@mention support (#1147)

NOTICE.txt

@@ -748,3 +748,36 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 
 ---
+
+## wiggin77/merror
+
+This product contains 'merror' by GitHub user 'wiggin77'.
+
+Multiple Error aggregator for Go.
+
+* HOMEPAGE:
+  * https://github.com/wiggin77/merror
+
+* LICENSE: MIT
+
+MIT License
+
+Copyright (c) 2018 wiggin77
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

linux/main.go

@@ -60,7 +60,17 @@ func runServer(port int) (*server.Server, error) {
 		return nil, err
 	}
 
-	server, err := server.New(config, sessionToken, db, logger, "", nil)
+	params := server.Params{
+		Cfg:             config,
+		SingleUserToken: sessionToken,
+		DBStore:         db,
+		Logger:          logger,
+		ServerID:        "",
+		WSAdapter:       nil,
+		NotifyBackends:  nil,
+	}
+
+	server, err := server.New(params)
 	if err != nil {
 		fmt.Println("ERROR INITIALIZING THE SERVER", err)
 		return nil, err

mattermost-plugin/server/notifications.go

@@ -0,0 +1,61 @@
+package main
+
+import (
+	"fmt"
+
+	"github.com/mattermost/focalboard/server/services/notify"
+	"github.com/mattermost/focalboard/server/services/notify/notifymentions"
+	"github.com/mattermost/focalboard/server/services/notify/plugindelivery"
+
+	pluginapi "github.com/mattermost/mattermost-plugin-api"
+
+	"github.com/mattermost/mattermost-server/v6/model"
+
+	"github.com/mattermost/mattermost-server/v6/shared/mlog"
+)
+
+const (
+	botUsername    = "boards"
+	botDisplayname = "Boards"
+	botDescription = "Created by Boards plugin."
+)
+
+func createMentionsNotifyBackend(client *pluginapi.Client, serverRoot string, logger *mlog.Logger) (notify.Backend, error) {
+	bot := &model.Bot{
+		Username:    botUsername,
+		DisplayName: botDisplayname,
+		Description: botDescription,
+	}
+	botID, err := client.Bot.EnsureBot(bot)
+	if err != nil {
+		return nil, fmt.Errorf("failed to ensure %s bot: %w", botDisplayname, err)
+	}
+
+	pluginAPI := &pluginAPIAdapter{client: client}
+
+	delivery := plugindelivery.New(botID, serverRoot, pluginAPI)
+
+	backend := notifymentions.New(delivery, logger)
+
+	return backend, nil
+}
+
+type pluginAPIAdapter struct {
+	client *pluginapi.Client
+}
+
+func (da *pluginAPIAdapter) GetDirectChannel(userID1, userID2 string) (*model.Channel, error) {
+	return da.client.Channel.GetDirect(userID1, userID2)
+}
+
+func (da *pluginAPIAdapter) CreatePost(post *model.Post) error {
+	return da.client.Post.CreatePost(post)
+}
+
+func (da *pluginAPIAdapter) GetUserByID(userID string) (*model.User, error) {
+	return da.client.User.Get(userID)
+}
+
+func (da *pluginAPIAdapter) GetUserByUsername(name string) (*model.User, error) {
+	return da.client.User.GetByUsername(name)
+}

mattermost-plugin/server/plugin.go

@@ -9,6 +9,7 @@ import (
 	"github.com/mattermost/focalboard/server/auth"
 	"github.com/mattermost/focalboard/server/server"
 	"github.com/mattermost/focalboard/server/services/config"
+	"github.com/mattermost/focalboard/server/services/notify"
 	"github.com/mattermost/focalboard/server/services/store"
 	"github.com/mattermost/focalboard/server/services/store/mattermostauthlayer"
 	"github.com/mattermost/focalboard/server/services/store/sqlstore"
@@ -132,7 +133,22 @@ func (p *Plugin) OnActivate() error {
 
 	p.wsPluginAdapter = ws.NewPluginAdapter(p.API, auth.New(cfg, db))
 
-	server, err := server.New(cfg, "", db, logger, serverID, p.wsPluginAdapter)
+	mentionsBackend, err := createMentionsNotifyBackend(client, cfg.ServerRoot, logger)
+	if err != nil {
+		return fmt.Errorf("error creating mentions notifications backend: %w", err)
+	}
+
+	params := server.Params{
+		Cfg:             cfg,
+		SingleUserToken: "",
+		DBStore:         db,
+		Logger:          logger,
+		ServerID:        serverID,
+		WSAdapter:       p.wsPluginAdapter,
+		NotifyBackends:  []notify.Backend{mentionsBackend},
+	}
+
+	server, err := server.New(params)
 	if err != nil {
 		fmt.Println("ERROR INITIALIZING THE SERVER", err)
 		return err

server/app/app.go

@@ -4,6 +4,7 @@ import (
 	"github.com/mattermost/focalboard/server/auth"
 	"github.com/mattermost/focalboard/server/services/config"
 	"github.com/mattermost/focalboard/server/services/metrics"
+	"github.com/mattermost/focalboard/server/services/notify"
 	"github.com/mattermost/focalboard/server/services/store"
 	"github.com/mattermost/focalboard/server/services/webhook"
 	"github.com/mattermost/focalboard/server/ws"
@@ -19,6 +20,7 @@ type Services struct {
 	FilesBackend  filestore.FileBackend
 	Webhook       *webhook.Client
 	Metrics       *metrics.Metrics
+	Notifications *notify.Service
 	Logger        *mlog.Logger
 }
 
@@ -30,6 +32,7 @@ type App struct {
 	filesBackend  filestore.FileBackend
 	webhook       *webhook.Client
 	metrics       *metrics.Metrics
+	notifications *notify.Service
 	logger        *mlog.Logger
 }
 
@@ -42,6 +45,7 @@ func New(config *config.Configuration, wsAdapter ws.Adapter, services Services)
 		filesBackend:  services.FilesBackend,
 		webhook:       services.Webhook,
 		metrics:       services.Metrics,
+		notifications: services.Notifications,
 		logger:        services.Logger,
 	}
 }

server/app/blocks.go

@@ -2,7 +2,10 @@ package app
 
 import (
 	"github.com/mattermost/focalboard/server/model"
+	"github.com/mattermost/focalboard/server/services/notify"
 	"github.com/mattermost/focalboard/server/services/store"
+
+	"github.com/mattermost/mattermost-server/v6/shared/mlog"
 )
 
 func (a *App) GetBlocks(c store.Container, parentID string, blockType string) ([]model.Block, error) {
@@ -30,40 +33,64 @@ func (a *App) GetParentID(c store.Container, blockID string) (string, error) {
 }
 
 func (a *App) PatchBlock(c store.Container, blockID string, blockPatch *model.BlockPatch, userID string) error {
-	err := a.store.PatchBlock(c, blockID, blockPatch, userID)
+	oldBlock, err := a.store.GetBlock(c, blockID)
+	if err != nil {
+		return nil
+	}
+
+	err = a.store.PatchBlock(c, blockID, blockPatch, userID)
 	if err != nil {
 		return err
 	}
+
 	a.metrics.IncrementBlocksPatched(1)
 	block, err := a.store.GetBlock(c, blockID)
 	if err != nil {
 		return nil
 	}
 	a.wsAdapter.BroadcastBlockChange(c.WorkspaceID, *block)
-	go a.webhook.NotifyUpdate(*block)
+	go func() {
+		a.webhook.NotifyUpdate(*block)
+		a.notifyBlockChanged(notify.Update, c, block, oldBlock, userID)
+	}()
 	return nil
 }
 
 func (a *App) InsertBlock(c store.Container, block model.Block, userID string) error {
 	err := a.store.InsertBlock(c, &block, userID)
 	if err == nil {
+		a.wsAdapter.BroadcastBlockChange(c.WorkspaceID, block)
 		a.metrics.IncrementBlocksInserted(1)
+		go func() {
+			a.webhook.NotifyUpdate(block)
+			a.notifyBlockChanged(notify.Add, c, &block, nil, userID)
+		}()
 	}
 	return err
 }
 
 func (a *App) InsertBlocks(c store.Container, blocks []model.Block, userID string) error {
+	needsNotify := make([]model.Block, 0, len(blocks))
 	for i := range blocks {
 		err := a.store.InsertBlock(c, &blocks[i], userID)
 		if err != nil {
 			return err
 		}
 
+		needsNotify = append(needsNotify, blocks[i])
+
 		a.wsAdapter.BroadcastBlockChange(c.WorkspaceID, blocks[i])
-		a.metrics.IncrementBlocksInserted(len(blocks))
+		a.metrics.IncrementBlocksInserted(1)
-		go a.webhook.NotifyUpdate(blocks[i])
 	}
 
+	go func() {
+		for _, b := range needsNotify {
+			block := b
+			a.webhook.NotifyUpdate(block)
+			a.notifyBlockChanged(notify.Add, c, &block, nil, userID)
+		}
+	}()
+
 	return nil
 }
 
@@ -80,7 +107,7 @@ func (a *App) GetAllBlocks(c store.Container) ([]model.Block, error) {
 }
 
 func (a *App) DeleteBlock(c store.Container, blockID string, modifiedBy string) error {
-	parentID, err := a.GetParentID(c, blockID)
+	block, err := a.store.GetBlock(c, blockID)
 	if err != nil {
 		return err
 	}
@@ -90,12 +117,69 @@ func (a *App) DeleteBlock(c store.Container, blockID string, modifiedBy string)
 		return err
 	}
 
-	a.wsAdapter.BroadcastBlockDelete(c.WorkspaceID, blockID, parentID)
+	a.wsAdapter.BroadcastBlockDelete(c.WorkspaceID, blockID, block.ParentID)
 	a.metrics.IncrementBlocksDeleted(1)
-
+	go func() {
+		a.notifyBlockChanged(notify.Update, c, block, block, modifiedBy)
+	}()
 	return nil
 }
 
 func (a *App) GetBlockCountsByType() (map[string]int64, error) {
 	return a.store.GetBlockCountsByType()
 }
+
+func (a *App) notifyBlockChanged(action notify.Action, c store.Container, block *model.Block, oldBlock *model.Block, userID string) {
+	if a.notifications == nil {
+		return
+	}
+
+	// find card and board for the changed block.
+	board, card, err := a.getBoardAndCard(c, block)
+	if err != nil {
+		a.logger.Error("Error notifying for block change; cannot determine board or card", mlog.Err(err))
+		return
+	}
+
+	evt := notify.BlockChangeEvent{
+		Action:       action,
+		Workspace:    c.WorkspaceID,
+		Board:        board,
+		Card:         card,
+		BlockChanged: block,
+		BlockOld:     oldBlock,
+		UserID:       userID,
+	}
+	a.notifications.BlockChanged(evt)
+}
+
+const (
+	maxSearchDepth = 50
+)
+
+// getBoardAndCard returns the first parent of type `card` and first parent of type `board` for the specified block.
+// `board` and/or `card` may return nil without error if the block does not belong to a board or card.
+func (a *App) getBoardAndCard(c store.Container, block *model.Block) (board *model.Block, card *model.Block, err error) {
+	var count int // don't let invalid blocks hierarchy cause infinite loop.
+	iter := block
+	for {
+		count++
+		if board == nil && iter.Type == "board" {
+			board = iter
+		}
+
+		if card == nil && iter.Type == "card" {
+			card = iter
+		}
+
+		if iter.ParentID == "" || (board != nil && card != nil) || count > maxSearchDepth {
+			break
+		}
+
+		iter, err = a.store.GetBlock(c, iter.ParentID)
+		if err != nil {
+			return board, card, err
+		}
+	}
+	return board, card, nil
+}

server/go.mod

@@ -25,6 +25,7 @@ require (
 	github.com/spf13/jwalterweatherman v1.1.0 // indirect
 	github.com/spf13/viper v1.7.1
 	github.com/stretchr/testify v1.7.0
+	github.com/wiggin77/merror v1.0.3
 	golang.org/x/crypto v0.0.0-20210616213533-5ff15b29337e
 	gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c // indirect
 )

server/integrationtests/clienttestlib.go

@@ -75,7 +75,15 @@ func newTestServer(singleUserToken string) *server.Server {
 	if err != nil {
 		panic(err)
 	}
-	srv, err := server.New(cfg, singleUserToken, db, logger, "", nil)
+
+	params := server.Params{
+		Cfg:             cfg,
+		SingleUserToken: singleUserToken,
+		DBStore:         db,
+		Logger:          logger,
+	}
+
+	srv, err := server.New(params)
 	if err != nil {
 		panic(err)
 	}

server/main/main.go

@@ -165,7 +165,14 @@ func main() {
 		logger.Fatal("server.NewStore ERROR", mlog.Err(err))
 	}
 
-	server, err := server.New(config, singleUserToken, db, logger, "", nil)
+	params := server.Params{
+		Cfg:             config,
+		SingleUserToken: singleUserToken,
+		DBStore:         db,
+		Logger:          logger,
+	}
+
+	server, err := server.New(params)
 	if err != nil {
 		logger.Fatal("server.New ERROR", mlog.Err(err))
 	}
@@ -245,7 +252,14 @@ func startServer(webPath string, filesPath string, port int, singleUserToken, db
 		logger.Fatal("server.NewStore ERROR", mlog.Err(err))
 	}
 
-	pServer, err = server.New(config, singleUserToken, db, logger, "", nil)
+	params := server.Params{
+		Cfg:             config,
+		SingleUserToken: singleUserToken,
+		DBStore:         db,
+		Logger:          logger,
+	}
+
+	pServer, err = server.New(params)
 	if err != nil {
 		logger.Fatal("server.New ERROR", mlog.Err(err))
 	}

server/server/params.go

@@ -0,0 +1,46 @@
+package server
+
+import (
+	"fmt"
+
+	"github.com/mattermost/focalboard/server/services/config"
+	"github.com/mattermost/focalboard/server/services/notify"
+	"github.com/mattermost/focalboard/server/services/store"
+	"github.com/mattermost/focalboard/server/ws"
+
+	"github.com/mattermost/mattermost-server/v6/shared/mlog"
+)
+
+type Params struct {
+	Cfg             *config.Configuration
+	SingleUserToken string
+	DBStore         store.Store
+	Logger          *mlog.Logger
+	ServerID        string
+	WSAdapter       ws.Adapter
+	NotifyBackends  []notify.Backend
+}
+
+func (p Params) CheckValid() error {
+	if p.Cfg == nil {
+		return ErrServerParam{name: "Cfg", issue: "cannot be nil"}
+	}
+
+	if p.DBStore == nil {
+		return ErrServerParam{name: "DbStore", issue: "cannot be nil"}
+	}
+
+	if p.Logger == nil {
+		return ErrServerParam{name: "Logger", issue: "cannot be nil"}
+	}
+	return nil
+}
+
+type ErrServerParam struct {
+	name  string
+	issue string
+}
+
+func (e ErrServerParam) Error() string {
+	return fmt.Sprintf("invalid server params: %s %s", e.name, e.issue)
+}

server/server/server.go

@@ -22,6 +22,8 @@ import (
 	"github.com/mattermost/focalboard/server/services/audit"
 	"github.com/mattermost/focalboard/server/services/config"
 	"github.com/mattermost/focalboard/server/services/metrics"
+	"github.com/mattermost/focalboard/server/services/notify"
+	"github.com/mattermost/focalboard/server/services/notify/notifylogger"
 	"github.com/mattermost/focalboard/server/services/scheduler"
 	"github.com/mattermost/focalboard/server/services/store"
 	"github.com/mattermost/focalboard/server/services/store/mattermostauthlayer"
@@ -60,6 +62,7 @@ type Server struct {
 	metricsService         *metrics.Metrics
 	metricsUpdaterTask     *scheduler.ScheduledTask
 	auditService           *audit.Audit
+	notificationService    *notify.Service
 	servicesStartStopMutex sync.Mutex
 
 	localRouter     *mux.Router
@@ -67,37 +70,41 @@ type Server struct {
 	api             *api.API
 }
 
-func New(cfg *config.Configuration, singleUserToken string, db store.Store,
+func New(params Params) (*Server, error) {
-	logger *mlog.Logger, serverID string, wsAdapter ws.Adapter) (*Server, error) {
+	if err := params.CheckValid(); err != nil {
-	authenticator := auth.New(cfg, db)
+		return nil, err
+	}
+
+	authenticator := auth.New(params.Cfg, params.DBStore)
 
 	// if no ws adapter is provided, we spin up a websocket server
+	wsAdapter := params.WSAdapter
 	if wsAdapter == nil {
-		wsAdapter = ws.NewServer(authenticator, singleUserToken, cfg.AuthMode == MattermostAuthMod, logger)
+		wsAdapter = ws.NewServer(authenticator, params.SingleUserToken, params.Cfg.AuthMode == MattermostAuthMod, params.Logger)
 	}
 
 	filesBackendSettings := filestore.FileBackendSettings{}
-	filesBackendSettings.DriverName = cfg.FilesDriver
+	filesBackendSettings.DriverName = params.Cfg.FilesDriver
-	filesBackendSettings.Directory = cfg.FilesPath
+	filesBackendSettings.Directory = params.Cfg.FilesPath
-	filesBackendSettings.AmazonS3AccessKeyId = cfg.FilesS3Config.AccessKeyID
+	filesBackendSettings.AmazonS3AccessKeyId = params.Cfg.FilesS3Config.AccessKeyID
-	filesBackendSettings.AmazonS3SecretAccessKey = cfg.FilesS3Config.SecretAccessKey
+	filesBackendSettings.AmazonS3SecretAccessKey = params.Cfg.FilesS3Config.SecretAccessKey
-	filesBackendSettings.AmazonS3Bucket = cfg.FilesS3Config.Bucket
+	filesBackendSettings.AmazonS3Bucket = params.Cfg.FilesS3Config.Bucket
-	filesBackendSettings.AmazonS3PathPrefix = cfg.FilesS3Config.PathPrefix
+	filesBackendSettings.AmazonS3PathPrefix = params.Cfg.FilesS3Config.PathPrefix
-	filesBackendSettings.AmazonS3Region = cfg.FilesS3Config.Region
+	filesBackendSettings.AmazonS3Region = params.Cfg.FilesS3Config.Region
-	filesBackendSettings.AmazonS3Endpoint = cfg.FilesS3Config.Endpoint
+	filesBackendSettings.AmazonS3Endpoint = params.Cfg.FilesS3Config.Endpoint
-	filesBackendSettings.AmazonS3SSL = cfg.FilesS3Config.SSL
+	filesBackendSettings.AmazonS3SSL = params.Cfg.FilesS3Config.SSL
-	filesBackendSettings.AmazonS3SignV2 = cfg.FilesS3Config.SignV2
+	filesBackendSettings.AmazonS3SignV2 = params.Cfg.FilesS3Config.SignV2
-	filesBackendSettings.AmazonS3SSE = cfg.FilesS3Config.SSE
+	filesBackendSettings.AmazonS3SSE = params.Cfg.FilesS3Config.SSE
-	filesBackendSettings.AmazonS3Trace = cfg.FilesS3Config.Trace
+	filesBackendSettings.AmazonS3Trace = params.Cfg.FilesS3Config.Trace
 
 	filesBackend, appErr := filestore.NewFileBackend(filesBackendSettings)
 	if appErr != nil {
-		logger.Error("Unable to initialize the files storage", mlog.Err(appErr))
+		params.Logger.Error("Unable to initialize the files storage", mlog.Err(appErr))
 
 		return nil, errors.New("unable to initialize the files storage")
 	}
 
-	webhookClient := webhook.NewClient(cfg, logger)
+	webhookClient := webhook.NewClient(params.Cfg, params.Logger)
 
 	// Init metrics
 	instanceInfo := metrics.InstanceInfo{
@@ -113,21 +120,28 @@ func New(cfg *config.Configuration, singleUserToken string, db store.Store,
 	if errAudit != nil {
 		return nil, fmt.Errorf("unable to create the audit service: %w", errAudit)
 	}
-	if err := auditService.Configure(cfg.AuditCfgFile, cfg.AuditCfgJSON); err != nil {
+	if err := auditService.Configure(params.Cfg.AuditCfgFile, params.Cfg.AuditCfgJSON); err != nil {
 		return nil, fmt.Errorf("unable to initialize the audit service: %w", err)
 	}
 
+	// Init notification services
+	notificationService, errNotify := initNotificationService(params.NotifyBackends, params.Logger)
+	if errNotify != nil {
+		return nil, fmt.Errorf("cannot initialize notification service: %w", errNotify)
+	}
+
 	appServices := app.Services{
 		Auth:          authenticator,
-		Store:        db,
+		Store:         params.DBStore,
 		FilesBackend:  filesBackend,
 		Webhook:       webhookClient,
 		Metrics:       metricsService,
-		Logger:       logger,
+		Notifications: notificationService,
+		Logger:        params.Logger,
 	}
-	app := app.New(cfg, wsAdapter, appServices)
+	app := app.New(params.Cfg, wsAdapter, appServices)
 
-	focalboardAPI := api.NewAPI(app, singleUserToken, cfg.AuthMode, logger, auditService)
+	focalboardAPI := api.NewAPI(app, params.SingleUserToken, params.Cfg.AuthMode, params.Logger, auditService)
 
 	// Local router for admin APIs
 	localRouter := mux.NewRouter()
@@ -135,18 +149,19 @@ func New(cfg *config.Configuration, singleUserToken string, db store.Store,
 
 	// Init workspace
 	if _, err := app.GetRootWorkspace(); err != nil {
-		logger.Error("Unable to get root workspace", mlog.Err(err))
+		params.Logger.Error("Unable to get root workspace", mlog.Err(err))
 		return nil, err
 	}
 
-	webServer := web.NewServer(cfg.WebPath, cfg.ServerRoot, cfg.Port, cfg.UseSSL, cfg.LocalOnly, logger)
+	webServer := web.NewServer(params.Cfg.WebPath, params.Cfg.ServerRoot, params.Cfg.Port,
+		params.Cfg.UseSSL, params.Cfg.LocalOnly, params.Logger)
 	// if the adapter is a routed service, register it before the API
 	if routedService, ok := wsAdapter.(web.RoutedService); ok {
 		webServer.AddRoutes(routedService)
 	}
 	webServer.AddRoutes(focalboardAPI)
 
-	settings, err := db.GetSystemSettings()
+	settings, err := params.DBStore.GetSystemSettings()
 	if err != nil {
 		return nil, err
 	}
@@ -155,31 +170,32 @@ func New(cfg *config.Configuration, singleUserToken string, db store.Store,
 	telemetryID := settings["TelemetryID"]
 	if len(telemetryID) == 0 {
 		telemetryID = uuid.New().String()
-		if err = db.SetSystemSetting("TelemetryID", uuid.New().String()); err != nil {
+		if err = params.DBStore.SetSystemSetting("TelemetryID", uuid.New().String()); err != nil {
 			return nil, err
 		}
 	}
 	telemetryOpts := telemetryOptions{
 		app:         app,
-		cfg:         cfg,
+		cfg:         params.Cfg,
 		telemetryID: telemetryID,
-		serverID:    serverID,
+		serverID:    params.ServerID,
-		logger:      logger,
+		logger:      params.Logger,
-		singleUser:  len(singleUserToken) > 0,
+		singleUser:  len(params.SingleUserToken) > 0,
 	}
 	telemetryService := initTelemetry(telemetryOpts)
 
 	server := Server{
-		config:         cfg,
+		config:              params.Cfg,
 		wsAdapter:           wsAdapter,
 		webServer:           webServer,
-		store:          db,
+		store:               params.DBStore,
 		filesBackend:        filesBackend,
 		telemetry:           telemetryService,
-		metricsServer:  metrics.NewMetricsServer(cfg.PrometheusAddress, metricsService, logger),
+		metricsServer:       metrics.NewMetricsServer(params.Cfg.PrometheusAddress, metricsService, params.Logger),
 		metricsService:      metricsService,
 		auditService:        auditService,
-		logger:         logger,
+		notificationService: notificationService,
+		logger:              params.Logger,
 		localRouter:         localRouter,
 		api:                 focalboardAPI,
 	}
@@ -314,6 +330,10 @@ func (s *Server) Shutdown() error {
 		s.logger.Warn("Error occurred when shutting down audit service", mlog.Err(err))
 	}
 
+	if err := s.notificationService.Shutdown(); err != nil {
+		s.logger.Warn("Error occurred when shutting down notification service", mlog.Err(err))
+	}
+
 	defer s.logger.Info("Server.Shutdown")
 
 	return s.store.Shutdown()
@@ -450,3 +470,12 @@ func initTelemetry(opts telemetryOptions) *telemetry.Service {
 	})
 	return telemetryService
 }
+
+func initNotificationService(backends []notify.Backend, logger *mlog.Logger) (*notify.Service, error) {
+	loggerBackend := notifylogger.New(logger, mlog.LvlDebug)
+
+	backends = append(backends, loggerBackend)
+
+	service, err := notify.New(logger, backends...)
+	return service, err
+}

server/services/notify/notifylogger/logger_backend.go

@@ -0,0 +1,59 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package notifylogger
+
+import (
+	"github.com/mattermost/focalboard/server/services/notify"
+
+	"github.com/mattermost/mattermost-server/v6/shared/mlog"
+)
+
+const (
+	backendName = "notifyLogger"
+)
+
+type Backend struct {
+	logger *mlog.Logger
+	level  mlog.Level
+}
+
+func New(logger *mlog.Logger, level mlog.Level) *Backend {
+	return &Backend{
+		logger: logger,
+		level:  level,
+	}
+}
+
+func (b *Backend) Start() error {
+	return nil
+}
+
+func (b *Backend) ShutDown() error {
+	_ = b.logger.Flush()
+	return nil
+}
+
+func (b *Backend) BlockChanged(evt notify.BlockChangeEvent) error {
+	var board string
+	var card string
+
+	if evt.Board != nil {
+		board = evt.Board.Title
+	}
+	if evt.Card != nil {
+		card = evt.Card.Title
+	}
+
+	b.logger.Log(b.level, "Block change event",
+		mlog.String("action", string(evt.Action)),
+		mlog.String("board", board),
+		mlog.String("card", card),
+		mlog.String("block_id", evt.BlockChanged.ID),
+	)
+	return nil
+}
+
+func (b *Backend) Name() string {
+	return backendName
+}

server/services/notify/notifymentions/delivery.go

@@ -0,0 +1,12 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package notifymentions
+
+import "github.com/mattermost/focalboard/server/services/notify"
+
+// Delivery provides an interface for delivering notifications to other systems, such as
+// MM server or email.
+type Delivery interface {
+	Deliver(mentionUsername string, extract string, evt notify.BlockChangeEvent) error
+}

server/services/notify/notifymentions/extract.go

@@ -0,0 +1,98 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package notifymentions
+
+import "strings"
+
+const (
+	defPrefixLines    = 2
+	defPrefixMaxChars = 100
+	defSuffixLines    = 2
+	defSuffixMaxChars = 100
+)
+
+type limits struct {
+	prefixLines    int
+	prefixMaxChars int
+	suffixLines    int
+	suffixMaxChars int
+}
+
+func newLimits() limits {
+	return limits{
+		prefixLines:    defPrefixLines,
+		prefixMaxChars: defPrefixMaxChars,
+		suffixLines:    defSuffixLines,
+		suffixMaxChars: defSuffixMaxChars,
+	}
+}
+
+// extractText returns all or a subset of the input string, such that
+// no more than `prefixLines` lines preceding the mention and `suffixLines`
+// lines after the mention are returned, and no more than approx
+// prefixMaxChars+suffixMaxChars are returned.
+func extractText(s string, mention string, limits limits) string {
+	if !strings.HasPrefix(mention, "@") {
+		mention = "@" + mention
+	}
+	lines := strings.Split(s, "\n")
+
+	// find first line with mention
+	found := -1
+	for i, l := range lines {
+		if strings.Contains(l, mention) {
+			found = i
+			break
+		}
+	}
+	if found == -1 {
+		return ""
+	}
+
+	prefix := safeConcat(lines, found-limits.prefixLines, found)
+	suffix := safeConcat(lines, found+1, found+limits.suffixLines+1)
+	combined := strings.TrimSpace(strings.Join([]string{prefix, lines[found], suffix}, "\n"))
+
+	// find mention position within
+	pos := strings.Index(combined, mention)
+	pos = max(pos, 0)
+
+	return safeSubstr(combined, pos-limits.prefixMaxChars, pos+limits.suffixMaxChars)
+}
+
+func safeConcat(lines []string, start int, end int) string {
+	count := len(lines)
+	start = min(max(start, 0), count)
+	end = min(max(end, start), count)
+
+	var sb strings.Builder
+	for i := start; i < end; i++ {
+		if lines[i] != "" {
+			sb.WriteString(lines[i])
+			sb.WriteByte('\n')
+		}
+	}
+	return strings.TrimSpace(sb.String())
+}
+
+func safeSubstr(s string, start int, end int) string {
+	count := len(s)
+	start = min(max(start, 0), count)
+	end = min(max(end, start), count)
+	return s[start:end]
+}
+
+func min(a int, b int) int {
+	if a < b {
+		return a
+	}
+	return b
+}
+
+func max(a int, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}

server/services/notify/notifymentions/extract_test.go

@@ -0,0 +1,115 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package notifymentions
+
+import (
+	"strings"
+	"testing"
+)
+
+const (
+	s0 = "Zero is in the mind @billy."
+	s1 = "This is line 1."
+	s2 = "Line two is right here."
+	s3 = "Three is the line I am."
+	s4 = "'Four score and seven years...', said @lincoln."
+	s5 = "Fast Five was arguably the best F&F film."
+	s6 = "Big Hero 6 may have an inflated sense of self."
+	s7 = "The seventh sign, @sarah, will be a failed unit test."
+)
+
+var (
+	all       = []string{s0, s1, s2, s3, s4, s5, s6, s7}
+	allConcat = strings.Join(all, "\n")
+
+	extractLimits = limits{
+		prefixLines:    2,
+		prefixMaxChars: 100,
+		suffixLines:    2,
+		suffixMaxChars: 100,
+	}
+)
+
+func join(s ...string) string {
+	return strings.Join(s, "\n")
+}
+
+func Test_extractText(t *testing.T) {
+	type args struct {
+		s       string
+		mention string
+		limits  limits
+	}
+	tests := []struct {
+		name string
+		args args
+		want string
+	}{
+		{name: "good", want: join(s2, s3, s4, s5, s6), args: args{mention: "@lincoln", limits: extractLimits, s: allConcat}},
+		{name: "not found", want: "", args: args{mention: "@bogus", limits: extractLimits, s: allConcat}},
+		{name: "one line", want: join(s4), args: args{mention: "@lincoln", limits: extractLimits, s: s4}},
+		{name: "two lines", want: join(s4, s5), args: args{mention: "@lincoln", limits: extractLimits, s: join(s4, s5)}},
+		{name: "zero lines", want: "", args: args{mention: "@lincoln", limits: extractLimits, s: ""}},
+		{name: "first line mention", want: join(s0, s1, s2), args: args{mention: "@billy", limits: extractLimits, s: allConcat}},
+		{name: "last line mention", want: join(s5[7:], s6, s7), args: args{mention: "@sarah", limits: extractLimits, s: allConcat}},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := extractText(tt.args.s, tt.args.mention, tt.args.limits); got != tt.want {
+				t.Errorf("extractText()\ngot:\n%v\nwant:\n%v\n", got, tt.want)
+			}
+		})
+	}
+}
+
+func Test_safeConcat(t *testing.T) {
+	type args struct {
+		lines []string
+		start int
+		end   int
+	}
+	tests := []struct {
+		name string
+		args args
+		want string
+	}{
+		{name: "out of range", want: join(s0, s1, s2, s3, s4, s5, s6, s7), args: args{start: -22, end: 99, lines: all}},
+		{name: "2,3", want: join(s2, s3), args: args{start: 2, end: 4, lines: all}},
+		{name: "mismatch", want: "", args: args{start: 4, end: 2, lines: all}},
+		{name: "empty", want: "", args: args{start: 2, end: 4, lines: []string{}}},
+		{name: "nil", want: "", args: args{start: 2, end: 4, lines: nil}},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := safeConcat(tt.args.lines, tt.args.start, tt.args.end); got != tt.want {
+				t.Errorf("safeConcat() = [%v], want [%v]", got, tt.want)
+			}
+		})
+	}
+}
+
+func Test_safeSubstr(t *testing.T) {
+	type args struct {
+		s     string
+		start int
+		end   int
+	}
+	tests := []struct {
+		name string
+		args args
+		want string
+	}{
+		{name: "good", want: "is line", args: args{start: 33, end: 40, s: join(s0, s1, s2)}},
+		{name: "out of range", want: allConcat, args: args{start: -10, end: 1000, s: allConcat}},
+		{name: "mismatch", want: "", args: args{start: 33, end: 26, s: allConcat}},
+		{name: "empty", want: "", args: args{start: 2, end: 4, s: ""}},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := safeSubstr(tt.args.s, tt.args.start, tt.args.end); got != tt.want {
+				t.Errorf("safeSubstr()\ngot:\n[%v]\nwant:\n[%v]\n", got, tt.want)
+			}
+		})
+	}
+}

server/services/notify/notifymentions/mentions.go

@@ -0,0 +1,34 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package notifymentions
+
+import (
+	"regexp"
+	"strings"
+
+	"github.com/mattermost/focalboard/server/model"
+
+	mm_model "github.com/mattermost/mattermost-server/v6/model"
+)
+
+var atMentionRegexp = regexp.MustCompile(`\B@[[:alnum:]][[:alnum:]\.\-_:]*`)
+
+// extractMentions extracts any mentions in the specified block and returns
+// a slice of usernames.
+func extractMentions(block *model.Block) map[string]struct{} {
+	mentions := make(map[string]struct{})
+	if block == nil || !strings.Contains(block.Title, "@") {
+		return mentions
+	}
+
+	str := block.Title
+
+	for _, match := range atMentionRegexp.FindAllString(str, -1) {
+		name := mm_model.NormalizeUsername(match[1:])
+		if mm_model.IsValidUsernameAllowRemote(name) {
+			mentions[name] = struct{}{}
+		}
+	}
+	return mentions
+}

server/services/notify/notifymentions/mentions_backend.go

@@ -0,0 +1,79 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package notifymentions
+
+import (
+	"fmt"
+
+	"github.com/mattermost/focalboard/server/services/notify"
+	"github.com/wiggin77/merror"
+
+	"github.com/mattermost/mattermost-server/v6/shared/mlog"
+)
+
+const (
+	backendName = "notifyMentions"
+)
+
+type Backend struct {
+	delivery Delivery
+	logger   *mlog.Logger
+}
+
+func New(delivery Delivery, logger *mlog.Logger) *Backend {
+	return &Backend{
+		delivery: delivery,
+		logger:   logger,
+	}
+}
+
+func (b *Backend) Start() error {
+	return nil
+}
+
+func (b *Backend) ShutDown() error {
+	_ = b.logger.Flush()
+	return nil
+}
+
+func (b *Backend) Name() string {
+	return backendName
+}
+
+func (b *Backend) BlockChanged(evt notify.BlockChangeEvent) error {
+	if evt.Board == nil || evt.Card == nil {
+		return nil
+	}
+
+	if evt.Action == notify.Delete {
+		return nil
+	}
+
+	if evt.BlockChanged.Type != "text" && evt.BlockChanged.Type != "comment" {
+		return nil
+	}
+
+	mentions := extractMentions(evt.BlockChanged)
+	if len(mentions) == 0 {
+		return nil
+	}
+
+	oldMentions := extractMentions(evt.BlockOld)
+	merr := merror.New()
+
+	for username := range mentions {
+		if _, exists := oldMentions[username]; exists {
+			// the mention already existed; no need to notify again
+			continue
+		}
+
+		extract := extractText(evt.BlockChanged.Title, username, newLimits())
+
+		err := b.delivery.Deliver(username, extract, evt)
+		if err != nil {
+			merr.Append(fmt.Errorf("cannot deliver notification for @%s: %w", username, err))
+		}
+	}
+	return merr.ErrorOrNil()
+}

server/services/notify/notifymentions/mentions_test.go

@@ -0,0 +1,52 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package notifymentions
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/mattermost/focalboard/server/model"
+
+	mm_model "github.com/mattermost/mattermost-server/v6/model"
+)
+
+func Test_extractMentions(t *testing.T) {
+	tests := []struct {
+		name  string
+		block *model.Block
+		want  map[string]struct{}
+	}{
+		{name: "empty", block: makeBlock(""), want: makeMap()},
+		{name: "zero mentions", block: makeBlock("This is some text."), want: makeMap()},
+		{name: "one mention", block: makeBlock("Hello @user1"), want: makeMap("user1")},
+		{name: "multiple mentions", block: makeBlock("Hello @user1, @user2 and @user3"), want: makeMap("user1", "user2", "user3")},
+		{name: "include period", block: makeBlock("Hello @user1."), want: makeMap("user1.")},
+		{name: "include underscore", block: makeBlock("Hello @user1_"), want: makeMap("user1_")},
+		{name: "don't include comma", block: makeBlock("Hello @user1,"), want: makeMap("user1")},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := extractMentions(tt.block); !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("extractMentions() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func makeBlock(text string) *model.Block {
+	return &model.Block{
+		ID:    mm_model.NewId(),
+		Type:  "comment",
+		Title: text,
+	}
+}
+
+func makeMap(mentions ...string) map[string]struct{} {
+	m := make(map[string]struct{})
+	for _, mention := range mentions {
+		m[mention] = struct{}{}
+	}
+	return m
+}

server/services/notify/plugindelivery/message.go

@@ -0,0 +1,28 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package plugindelivery
+
+import (
+	"fmt"
+
+	"github.com/mattermost/focalboard/server/model"
+)
+
+const (
+	// TODO: localize these when i18n is available.
+	defCommentTemplate     = "@%s mentioned you in a comment on the card [%s](%s)\n> %s"
+	defDescriptionTemplate = "@%s mentioned you in the card [%s](%s)\n> %s"
+)
+
+func formatMessage(author string, extract string, card string, link string, block *model.Block) string {
+	template := defDescriptionTemplate
+	if block.Type == "comment" {
+		template = defCommentTemplate
+	}
+	return fmt.Sprintf(template, author, card, link, extract)
+}
+
+func makeLink(serverRoot string, workspace string, board string, card string) string {
+	return fmt.Sprintf("%s/workspace/%s/%s/0/%s/", serverRoot, workspace, board, card)
+}

server/services/notify/plugindelivery/plugin_delivery.go

@@ -0,0 +1,72 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package plugindelivery
+
+import (
+	"fmt"
+
+	"github.com/mattermost/focalboard/server/services/notify"
+
+	"github.com/mattermost/mattermost-server/v6/model"
+)
+
+type PluginAPI interface {
+	// GetDirectChannel gets a direct message channel.
+	// If the channel does not exist it will create it.
+	GetDirectChannel(userID1, userID2 string) (*model.Channel, error)
+
+	// CreatePost creates a post.
+	CreatePost(post *model.Post) error
+
+	// GetUserByIS gets a user by their ID.
+	GetUserByID(userID string) (*model.User, error)
+
+	// GetUserByUsername gets a user by their username.
+	GetUserByUsername(name string) (*model.User, error)
+}
+
+// PluginDelivery provides ability to send notifications to direct message channels via Mattermost plugin API.
+type PluginDelivery struct {
+	botID      string
+	serverRoot string
+	api        PluginAPI
+}
+
+func New(botID string, serverRoot string, api PluginAPI) *PluginDelivery {
+	return &PluginDelivery{
+		botID:      botID,
+		serverRoot: serverRoot,
+		api:        api,
+	}
+}
+
+func (pd *PluginDelivery) Deliver(mentionUsername string, extract string, evt notify.BlockChangeEvent) error {
+	user, err := userFromUsername(pd.api, mentionUsername)
+	if err != nil {
+		if isErrNotFound(err) {
+			// not really an error; could just be someone typed "@sometext"
+			return nil
+		} else {
+			return fmt.Errorf("cannot lookup mentioned user: %w", err)
+		}
+	}
+
+	author, err := pd.api.GetUserByID(evt.UserID)
+	if err != nil {
+		return fmt.Errorf("cannot find user: %w", err)
+	}
+
+	channel, err := pd.api.GetDirectChannel(user.Id, pd.botID)
+	if err != nil {
+		return fmt.Errorf("cannot get direct channel: %w", err)
+	}
+	link := makeLink(pd.serverRoot, evt.Workspace, evt.Board.ID, evt.Card.ID)
+
+	post := &model.Post{
+		UserId:    pd.botID,
+		ChannelId: channel.Id,
+		Message:   formatMessage(author.Username, extract, evt.Card.Title, link, evt.BlockChanged),
+	}
+	return pd.api.CreatePost(post)
+}

server/services/notify/plugindelivery/user.go

@@ -0,0 +1,60 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package plugindelivery
+
+import (
+	"strings"
+
+	mm_model "github.com/mattermost/mattermost-server/v6/model"
+)
+
+const (
+	usernameSpecialChars = ".-_ "
+)
+
+func userFromUsername(api PluginAPI, username string) (*mm_model.User, error) {
+	user, err := api.GetUserByUsername(username)
+	if err == nil {
+		return user, nil
+	}
+
+	// only continue if the error is `ErrNotFound`
+	if !isErrNotFound(err) {
+		return nil, err
+	}
+
+	// check for usernames in substrings without trailing punctuation
+	trimmed, ok := trimUsernameSpecialChar(username)
+	for ; ok; trimmed, ok = trimUsernameSpecialChar(trimmed) {
+		userFromTrimmed, err2 := api.GetUserByUsername(trimmed)
+		if err2 != nil && !isErrNotFound(err2) {
+			return nil, err2
+		}
+
+		if err2 == nil {
+			return userFromTrimmed, nil
+		}
+	}
+	return nil, err
+}
+
+// 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
+}
+
+// isErrNotFound returns true if the error is a plugin.ErrNotFound. The pluginAPI converts
+// AppError to the plugin.ErrNotFound var.
+// TODO: add a `IsErrNotFound` method to the plugin API.
+func isErrNotFound(err error) bool {
+	return err != nil && err.Error() == "not found"
+}

server/services/notify/plugindelivery/user_test.go

@@ -0,0 +1,105 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package plugindelivery
+
+import (
+	"reflect"
+	"testing"
+
+	mm_model "github.com/mattermost/mattermost-server/v6/model"
+)
+
+var (
+	user1 = &mm_model.User{
+		Id:       mm_model.NewId(),
+		Username: "dlauder",
+	}
+	user2 = &mm_model.User{
+		Id:       mm_model.NewId(),
+		Username: "steve.mqueen",
+	}
+	user3 = &mm_model.User{
+		Id:       mm_model.NewId(),
+		Username: "bart_",
+	}
+	user4 = &mm_model.User{
+		Id:       mm_model.NewId(),
+		Username: "missing_",
+	}
+
+	mockUsers = map[string]*mm_model.User{
+		"dlauder":      user1,
+		"steve.mqueen": user2,
+		"bart_":        user3,
+	}
+)
+
+func Test_userFromUsername(t *testing.T) {
+	delivery := newPlugAPIMock(mockUsers)
+
+	tests := []struct {
+		name    string
+		uname   string
+		want    *mm_model.User
+		wantErr bool
+	}{
+		{name: "user1", uname: user1.Username, want: user1, wantErr: false},
+		{name: "user1 with period", uname: user1.Username + ".", want: user1, wantErr: false},
+		{name: "user1 with period plus more", uname: user1.Username + ". ", want: user1, wantErr: false},
+		{name: "user2 with periods", uname: user2.Username + "...", want: user2, wantErr: false},
+		{name: "user2 with underscore", uname: user2.Username + "_", want: user2, wantErr: false},
+		{name: "user2 with hyphen plus more", uname: user2.Username + "- ", want: user2, wantErr: false},
+		{name: "user2 with hyphen plus all", uname: user2.Username + ".-_ ", want: user2, wantErr: false},
+		{name: "user3 with underscore", uname: user3.Username + "_", want: user3, wantErr: false},
+		{name: "user4 missing", uname: user4.Username, want: nil, wantErr: true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := userFromUsername(delivery, tt.uname)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("userFromUsername() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("userFromUsername() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+type pluginAPIMock struct {
+	users map[string]*mm_model.User
+}
+
+func newPlugAPIMock(users map[string]*mm_model.User) pluginAPIMock {
+	return pluginAPIMock{
+		users: users,
+	}
+}
+
+func (m pluginAPIMock) GetUserByUsername(name string) (*mm_model.User, error) {
+	user, ok := m.users[name]
+	if !ok {
+		return nil, ErrNotFound{}
+	}
+	return user, nil
+}
+
+func (m pluginAPIMock) GetDirectChannel(userID1, userID2 string) (*mm_model.Channel, error) {
+	return nil, nil
+}
+
+func (m pluginAPIMock) CreatePost(post *mm_model.Post) error {
+	return nil
+}
+
+func (m pluginAPIMock) GetUserByID(userID string) (*mm_model.User, error) {
+	return nil, nil
+}
+
+type ErrNotFound struct{}
+
+func (e ErrNotFound) Error() string {
+	return "not found"
+}

server/services/notify/service.go

@@ -0,0 +1,108 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package notify
+
+import (
+	"sync"
+
+	"github.com/mattermost/focalboard/server/model"
+	"github.com/wiggin77/merror"
+
+	"github.com/mattermost/mattermost-server/v6/shared/mlog"
+)
+
+type Action string
+
+const (
+	Add    Action = "add"
+	Update Action = "update"
+	Delete Action = "delete"
+)
+
+type BlockChangeEvent struct {
+	Action       Action
+	Workspace    string
+	Board        *model.Block
+	Card         *model.Block
+	BlockChanged *model.Block
+	BlockOld     *model.Block
+	UserID       string
+}
+
+// Backend provides an interface for sending notifications.
+type Backend interface {
+	Start() error
+	ShutDown() error
+	BlockChanged(evt BlockChangeEvent) error
+	Name() string
+}
+
+// Service is a service that sends notifications based on block activity using one or more backends.
+type Service struct {
+	mux      sync.RWMutex
+	backends []Backend
+	logger   *mlog.Logger
+}
+
+// New creates a notification service with one or more Backends capable of sending notifications.
+func New(logger *mlog.Logger, backends ...Backend) (*Service, error) {
+	notify := &Service{
+		backends: make([]Backend, 0, len(backends)),
+		logger:   logger,
+	}
+
+	merr := merror.New()
+	for _, backend := range backends {
+		if err := notify.AddBackend(backend); err != nil {
+			merr.Append(err)
+		} else {
+			logger.Info("Initialized notification backend", mlog.String("name", backend.Name()))
+		}
+	}
+	return notify, merr.ErrorOrNil()
+}
+
+// AddBackend adds a backend to the list that will be informed of any block changes.
+func (s *Service) AddBackend(backend Backend) error {
+	if err := backend.Start(); err != nil {
+		return err
+	}
+	s.mux.Lock()
+	defer s.mux.Unlock()
+	s.backends = append(s.backends, backend)
+	return nil
+}
+
+// Shutdown calls shutdown for all backends.
+func (s *Service) Shutdown() error {
+	s.mux.Lock()
+	defer s.mux.Unlock()
+
+	merr := merror.New()
+	for _, backend := range s.backends {
+		if err := backend.ShutDown(); err != nil {
+			merr.Append(err)
+		}
+	}
+	s.backends = nil
+	return merr.ErrorOrNil()
+}
+
+// BlockChanged should be called whenever a block is added/updated/deleted.
+// All backends are informed of the event.
+func (s *Service) BlockChanged(evt BlockChangeEvent) {
+	s.mux.RLock()
+	defer s.mux.RUnlock()
+
+	for _, backend := range s.backends {
+		if err := backend.BlockChanged(evt); err != nil {
+			s.logger.Error("Error delivering notification",
+				mlog.String("backend", backend.Name()),
+				mlog.String("action", string(evt.Action)),
+				mlog.String("block_id", evt.BlockChanged.ID),
+				mlog.Err(err),
+			)
+		}
+	}
+}