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gitea/vendor/github.com/blevesearch/bleve/analysis/token/lowercase/lowercase.go

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This file contains ambiguous Unicode characters

This file contains Unicode characters that might be confused with other characters. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

// 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 lowercase implements a TokenFilter which converts
// tokens to lower case according to unicode rules.
package lowercase
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)
// If the rune is already lowercased, just move to the
// next rune.
if l == r {
i += wid
j += wid
continue
}
// Handles the Unicode edge-case where the last
// rune in a word on the greek Σ needs to be converted
// differently.
if l == 'σ' && i+2 == len(s) {
l = 'ς'
}
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]
}