84 lines
2.4 KiB
Go
84 lines
2.4 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 lower_case_filter implements a TokenFilter which converts
|
|
// tokens to lower case according to unicode rules.
|
|
package lower_case_filter
|
|
|
|
import (
|
|
"bytes"
|
|
"unicode"
|
|
"unicode/utf8"
|
|
|
|
"github.com/blevesearch/bleve/analysis"
|
|
"github.com/blevesearch/bleve/registry"
|
|
)
|
|
|
|
// Name is the name used to register LowerCaseFilter in the bleve registry
|
|
const Name = "to_lower"
|
|
|
|
type LowerCaseFilter struct {
|
|
}
|
|
|
|
func NewLowerCaseFilter() *LowerCaseFilter {
|
|
return &LowerCaseFilter{}
|
|
}
|
|
|
|
func (f *LowerCaseFilter) Filter(input analysis.TokenStream) analysis.TokenStream {
|
|
for _, token := range input {
|
|
token.Term = toLowerDeferredCopy(token.Term)
|
|
}
|
|
return input
|
|
}
|
|
|
|
func LowerCaseFilterConstructor(config map[string]interface{}, cache *registry.Cache) (analysis.TokenFilter, error) {
|
|
return NewLowerCaseFilter(), nil
|
|
}
|
|
|
|
func init() {
|
|
registry.RegisterTokenFilter(Name, LowerCaseFilterConstructor)
|
|
}
|
|
|
|
// toLowerDeferredCopy will function exactly like
|
|
// bytes.ToLower() only it will reuse (overwrite)
|
|
// the original byte array when possible
|
|
// NOTE: because its possible that the lower-case
|
|
// form of a rune has a different utf-8 encoded
|
|
// length, in these cases a new byte array is allocated
|
|
func toLowerDeferredCopy(s []byte) []byte {
|
|
j := 0
|
|
for i := 0; i < len(s); {
|
|
wid := 1
|
|
r := rune(s[i])
|
|
if r >= utf8.RuneSelf {
|
|
r, wid = utf8.DecodeRune(s[i:])
|
|
}
|
|
l := unicode.ToLower(r)
|
|
lwid := utf8.RuneLen(l)
|
|
if lwid > wid {
|
|
// utf-8 encoded replacement is wider
|
|
// for now, punt and defer
|
|
// to bytes.ToLower() for the remainder
|
|
// only known to happen with chars
|
|
// Rune Ⱥ(570) width 2 - Lower ⱥ(11365) width 3
|
|
// Rune Ⱦ(574) width 2 - Lower ⱦ(11366) width 3
|
|
rest := bytes.ToLower(s[i:])
|
|
rv := make([]byte, j+len(rest))
|
|
copy(rv[:j], s[:j])
|
|
copy(rv[j:], rest)
|
|
return rv
|
|
} else {
|
|
utf8.EncodeRune(s[j:], l)
|
|
}
|
|
i += wid
|
|
j += lwid
|
|
}
|
|
return s[:j]
|
|
}
|