diff --git a/build.gradle b/build.gradle
index c5e9b34..d6a397d 100644
--- a/build.gradle
+++ b/build.gradle
@@ -83,7 +83,6 @@ kotlin {
                 implementation "io.ktor:ktor-server-netty:$ktor_version"
                 implementation "io.ktor:ktor-auth:$ktor_version"
                 implementation "io.ktor:ktor-server-sessions:$ktor_version"
-                implementation "io.ktor:ktor-websockets:$ktor_version"
                 implementation "io.ktor:ktor-jackson:$ktor_version"
                 implementation 'org.jetbrains:kotlin-css-jvm:1.0.0-pre.70-kotlin-1.3.21'
 
diff --git a/src/commonMain/kotlin/de/kif/common/Message.kt b/src/commonMain/kotlin/de/kif/common/Message.kt
index e239280..2e70a49 100644
--- a/src/commonMain/kotlin/de/kif/common/Message.kt
+++ b/src/commonMain/kotlin/de/kif/common/Message.kt
@@ -1,30 +1,24 @@
 package de.kif.common
 
+import kotlinx.serialization.DeserializationStrategy
 import kotlinx.serialization.Serializable
+import kotlinx.serialization.SerializationStrategy
 import kotlinx.serialization.json.Json
 import kotlinx.serialization.modules.SerializersModule
 
+@Serializable
+data class MessageBox(
+    val timestamp: Long,
+    val valid: Boolean,
+    val messages: List<Message>
+)
+
 @Serializable
 data class Message(
     val type: MessageType,
     val repository: RepositoryType,
     val id: Long
-) {
-
-    fun stringify(): String {
-        return json.stringify(serializer(), this)
-    }
-
-    companion object {
-        private val jsonContext = SerializersModule {}
-
-        val json = Json(context = jsonContext)
-
-        fun parse(data: String): Message {
-            return json.parse(serializer(), data)
-        }
-    }
-}
+)
 
 enum class MessageType {
     CREATE, UPDATE, DELETE
@@ -33,3 +27,12 @@ enum class MessageType {
 enum class RepositoryType {
     ROOM, SCHEDULE, TRACK, USER, WORK_GROUP, POST
 }
+
+object Serialization {
+    private val jsonContext = SerializersModule {}
+
+    val json = Json(context = jsonContext)
+
+    fun <T> stringify(serializer: SerializationStrategy<T>, obj: T) = json.stringify(serializer, obj)
+    fun <T> parse(serializer: DeserializationStrategy<T>, str: String) = json.parse(serializer, str)
+}
diff --git a/src/commonMain/kotlin/de/kif/common/Search.kt b/src/commonMain/kotlin/de/kif/common/Search.kt
index fadef97..184518d 100644
--- a/src/commonMain/kotlin/de/kif/common/Search.kt
+++ b/src/commonMain/kotlin/de/kif/common/Search.kt
@@ -10,12 +10,12 @@ data class SearchElement(
 ) {
 
     fun stringify(): String {
-        return Message.json.stringify(serializer(), this)
+        return Serialization.stringify(serializer(), this)
     }
 
     companion object {
         fun parse(data: String): SearchElement {
-            return Message.json.parse(serializer(), data)
+            return Serialization.parse(serializer(), data)
         }
     }
 }
diff --git a/src/jsMain/kotlin/de/kif/frontend/WebSocketClient.kt b/src/jsMain/kotlin/de/kif/frontend/WebSocketClient.kt
index 62464af..22cd247 100644
--- a/src/jsMain/kotlin/de/kif/frontend/WebSocketClient.kt
+++ b/src/jsMain/kotlin/de/kif/frontend/WebSocketClient.kt
@@ -1,68 +1,92 @@
 package de.kif.frontend
 
-import de.kif.common.Message
+import de.kif.common.MessageBox
 import de.kif.common.MessageType
 import de.kif.common.RepositoryType
 import de.kif.frontend.repository.*
-import de.westermann.kwebview.async
-import org.w3c.dom.MessageEvent
-import org.w3c.dom.WebSocket
-import org.w3c.dom.events.Event
+import de.westermann.kwebview.clearInterval
+import de.westermann.kwebview.createHtmlView
+import de.westermann.kwebview.interval
+import kotlinx.serialization.DynamicObjectParser
+import org.w3c.dom.get
+import org.w3c.xhr.XMLHttpRequest
+import kotlin.browser.document
 import kotlin.browser.window
 
-class WebSocketClient() {
+class WebSocketClient {
     private val prefix = js("prefix")
+    private val url = "$prefix/api/updates"
+    private val body = document.body ?: createHtmlView()
+    private val parser = DynamicObjectParser()
 
-    private val useSsl = "https" in window.location.protocol
-    private val wsProtocol = if (useSsl) "wss" else "ws"
-    private val url = "$wsProtocol://${window.location.host}$prefix/websocket"
+    private var timestamp = body.dataset["timestamp"]?.toLongOrNull() ?: 0L
+    private var intervalId: Int? = null
 
-    private lateinit var ws: WebSocket
-    private var reconnect = false
+    private fun reload() {
+        val id = intervalId ?: return
+        clearInterval(id)
+        intervalId = null
 
-    @Suppress("UNUSED_PARAMETER")
-    private fun onOpen(event: Event) {
-        console.log("Connected!")
-        if (reconnect) {
-            window.location.reload()
-        }
+        window.location.reload()
     }
 
-    private fun onMessage(messageEvent: MessageEvent) {
-        val message = Message.parse(messageEvent.data?.toString() ?: "")
+    private fun onMessage(messageBox: MessageBox) {
+        body.classList.remove("offline")
 
-        for (handler in messageHandlers) {
-            if (handler.repository == message.repository) {
-                when (message.type) {
-                    MessageType.CREATE -> handler.onCreate(message.id)
-                    MessageType.UPDATE -> handler.onUpdate(message.id)
-                    MessageType.DELETE -> handler.onDelete(message.id)
+        if (messageBox.valid) {
+            timestamp = messageBox.timestamp
+
+            for (message in messageBox.messages) {
+                for (handler in messageHandlers) {
+                    if (handler.repository == message.repository) {
+                        when (message.type) {
+                            MessageType.CREATE -> handler.onCreate(message.id)
+                            MessageType.UPDATE -> handler.onUpdate(message.id)
+                            MessageType.DELETE -> handler.onDelete(message.id)
+                        }
+                    }
                 }
             }
+        } else {
+            reload()
         }
     }
 
-    @Suppress("UNUSED_PARAMETER")
-    private fun onClose(event: Event) {
-        console.log("Disconnected!")
-        reconnect = true
-        async(1000) {
-            connect()
+    private fun onError(code: Int) {
+        if (!body.classList.contains("offline")) {
+            console.log("Offline reason: $code")
         }
+        body.classList.add("offline")
     }
 
-    @Suppress("UNUSED_PARAMETER")
-    private fun onError(event: Event) {
-        console.log("An error occurred!")
-    }
+    private fun request() {
+        val xmlHttpRequest = XMLHttpRequest()
 
-    private fun connect() {
-        ws = WebSocket(url)
+        xmlHttpRequest.onreadystatechange = {
+            try {
+                if (xmlHttpRequest.readyState == 4.toShort()) {
+                    if (xmlHttpRequest.status == 200.toShort() || xmlHttpRequest.status == 304.toShort()) {
+                        val json = JSON.parse<JsonResponse>(xmlHttpRequest.responseText)
 
-        ws.onopen = this::onOpen
-        ws.onmessage = this::onMessage
-        ws.onclose = this::onClose
-        ws.onerror = this::onError
+                        if (json.OK) {
+                            val message = parser.parse(json.data, MessageBox.serializer())
+                            onMessage(message)
+                        } else {
+                            onError(-1)
+                        }
+
+                    } else {
+                        onError(xmlHttpRequest.status.toInt())
+                    }
+                }
+            } catch (e: Exception) {
+                console.error(e)
+                onError(-2)
+            }
+        }
+        xmlHttpRequest.open("GET", "$url?timestamp=$timestamp", true)
+        xmlHttpRequest.overrideMimeType("application/json")
+        xmlHttpRequest.send()
     }
 
     private val messageHandlers: List<MessageHandler> = listOf(
@@ -75,7 +99,9 @@ class WebSocketClient() {
     )
 
     init {
-        connect()
+        intervalId = interval(500) {
+            request()
+        }
     }
 }
 
diff --git a/src/jsMain/kotlin/de/kif/frontend/repository/Ajax.kt b/src/jsMain/kotlin/de/kif/frontend/repository/Ajax.kt
index a08991d..1f5446b 100644
--- a/src/jsMain/kotlin/de/kif/frontend/repository/Ajax.kt
+++ b/src/jsMain/kotlin/de/kif/frontend/repository/Ajax.kt
@@ -8,10 +8,15 @@ import kotlin.coroutines.resumeWithException
 import kotlin.coroutines.suspendCoroutine
 import kotlin.js.Promise
 
+interface JsonResponse {
+    val OK: Boolean
+    val data: dynamic
+}
+
 suspend fun repositoryGet(
     url: String
 ): dynamic {
-    val promise = Promise<dynamic> { resolve, reject ->
+    val promise = Promise<JsonResponse> { resolve, reject ->
         val xhttp = XMLHttpRequest()
 
         xhttp.onreadystatechange = {
@@ -47,7 +52,7 @@ suspend fun repositoryPost(
     url: String,
     data: String? = null
 ): dynamic {
-    val promise = Promise<dynamic> { resolve, reject ->
+    val promise = Promise<JsonResponse> { resolve, reject ->
         val xhttp = XMLHttpRequest()
 
         xhttp.onreadystatechange = {
diff --git a/src/jsMain/kotlin/de/kif/frontend/repository/PostRepository.kt b/src/jsMain/kotlin/de/kif/frontend/repository/PostRepository.kt
index aa56570..13c459e 100644
--- a/src/jsMain/kotlin/de/kif/frontend/repository/PostRepository.kt
+++ b/src/jsMain/kotlin/de/kif/frontend/repository/PostRepository.kt
@@ -3,6 +3,7 @@ package de.kif.frontend.repository
 import de.kif.common.Message
 import de.kif.common.Repository
 import de.kif.common.RepositoryType
+import de.kif.common.Serialization
 import de.kif.common.model.Post
 import de.kif.frontend.MessageHandler
 import de.westermann.kobserve.event.EventHandler
@@ -25,13 +26,13 @@ object PostRepository : Repository<Post> {
     }
 
     override suspend fun create(model: Post): Long {
-        return repositoryPost("$prefix/api/posts", Message.json.stringify(Post.serializer(), model))
+        return repositoryPost("$prefix/api/posts", Serialization.stringify(Post.serializer(), model))
             ?: throw IllegalStateException("Cannot create model!")
     }
 
     override suspend fun update(model: Post) {
         if (model.id == null) throw IllegalStateException("Cannot update model which was not created!")
-        repositoryPost("$prefix/api/post/${model.id}", Message.json.stringify(Post.serializer(), model))
+        repositoryPost("$prefix/api/post/${model.id}", Serialization.stringify(Post.serializer(), model))
     }
 
     override suspend fun delete(id: Long) {
diff --git a/src/jsMain/kotlin/de/kif/frontend/repository/RoomRepository.kt b/src/jsMain/kotlin/de/kif/frontend/repository/RoomRepository.kt
index 1dc88ee..9d933f3 100644
--- a/src/jsMain/kotlin/de/kif/frontend/repository/RoomRepository.kt
+++ b/src/jsMain/kotlin/de/kif/frontend/repository/RoomRepository.kt
@@ -3,6 +3,7 @@ package de.kif.frontend.repository
 import de.kif.common.Message
 import de.kif.common.Repository
 import de.kif.common.RepositoryType
+import de.kif.common.Serialization
 import de.kif.common.model.Room
 import de.kif.frontend.MessageHandler
 import de.westermann.kobserve.event.EventHandler
@@ -25,13 +26,13 @@ object RoomRepository : Repository<Room> {
     }
 
     override suspend fun create(model: Room): Long {
-        return repositoryPost("$prefix/api/rooms", Message.json.stringify(Room.serializer(), model))
+        return repositoryPost("$prefix/api/rooms", Serialization.stringify(Room.serializer(), model))
             ?: throw IllegalStateException("Cannot create model!")
     }
 
     override suspend fun update(model: Room) {
         if (model.id == null) throw IllegalStateException("Cannot update model which was not created!")
-        repositoryPost("$prefix/api/room/${model.id}", Message.json.stringify(Room.serializer(), model))
+        repositoryPost("$prefix/api/room/${model.id}", Serialization.stringify(Room.serializer(), model))
     }
 
     override suspend fun delete(id: Long) {
diff --git a/src/jsMain/kotlin/de/kif/frontend/repository/ScheduleRepository.kt b/src/jsMain/kotlin/de/kif/frontend/repository/ScheduleRepository.kt
index 60a2b73..3da61bf 100644
--- a/src/jsMain/kotlin/de/kif/frontend/repository/ScheduleRepository.kt
+++ b/src/jsMain/kotlin/de/kif/frontend/repository/ScheduleRepository.kt
@@ -1,9 +1,6 @@
 package de.kif.frontend.repository
 
-import de.kif.common.ConstraintMap
-import de.kif.common.Message
-import de.kif.common.Repository
-import de.kif.common.RepositoryType
+import de.kif.common.*
 import de.kif.common.model.Schedule
 import de.kif.frontend.MessageHandler
 import de.westermann.kobserve.event.EventHandler
@@ -31,13 +28,13 @@ object ScheduleRepository : Repository<Schedule> {
     }
 
     override suspend fun create(model: Schedule): Long {
-        return repositoryPost("$prefix/api/schedules", Message.json.stringify(Schedule.serializer(), model))
+        return repositoryPost("$prefix/api/schedules", Serialization.stringify(Schedule.serializer(), model))
             ?: throw IllegalStateException("Cannot create model!")
     }
 
     override suspend fun update(model: Schedule) {
         if (model.id == null) throw IllegalStateException("Cannot update model which was not created!")
-        repositoryPost("$prefix/api/schedule/${model.id}", Message.json.stringify(Schedule.serializer(), model))
+        repositoryPost("$prefix/api/schedule/${model.id}", Serialization.stringify(Schedule.serializer(), model))
     }
 
     override suspend fun delete(id: Long) {
diff --git a/src/jsMain/kotlin/de/kif/frontend/repository/TrackRepository.kt b/src/jsMain/kotlin/de/kif/frontend/repository/TrackRepository.kt
index cf5dcae..754cdef 100644
--- a/src/jsMain/kotlin/de/kif/frontend/repository/TrackRepository.kt
+++ b/src/jsMain/kotlin/de/kif/frontend/repository/TrackRepository.kt
@@ -3,6 +3,7 @@ package de.kif.frontend.repository
 import de.kif.common.Message
 import de.kif.common.Repository
 import de.kif.common.RepositoryType
+import de.kif.common.Serialization
 import de.kif.common.model.Track
 import de.kif.frontend.MessageHandler
 import de.westermann.kobserve.event.EventHandler
@@ -25,13 +26,13 @@ object TrackRepository : Repository<Track> {
     }
 
     override suspend fun create(model: Track): Long {
-        return repositoryPost("$prefix/api/tracks", Message.json.stringify(Track.serializer(), model))
+        return repositoryPost("$prefix/api/tracks", Serialization.stringify(Track.serializer(), model))
             ?: throw IllegalStateException("Cannot create model!")
     }
 
     override suspend fun update(model: Track) {
         if (model.id == null) throw IllegalStateException("Cannot update model which was not created!")
-        repositoryPost("$prefix/api/track/${model.id}", Message.json.stringify(Track.serializer(), model))
+        repositoryPost("$prefix/api/track/${model.id}", Serialization.stringify(Track.serializer(), model))
     }
 
     override suspend fun delete(id: Long) {
diff --git a/src/jsMain/kotlin/de/kif/frontend/repository/UserRepository.kt b/src/jsMain/kotlin/de/kif/frontend/repository/UserRepository.kt
index b5a42db..90c0438 100644
--- a/src/jsMain/kotlin/de/kif/frontend/repository/UserRepository.kt
+++ b/src/jsMain/kotlin/de/kif/frontend/repository/UserRepository.kt
@@ -3,6 +3,7 @@ package de.kif.frontend.repository
 import de.kif.common.Message
 import de.kif.common.Repository
 import de.kif.common.RepositoryType
+import de.kif.common.Serialization
 import de.kif.common.model.User
 import de.kif.frontend.MessageHandler
 import de.westermann.kobserve.event.EventHandler
@@ -25,13 +26,13 @@ object UserRepository : Repository<User> {
     }
 
     override suspend fun create(model: User): Long {
-        return repositoryPost("$prefix/api/users", Message.json.stringify(User.serializer(), model))
+        return repositoryPost("$prefix/api/users", Serialization.stringify(User.serializer(), model))
             ?: throw IllegalStateException("Cannot create model!")
     }
 
     override suspend fun update(model: User) {
         if (model.id == null) throw IllegalStateException("Cannot update model which was not created!")
-        repositoryPost("$prefix/api/user/${model.id}", Message.json.stringify(User.serializer(), model))
+        repositoryPost("$prefix/api/user/${model.id}", Serialization.stringify(User.serializer(), model))
     }
 
     override suspend fun delete(id: Long) {
diff --git a/src/jsMain/kotlin/de/kif/frontend/repository/WorkGroupRepository.kt b/src/jsMain/kotlin/de/kif/frontend/repository/WorkGroupRepository.kt
index 18c240c..6714c71 100644
--- a/src/jsMain/kotlin/de/kif/frontend/repository/WorkGroupRepository.kt
+++ b/src/jsMain/kotlin/de/kif/frontend/repository/WorkGroupRepository.kt
@@ -3,6 +3,7 @@ package de.kif.frontend.repository
 import de.kif.common.Message
 import de.kif.common.Repository
 import de.kif.common.RepositoryType
+import de.kif.common.Serialization
 import de.kif.common.model.WorkGroup
 import de.kif.frontend.MessageHandler
 import de.westermann.kobserve.event.EventHandler
@@ -25,13 +26,13 @@ object WorkGroupRepository : Repository<WorkGroup> {
     }
 
     override suspend fun create(model: WorkGroup): Long {
-        return repositoryPost("$prefix/api/workgroups", Message.json.stringify(WorkGroup.serializer(), model))
+        return repositoryPost("$prefix/api/workgroups", Serialization.stringify(WorkGroup.serializer(), model))
             ?: throw IllegalStateException("Cannot create model!")
     }
 
     override suspend fun update(model: WorkGroup) {
         if (model.id == null) throw IllegalStateException("Cannot update model which was not created!")
-        repositoryPost("$prefix/api/workgroup/${model.id}", Message.json.stringify(WorkGroup.serializer(), model))
+        repositoryPost("$prefix/api/workgroup/${model.id}", Serialization.stringify(WorkGroup.serializer(), model))
     }
 
     override suspend fun delete(id: Long) {
diff --git a/src/jsMain/resources/style/components/_board.scss b/src/jsMain/resources/style/components/_board.scss
index 4abf210..f037179 100644
--- a/src/jsMain/resources/style/components/_board.scss
+++ b/src/jsMain/resources/style/components/_board.scss
@@ -58,7 +58,7 @@
     width: 100%;
     height: 100%;
     border-bottom: solid 1px var(--table-border-color);
-    box-shadow: 0 0 4px black;
+    box-shadow: 0 0 4px var(--shadow-color);
     top: -1rem;
     padding-top: 1.2rem;
   }
diff --git a/src/jsMain/resources/style/style.scss b/src/jsMain/resources/style/style.scss
index a55129c..b080704 100644
--- a/src/jsMain/resources/style/style.scss
+++ b/src/jsMain/resources/style/style.scss
@@ -160,3 +160,25 @@ a {
     }
   }
 }
+
+.offline-banner {
+  position: fixed;
+  bottom: 3rem;
+  left: 0;
+  right: 0;
+  height: 3rem;
+  line-height: 3rem;
+  text-align: center;
+  font-size: 1.2rem;
+  background-color: var(--primary-color);
+  color: var(--primary-text-color);
+  z-index: 12;
+  box-shadow: 0 1px 4px var(--shadow-color);
+  display: none;
+}
+
+body.offline {
+  .offline-banner {
+    display: block;
+  }
+}
\ No newline at end of file
diff --git a/src/jvmMain/kotlin/de/kif/backend/repository/WorkGroupRepository.kt b/src/jvmMain/kotlin/de/kif/backend/repository/WorkGroupRepository.kt
index a4ef155..46a1330 100644
--- a/src/jvmMain/kotlin/de/kif/backend/repository/WorkGroupRepository.kt
+++ b/src/jvmMain/kotlin/de/kif/backend/repository/WorkGroupRepository.kt
@@ -3,10 +3,7 @@ package de.kif.backend.repository
 import de.kif.backend.database.DbWorkGroup
 import de.kif.backend.database.dbQuery
 import de.kif.backend.util.PushService
-import de.kif.common.Message
-import de.kif.common.MessageType
-import de.kif.common.Repository
-import de.kif.common.RepositoryType
+import de.kif.common.*
 import de.kif.common.model.Constraint
 import de.kif.common.model.WorkGroup
 import de.westermann.kobserve.event.EventHandler
@@ -36,8 +33,8 @@ object WorkGroupRepository : Repository<WorkGroup> {
         val accessible = row[DbWorkGroup.accessible]
         val length = row[DbWorkGroup.length]
         val language = row[DbWorkGroup.language]
-        val leader = Message.json.parse(String.serializer().list, row[DbWorkGroup.leader])
-        val constraints = Message.json.parse(Constraint.serializer().list, row[DbWorkGroup.constraints])
+        val leader = Serialization.parse(String.serializer().list, row[DbWorkGroup.leader])
+        val constraints = Serialization.parse(Constraint.serializer().list, row[DbWorkGroup.constraints])
 
         val createdAt = row[DbWorkGroup.createdAt]
         val updatedAt = row[DbWorkGroup.updatedAt]
@@ -92,8 +89,8 @@ object WorkGroupRepository : Repository<WorkGroup> {
                 it[accessible] = model.accessible
                 it[length] = model.length
                 it[language] = model.language
-                it[leader] = Message.json.stringify(String.serializer().list, model.leader)
-                it[constraints] = Message.json.stringify(Constraint.serializer().list, model.constraints)
+                it[leader] = Serialization.stringify(String.serializer().list, model.leader)
+                it[constraints] = Serialization.stringify(Constraint.serializer().list, model.constraints)
 
                 it[createdAt] = now
                 it[updatedAt] = now
@@ -124,8 +121,8 @@ object WorkGroupRepository : Repository<WorkGroup> {
                 it[accessible] = model.accessible
                 it[length] = model.length
                 it[language] = model.language
-                it[leader] = Message.json.stringify(String.serializer().list, model.leader)
-                it[constraints] = Message.json.stringify(Constraint.serializer().list, model.constraints)
+                it[leader] = Serialization.stringify(String.serializer().list, model.leader)
+                it[constraints] = Serialization.stringify(Constraint.serializer().list, model.constraints)
 
                 it[updatedAt] = now
             }
diff --git a/src/jvmMain/kotlin/de/kif/backend/util/Backup.kt b/src/jvmMain/kotlin/de/kif/backend/util/Backup.kt
index b9f758f..63b7843 100644
--- a/src/jvmMain/kotlin/de/kif/backend/util/Backup.kt
+++ b/src/jvmMain/kotlin/de/kif/backend/util/Backup.kt
@@ -4,6 +4,7 @@ import de.kif.backend.database.Connection
 import de.kif.backend.repository.*
 import de.kif.common.Message
 import de.kif.common.RepositoryType
+import de.kif.common.Serialization
 import de.kif.common.model.*
 import kotlinx.serialization.Serializable
 
@@ -42,12 +43,12 @@ data class Backup(
                 }
             }
 
-            return Message.json.stringify(serializer(), backup)
+            return Serialization.stringify(serializer(), backup)
         }
 
         @Suppress("UNUSED_VARIABLE")
         suspend fun import(data: String) {
-            val backup = Message.json.parse(serializer(), data)
+            val backup = Serialization.parse(serializer(), data)
 
             backup.users.forEach { UserRepository.create(it); println("Import user ${it.username}") }
             backup.posts.forEach { PostRepository.create(it); println("Import post") }
diff --git a/src/jvmMain/kotlin/de/kif/backend/util/PushService.kt b/src/jvmMain/kotlin/de/kif/backend/util/PushService.kt
index 12f07e3..ed3f172 100644
--- a/src/jvmMain/kotlin/de/kif/backend/util/PushService.kt
+++ b/src/jvmMain/kotlin/de/kif/backend/util/PushService.kt
@@ -1,48 +1,60 @@
 package de.kif.backend.util
 
-import de.kif.backend.prefix
 import de.kif.backend.repository.*
-import de.kif.common.*
+import de.kif.backend.route.api.error
+import de.kif.backend.route.api.success
+import de.kif.common.Message
+import de.kif.common.MessageBox
+import de.kif.common.MessageType
 import de.kif.common.RepositoryType
-import io.ktor.http.cio.websocket.Frame
-import io.ktor.http.cio.websocket.readText
+import io.ktor.application.call
+import io.ktor.http.HttpStatusCode
 import io.ktor.routing.Route
-import io.ktor.websocket.WebSocketServerSession
-import io.ktor.websocket.webSocket
-import kotlinx.coroutines.channels.ClosedReceiveChannelException
+import io.ktor.routing.get
 
 object PushService {
 
-    var clients: List<WebSocketServerSession> = emptyList()
+    var leastValidTimestamp = System.currentTimeMillis()
 
-    suspend fun notify(type: MessageType, repository: RepositoryType, id: Long) {
-        try {
-            val data = Message(type, repository, id).stringify()
-            for (client in clients) {
-                client.outgoing.send(Frame.Text(data))
-            }
-        } catch (e: Exception) {
-            e.printStackTrace()
-        }
+    /**
+     * Save the message with the current timestamp
+     */
+    fun notify(type: MessageType, repository: RepositoryType, id: Long) {
+        val timestamp = System.currentTimeMillis()
+        val message = Message(type, repository, id)
+    }
+
+    /**
+     * Get all messages created after the given timestamp.
+     * The return Box has the current timestamp. If the leastValidTimestamp is less then the current timestamp set the
+     * valid flag to false and return an empty message list.
+     */
+    fun getMessages(timestamp: Long?): MessageBox {
+        return MessageBox(
+            System.currentTimeMillis(),
+            true,
+            emptyList()
+        )
+    }
+
+    /**
+     * Delete all messages before the given timestamp
+     */
+    fun gc(timestamp: Long) {
+        leastValidTimestamp = timestamp
     }
 }
 
 fun Route.pushService() {
-    webSocket("/websocket") {
-        PushService.clients += this
-
+    get("/api/updates") {
         try {
-            while (true) {
-                val text = (incoming.receive() as Frame.Text).readText()
-                println("onMessage($text)")
-                outgoing.send(Frame.Text(text))
-            }
-        } catch (_: ClosedReceiveChannelException) {
-            PushService.clients -= this
-        } catch (e: Throwable) {
-            println("onFailure ${closeReason.await()}")
-            e.printStackTrace()
-            PushService.clients -= this
+            val timestamp = call.request.queryParameters["timestamp"]?.toLongOrNull()
+
+            val messageBox = PushService.getMessages(timestamp)
+
+            call.success(messageBox)
+        } catch (_: Exception) {
+            call.error(HttpStatusCode.InternalServerError)
         }
     }
 
diff --git a/src/jvmMain/kotlin/de/kif/backend/view/MainTemplate.kt b/src/jvmMain/kotlin/de/kif/backend/view/MainTemplate.kt
index f96a52e..5bc149d 100644
--- a/src/jvmMain/kotlin/de/kif/backend/view/MainTemplate.kt
+++ b/src/jvmMain/kotlin/de/kif/backend/view/MainTemplate.kt
@@ -73,6 +73,8 @@ class MainTemplate(
             }
         }
         body {
+            attributes["data-timestamp"] = currentTimeMillis().toString()
+
             if (!noMenu) {
                 insert(MenuTemplate(url, user)) {}
             }
@@ -84,6 +86,10 @@ class MainTemplate(
                 }
             }
 
+            div("offline-banner") {
+                span { +"Die Verbindung zum Server ist unterbrochen" }
+            }
+
             if (!noMenu) {
                 div("footer") {
                     div("container") {