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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 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)
}
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