Subscriptions and notifications for namespaces, tasks and lists (#786)

Co-authored-by: kolaente <k@knt.li>
Reviewed-on: https://kolaente.dev/vikunja/api/pulls/786
Co-authored-by: konrad <konrad@kola-entertainments.de>
Co-committed-by: konrad <konrad@kola-entertainments.de>

docs/content/doc/usage/errors.md

@@ -1,11 +1,10 @@
 ---
 date: "2019-02-12:00:00+02:00"
 title: "Errors"
-draft: false
+draft: false type: "doc"
-type: "doc"
 menu:
-  sidebar:
+sidebar:
-    parent: "usage"
+parent: "usage"
 ---
 
 # Errors
@@ -142,3 +141,10 @@ This document describes the different errors Vikunja can return.
 |-----------|------------------|-------------|
 | 11001 | 404 | The saved filter does not exist. |
 | 11002 | 412 | Saved filters are not available for link shares. | 
+
+## Subscriptions
+
+| ErrorCode | HTTP Status Code | Description |
+|-----------|------------------|-------------|
+| 12001 | 412 | The subscription entity type is invalid. |
+| 12002 | 412 | The user is already subscribed to the entity itself or a parent entity. |

magefile.go

@@ -827,7 +827,7 @@ func (s *` + name + `) Name() string {
 	return "` + listenerName + `"
 }
 
-// Hanlde is executed when the event ` + name + ` listens on is fired
+// Handle is executed when the event ` + name + ` listens on is fired
 func (s *` + name + `) Handle(payload message.Payload) (err error) {
 	event := &` + event + `{}
 	err = json.Unmarshal(payload, event)

pkg/db/fixtures/subscriptions.yml

@@ -0,0 +1,35 @@
+- id: 1
+  entity_type: 3 # Task
+  entity_id: 2
+  user_id: 1
+  created: 2021-02-01 15:13:12
+- id: 2
+  entity_type: 1 # Namespace
+  entity_id: 6
+  user_id: 6
+  created: 2021-02-01 15:13:12
+- id: 3
+  entity_type: 2 # List
+  entity_id: 12 # belongs to namespace 7
+  user_id: 6
+  created: 2021-02-01 15:13:12
+- id: 4
+  entity_type: 3 # Task
+  entity_id: 22 # belongs to list 13 which belongs to namespace 8
+  user_id: 6
+  created: 2021-02-01 15:13:12
+- id: 5
+  entity_type: 1 # Namespace
+  entity_id: 8
+  user_id: 6
+  created: 2021-02-01 15:13:12
+- id: 6
+  entity_type: 2 # List
+  entity_id: 13
+  user_id: 6
+  created: 2021-02-01 15:13:12
+- id: 7
+  entity_type: 3 # Task
+  entity_id: 26
+  user_id: 6
+  created: 2021-02-01 15:13:12

pkg/migration/20210209204715.go

@@ -0,0 +1,49 @@
+// Vikunja is a to-do list application to facilitate your life.
+// Copyright 2018-2021 Vikunja and contributors. All rights reserved.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public Licensee 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 Licensee for more details.
+//
+// You should have received a copy of the GNU Affero General Public Licensee
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package migration
+
+import (
+	"time"
+
+	"src.techknowlogick.com/xormigrate"
+	"xorm.io/xorm"
+)
+
+type subscriptions20210209204715 struct {
+	ID         int64     `xorm:"autoincr not null unique pk" json:"id"`
+	EntityType int       `xorm:"index not null" json:"-"`
+	EntityID   int64     `xorm:"bigint index not null" json:"entity_id"`
+	UserID     int64     `xorm:"bigint index not null" json:"-"`
+	Created    time.Time `xorm:"created not null" json:"created"`
+}
+
+func (subscriptions20210209204715) TableName() string {
+	return "subscriptions"
+}
+
+func init() {
+	migrations = append(migrations, &xormigrate.Migration{
+		ID:          "20210209204715",
+		Description: "",
+		Migrate: func(tx *xorm.Engine) error {
+			return tx.Sync2(subscriptions20210209204715{})
+		},
+		Rollback: func(tx *xorm.Engine) error {
+			return nil
+		},
+	})
+}

pkg/models/error.go

@@ -1423,3 +1423,63 @@ func (err ErrSavedFilterNotAvailableForLinkShare) HTTPError() web.HTTPError {
 		Message:  "Saved filters are not available for link shares.",
 	}
 }
+
+// =============
+// Subscriptions
+// =============
+
+// ErrUnknownSubscriptionEntityType represents an error where a subscription entity type is unknown
+type ErrUnknownSubscriptionEntityType struct {
+	EntityType SubscriptionEntityType
+}
+
+// IsErrUnknownSubscriptionEntityType checks if an error is ErrUnknownSubscriptionEntityType.
+func IsErrUnknownSubscriptionEntityType(err error) bool {
+	_, ok := err.(*ErrUnknownSubscriptionEntityType)
+	return ok
+}
+
+func (err *ErrUnknownSubscriptionEntityType) Error() string {
+	return fmt.Sprintf("Subscription entity type is unkowns [EntityType: %d]", err.EntityType)
+}
+
+// ErrCodeUnknownSubscriptionEntityType holds the unique world-error code of this error
+const ErrCodeUnknownSubscriptionEntityType = 12001
+
+// HTTPError holds the http error description
+func (err ErrUnknownSubscriptionEntityType) HTTPError() web.HTTPError {
+	return web.HTTPError{
+		HTTPCode: http.StatusPreconditionFailed,
+		Code:     ErrCodeUnknownSubscriptionEntityType,
+		Message:  "The subscription entity type is invalid.",
+	}
+}
+
+// ErrSubscriptionAlreadyExists represents an error where a subscription entity already exists
+type ErrSubscriptionAlreadyExists struct {
+	EntityID   int64
+	EntityType SubscriptionEntityType
+	UserID     int64
+}
+
+// IsErrSubscriptionAlreadyExists checks if an error is ErrSubscriptionAlreadyExists.
+func IsErrSubscriptionAlreadyExists(err error) bool {
+	_, ok := err.(*ErrSubscriptionAlreadyExists)
+	return ok
+}
+
+func (err *ErrSubscriptionAlreadyExists) Error() string {
+	return fmt.Sprintf("Subscription for this (entity_id, entity_type, user_id) already exists [EntityType: %d, EntityID: %d, UserID: %d]", err.EntityType, err.EntityID, err.UserID)
+}
+
+// ErrCodeSubscriptionAlreadyExists holds the unique world-error code of this error
+const ErrCodeSubscriptionAlreadyExists = 12002
+
+// HTTPError holds the http error description
+func (err ErrSubscriptionAlreadyExists) HTTPError() web.HTTPError {
+	return web.HTTPError{
+		HTTPCode: http.StatusPreconditionFailed,
+		Code:     ErrCodeSubscriptionAlreadyExists,
+		Message:  "You're already subscribed.",
+	}
+}

pkg/models/events.go

@@ -28,7 +28,7 @@ import (
 // TaskCreatedEvent represents an event where a task has been created
 type TaskCreatedEvent struct {
 	Task *Task
-	Doer web.Auth
+	Doer *user.User
 }
 
 // Name defines the name for TaskCreatedEvent
@@ -39,7 +39,7 @@ func (t *TaskCreatedEvent) Name() string {
 // TaskUpdatedEvent represents an event where a task has been updated
 type TaskUpdatedEvent struct {
 	Task *Task
-	Doer web.Auth
+	Doer *user.User
 }
 
 // Name defines the name for TaskUpdatedEvent
@@ -50,7 +50,7 @@ func (t *TaskUpdatedEvent) Name() string {
 // TaskDeletedEvent represents a TaskDeletedEvent event
 type TaskDeletedEvent struct {
 	Task *Task
-	Doer web.Auth
+	Doer *user.User
 }
 
 // Name defines the name for TaskDeletedEvent
@@ -62,7 +62,7 @@ func (t *TaskDeletedEvent) Name() string {
 type TaskAssigneeCreatedEvent struct {
 	Task     *Task
 	Assignee *user.User
-	Doer     web.Auth
+	Doer     *user.User
 }
 
 // Name defines the name for TaskAssigneeCreatedEvent
@@ -74,7 +74,7 @@ func (t *TaskAssigneeCreatedEvent) Name() string {
 type TaskCommentCreatedEvent struct {
 	Task    *Task
 	Comment *TaskComment
-	Doer    web.Auth
+	Doer    *user.User
 }
 
 // Name defines the name for TaskCommentCreatedEvent
@@ -126,7 +126,7 @@ func (t *NamespaceDeletedEvent) Name() string {
 // ListCreatedEvent represents an event where a list has been created
 type ListCreatedEvent struct {
 	List *List
-	Doer web.Auth
+	Doer *user.User
 }
 
 // Name defines the name for ListCreatedEvent

pkg/models/list.go

@@ -68,6 +68,10 @@ type List struct {
 	// True if a list is a favorite. Favorite lists show up in a separate namespace.
 	IsFavorite bool `xorm:"default false" json:"is_favorite"`
 
+	// The subscription status for the user reading this list. You can only read this property, use the subscription endpoints to modify it.
+	// Will only returned when retreiving one list.
+	Subscription *Subscription `xorm:"-" json:"subscription,omitempty"`
+
 	// A timestamp when this list was created. You cannot change this value.
 	Created time.Time `xorm:"created not null" json:"created"`
 	// A timestamp when this list was last updated. You cannot change this value.
@@ -236,7 +240,8 @@ func (l *List) ReadOne(s *xorm.Session, a web.Auth) (err error) {
 		}
 	}
 
-	return nil
+	l.Subscription, err = GetSubscription(s, SubscriptionEntityList, l.ID, a)
+	return
 }
 
 // GetListSimpleByID gets a list with only the basic items, aka no tasks or user objects. Returns an error if the list does not exist.
@@ -622,7 +627,7 @@ func (l *List) Create(s *xorm.Session, a web.Auth) (err error) {
 
 	return events.Dispatch(&ListCreatedEvent{
 		List: l,
-		Doer: a,
+		Doer: doer,
 	})
 }
 

pkg/models/list_test.go

@@ -215,3 +215,34 @@ func TestList_ReadAll(t *testing.T) {
 		_ = s.Close()
 	})
 }
+
+func TestList_ReadOne(t *testing.T) {
+	t.Run("normal", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		u := &user.User{ID: 1}
+		l := &List{ID: 1}
+		can, _, err := l.CanRead(s, u)
+		assert.NoError(t, err)
+		assert.True(t, can)
+		err = l.ReadOne(s, u)
+		assert.NoError(t, err)
+		assert.Equal(t, "Test1", l.Title)
+	})
+	t.Run("with subscription", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		u := &user.User{ID: 6}
+		l := &List{ID: 12}
+		can, _, err := l.CanRead(s, u)
+		assert.NoError(t, err)
+		assert.True(t, can)
+		err = l.ReadOne(s, u)
+		assert.NoError(t, err)
+		assert.NotNil(t, l.Subscription)
+	})
+}

pkg/models/listeners.go

@@ -17,9 +17,14 @@
 package models
 
 import (
+	"encoding/json"
+
+	"code.vikunja.io/api/pkg/db"
 	"code.vikunja.io/api/pkg/events"
+	"code.vikunja.io/api/pkg/log"
 	"code.vikunja.io/api/pkg/metrics"
 	"code.vikunja.io/api/pkg/modules/keyvalue"
+	"code.vikunja.io/api/pkg/notifications"
 	"github.com/ThreeDotsLabs/watermill/message"
 )
 
@@ -33,6 +38,10 @@ func RegisterListeners() {
 	events.RegisterListener((&TaskDeletedEvent{}).Name(), &DecreaseTaskCounter{})
 	events.RegisterListener((&TeamDeletedEvent{}).Name(), &DecreaseTeamCounter{})
 	events.RegisterListener((&TeamCreatedEvent{}).Name(), &IncreaseTeamCounter{})
+	events.RegisterListener((&TaskCommentCreatedEvent{}).Name(), &SendTaskCommentNotification{})
+	events.RegisterListener((&TaskAssigneeCreatedEvent{}).Name(), &SendTaskAssignedNotification{})
+	events.RegisterListener((&TaskDeletedEvent{}).Name(), &SendTaskDeletedNotification{})
+	events.RegisterListener((&ListCreatedEvent{}).Name(), &SendListCreatedNotification{})
 }
 
 //////
@@ -66,6 +75,143 @@ func (s *DecreaseTaskCounter) Handle(payload message.Payload) (err error) {
 	return keyvalue.DecrBy(metrics.TaskCountKey, 1)
 }
 
+// SendTaskCommentNotification  represents a listener
+type SendTaskCommentNotification struct {
+}
+
+// Name defines the name for the SendTaskCommentNotification listener
+func (s *SendTaskCommentNotification) Name() string {
+	return "send.task.comment.notification"
+}
+
+// Handle is executed when the event SendTaskCommentNotification listens on is fired
+func (s *SendTaskCommentNotification) Handle(payload message.Payload) (err error) {
+	event := &TaskCommentCreatedEvent{}
+	err = json.Unmarshal(payload, event)
+	if err != nil {
+		return err
+	}
+
+	sess := db.NewSession()
+	defer sess.Close()
+
+	subscribers, err := getSubscribersForEntity(sess, SubscriptionEntityTask, event.Task.ID)
+	if err != nil {
+		return err
+	}
+
+	log.Debugf("Sending task comment notifications to %d subscribers for task %d", len(subscribers), event.Task.ID)
+
+	for _, subscriber := range subscribers {
+		if subscriber.UserID == event.Doer.ID {
+			continue
+		}
+
+		n := &TaskCommentNotification{
+			Doer:    event.Doer,
+			Task:    event.Task,
+			Comment: event.Comment,
+		}
+		err = notifications.Notify(subscriber.User, n)
+		if err != nil {
+			return
+		}
+	}
+
+	return
+}
+
+// SendTaskAssignedNotification  represents a listener
+type SendTaskAssignedNotification struct {
+}
+
+// Name defines the name for the SendTaskAssignedNotification listener
+func (s *SendTaskAssignedNotification) Name() string {
+	return "send.task.assigned.notification"
+}
+
+// Handle is executed when the event SendTaskAssignedNotification listens on is fired
+func (s *SendTaskAssignedNotification) Handle(payload message.Payload) (err error) {
+	event := &TaskAssigneeCreatedEvent{}
+	err = json.Unmarshal(payload, event)
+	if err != nil {
+		return err
+	}
+
+	sess := db.NewSession()
+	defer sess.Close()
+
+	subscribers, err := getSubscribersForEntity(sess, SubscriptionEntityTask, event.Task.ID)
+	if err != nil {
+		return err
+	}
+
+	log.Debugf("Sending task assigned notifications to %d subscribers for task %d", len(subscribers), event.Task.ID)
+
+	for _, subscriber := range subscribers {
+		if subscriber.UserID == event.Doer.ID {
+			continue
+		}
+
+		n := &TaskAssignedNotification{
+			Doer:     event.Doer,
+			Task:     event.Task,
+			Assignee: event.Assignee,
+		}
+		err = notifications.Notify(subscriber.User, n)
+		if err != nil {
+			return
+		}
+	}
+
+	return nil
+}
+
+// SendTaskDeletedNotification  represents a listener
+type SendTaskDeletedNotification struct {
+}
+
+// Name defines the name for the SendTaskDeletedNotification listener
+func (s *SendTaskDeletedNotification) Name() string {
+	return "send.task.deleted.notification"
+}
+
+// Handle is executed when the event SendTaskDeletedNotification listens on is fired
+func (s *SendTaskDeletedNotification) Handle(payload message.Payload) (err error) {
+	event := &TaskDeletedEvent{}
+	err = json.Unmarshal(payload, event)
+	if err != nil {
+		return err
+	}
+
+	sess := db.NewSession()
+	defer sess.Close()
+
+	subscribers, err := getSubscribersForEntity(sess, SubscriptionEntityTask, event.Task.ID)
+	if err != nil {
+		return err
+	}
+
+	log.Debugf("Sending task deleted notifications to %d subscribers for task %d", len(subscribers), event.Task.ID)
+
+	for _, subscriber := range subscribers {
+		if subscriber.UserID == event.Doer.ID {
+			continue
+		}
+
+		n := &TaskDeletedNotification{
+			Doer: event.Doer,
+			Task: event.Task,
+		}
+		err = notifications.Notify(subscriber.User, n)
+		if err != nil {
+			return
+		}
+	}
+
+	return nil
+}
+
 ///////
 // List Event Listeners
 
@@ -91,6 +237,51 @@ func (s *DecreaseListCounter) Handle(payload message.Payload) (err error) {
 	return keyvalue.DecrBy(metrics.ListCountKey, 1)
 }
 
+// SendListCreatedNotification  represents a listener
+type SendListCreatedNotification struct {
+}
+
+// Name defines the name for the SendListCreatedNotification listener
+func (s *SendListCreatedNotification) Name() string {
+	return "send.list.created.notification"
+}
+
+// Handle is executed when the event SendListCreatedNotification listens on is fired
+func (s *SendListCreatedNotification) Handle(payload message.Payload) (err error) {
+	event := &ListCreatedEvent{}
+	err = json.Unmarshal(payload, event)
+	if err != nil {
+		return err
+	}
+
+	sess := db.NewSession()
+	defer sess.Close()
+
+	subscribers, err := getSubscribersForEntity(sess, SubscriptionEntityList, event.List.ID)
+	if err != nil {
+		return err
+	}
+
+	log.Debugf("Sending list created notifications to %d subscribers for list %d", len(subscribers), event.List.ID)
+
+	for _, subscriber := range subscribers {
+		if subscriber.UserID == event.Doer.ID {
+			continue
+		}
+
+		n := &ListCreatedNotification{
+			Doer: event.Doer,
+			List: event.List,
+		}
+		err = notifications.Notify(subscriber.User, n)
+		if err != nil {
+			return
+		}
+	}
+
+	return nil
+}
+
 //////
 // Namespace events
 

pkg/models/models.go

@@ -59,6 +59,7 @@ func GetTables() []interface{} {
 		&Bucket{},
 		&UnsplashPhoto{},
 		&SavedFilter{},
+		&Subscription{},
 	}
 }
 

pkg/models/namespace.go

@@ -50,6 +50,10 @@ type Namespace struct {
 	// The user who owns this namespace
 	Owner *user.User `xorm:"-" json:"owner" valid:"-"`
 
+	// The subscription status for the user reading this namespace. You can only read this property, use the subscription endpoints to modify it.
+	// Will only returned when retreiving one namespace.
+	Subscription *Subscription `xorm:"-" json:"subscription,omitempty"`
+
 	// A timestamp when this namespace was created. You cannot change this value.
 	Created time.Time `xorm:"created not null" json:"created"`
 	// A timestamp when this namespace was last updated. You cannot change this value.
@@ -166,6 +170,8 @@ func (n *Namespace) ReadOne(s *xorm.Session, a web.Auth) (err error) {
 		return err
 	}
 	*n = *nn
+
+	n.Subscription, err = GetSubscription(s, SubscriptionEntityNamespace, n.ID, a)
 	return
 }
 
@@ -175,10 +181,11 @@ type NamespaceWithLists struct {
 	Lists     []*List `xorm:"-" json:"lists"`
 }
 
-func makeNamespaceSliceFromMap(namespaces map[int64]*NamespaceWithLists, userMap map[int64]*user.User) []*NamespaceWithLists {
+func makeNamespaceSliceFromMap(namespaces map[int64]*NamespaceWithLists, userMap map[int64]*user.User, subscriptions map[int64]*Subscription) []*NamespaceWithLists {
 	all := make([]*NamespaceWithLists, 0, len(namespaces))
 	for _, n := range namespaces {
 		n.Owner = userMap[n.OwnerID]
+		n.Subscription = subscriptions[n.ID]
 		all = append(all, n)
 	}
 	sort.Slice(all, func(i, j int) bool {
@@ -289,6 +296,21 @@ func (n *Namespace) ReadAll(s *xorm.Session, a web.Auth, search string, page int
 		userIDs = append(userIDs, nsp.OwnerID)
 	}
 
+	// Get all subscriptions
+	subscriptions := []*Subscription{}
+	err = s.
+		Where("entity_type = ? AND user_id = ?", SubscriptionEntityNamespace, a.GetID()).
+		In("entity_id", namespaceids).
+		Find(&subscriptions)
+	if err != nil {
+		return nil, 0, 0, err
+	}
+	subscriptionsMap := make(map[int64]*Subscription)
+	for _, sub := range subscriptions {
+		sub.Entity = sub.EntityType.String()
+		subscriptionsMap[sub.EntityID] = sub
+	}
+
 	// Get all owners
 	userMap := make(map[int64]*user.User)
 	err = s.In("id", userIDs).Find(&userMap)
@@ -297,7 +319,7 @@ func (n *Namespace) ReadAll(s *xorm.Session, a web.Auth, search string, page int
 	}
 
 	if n.NamespacesOnly {
-		all := makeNamespaceSliceFromMap(namespaces, userMap)
+		all := makeNamespaceSliceFromMap(namespaces, userMap, subscriptionsMap)
 		return all, len(all), numberOfTotalItems, nil
 	}
 
@@ -443,7 +465,7 @@ func (n *Namespace) ReadAll(s *xorm.Session, a web.Auth, search string, page int
 
 	//////////////////////
 	// Put it all together (and sort it)
-	all := makeNamespaceSliceFromMap(namespaces, userMap)
+	all := makeNamespaceSliceFromMap(namespaces, userMap, subscriptionsMap)
 	return all, len(all), numberOfTotalItems, nil
 }
 

pkg/models/namespace_test.go

@@ -75,19 +75,31 @@ func TestNamespace_ReadOne(t *testing.T) {
 		n := &Namespace{ID: 1}
 		db.LoadAndAssertFixtures(t)
 		s := db.NewSession()
+		defer s.Close()
+
 		err := n.ReadOne(s, u)
 		assert.NoError(t, err)
 		assert.Equal(t, n.Title, "testnamespace")
-		_ = s.Close()
 	})
 	t.Run("nonexistant", func(t *testing.T) {
 		n := &Namespace{ID: 99999}
 		db.LoadAndAssertFixtures(t)
 		s := db.NewSession()
+		defer s.Close()
+
 		err := n.ReadOne(s, u)
 		assert.Error(t, err)
 		assert.True(t, IsErrNamespaceDoesNotExist(err))
-		_ = s.Close()
+	})
+	t.Run("with subscription", func(t *testing.T) {
+		n := &Namespace{ID: 8}
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		err := n.ReadOne(s, &user.User{ID: 6})
+		assert.NoError(t, err)
+		assert.NotNil(t, n.Subscription)
 	})
 }
 

pkg/models/notifications.go

@@ -17,7 +17,9 @@
 package models
 
 import (
+	"bufio"
 	"strconv"
+	"strings"
 
 	"code.vikunja.io/api/pkg/config"
 	"code.vikunja.io/api/pkg/notifications"
@@ -45,3 +47,88 @@ func (n *ReminderDueNotification) ToMail() *notifications.Mail {
 func (n *ReminderDueNotification) ToDB() interface{} {
 	return nil
 }
+
+// TaskCommentNotification represents a TaskCommentNotification notification
+type TaskCommentNotification struct {
+	Doer    *user.User
+	Task    *Task
+	Comment *TaskComment
+}
+
+// ToMail returns the mail notification for TaskCommentNotification
+func (n *TaskCommentNotification) ToMail() *notifications.Mail {
+
+	mail := notifications.NewMail().
+		From(n.Doer.GetName() + " via Vikunja <" + config.MailerFromEmail.GetString() + ">").
+		Subject("Re: " + n.Task.Title)
+
+	lines := bufio.NewScanner(strings.NewReader(n.Comment.Comment))
+	for lines.Scan() {
+		mail.Line(lines.Text())
+	}
+
+	return mail.
+		Action("View Task", n.Task.GetFrontendURL())
+}
+
+// ToDB returns the TaskCommentNotification notification in a format which can be saved in the db
+func (n *TaskCommentNotification) ToDB() interface{} {
+	return n
+}
+
+// TaskAssignedNotification represents a TaskAssignedNotification notification
+type TaskAssignedNotification struct {
+	Doer     *user.User
+	Task     *Task
+	Assignee *user.User
+}
+
+// ToMail returns the mail notification for TaskAssignedNotification
+func (n *TaskAssignedNotification) ToMail() *notifications.Mail {
+	return notifications.NewMail().
+		Subject(n.Task.Title+"("+n.Task.GetFullIdentifier()+")"+" has been assigned to "+n.Assignee.GetName()).
+		Line(n.Doer.GetName()+" has assigned this task to "+n.Assignee.GetName()).
+		Action("View Task", n.Task.GetFrontendURL())
+}
+
+// ToDB returns the TaskAssignedNotification notification in a format which can be saved in the db
+func (n *TaskAssignedNotification) ToDB() interface{} {
+	return n
+}
+
+// TaskDeletedNotification represents a TaskDeletedNotification notification
+type TaskDeletedNotification struct {
+	Doer *user.User
+	Task *Task
+}
+
+// ToMail returns the mail notification for TaskDeletedNotification
+func (n *TaskDeletedNotification) ToMail() *notifications.Mail {
+	return notifications.NewMail().
+		Subject(n.Task.Title + "(" + n.Task.GetFullIdentifier() + ")" + " has been delete").
+		Line(n.Doer.GetName() + " has deleted the task " + n.Task.Title + "(" + n.Task.GetFullIdentifier() + ")")
+}
+
+// ToDB returns the TaskDeletedNotification notification in a format which can be saved in the db
+func (n *TaskDeletedNotification) ToDB() interface{} {
+	return n
+}
+
+// ListCreatedNotification represents a ListCreatedNotification notification
+type ListCreatedNotification struct {
+	Doer *user.User
+	List *List
+}
+
+// ToMail returns the mail notification for ListCreatedNotification
+func (n *ListCreatedNotification) ToMail() *notifications.Mail {
+	return notifications.NewMail().
+		Subject(n.Doer.GetName()+` created the list "`+n.List.Title+`"`).
+		Line(n.Doer.GetName()+` created the list "`+n.List.Title+`"`).
+		Action("View List", config.ServiceFrontendurl.GetString()+"lists/")
+}
+
+// ToDB returns the ListCreatedNotification notification in a format which can be saved in the db
+func (n *ListCreatedNotification) ToDB() interface{} {
+	return nil
+}

pkg/models/subscription.go

@@ -0,0 +1,282 @@
+// Vikunja is a to-do list application to facilitate your life.
+// Copyright 2018-2021 Vikunja and contributors. All rights reserved.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public Licensee 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 Licensee for more details.
+//
+// You should have received a copy of the GNU Affero General Public Licensee
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package models
+
+import (
+	"time"
+
+	"xorm.io/builder"
+
+	"code.vikunja.io/api/pkg/user"
+	"code.vikunja.io/web"
+	"xorm.io/xorm"
+)
+
+// SubscriptionEntityType represents all entities which can be subscribed to
+type SubscriptionEntityType int
+
+const (
+	SubscriptionEntityUnknown = iota
+	SubscriptionEntityNamespace
+	SubscriptionEntityList
+	SubscriptionEntityTask
+)
+
+const (
+	entityNamespace = `namespace`
+	entityList      = `list`
+	entityTask      = `task`
+)
+
+// Subscription represents a subscription for an entity
+type Subscription struct {
+	// The numeric ID of the subscription
+	ID int64 `xorm:"autoincr not null unique pk" json:"id"`
+
+	EntityType SubscriptionEntityType `xorm:"index not null" json:"-"`
+	Entity     string                 `xorm:"-" json:"entity" param:"entity"`
+	// The id of the entity to subscribe to.
+	EntityID int64 `xorm:"bigint index not null" json:"entity_id" param:"entityID"`
+
+	// The user who made this subscription
+	User   *user.User `xorm:"-" json:"user"`
+	UserID int64      `xorm:"bigint index not null" json:"-"`
+
+	// A timestamp when this subscription was created. You cannot change this value.
+	Created time.Time `xorm:"created not null" json:"created"`
+
+	web.CRUDable `xorm:"-" json:"-"`
+	web.Rights   `xorm:"-" json:"-"`
+}
+
+// TableName gives us a better tabel name for the subscriptions table
+func (sb *Subscription) TableName() string {
+	return "subscriptions"
+}
+
+func getEntityTypeFromString(entityType string) SubscriptionEntityType {
+	switch entityType {
+	case entityNamespace:
+		return SubscriptionEntityNamespace
+	case entityList:
+		return SubscriptionEntityList
+	case entityTask:
+		return SubscriptionEntityTask
+	}
+
+	return SubscriptionEntityUnknown
+}
+
+// String returns a human-readable string of an entity
+func (et SubscriptionEntityType) String() string {
+	switch et {
+	case SubscriptionEntityNamespace:
+		return entityNamespace
+	case SubscriptionEntityList:
+		return entityList
+	case SubscriptionEntityTask:
+		return entityTask
+	}
+
+	return ""
+}
+
+func (et SubscriptionEntityType) validate() error {
+	if et == SubscriptionEntityNamespace ||
+		et == SubscriptionEntityList ||
+		et == SubscriptionEntityTask {
+		return nil
+	}
+
+	return &ErrUnknownSubscriptionEntityType{EntityType: et}
+}
+
+// Create subscribes the current user to an entity
+// @Summary Subscribes the current user to an entity.
+// @Description Subscribes the current user to an entity.
+// @tags subscriptions
+// @Accept json
+// @Produce json
+// @Security JWTKeyAuth
+// @Param entity path string true "The entity the user subscribes to. Can be either `namespace`, `list` or `task`."
+// @Param entityID path string true "The numeric id of the entity to subscribe to."
+// @Success 200 {object} models.Subscription "The subscription"
+// @Failure 403 {object} web.HTTPError "The user does not have access to subscribe to this entity."
+// @Failure 412 {object} web.HTTPError "The subscription already exists."
+// @Failure 412 {object} web.HTTPError "The subscription entity is invalid."
+// @Failure 500 {object} models.Message "Internal error"
+// @Router /subscriptions/{entity}/{entityID} [put]
+func (sb *Subscription) Create(s *xorm.Session, auth web.Auth) (err error) {
+	// Rights method alread does the validation of the entity type so we don't need to do that here
+
+	sb.UserID = auth.GetID()
+
+	sub, err := GetSubscription(s, sb.EntityType, sb.EntityID, auth)
+	if err != nil {
+		return err
+	}
+	if sub != nil {
+		return &ErrSubscriptionAlreadyExists{
+			EntityID:   sb.EntityID,
+			EntityType: sb.EntityType,
+			UserID:     sb.UserID,
+		}
+	}
+
+	_, err = s.Insert(sb)
+	if err != nil {
+		return
+	}
+
+	sb.User, err = user.GetFromAuth(auth)
+	return
+}
+
+// Delete unsubscribes the current user to an entity
+// @Summary Unsubscribe the current user from an entity.
+// @Description Unsubscribes the current user to an entity.
+// @tags subscriptions
+// @Accept json
+// @Produce json
+// @Security JWTKeyAuth
+// @Param entity path string true "The entity the user subscribed to. Can be either `namespace`, `list` or `task`."
+// @Param entityID path string true "The numeric id of the subscribed entity to."
+// @Success 200 {object} models.Subscription "The subscription"
+// @Failure 403 {object} web.HTTPError "The user does not have access to subscribe to this entity."
+// @Failure 404 {object} web.HTTPError "The subscription does not exist."
+// @Failure 500 {object} models.Message "Internal error"
+// @Router /subscriptions/{entity}/{entityID} [delete]
+func (sb *Subscription) Delete(s *xorm.Session, auth web.Auth) (err error) {
+	sb.UserID = auth.GetID()
+
+	_, err = s.
+		Where("entity_id = ? AND entity_type = ? AND user_id = ?", sb.EntityID, sb.EntityType, sb.UserID).
+		Delete(&Subscription{})
+	return
+}
+
+func getSubscriberCondForEntity(entityType SubscriptionEntityType, entityID int64) (cond builder.Cond) {
+	if entityType == SubscriptionEntityNamespace {
+		cond = builder.And(
+			builder.Eq{"entity_id": entityID},
+			builder.Eq{"entity_type": SubscriptionEntityNamespace},
+		)
+	}
+
+	if entityType == SubscriptionEntityList {
+		cond = builder.Or(
+			builder.And(
+				builder.Eq{"entity_id": entityID},
+				builder.Eq{"entity_type": SubscriptionEntityList},
+			),
+			builder.And(
+				builder.Eq{"entity_id": builder.
+					Select("namespace_id").
+					From("list").
+					Where(builder.Eq{"id": entityID}),
+				},
+				builder.Eq{"entity_type": SubscriptionEntityNamespace},
+			),
+		)
+	}
+
+	if entityType == SubscriptionEntityTask {
+		cond = builder.Or(
+			builder.And(
+				builder.Eq{"entity_id": entityID},
+				builder.Eq{"entity_type": SubscriptionEntityTask},
+			),
+			builder.And(
+				builder.Eq{"entity_id": builder.
+					Select("namespace_id").
+					From("list").
+					Join("INNER", "tasks", "list.id = tasks.list_id").
+					Where(builder.Eq{"tasks.id": entityID}),
+				},
+				builder.Eq{"entity_type": SubscriptionEntityNamespace},
+			),
+			builder.And(
+				builder.Eq{"entity_id": builder.
+					Select("list_id").
+					From("tasks").
+					Where(builder.Eq{"id": entityID}),
+				},
+				builder.Eq{"entity_type": SubscriptionEntityList},
+			),
+		)
+	}
+
+	return
+}
+
+// GetSubscription returns a matching subscription for an entity and user.
+// It will return the next parent of a subscription. That means for tasks, it will first look for a subscription for
+// that task, if there is none it will look for a subscription on the list the task belongs to and if that also
+// doesn't exist it will check for a subscription for the namespace the list is belonging to.
+func GetSubscription(s *xorm.Session, entityType SubscriptionEntityType, entityID int64, a web.Auth) (subscription *Subscription, err error) {
+	u, is := a.(*user.User)
+	if !is {
+		return
+	}
+
+	if err := entityType.validate(); err != nil {
+		return nil, err
+	}
+
+	subscription = &Subscription{}
+	cond := getSubscriberCondForEntity(entityType, entityID)
+	exists, err := s.
+		Where("user_id = ?", u.ID).
+		And(cond).
+		Get(subscription)
+	if !exists {
+		return nil, err
+	}
+
+	subscription.Entity = subscription.EntityType.String()
+
+	return subscription, err
+}
+
+func getSubscribersForEntity(s *xorm.Session, entityType SubscriptionEntityType, entityID int64) (subscriptions []*Subscription, err error) {
+	if err := entityType.validate(); err != nil {
+		return nil, err
+	}
+
+	cond := getSubscriberCondForEntity(entityType, entityID)
+	err = s.
+		Where(cond).
+		Find(&subscriptions)
+	if err != nil {
+		return
+	}
+
+	userIDs := []int64{}
+	for _, subscription := range subscriptions {
+		userIDs = append(userIDs, subscription.UserID)
+	}
+
+	users, err := user.GetUsersByIDs(s, userIDs)
+	if err != nil {
+		return
+	}
+
+	for _, subscription := range subscriptions {
+		subscription.User = users[subscription.UserID]
+	}
+	return
+}

pkg/models/subscription_rights.go

@@ -0,0 +1,66 @@
+// Vikunja is a to-do list application to facilitate your life.
+// Copyright 2018-2021 Vikunja and contributors. All rights reserved.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public Licensee 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 Licensee for more details.
+//
+// You should have received a copy of the GNU Affero General Public Licensee
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package models
+
+import (
+	"code.vikunja.io/web"
+	"xorm.io/xorm"
+)
+
+// CanCreate checks if a user can subscribe to an entity
+func (sb *Subscription) CanCreate(s *xorm.Session, a web.Auth) (can bool, err error) {
+	if _, is := a.(*LinkSharing); is {
+		return false, &ErrGenericForbidden{}
+	}
+
+	sb.EntityType = getEntityTypeFromString(sb.Entity)
+
+	switch sb.EntityType {
+	case SubscriptionEntityNamespace:
+		n := &Namespace{ID: sb.EntityID}
+		can, _, err = n.CanRead(s, a)
+	case SubscriptionEntityList:
+		l := &List{ID: sb.EntityID}
+		can, _, err = l.CanRead(s, a)
+	case SubscriptionEntityTask:
+		t := &Task{ID: sb.EntityID}
+		can, _, err = t.CanRead(s, a)
+	default:
+		return false, &ErrUnknownSubscriptionEntityType{EntityType: sb.EntityType}
+	}
+
+	return
+}
+
+// CanDelete checks if a user can delete a subscription
+func (sb *Subscription) CanDelete(s *xorm.Session, a web.Auth) (can bool, err error) {
+	if _, is := a.(*LinkSharing); is {
+		return false, &ErrGenericForbidden{}
+	}
+
+	sb.EntityType = getEntityTypeFromString(sb.Entity)
+
+	realSb := &Subscription{}
+	exists, err := s.
+		Where("entity_id = ? AND entity_type = ? AND user_id = ?", sb.EntityID, sb.EntityType, a.GetID()).
+		Get(realSb)
+	if err != nil {
+		return false, err
+	}
+
+	return exists, nil
+}

pkg/models/subscription_test.go

@@ -0,0 +1,346 @@
+// Vikunja is a to-do list application to facilitate your life.
+// Copyright 2018-2021 Vikunja and contributors. All rights reserved.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public Licensee 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 Licensee for more details.
+//
+// You should have received a copy of the GNU Affero General Public Licensee
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package models
+
+import (
+	"testing"
+
+	"code.vikunja.io/api/pkg/db"
+	"code.vikunja.io/api/pkg/user"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestSubscriptionGetTypeFromString(t *testing.T) {
+	t.Run("namespace", func(t *testing.T) {
+		entityType := getEntityTypeFromString("namespace")
+		assert.Equal(t, SubscriptionEntityType(SubscriptionEntityNamespace), entityType)
+	})
+	t.Run("list", func(t *testing.T) {
+		entityType := getEntityTypeFromString("list")
+		assert.Equal(t, SubscriptionEntityType(SubscriptionEntityList), entityType)
+	})
+	t.Run("task", func(t *testing.T) {
+		entityType := getEntityTypeFromString("task")
+		assert.Equal(t, SubscriptionEntityType(SubscriptionEntityTask), entityType)
+	})
+	t.Run("invalid", func(t *testing.T) {
+		entityType := getEntityTypeFromString("someomejghsd")
+		assert.Equal(t, SubscriptionEntityType(SubscriptionEntityUnknown), entityType)
+	})
+}
+
+func TestSubscription_Create(t *testing.T) {
+	u := &user.User{ID: 1}
+
+	t.Run("normal", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		sb := &Subscription{
+			Entity:   "task",
+			EntityID: 1,
+			UserID:   u.ID,
+		}
+
+		can, err := sb.CanCreate(s, u)
+		assert.NoError(t, err)
+		assert.True(t, can)
+
+		err = sb.Create(s, u)
+		assert.NoError(t, err)
+		assert.NotNil(t, sb.User)
+
+		db.AssertExists(t, "subscriptions", map[string]interface{}{
+			"entity_type": 3,
+			"entity_id":   1,
+			"user_id":     u.ID,
+		}, false)
+	})
+	t.Run("forbidden for link shares", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		linkShare := &LinkSharing{}
+
+		sb := &Subscription{
+			Entity:   "task",
+			EntityID: 1,
+			UserID:   u.ID,
+		}
+
+		can, err := sb.CanCreate(s, linkShare)
+		assert.Error(t, err)
+		assert.False(t, can)
+	})
+	t.Run("noneixsting namespace", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		sb := &Subscription{
+			Entity:   "namespace",
+			EntityID: 99999999,
+			UserID:   u.ID,
+		}
+
+		can, err := sb.CanCreate(s, u)
+		assert.Error(t, err)
+		assert.True(t, IsErrNamespaceDoesNotExist(err))
+		assert.False(t, can)
+	})
+	t.Run("noneixsting list", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		sb := &Subscription{
+			Entity:   "list",
+			EntityID: 99999999,
+			UserID:   u.ID,
+		}
+
+		can, err := sb.CanCreate(s, u)
+		assert.Error(t, err)
+		assert.True(t, IsErrListDoesNotExist(err))
+		assert.False(t, can)
+	})
+	t.Run("noneixsting task", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		sb := &Subscription{
+			Entity:   "task",
+			EntityID: 99999999,
+			UserID:   u.ID,
+		}
+
+		can, err := sb.CanCreate(s, u)
+		assert.Error(t, err)
+		assert.True(t, IsErrTaskDoesNotExist(err))
+		assert.False(t, can)
+	})
+	t.Run("no rights to see namespace", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		sb := &Subscription{
+			Entity:   "namespace",
+			EntityID: 6,
+			UserID:   u.ID,
+		}
+
+		can, err := sb.CanCreate(s, u)
+		assert.NoError(t, err)
+		assert.False(t, can)
+	})
+	t.Run("no rights to see list", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		sb := &Subscription{
+			Entity:   "list",
+			EntityID: 20,
+			UserID:   u.ID,
+		}
+
+		can, err := sb.CanCreate(s, u)
+		assert.NoError(t, err)
+		assert.False(t, can)
+	})
+	t.Run("no rights to see task", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		sb := &Subscription{
+			Entity:   "task",
+			EntityID: 14,
+			UserID:   u.ID,
+		}
+
+		can, err := sb.CanCreate(s, u)
+		assert.NoError(t, err)
+		assert.False(t, can)
+	})
+	t.Run("existing subscription for (entity_id, entity_type, user_id) ", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		sb := &Subscription{
+			Entity:   "task",
+			EntityID: 2,
+			UserID:   u.ID,
+		}
+
+		can, err := sb.CanCreate(s, u)
+		assert.NoError(t, err)
+		assert.True(t, can)
+
+		err = sb.Create(s, u)
+		assert.Error(t, err)
+		assert.True(t, IsErrSubscriptionAlreadyExists(err))
+	})
+
+	// TODO: Add tests to test triggering of notifications for subscribed things
+}
+
+func TestSubscription_Delete(t *testing.T) {
+	t.Run("normal", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		u := &user.User{ID: 1}
+		sb := &Subscription{
+			Entity:   "task",
+			EntityID: 2,
+			UserID:   u.ID,
+		}
+
+		can, err := sb.CanDelete(s, u)
+		assert.NoError(t, err)
+		assert.True(t, can)
+
+		err = sb.Delete(s, u)
+		assert.NoError(t, err)
+		db.AssertMissing(t, "subscriptions", map[string]interface{}{
+			"entity_type": 3,
+			"entity_id":   2,
+			"user_id":     u.ID,
+		})
+	})
+	t.Run("forbidden for link shares", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		linkShare := &LinkSharing{}
+
+		sb := &Subscription{
+			Entity:   "task",
+			EntityID: 1,
+			UserID:   1,
+		}
+
+		can, err := sb.CanDelete(s, linkShare)
+		assert.Error(t, err)
+		assert.False(t, can)
+	})
+	t.Run("not owner of the subscription", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		u := &user.User{ID: 2}
+		sb := &Subscription{
+			Entity:   "task",
+			EntityID: 2,
+			UserID:   u.ID,
+		}
+
+		can, err := sb.CanDelete(s, u)
+		assert.NoError(t, err)
+		assert.False(t, can)
+	})
+}
+
+func TestSubscriptionGet(t *testing.T) {
+	u := &user.User{ID: 6}
+
+	t.Run("test each individually", func(t *testing.T) {
+		t.Run("namespace", func(t *testing.T) {
+			db.LoadAndAssertFixtures(t)
+			s := db.NewSession()
+			defer s.Close()
+
+			sub, err := GetSubscription(s, SubscriptionEntityNamespace, 6, u)
+			assert.NoError(t, err)
+			assert.NotNil(t, sub)
+			assert.Equal(t, int64(2), sub.ID)
+		})
+		t.Run("list", func(t *testing.T) {
+			db.LoadAndAssertFixtures(t)
+			s := db.NewSession()
+			defer s.Close()
+
+			sub, err := GetSubscription(s, SubscriptionEntityList, 12, u)
+			assert.NoError(t, err)
+			assert.NotNil(t, sub)
+			assert.Equal(t, int64(3), sub.ID)
+		})
+		t.Run("task", func(t *testing.T) {
+			db.LoadAndAssertFixtures(t)
+			s := db.NewSession()
+			defer s.Close()
+
+			sub, err := GetSubscription(s, SubscriptionEntityTask, 22, u)
+			assert.NoError(t, err)
+			assert.NotNil(t, sub)
+			assert.Equal(t, int64(4), sub.ID)
+		})
+	})
+	t.Run("inherited", func(t *testing.T) {
+		t.Run("list from namespace", func(t *testing.T) {
+			db.LoadAndAssertFixtures(t)
+			s := db.NewSession()
+			defer s.Close()
+
+			// List 6 belongs to namespace 6 where user 6 has subscribed to
+			sub, err := GetSubscription(s, SubscriptionEntityList, 6, u)
+			assert.NoError(t, err)
+			assert.NotNil(t, sub)
+			assert.Equal(t, int64(2), sub.ID)
+		})
+		t.Run("task from namespace", func(t *testing.T) {
+			db.LoadAndAssertFixtures(t)
+			s := db.NewSession()
+			defer s.Close()
+
+			// Task 20 belongs to list 11 which belongs to namespace 6 where the user has subscribed
+			sub, err := GetSubscription(s, SubscriptionEntityTask, 20, u)
+			assert.NoError(t, err)
+			assert.NotNil(t, sub)
+			assert.Equal(t, int64(2), sub.ID)
+		})
+		t.Run("task from list", func(t *testing.T) {
+			db.LoadAndAssertFixtures(t)
+			s := db.NewSession()
+			defer s.Close()
+
+			// Task 21 belongs to list 12 which the user has subscribed to
+			sub, err := GetSubscription(s, SubscriptionEntityTask, 21, u)
+			assert.NoError(t, err)
+			assert.NotNil(t, sub)
+			assert.Equal(t, int64(3), sub.ID)
+		})
+	})
+	t.Run("invalid type", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		_, err := GetSubscription(s, 2342, 21, u)
+		assert.Error(t, err)
+		assert.True(t, IsErrUnknownSubscriptionEntityType(err))
+	})
+}

pkg/models/task_assignees.go

@@ -225,10 +225,11 @@ func (t *Task) addNewAssigneeByID(s *xorm.Session, newAssigneeID int64, list *Li
 		return err
 	}
 
+	doer, _ := user.GetFromAuth(auth)
 	err = events.Dispatch(&TaskAssigneeCreatedEvent{
 		Task:     t,
 		Assignee: newAssignee,
-		Doer:     auth,
+		Doer:     doer,
 	})
 	if err != nil {
 		return err

pkg/models/task_comments.go

@@ -73,10 +73,11 @@ func (tc *TaskComment) Create(s *xorm.Session, a web.Auth) (err error) {
 		return
 	}
 
+	doer, _ := user.GetFromAuth(a)
 	err = events.Dispatch(&TaskCommentCreatedEvent{
 		Task:    &task,
 		Comment: tc,
-		Doer:    a,
+		Doer:    doer,
 	})
 	if err != nil {
 		return err

pkg/models/tasks.go

@@ -91,6 +91,10 @@ type Task struct {
 	// True if a task is a favorite task. Favorite tasks show up in a separate "Important" list
 	IsFavorite bool `xorm:"default false" json:"is_favorite"`
 
+	// The subscription status for the user reading this task. You can only read this property, use the subscription endpoints to modify it.
+	// Will only returned when retreiving one task.
+	Subscription *Subscription `xorm:"-" json:"subscription,omitempty"`
+
 	// A timestamp when this task was created. You cannot change this value.
 	Created time.Time `xorm:"created not null" json:"created"`
 	// A timestamp when this task was last updated. You cannot change this value.
@@ -119,6 +123,19 @@ func (Task) TableName() string {
 	return "tasks"
 }
 
+// GetFullIdentifier returns the task identifier if the task has one and the index prefixed with # otherwise.
+func (t *Task) GetFullIdentifier() string {
+	if t.Identifier != "" {
+		return t.Identifier
+	}
+
+	return "#" + strconv.FormatInt(t.Index, 10)
+}
+
+func (t *Task) GetFrontendURL() string {
+	return config.ServiceFrontendurl.GetString() + "tasks/" + strconv.FormatInt(t.ID, 10)
+}
+
 type taskFilterConcatinator string
 
 const (
@@ -832,9 +849,10 @@ func createTask(s *xorm.Session, t *Task, a web.Auth, updateAssignees bool) (err
 
 	t.setIdentifier(l)
 
+	doer, _ := user.GetFromAuth(a)
 	err = events.Dispatch(&TaskCreatedEvent{
 		Task: t,
-		Doer: a,
+		Doer: doer,
 	})
 	if err != nil {
 		return err
@@ -1040,9 +1058,10 @@ func (t *Task) Update(s *xorm.Session, a web.Auth) (err error) {
 	}
 	t.Updated = nt.Updated
 
+	doer, _ := user.GetFromAuth(a)
 	err = events.Dispatch(&TaskUpdatedEvent{
 		Task: t,
-		Doer: a,
+		Doer: doer,
 	})
 	if err != nil {
 		return err
@@ -1197,9 +1216,10 @@ func (t *Task) Delete(s *xorm.Session, a web.Auth) (err error) {
 		return err
 	}
 
+	doer, _ := user.GetFromAuth(a)
 	err = events.Dispatch(&TaskDeletedEvent{
 		Task: t,
-		Doer: a,
+		Doer: doer,
 	})
 	if err != nil {
 		return
@@ -1241,5 +1261,6 @@ func (t *Task) ReadOne(s *xorm.Session, a web.Auth) (err error) {
 
 	*t = *taskMap[t.ID]
 
+	t.Subscription, err = GetSubscription(s, SubscriptionEntityTask, t.ID, a)
 	return
 }

pkg/models/tasks_test.go

@@ -467,4 +467,16 @@ func TestTask_ReadOne(t *testing.T) {
 		assert.Error(t, err)
 		assert.True(t, IsErrTaskDoesNotExist(err))
 	})
+	t.Run("with subscription", func(t *testing.T) {
+		u = &user.User{ID: 6}
+
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		task := &Task{ID: 22}
+		err := task.ReadOne(s, u)
+		assert.NoError(t, err)
+		assert.NotNil(t, task.Subscription)
+	})
 }

pkg/models/unit_tests.go

@@ -59,6 +59,7 @@ func SetupTests() {
 		"users_namespace",
 		"buckets",
 		"saved_filters",
+		"subscriptions",
 	)
 	if err != nil {
 		log.Fatal(err)

pkg/routes/routes.go

@@ -512,6 +512,15 @@ func registerAPIRoutes(a *echo.Group) {
 	a.DELETE("/teams/:team/members/:user", teamMemberHandler.DeleteWeb)
 	a.POST("/teams/:team/members/:user/admin", teamMemberHandler.UpdateWeb)
 
+	// Subscriptions
+	subscriptionHandler := &handler.WebHandler{
+		EmptyStruct: func() handler.CObject {
+			return &models.Subscription{}
+		},
+	}
+	a.PUT("/subscriptions/:entity/:entityID", subscriptionHandler.CreateWeb)
+	a.DELETE("/subscriptions/:entity/:entityID", subscriptionHandler.DeleteWeb)
+
 	// Migrations
 	m := a.Group("/migration")
 

pkg/swagger/docs.go

@@ -3991,6 +3991,128 @@ var doc = `{
                 }
             }
         },
+        "/subscriptions/{entity}/{entityID}": {
+            "put": {
+                "security": [
+                    {
+                        "JWTKeyAuth": []
+                    }
+                ],
+                "description": "Subscribes the current user to an entity.",
+                "consumes": [
+                    "application/json"
+                ],
+                "produces": [
+                    "application/json"
+                ],
+                "tags": [
+                    "subscriptions"
+                ],
+                "summary": "Subscribes the current user to an entity.",
+                "parameters": [
+                    {
+                        "type": "string",
+                        "description": "The entity the user subscribes to. Can be either ` + "`" + `namespace` + "`" + `, ` + "`" + `list` + "`" + ` or ` + "`" + `task` + "`" + `.",
+                        "name": "entity",
+                        "in": "path",
+                        "required": true
+                    },
+                    {
+                        "type": "string",
+                        "description": "The numeric id of the entity to subscribe to.",
+                        "name": "entityID",
+                        "in": "path",
+                        "required": true
+                    }
+                ],
+                "responses": {
+                    "200": {
+                        "description": "The subscription",
+                        "schema": {
+                            "$ref": "#/definitions/models.Subscription"
+                        }
+                    },
+                    "403": {
+                        "description": "The user does not have access to subscribe to this entity.",
+                        "schema": {
+                            "$ref": "#/definitions/web.HTTPError"
+                        }
+                    },
+                    "412": {
+                        "description": "The subscription entity is invalid.",
+                        "schema": {
+                            "$ref": "#/definitions/web.HTTPError"
+                        }
+                    },
+                    "500": {
+                        "description": "Internal error",
+                        "schema": {
+                            "$ref": "#/definitions/models.Message"
+                        }
+                    }
+                }
+            },
+            "delete": {
+                "security": [
+                    {
+                        "JWTKeyAuth": []
+                    }
+                ],
+                "description": "Unsubscribes the current user to an entity.",
+                "consumes": [
+                    "application/json"
+                ],
+                "produces": [
+                    "application/json"
+                ],
+                "tags": [
+                    "subscriptions"
+                ],
+                "summary": "Unsubscribe the current user from an entity.",
+                "parameters": [
+                    {
+                        "type": "string",
+                        "description": "The entity the user subscribed to. Can be either ` + "`" + `namespace` + "`" + `, ` + "`" + `list` + "`" + ` or ` + "`" + `task` + "`" + `.",
+                        "name": "entity",
+                        "in": "path",
+                        "required": true
+                    },
+                    {
+                        "type": "string",
+                        "description": "The numeric id of the subscribed entity to.",
+                        "name": "entityID",
+                        "in": "path",
+                        "required": true
+                    }
+                ],
+                "responses": {
+                    "200": {
+                        "description": "The subscription",
+                        "schema": {
+                            "$ref": "#/definitions/models.Subscription"
+                        }
+                    },
+                    "403": {
+                        "description": "The user does not have access to subscribe to this entity.",
+                        "schema": {
+                            "$ref": "#/definitions/web.HTTPError"
+                        }
+                    },
+                    "404": {
+                        "description": "The subscription does not exist.",
+                        "schema": {
+                            "$ref": "#/definitions/web.HTTPError"
+                        }
+                    },
+                    "500": {
+                        "description": "Internal error",
+                        "schema": {
+                            "$ref": "#/definitions/models.Message"
+                        }
+                    }
+                }
+            }
+        },
         "/tasks/all": {
             "get": {
                 "security": [
@@ -7039,6 +7161,10 @@ var doc = `{
                     "description": "When this task starts.",
                     "type": "string"
                 },
+                "subscription": {
+                    "description": "The subscription status for the user reading this task. You can only read this property, use the subscription endpoints to modify it.\nWill only returned when retreiving one task.",
+                    "$ref": "#/definitions/models.Subscription"
+                },
                 "task_ids": {
                     "description": "A list of task ids to update",
                     "type": "array",
@@ -7201,6 +7327,10 @@ var doc = `{
                     "description": "The user who created this list.",
                     "$ref": "#/definitions/user.User"
                 },
+                "subscription": {
+                    "description": "The subscription status for the user reading this list. You can only read this property, use the subscription endpoints to modify it.\nWill only returned when retreiving one list.",
+                    "$ref": "#/definitions/models.Subscription"
+                },
                 "title": {
                     "description": "The title of the list. You'll see this in the namespace overview.",
                     "type": "string",
@@ -7290,6 +7420,10 @@ var doc = `{
                     "description": "The user who owns this namespace",
                     "$ref": "#/definitions/user.User"
                 },
+                "subscription": {
+                    "description": "The subscription status for the user reading this namespace. You can only read this property, use the subscription endpoints to modify it.\nWill only returned when retreiving one namespace.",
+                    "$ref": "#/definitions/models.Subscription"
+                },
                 "title": {
                     "description": "The name of this namespace.",
                     "type": "string",
@@ -7363,6 +7497,10 @@ var doc = `{
                     "description": "The user who owns this namespace",
                     "$ref": "#/definitions/user.User"
                 },
+                "subscription": {
+                    "description": "The subscription status for the user reading this namespace. You can only read this property, use the subscription endpoints to modify it.\nWill only returned when retreiving one namespace.",
+                    "$ref": "#/definitions/models.Subscription"
+                },
                 "title": {
                     "description": "The name of this namespace.",
                     "type": "string",
@@ -7419,6 +7557,30 @@ var doc = `{
                 }
             }
         },
+        "models.Subscription": {
+            "type": "object",
+            "properties": {
+                "created": {
+                    "description": "A timestamp when this subscription was created. You cannot change this value.",
+                    "type": "string"
+                },
+                "entity": {
+                    "type": "string"
+                },
+                "entity_id": {
+                    "description": "The id of the entity to subscribe to.",
+                    "type": "integer"
+                },
+                "id": {
+                    "description": "The numeric ID of the subscription",
+                    "type": "integer"
+                },
+                "user": {
+                    "description": "The user who made this subscription",
+                    "$ref": "#/definitions/user.User"
+                }
+            }
+        },
         "models.Task": {
             "type": "object",
             "properties": {
@@ -7535,6 +7697,10 @@ var doc = `{
                     "description": "When this task starts.",
                     "type": "string"
                 },
+                "subscription": {
+                    "description": "The subscription status for the user reading this task. You can only read this property, use the subscription endpoints to modify it.\nWill only returned when retreiving one task.",
+                    "$ref": "#/definitions/models.Subscription"
+                },
                 "title": {
                     "description": "The task text. This is what you'll see in the list.",
                     "type": "string",

pkg/swagger/swagger.json

@@ -3974,6 +3974,128 @@
                 }
             }
         },
+        "/subscriptions/{entity}/{entityID}": {
+            "put": {
+                "security": [
+                    {
+                        "JWTKeyAuth": []
+                    }
+                ],
+                "description": "Subscribes the current user to an entity.",
+                "consumes": [
+                    "application/json"
+                ],
+                "produces": [
+                    "application/json"
+                ],
+                "tags": [
+                    "subscriptions"
+                ],
+                "summary": "Subscribes the current user to an entity.",
+                "parameters": [
+                    {
+                        "type": "string",
+                        "description": "The entity the user subscribes to. Can be either `namespace`, `list` or `task`.",
+                        "name": "entity",
+                        "in": "path",
+                        "required": true
+                    },
+                    {
+                        "type": "string",
+                        "description": "The numeric id of the entity to subscribe to.",
+                        "name": "entityID",
+                        "in": "path",
+                        "required": true
+                    }
+                ],
+                "responses": {
+                    "200": {
+                        "description": "The subscription",
+                        "schema": {
+                            "$ref": "#/definitions/models.Subscription"
+                        }
+                    },
+                    "403": {
+                        "description": "The user does not have access to subscribe to this entity.",
+                        "schema": {
+                            "$ref": "#/definitions/web.HTTPError"
+                        }
+                    },
+                    "412": {
+                        "description": "The subscription entity is invalid.",
+                        "schema": {
+                            "$ref": "#/definitions/web.HTTPError"
+                        }
+                    },
+                    "500": {
+                        "description": "Internal error",
+                        "schema": {
+                            "$ref": "#/definitions/models.Message"
+                        }
+                    }
+                }
+            },
+            "delete": {
+                "security": [
+                    {
+                        "JWTKeyAuth": []
+                    }
+                ],
+                "description": "Unsubscribes the current user to an entity.",
+                "consumes": [
+                    "application/json"
+                ],
+                "produces": [
+                    "application/json"
+                ],
+                "tags": [
+                    "subscriptions"
+                ],
+                "summary": "Unsubscribe the current user from an entity.",
+                "parameters": [
+                    {
+                        "type": "string",
+                        "description": "The entity the user subscribed to. Can be either `namespace`, `list` or `task`.",
+                        "name": "entity",
+                        "in": "path",
+                        "required": true
+                    },
+                    {
+                        "type": "string",
+                        "description": "The numeric id of the subscribed entity to.",
+                        "name": "entityID",
+                        "in": "path",
+                        "required": true
+                    }
+                ],
+                "responses": {
+                    "200": {
+                        "description": "The subscription",
+                        "schema": {
+                            "$ref": "#/definitions/models.Subscription"
+                        }
+                    },
+                    "403": {
+                        "description": "The user does not have access to subscribe to this entity.",
+                        "schema": {
+                            "$ref": "#/definitions/web.HTTPError"
+                        }
+                    },
+                    "404": {
+                        "description": "The subscription does not exist.",
+                        "schema": {
+                            "$ref": "#/definitions/web.HTTPError"
+                        }
+                    },
+                    "500": {
+                        "description": "Internal error",
+                        "schema": {
+                            "$ref": "#/definitions/models.Message"
+                        }
+                    }
+                }
+            }
+        },
         "/tasks/all": {
             "get": {
                 "security": [
@@ -7022,6 +7144,10 @@
                     "description": "When this task starts.",
                     "type": "string"
                 },
+                "subscription": {
+                    "description": "The subscription status for the user reading this task. You can only read this property, use the subscription endpoints to modify it.\nWill only returned when retreiving one task.",
+                    "$ref": "#/definitions/models.Subscription"
+                },
                 "task_ids": {
                     "description": "A list of task ids to update",
                     "type": "array",
@@ -7184,6 +7310,10 @@
                     "description": "The user who created this list.",
                     "$ref": "#/definitions/user.User"
                 },
+                "subscription": {
+                    "description": "The subscription status for the user reading this list. You can only read this property, use the subscription endpoints to modify it.\nWill only returned when retreiving one list.",
+                    "$ref": "#/definitions/models.Subscription"
+                },
                 "title": {
                     "description": "The title of the list. You'll see this in the namespace overview.",
                     "type": "string",
@@ -7273,6 +7403,10 @@
                     "description": "The user who owns this namespace",
                     "$ref": "#/definitions/user.User"
                 },
+                "subscription": {
+                    "description": "The subscription status for the user reading this namespace. You can only read this property, use the subscription endpoints to modify it.\nWill only returned when retreiving one namespace.",
+                    "$ref": "#/definitions/models.Subscription"
+                },
                 "title": {
                     "description": "The name of this namespace.",
                     "type": "string",
@@ -7346,6 +7480,10 @@
                     "description": "The user who owns this namespace",
                     "$ref": "#/definitions/user.User"
                 },
+                "subscription": {
+                    "description": "The subscription status for the user reading this namespace. You can only read this property, use the subscription endpoints to modify it.\nWill only returned when retreiving one namespace.",
+                    "$ref": "#/definitions/models.Subscription"
+                },
                 "title": {
                     "description": "The name of this namespace.",
                     "type": "string",
@@ -7402,6 +7540,30 @@
                 }
             }
         },
+        "models.Subscription": {
+            "type": "object",
+            "properties": {
+                "created": {
+                    "description": "A timestamp when this subscription was created. You cannot change this value.",
+                    "type": "string"
+                },
+                "entity": {
+                    "type": "string"
+                },
+                "entity_id": {
+                    "description": "The id of the entity to subscribe to.",
+                    "type": "integer"
+                },
+                "id": {
+                    "description": "The numeric ID of the subscription",
+                    "type": "integer"
+                },
+                "user": {
+                    "description": "The user who made this subscription",
+                    "$ref": "#/definitions/user.User"
+                }
+            }
+        },
         "models.Task": {
             "type": "object",
             "properties": {
@@ -7518,6 +7680,10 @@
                     "description": "When this task starts.",
                     "type": "string"
                 },
+                "subscription": {
+                    "description": "The subscription status for the user reading this task. You can only read this property, use the subscription endpoints to modify it.\nWill only returned when retreiving one task.",
+                    "$ref": "#/definitions/models.Subscription"
+                },
                 "title": {
                     "description": "The task text. This is what you'll see in the list.",
                     "type": "string",

pkg/swagger/swagger.yaml

@@ -210,6 +210,11 @@ definitions:
       start_date:
         description: When this task starts.
         type: string
+      subscription:
+        $ref: '#/definitions/models.Subscription'
+        description: |-
+          The subscription status for the user reading this task. You can only read this property, use the subscription endpoints to modify it.
+          Will only returned when retreiving one task.
       task_ids:
         description: A list of task ids to update
         items:
@@ -330,6 +335,11 @@ definitions:
       owner:
         $ref: '#/definitions/user.User'
         description: The user who created this list.
+      subscription:
+        $ref: '#/definitions/models.Subscription'
+        description: |-
+          The subscription status for the user reading this list. You can only read this property, use the subscription endpoints to modify it.
+          Will only returned when retreiving one list.
       title:
         description: The title of the list. You'll see this in the namespace overview.
         maxLength: 250
@@ -395,6 +405,11 @@ definitions:
       owner:
         $ref: '#/definitions/user.User'
         description: The user who owns this namespace
+      subscription:
+        $ref: '#/definitions/models.Subscription'
+        description: |-
+          The subscription status for the user reading this namespace. You can only read this property, use the subscription endpoints to modify it.
+          Will only returned when retreiving one namespace.
       title:
         description: The name of this namespace.
         maxLength: 250
@@ -449,6 +464,11 @@ definitions:
       owner:
         $ref: '#/definitions/user.User'
         description: The user who owns this namespace
+      subscription:
+        $ref: '#/definitions/models.Subscription'
+        description: |-
+          The subscription status for the user reading this namespace. You can only read this property, use the subscription endpoints to modify it.
+          Will only returned when retreiving one namespace.
       title:
         description: The name of this namespace.
         maxLength: 250
@@ -490,6 +510,23 @@ definitions:
         description: A timestamp when this filter was last updated. You cannot change this value.
         type: string
     type: object
+  models.Subscription:
+    properties:
+      created:
+        description: A timestamp when this subscription was created. You cannot change this value.
+        type: string
+      entity:
+        type: string
+      entity_id:
+        description: The id of the entity to subscribe to.
+        type: integer
+      id:
+        description: The numeric ID of the subscription
+        type: integer
+      user:
+        $ref: '#/definitions/user.User'
+        description: The user who made this subscription
+    type: object
   models.Task:
     properties:
       assignees:
@@ -582,6 +619,11 @@ definitions:
       start_date:
         description: When this task starts.
         type: string
+      subscription:
+        $ref: '#/definitions/models.Subscription'
+        description: |-
+          The subscription status for the user reading this task. You can only read this property, use the subscription endpoints to modify it.
+          Will only returned when retreiving one task.
       title:
         description: The task text. This is what you'll see in the list.
         maxLength: 250
@@ -3660,6 +3702,85 @@ paths:
       summary: Get an auth token for a share
       tags:
       - sharing
+  /subscriptions/{entity}/{entityID}:
+    delete:
+      consumes:
+      - application/json
+      description: Unsubscribes the current user to an entity.
+      parameters:
+      - description: The entity the user subscribed to. Can be either `namespace`, `list` or `task`.
+        in: path
+        name: entity
+        required: true
+        type: string
+      - description: The numeric id of the subscribed entity to.
+        in: path
+        name: entityID
+        required: true
+        type: string
+      produces:
+      - application/json
+      responses:
+        "200":
+          description: The subscription
+          schema:
+            $ref: '#/definitions/models.Subscription'
+        "403":
+          description: The user does not have access to subscribe to this entity.
+          schema:
+            $ref: '#/definitions/web.HTTPError'
+        "404":
+          description: The subscription does not exist.
+          schema:
+            $ref: '#/definitions/web.HTTPError'
+        "500":
+          description: Internal error
+          schema:
+            $ref: '#/definitions/models.Message'
+      security:
+      - JWTKeyAuth: []
+      summary: Unsubscribe the current user from an entity.
+      tags:
+      - subscriptions
+    put:
+      consumes:
+      - application/json
+      description: Subscribes the current user to an entity.
+      parameters:
+      - description: The entity the user subscribes to. Can be either `namespace`, `list` or `task`.
+        in: path
+        name: entity
+        required: true
+        type: string
+      - description: The numeric id of the entity to subscribe to.
+        in: path
+        name: entityID
+        required: true
+        type: string
+      produces:
+      - application/json
+      responses:
+        "200":
+          description: The subscription
+          schema:
+            $ref: '#/definitions/models.Subscription'
+        "403":
+          description: The user does not have access to subscribe to this entity.
+          schema:
+            $ref: '#/definitions/web.HTTPError'
+        "412":
+          description: The subscription entity is invalid.
+          schema:
+            $ref: '#/definitions/web.HTTPError'
+        "500":
+          description: Internal error
+          schema:
+            $ref: '#/definitions/models.Message'
+      security:
+      - JWTKeyAuth: []
+      summary: Subscribes the current user to an entity.
+      tags:
+      - subscriptions
   /tasks/{ID}:
     get:
       consumes: