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// GoToSocial
// Copyright (C) GoToSocial Authors admin@gotosocial.org
// SPDX-License-Identifier: AGPL-3.0-or-later
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
package text
import (
"strings"
"golang.org/x/text/unicode/norm"
)
const (
maximumHashtagLength = 100
)
// NormalizeHashtag normalizes the given hashtag text by
// removing the initial '#' symbol, and then decomposing
// and canonically recomposing chars + combining diacritics
// in the text to single unicode characters, following
// Normalization Form C (https://unicode.org/reports/tr15/).
//
// Finally, it will do a check on the normalized string to
// ensure that it's below maximumHashtagLength chars, and
// contains only letters, numbers, and underscores (and not
// *JUST* underscores).
//
// If all this passes, returned bool will be true.
func NormalizeHashtag(text string) (string, bool) {
// This normalization is specifically to avoid cases
// where visually-identical hashtags are stored with
// different unicode representations (e.g. with combining
// diacritics). It allows a tasteful number of combining
// diacritics to be used, as long as they can be combined
// with parent characters to form regular letter symbols.
normalized := norm.NFC.String(strings.TrimPrefix(text, "#"))
// Validate normalized result.
var (
atLeastOneRequiredChar = false
onlyPermittedChars = true
lengthOK = true
)
for i, r := range normalized {
if !isPermittedIfNotEntireHashtag(r) {
// This isn't an underscore, mark, etc,
// so the hashtag contains at least one
atLeastOneRequiredChar = true
}
if i >= maximumHashtagLength {
lengthOK = false
break
}
if !isPermittedInHashtag(r) {
onlyPermittedChars = false
break
}
}
return normalized, lengthOK && onlyPermittedChars && atLeastOneRequiredChar
}
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