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122 lines
2.7 KiB
Go
122 lines
2.7 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 ar
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import (
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"bytes"
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"github.com/blevesearch/bleve/v2/analysis"
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"github.com/blevesearch/bleve/v2/registry"
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)
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const StemmerName = "stemmer_ar"
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// These were obtained from org.apache.lucene.analysis.ar.ArabicStemmer
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var prefixes = [][]rune{
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[]rune("ال"),
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[]rune("وال"),
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[]rune("بال"),
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[]rune("كال"),
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[]rune("فال"),
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[]rune("لل"),
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[]rune("و"),
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}
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var suffixes = [][]rune{
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[]rune("ها"),
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[]rune("ان"),
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[]rune("ات"),
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[]rune("ون"),
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[]rune("ين"),
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[]rune("يه"),
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[]rune("ية"),
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[]rune("ه"),
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[]rune("ة"),
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[]rune("ي"),
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}
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type ArabicStemmerFilter struct{}
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func NewArabicStemmerFilter() *ArabicStemmerFilter {
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return &ArabicStemmerFilter{}
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}
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func (s *ArabicStemmerFilter) Filter(input analysis.TokenStream) analysis.TokenStream {
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for _, token := range input {
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term := stem(token.Term)
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token.Term = term
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}
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return input
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}
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func canStemPrefix(input, prefix []rune) bool {
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// Wa- prefix requires at least 3 characters.
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if len(prefix) == 1 && len(input) < 4 {
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return false
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}
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// Other prefixes require only 2.
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if len(input)-len(prefix) < 2 {
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return false
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}
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for i := range prefix {
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if prefix[i] != input[i] {
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return false
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}
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}
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return true
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}
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func canStemSuffix(input, suffix []rune) bool {
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// All suffixes require at least 2 characters after stemming.
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if len(input)-len(suffix) < 2 {
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return false
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}
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stemEnd := len(input) - len(suffix)
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for i := range suffix {
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if suffix[i] != input[stemEnd+i] {
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return false
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}
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}
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return true
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}
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func stem(input []byte) []byte {
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runes := bytes.Runes(input)
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// Strip a single prefix.
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for _, p := range prefixes {
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if canStemPrefix(runes, p) {
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runes = runes[len(p):]
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break
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}
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}
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// Strip off multiple suffixes, in their order in the suffixes array.
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for _, s := range suffixes {
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if canStemSuffix(runes, s) {
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runes = runes[:len(runes)-len(s)]
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}
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}
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return analysis.BuildTermFromRunes(runes)
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}
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func StemmerFilterConstructor(config map[string]interface{}, cache *registry.Cache) (analysis.TokenFilter, error) {
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return NewArabicStemmerFilter(), nil
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}
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func init() {
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err := registry.RegisterTokenFilter(StemmerName, StemmerFilterConstructor)
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if err != nil {
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panic(err)
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}
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}
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