Use mattermost v5 module (#1192)

vendor/github.com/mattermost/mattermost-server/v5/model/at_mentions.go

@@ -0,0 +1,47 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package model
+
+import (
+	"regexp"
+	"strings"
+)
+
+var atMentionRegexp = regexp.MustCompile(`\B@[[:alnum:]][[:alnum:]\.\-_]*`)
+
+const usernameSpecialChars = ".-_"
+
+// PossibleAtMentions returns all substrings in message that look like valid @
+// mentions.
+func PossibleAtMentions(message string) []string {
+	var names []string
+
+	if !strings.Contains(message, "@") {
+		return names
+	}
+
+	alreadyMentioned := make(map[string]bool)
+	for _, match := range atMentionRegexp.FindAllString(message, -1) {
+		name := NormalizeUsername(match[1:])
+		if !alreadyMentioned[name] && IsValidUsername(name) {
+			names = append(names, name)
+			alreadyMentioned[name] = true
+		}
+	}
+
+	return names
+}
+
+// TrimUsernameSpecialChar tries to remove the last character from word if it
+// is a special character for usernames (dot, dash or underscore). If not, it
+// returns the same string.
+func TrimUsernameSpecialChar(word string) (string, bool) {
+	len := len(word)
+
+	if len > 0 && strings.LastIndexAny(word, usernameSpecialChars) == (len-1) {
+		return word[:len-1], true
+	}
+
+	return word, false
+}