frontend: show snackbar notifications on parameter changes

Emit an info-level snackbar when a MAVLink parameter value changes
after initial loading is complete, only in developer mode. Refactor
Alerter to render a stack of v-alert components so multiple
notifications are visible at once, with auto-dismiss timers and a cap
of 5 visible alerts. Persistent alerts (error/critical) are preserved
when evicting to stay within the cap.

Made-with: Cursor

Author: Williangalvani

core/frontend/src/components/app/Alerter.vue

@@ -1,56 +1,127 @@
 <template>
-  <v-snackbar
-    v-model="show"
-    :timeout="timeout"
-  >
-    {{ message }}
-
-    <template #action="{ attrs }">
-      <v-btn
-        :color="color"
-        text
-        v-bind="attrs"
-        @click="show = false"
+  <div class="alerter-stack">
+    <v-slide-y-reverse-transition
+      group
+      leave-absolute
+    >
+      <v-alert
+        v-for="alert in alerts"
+        :key="alert.id"
+        :value="true"
+        :type="alertType(alert.level)"
+        class="alerter-item"
+        dense
+        dismissible
+        elevation="6"
+        @input="dismiss(alert.id)"
       >
-        Close
-      </v-btn>
-    </template>
-  </v-snackbar>
+        {{ alert.message }}
+      </v-alert>
+    </v-slide-y-reverse-transition>
+  </div>
 </template>
 
 <script lang="ts">
 import Vue from 'vue'
 
 import message_manager, { MessageLevel } from '@/libs/message-manager'
 
+const MAX_VISIBLE = 5
+const DRAIN_INTERVAL_MS = 1000
+
+interface AlertEntry {
+  id: number
+  level: MessageLevel
+  message: string
+}
+
+let nextId = 0
+
 export default Vue.extend({
   name: 'ErrorMessage',
   data() {
     return {
-      level: undefined as MessageLevel|undefined,
-      message: '',
-      show: false,
+      alerts: [] as AlertEntry[],
+      queue: [] as AlertEntry[],
+      drainTimer: null as ReturnType<typeof setInterval> | null,
+      boundCallback: null as ((level: MessageLevel, msg: string) => void) | null,
+    }
+  },
+  mounted() {
+    this.boundCallback = (level: MessageLevel, message: string) => {
+      nextId += 1
+      const entry = { id: nextId, level, message }
+      if (this.alerts.length < MAX_VISIBLE) {
+        this.showAlert(entry)
+      } else {
+        this.queue.push(entry)
+        this.startDrain()
+      }
+    }
+    message_manager.addCallback(this.boundCallback)
+  },
+  beforeDestroy() {
+    if (this.boundCallback) {
+      message_manager.removeCallback(this.boundCallback)
+      this.boundCallback = null
     }
+    this.stopDrain()
   },
-  computed: {
-    color(): string {
-      switch (this.level) {
+  methods: {
+    showAlert(entry: AlertEntry) {
+      this.alerts.push(entry)
+      const timeout = this.getTimeout(entry.level)
+      if (timeout > 0) {
+        setTimeout(() => this.dismiss(entry.id), timeout)
+      }
+    },
+    dismiss(id: number) {
+      const idx = this.alerts.findIndex((a) => a.id === id)
+      if (idx !== -1) {
+        this.alerts.splice(idx, 1)
+        this.promoteFromQueue()
+      }
+    },
+    promoteFromQueue() {
+      while (this.queue.length > 0 && this.alerts.length < MAX_VISIBLE) {
+        this.showAlert(this.queue.shift()!)
+      }
+      if (this.queue.length === 0) {
+        this.stopDrain()
+      }
+    },
+    startDrain() {
+      if (this.drainTimer) return
+      this.drainTimer = setInterval(() => {
+        const evictIdx = this.alerts.findIndex((a) => this.getTimeout(a.level) > 0)
+        if (evictIdx !== -1) {
+          this.dismiss(this.alerts[evictIdx].id)
+        } else if (this.queue.length > 0 && this.alerts.length > 0) {
+          this.dismiss(this.alerts[0].id)
+        }
+      }, DRAIN_INTERVAL_MS)
+    },
+    stopDrain() {
+      if (this.drainTimer) {
+        clearInterval(this.drainTimer)
+        this.drainTimer = null
+      }
+    },
+    alertType(level: MessageLevel): string {
+      switch (level) {
         case MessageLevel.Success:
           return 'success'
         case MessageLevel.Error:
+        case MessageLevel.Critical:
           return 'error'
-        case MessageLevel.Info:
-          return 'info'
         case MessageLevel.Warning:
           return 'warning'
-        case MessageLevel.Critical:
-          return 'critical'
         default:
           return 'info'
       }
     },
-    timeout(): number {
-      switch (this.level) {
+    getTimeout(level: MessageLevel): number {
+      switch (level) {
         case MessageLevel.Success:
         case MessageLevel.Info:
           return 5000
@@ -61,12 +132,21 @@ export default Vue.extend({
       }
     },
   },
-  mounted() {
-    message_manager.addCallback((level: MessageLevel, message: string) => {
-      this.level = level
-      this.message = message
-      this.show = true
-    })
-  },
 })
 </script>
+
+<style scoped>
+.alerter-stack {
+  position: fixed;
+  bottom: 16px;
+  left: 50%;
+  transform: translateX(-50%);
+  z-index: 1000;
+  min-width: 344px;
+  max-width: 672px;
+}
+
+.alerter-item {
+  margin-bottom: 8px;
+}
+</style>

core/frontend/src/libs/message-manager.ts

@@ -48,6 +48,16 @@ class MessageManager {
     this.callbacks.push(callback)
   }
 
+  /**
+   * Remove a previously added callback
+   */
+  removeCallback(callback:(level: MessageLevel, msg: string) => void): void {
+    const index = this.callbacks.indexOf(callback)
+    if (index !== -1) {
+      this.callbacks.splice(index, 1)
+    }
+  }
+
   /**
    * Emit a new message to be used in all callbacks
    */

core/frontend/src/types/autopilot/parameter-fetcher.ts

@@ -1,4 +1,6 @@
 import mavlink2rest from '@/libs/MAVLink2Rest'
+import message_manager, { MessageLevel } from '@/libs/message-manager'
+import settings from '@/libs/settings'
 // eslint-disable-next-line import/no-cycle
 import ardupilot_data from '@/store/autopilot'
 import { AutopilotStore } from '@/store/autopilot'
@@ -33,6 +35,10 @@ export default class ParameterFetcher {
     this.store = store
   }
 
+  allParametersLoaded(): boolean {
+    return this.total_params_count !== null && this.loaded_params_count >= this.total_params_count
+  }
+
   reset(): void {
     this.loaded_params_count = 0
     this.total_params_count = null
@@ -57,9 +63,7 @@ export default class ParameterFetcher {
   }
 
   requestParamsWatchdog(): void {
-    if (this.total_params_count !== null
-      && this.loaded_params_count > 0
-      && this.loaded_params_count >= this.total_params_count) {
+    if (this.loaded_params_count > 0 && this.allParametersLoaded()) {
       return
     }
     if (autopilot.restarting) {
@@ -107,7 +111,13 @@ export default class ParameterFetcher {
       // We need this due to mismatches between js 64-bit floats and REAL32 in MAVLink
       const trimmed_value = Math.round(param_value * 10000) / 10000
       if (param_index === 65535) {
-        this.parameter_table.updateParam(param_name, trimmed_value)
+        const change = this.parameter_table.updateParam(param_name, trimmed_value)
+        if (change && this.allParametersLoaded() && settings.is_dev_mode) {
+          message_manager.emitMessage(
+            MessageLevel.Info,
+            `Parameter ${param_name} changed: ${change.oldValue} → ${trimmed_value}`,
+          )
+        }
       } else {
         this.parameter_table.addParam(
           {

core/frontend/src/types/autopilot/parameter-table.ts

@@ -190,15 +190,21 @@ export default class ParametersTable {
     this.parametersDict[param.id] = param
   }
 
-  updateParam(param_name: string, param_value: number): void {
+  updateParam(param_name: string, param_value: number): { oldValue: number } | null {
     const index = Object.entries(this.parametersDict).find(([_key, value]) => value.name === param_name)
     if (!index) {
       // This is benign and will happen if we receive a parameter update before the parameters table
       // is fully populated. We can safely ignore it.
       console.info(`Unable to update param in store: ${param_name}. Parameter not yet loaded into ParametersTable.`)
-      return
+      return null
+    }
+    const paramKey = parseInt(index[0], 10)
+    const oldValue = this.parametersDict[paramKey].value
+    this.parametersDict[paramKey].value = param_value
+    if (oldValue !== param_value) {
+      return { oldValue }
     }
-    this.parametersDict[parseInt(index[0], 10)].value = param_value
+    return null
   }
 
   parameters(): Parameter[] {