[MM-59361] custom groups & read only channels (#28892)

* added group mention, read only view and post event tracking

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/store/sqlstore/channel_store.go

@@ -17,6 +17,7 @@ import (
 	"github.com/pkg/errors"
 
 	"github.com/mattermost/mattermost/server/public/model"
+	"github.com/mattermost/mattermost/server/public/shared/mlog"
 	"github.com/mattermost/mattermost/server/public/shared/request"
 	"github.com/mattermost/mattermost/server/v8/channels/store"
 	"github.com/mattermost/mattermost/server/v8/einterfaces"
@@ -4322,3 +4323,40 @@ func (s SqlChannelStore) GetTeamForChannel(channelID string) (*model.Team, error
 	}
 	return &team, nil
 }
+
+func (s SqlChannelStore) IsReadOnlyChannel(channelID string) (bool, error) {
+	query := s.getQueryBuilder().Select("schemeid").From("channels").Where(sq.Eq{"id": channelID}).Limit(1)
+	squery, args, err := query.ToSql()
+	if err != nil {
+		return false, err
+	}
+	// we look for schemeID to look for a custom scheme, if there is none chances are it is a writeable
+	// there might be in effect a custom scheme for the user that doesn't allow to create posts, but that wouldn't
+	// be a readonly channel but a readonly user
+	var schemaId string
+	err = s.GetReplicaX().Get(&schemaId, squery, args...)
+	if err != nil {
+		return false, nil
+	}
+	if schemaId == "" {
+		return false, nil
+	}
+	return s.IsChannelReadOnlyScheme(schemaId)
+}
+
+func (s SqlChannelStore) IsChannelReadOnlyScheme(schemeID string) (bool, error) {
+	query := s.getQueryBuilder().Select("roles.permissions").From("roles").InnerJoin("schemes ON roles.name = schemes.defaultchanneluserrole").Where(sq.Eq{"schemes.id": schemeID}).Limit(1)
+	squery, args, err := query.ToSql()
+	if err != nil {
+		mlog.Err(err)
+		return false, err
+	}
+	var permissions string
+	err = s.GetReplicaX().Get(&permissions, squery, args...)
+	if err != nil {
+		mlog.Err(err)
+		return false, err
+	}
+	permissionList := strings.Split(permissions, " ")
+	return slices.Index(permissionList, model.PermissionCreatePost.Id) == -1, nil
+}