91a8d5da9f
This invloves converting tokens to a rune slice in the filter, but at least we're now compatable with Lucene's stemmer.
114 lines
2.7 KiB
Go
114 lines
2.7 KiB
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 ar
|
||
|
||
import (
|
||
"bytes"
|
||
|
||
"github.com/blevesearch/bleve/analysis"
|
||
"github.com/blevesearch/bleve/registry"
|
||
)
|
||
|
||
const StemmerName = "stemmer_ar"
|
||
|
||
// These were obtained from org.apache.lucene.analysis.ar.ArabicStemmer
|
||
var prefixes = [][]rune{
|
||
[]rune("ال"),
|
||
[]rune("وال"),
|
||
[]rune("بال"),
|
||
[]rune("كال"),
|
||
[]rune("فال"),
|
||
[]rune("لل"),
|
||
[]rune("و"),
|
||
}
|
||
var suffixes = [][]rune{
|
||
[]rune("ها"),
|
||
[]rune("ان"),
|
||
[]rune("ات"),
|
||
[]rune("ون"),
|
||
[]rune("ين"),
|
||
[]rune("يه"),
|
||
[]rune("ية"),
|
||
[]rune("ه"),
|
||
[]rune("ة"),
|
||
[]rune("ي"),
|
||
}
|
||
|
||
type ArabicStemmerFilter struct{}
|
||
|
||
func NewArabicStemmerFilter() *ArabicStemmerFilter {
|
||
return &ArabicStemmerFilter{}
|
||
}
|
||
|
||
func (s *ArabicStemmerFilter) Filter(input analysis.TokenStream) analysis.TokenStream {
|
||
for _, token := range input {
|
||
term := stem(token.Term)
|
||
token.Term = term
|
||
}
|
||
return input
|
||
}
|
||
|
||
func canStemPrefix(input, prefix []rune) bool {
|
||
// Wa- prefix requires at least 3 characters.
|
||
if len(prefix) == 1 && len(input) < 4 {
|
||
return false
|
||
}
|
||
// Other prefixes require only 2.
|
||
if len(input)-len(prefix) < 2 {
|
||
return false
|
||
}
|
||
for i := range prefix {
|
||
if prefix[i] != input[i] {
|
||
return false
|
||
}
|
||
}
|
||
return true
|
||
}
|
||
|
||
func canStemSuffix(input, suffix []rune) bool {
|
||
// All suffixes require at least 2 characters after stemming.
|
||
if len(input)-len(suffix) < 2 {
|
||
return false
|
||
}
|
||
stemEnd := len(input) - len(suffix)
|
||
for i := range suffix {
|
||
if suffix[i] != input[stemEnd+i] {
|
||
return false
|
||
}
|
||
}
|
||
return true
|
||
}
|
||
|
||
func stem(input []byte) []byte {
|
||
runes := bytes.Runes(input)
|
||
// Strip a single prefix.
|
||
for _, p := range prefixes {
|
||
if canStemPrefix(runes, p) {
|
||
runes = runes[len(p):]
|
||
break
|
||
}
|
||
}
|
||
// Strip off multiple suffixes, in their order in the suffixes array.
|
||
for _, s := range suffixes {
|
||
if canStemSuffix(runes, s) {
|
||
runes = runes[:len(runes)-len(s)]
|
||
}
|
||
}
|
||
return analysis.BuildTermFromRunes(runes)
|
||
}
|
||
|
||
func StemmerFilterConstructor(config map[string]interface{}, cache *registry.Cache) (analysis.TokenFilter, error) {
|
||
return NewArabicStemmerFilter(), nil
|
||
}
|
||
|
||
func init() {
|
||
registry.RegisterTokenFilter(StemmerName, StemmerFilterConstructor)
|
||
}
|