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// 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 edgengram
import (
"bytes"
"fmt"
"unicode/utf8"
"github.com/blevesearch/bleve/analysis"
"github.com/blevesearch/bleve/registry"
)
const Name = "edge_ngram"
type Side bool
const BACK Side = true
const FRONT Side = false
type EdgeNgramFilter struct {
back Side
minLength int
maxLength int
}
func NewEdgeNgramFilter(side Side, minLength, maxLength int) *EdgeNgramFilter {
return &EdgeNgramFilter{
back: side,
minLength: minLength,
maxLength: maxLength,
}
}
func (s *EdgeNgramFilter) Filter(input analysis.TokenStream) analysis.TokenStream {
rv := make(analysis.TokenStream, 0, len(input))
for _, token := range input {
runeCount := utf8.RuneCount(token.Term)
runes := bytes.Runes(token.Term)
if s.back {
i := runeCount
// index of the starting rune for this token
for ngramSize := s.minLength; ngramSize <= s.maxLength; ngramSize++ {
// build an ngram of this size starting at i
if i-ngramSize >= 0 {
ngramTerm := analysis.BuildTermFromRunes(runes[i-ngramSize : i])
token := analysis.Token{
Position: token.Position,
Start: token.Start,
End: token.End,
Type: token.Type,
Term: ngramTerm,
}
rv = append(rv, &token)
}
}
} else {
i := 0
// index of the starting rune for this token
for ngramSize := s.minLength; ngramSize <= s.maxLength; ngramSize++ {
// build an ngram of this size starting at i
if i+ngramSize <= runeCount {
ngramTerm := analysis.BuildTermFromRunes(runes[i : i+ngramSize])
token := analysis.Token{
Position: token.Position,
Start: token.Start,
End: token.End,
Type: token.Type,
Term: ngramTerm,
}
rv = append(rv, &token)
}
}
}
}
return rv
}
func EdgeNgramFilterConstructor(config map[string]interface{}, cache *registry.Cache) (analysis.TokenFilter, error) {
side := FRONT
back, ok := config["back"].(bool)
if ok && back {
side = BACK
}
minVal, ok := config["min"].(float64)
if !ok {
return nil, fmt.Errorf("must specify min")
}
min := int(minVal)
maxVal, ok := config["max"].(float64)
if !ok {
return nil, fmt.Errorf("must specify max")
}
max := int(maxVal)
return NewEdgeNgramFilter(side, min, max), nil
}
func init() {
registry.RegisterTokenFilter(Name, EdgeNgramFilterConstructor)
}
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