117 lines
2.5 KiB
Go
117 lines
2.5 KiB
Go
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// Copyright (c) 2017 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 de
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import (
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"bytes"
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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 LightStemmerName = "stemmer_de_light"
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type GermanLightStemmerFilter struct {
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}
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func NewGermanLightStemmerFilter() *GermanLightStemmerFilter {
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return &GermanLightStemmerFilter{}
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}
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func (s *GermanLightStemmerFilter) Filter(input analysis.TokenStream) analysis.TokenStream {
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for _, token := range input {
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runes := bytes.Runes(token.Term)
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runes = stem(runes)
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token.Term = analysis.BuildTermFromRunes(runes)
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}
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return input
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}
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func stem(input []rune) []rune {
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for i, r := range input {
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switch r {
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case 'ä', 'à', 'á', 'â':
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input[i] = 'a'
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case 'ö', 'ò', 'ó', 'ô':
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input[i] = 'o'
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case 'ï', 'ì', 'í', 'î':
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input[i] = 'i'
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case 'ü', 'ù', 'ú', 'û':
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input[i] = 'u'
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}
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}
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input = step1(input)
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return step2(input)
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}
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func stEnding(ch rune) bool {
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switch ch {
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case 'b', 'd', 'f', 'g', 'h', 'k', 'l', 'm', 'n', 't':
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return true
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}
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return false
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}
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func step1(s []rune) []rune {
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l := len(s)
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if l > 5 && s[l-3] == 'e' && s[l-2] == 'r' && s[l-1] == 'n' {
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return s[:l-3]
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}
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if l > 4 && s[l-2] == 'e' {
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switch s[l-1] {
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case 'm', 'n', 'r', 's':
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return s[:l-2]
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}
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}
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if l > 3 && s[l-1] == 'e' {
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return s[:l-1]
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}
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if l > 3 && s[l-1] == 's' && stEnding(s[l-2]) {
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return s[:l-1]
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}
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return s
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}
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func step2(s []rune) []rune {
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l := len(s)
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if l > 5 && s[l-3] == 'e' && s[l-2] == 's' && s[l-1] == 't' {
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return s[:l-3]
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}
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if l > 4 && s[l-2] == 'e' && (s[l-1] == 'r' || s[l-1] == 'n') {
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return s[:l-2]
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}
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if l > 4 && s[l-2] == 's' && s[l-1] == 't' && stEnding(s[l-3]) {
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return s[:l-2]
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}
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return s
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}
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func GermanLightStemmerFilterConstructor(config map[string]interface{}, cache *registry.Cache) (analysis.TokenFilter, error) {
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return NewGermanLightStemmerFilter(), nil
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}
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func init() {
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registry.RegisterTokenFilter(LightStemmerName, GermanLightStemmerFilterConstructor)
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}
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