feat(frontend): implement basic frontend interface

frontend/src/utils/toast.js

@@ -0,0 +1,39 @@
+import { reactive } from 'vue';
+
+let seq = 0;
+
+export const toasts = reactive([]);
+
+function dismiss(id) {
+    const idx = toasts.findIndex((t) => t.id === id);
+    if (idx !== -1) toasts[idx].leaving = true;
+    setTimeout(() => {
+        const i = toasts.findIndex((t) => t.id === id);
+        if (i !== -1) toasts.splice(i, 1);
+    }, 240);
+}
+
+function push(type, message, timeout) {
+    const id = ++seq;
+    toasts.push({ id, type, message, leaving: false });
+    if (timeout > 0) {
+        setTimeout(() => dismiss(id), timeout);
+    }
+    return id;
+}
+
+export const toast = {
+    success(message, timeout = 3600) {
+        return push('success', message, timeout);
+    },
+    error(message, timeout = 5200) {
+        return push('error', message, timeout);
+    },
+    info(message, timeout = 3200) {
+        return push('info', message, timeout);
+    },
+    warn(message, timeout = 4200) {
+        return push('warn', message, timeout);
+    },
+    dismiss
+};