rvtlm := s.checkCurrMustMatchField(ctx, field)
		if f > 0 {
			freq += f
			rvftlm[field] = rvtlm
		}
	}

	if freq > 0 {
		// return match
		rv := s.currMust
		rv.Locations = rvftlm
		return rv
	}

	return nil
}

// checkCurrMustMatchField is soley concerned with determining if one particular
// field within the currMust DocumentMatch Locations satisfies the phase
// constraints (possibly more than once).  if so, the number of times it was
// satisfied, and these locations are returned.  otherwise 0 and either
// a nil or empty TermLocationMap
func (s *PhraseSearcher) checkCurrMustMatchField(ctx *search.SearchContext, field string) (int, search.TermLocationMap) {
	firstTerm := s.terms[0]
	freq := 0
	termLocMap := s.currMust.Locations[field]
	locations, ok := termLocMap[firstTerm]
	if !ok {
		return 0, nil
	}

	rvtlm := make(search.TermLocationMap, 0)

OUTER:
	for _, location := range locations {
		crvtlm := make(search.TermLocationMap, 0)
		crvtlm.AddLocation(firstTerm, location)
	INNER:
		for i := 1; i < len(s.terms); i++ {
			nextTerm := s.terms[i]
			if nextTerm == "" {
				continue
			}
			// look through all these term locations
			// to try and find the correct offsets
			nextLocations, ok := termLocMap[nextTerm]
			if !ok {
				continue OUTER
			}
			for _, nextLocation := range nextLocations {
				if nextLocation.Pos == location.Pos+float64(i) && nextLocation.SameArrayElement(location) {
					// found a location match for this term
					crvtlm.AddLocation(nextTerm, nextLocation)
					continue INNER
				}
			}
			// if we got here we didn't find a location match for this term
			continue OUTER
		}
		// if we got here all the terms matched
		freq++
		search.MergeTermLocationMaps(rvtlm, crvtlm)
	}

	return freq, rvtlm
}

func (s *PhraseSearcher) Advance(ctx *search.SearchContext, ID index.IndexInternalID) (*search.DocumentMatch, error) {
	if !s.initialized {
		err := s.initSearchers(ctx)
		if err != nil {
			return nil, err
		}
	}
	var err error
	s.currMust, err = s.mustSearcher.Advance(ctx, ID)
	if err != nil {
		return nil, err
	}
	return s.Next(ctx)
}

func (s *PhraseSearcher) Count() uint64 {
	// for now return a worst case
	return s.mustSearcher.Count()
}

func (s *PhraseSearcher) Close() error {
	if s.mustSearcher != nil {
		err := s.mustSearcher.Close()
		if err != nil {
			return err
		}
	}
	return nil
}

func (s *PhraseSearcher) Min() int {
	return 0
}

func (s *PhraseSearcher) DocumentMatchPoolSize() int {
	return s.mustSearcher.DocumentMatchPoolSize() + 1
}