116 lines
2.9 KiB
Go
116 lines
2.9 KiB
Go
// Copyright (c) 2014 Couchbase, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package edgengram
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import (
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"bytes"
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"fmt"
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"unicode/utf8"
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"github.com/blevesearch/bleve/analysis"
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"github.com/blevesearch/bleve/registry"
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)
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const Name = "edge_ngram"
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type Side bool
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const BACK Side = true
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const FRONT Side = false
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type EdgeNgramFilter struct {
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back Side
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minLength int
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maxLength int
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}
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func NewEdgeNgramFilter(side Side, minLength, maxLength int) *EdgeNgramFilter {
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return &EdgeNgramFilter{
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back: side,
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minLength: minLength,
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maxLength: maxLength,
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}
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}
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func (s *EdgeNgramFilter) Filter(input analysis.TokenStream) analysis.TokenStream {
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rv := make(analysis.TokenStream, 0, len(input))
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for _, token := range input {
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runeCount := utf8.RuneCount(token.Term)
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runes := bytes.Runes(token.Term)
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if s.back {
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i := runeCount
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// index of the starting rune for this token
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for ngramSize := s.minLength; ngramSize <= s.maxLength; ngramSize++ {
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// build an ngram of this size starting at i
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if i-ngramSize > 0 {
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ngramTerm := analysis.BuildTermFromRunes(runes[i-ngramSize : i])
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token := analysis.Token{
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Position: token.Position,
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Start: token.Start,
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End: token.End,
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Type: token.Type,
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Term: ngramTerm,
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}
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rv = append(rv, &token)
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}
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}
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} else {
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i := 0
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// index of the starting rune for this token
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for ngramSize := s.minLength; ngramSize <= s.maxLength; ngramSize++ {
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// build an ngram of this size starting at i
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if i+ngramSize <= runeCount {
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ngramTerm := analysis.BuildTermFromRunes(runes[i : i+ngramSize])
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token := analysis.Token{
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Position: token.Position,
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Start: token.Start,
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End: token.End,
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Type: token.Type,
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Term: ngramTerm,
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}
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rv = append(rv, &token)
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}
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}
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}
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}
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return rv
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}
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func EdgeNgramFilterConstructor(config map[string]interface{}, cache *registry.Cache) (analysis.TokenFilter, error) {
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side := FRONT
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back, ok := config["back"].(bool)
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if ok && back {
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side = BACK
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}
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minVal, ok := config["min"].(float64)
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if !ok {
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return nil, fmt.Errorf("must specify min")
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}
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min := int(minVal)
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maxVal, ok := config["max"].(float64)
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if !ok {
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return nil, fmt.Errorf("must specify max")
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}
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max := int(maxVal)
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return NewEdgeNgramFilter(side, min, max), nil
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}
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func init() {
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registry.RegisterTokenFilter(Name, EdgeNgramFilterConstructor)
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}
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