Move some variables out of model (#17909)

* Move some variables out of model

There were some stuff that's not necessary to be in model
and can just remain unexported variables.

```release-note
NONE
```

* Add license

```release-note
NONE
```

app/command.go

@@ -10,6 +10,7 @@ import (
 	"io/ioutil"
 	"net/http"
 	"net/url"
+	"regexp"
 	"strings"
 	"sync"
 	"unicode"
@@ -23,8 +24,11 @@ import (
 
 const (
 	CmdCustomStatusTrigger = "status"
+	usernameSpecialChars   = ".-_"
 )
 
+var atMentionRegexp = regexp.MustCompile(`\B@[[:alnum:]][[:alnum:]\.\-_:]*`)
+
 type CommandProvider interface {
 	GetTrigger() string
 	GetCommand(a *App, T i18n.TranslateFunc) *model.Command
@@ -233,7 +237,7 @@ func (a *App) MentionsToTeamMembers(message, teamID string) model.UserMentionMap
 		Id   string
 	}
 
-	possibleMentions := model.PossibleAtMentions(message)
+	possibleMentions := possibleAtMentions(message)
 	mentionChan := make(chan *mentionMapItem, len(possibleMentions))
 
 	var wg sync.WaitGroup
@@ -252,8 +256,8 @@ func (a *App) MentionsToTeamMembers(message, teamID string) model.UserMentionMap
 			// If it's a http.StatusNotFound error, check for usernames in substrings
 			// without trailing punctuation
 			if nErr != nil {
-				trimmed, ok := model.TrimUsernameSpecialChar(mention)
-				for ; ok; trimmed, ok = model.TrimUsernameSpecialChar(trimmed) {
+				trimmed, ok := trimUsernameSpecialChar(mention)
+				for ; ok; trimmed, ok = trimUsernameSpecialChar(trimmed) {
 					userFromTrimmed, nErr := a.Srv().Store.User().GetByUsername(trimmed)
 					if nErr != nil && !errors.As(nErr, &nfErr) {
 						return
@@ -770,3 +774,37 @@ func (a *App) DeleteCommand(commandID string) *model.AppError {
 
 	return nil
 }
+
+// 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 := model.NormalizeUsername(match[1:])
+		if !alreadyMentioned[name] && model.IsValidUsernameAllowRemote(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
+}

app/command_test.go

@@ -0,0 +1,84 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package app
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestPossibleAtMentions(t *testing.T) {
+	fixture := []struct {
+		message  string
+		expected []string
+	}{
+		{
+			"",
+			[]string{},
+		},
+		{
+			"@user",
+			[]string{"user"},
+		},
+		{
+			"@user-with_special.chars @multiple.-_chars",
+			[]string{"user-with_special.chars", "multiple.-_chars"},
+		},
+		{
+			"@repeated @user @repeated",
+			[]string{"repeated", "user"},
+		},
+		{
+			"@user1 @user2 @user3",
+			[]string{"user1", "user2", "user3"},
+		},
+		{
+			"@李",
+			[]string{},
+		},
+		{
+			"@withfinaldot. @withfinaldash- @withfinalunderscore_",
+			[]string{
+				"withfinaldot.",
+				"withfinaldash-",
+				"withfinalunderscore_",
+			},
+		},
+	}
+
+	for _, data := range fixture {
+		actual := possibleAtMentions(data.message)
+		require.ElementsMatch(t, actual, data.expected)
+	}
+}
+
+func TestTrimUsernameSpecialChar(t *testing.T) {
+	fixture := []struct {
+		word           string
+		expectedString string
+		expectedBool   bool
+	}{
+		{"user...", "user..", true},
+		{"user..", "user.", true},
+		{"user.", "user", true},
+		{"user--", "user-", true},
+		{"user-", "user", true},
+		{"user_.-", "user_.", true},
+		{"user_.", "user_", true},
+		{"user_", "user", true},
+		{"user", "user", false},
+		{"user.with-inner_chars", "user.with.inner.chars", false},
+	}
+
+	for _, data := range fixture {
+		actualString, actualBool := trimUsernameSpecialChar(data.word)
+		require.Equal(t, actualBool, data.expectedBool)
+		if actualBool {
+			require.Equal(t, actualString, data.expectedString)
+		} else {
+			require.Equal(t, actualString, data.word)
+		}
+	}
+}

app/post.go

@@ -9,6 +9,7 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
+	"regexp"
 	"strings"
 	"sync"
 	"time"
@@ -29,6 +30,8 @@ const (
 	PageDefault             = 0
 )
 
+var atMentionPattern = regexp.MustCompile(`\B@`)
+
 func (a *App) CreatePostAsUser(c *request.Context, post *model.Post, currentSessionId string, setOnline bool) (*model.Post, *model.AppError) {
 	// Check that channel has not been deleted
 	channel, errCh := a.Srv().Store.Channel().Get(post.ChannelId, true)
@@ -442,7 +445,7 @@ func (a *App) FillInPostProps(post *model.Post, channel *model.Channel) *model.A
 		post.DelProp("channel_mentions")
 	}
 
-	matched := model.AtMentionPattern.MatchString(post.Message)
+	matched := atMentionPattern.MatchString(post.Message)
 	if a.Srv().License() != nil && *a.Srv().License().Features.LDAPGroups && matched && !a.HasPermissionToChannel(post.UserId, post.ChannelId, model.PermissionUseGroupMentions) {
 		post.AddProp(model.PostPropsGroupHighlightDisabled, true)
 	}