web/admin: add new base form to handle refresh events

Signed-off-by: Jens Langhammer <jens.langhammer@beryju.org>

web/src/elements/forms/ModelForm.ts

@@ -0,0 +1,32 @@
+import { property } from "lit-element";
+import { EVENT_REFRESH } from "../../constants";
+import { Form } from "./Form";
+
+export abstract class ModelForm<T, PKT> extends Form<T> {
+
+    abstract loadInstance(pk: PKT): Promise<T>;
+
+    @property()
+    set instancePk(value: PKT) {
+        this._instancePk = value;
+        this.loadInstance(value).then(instance => {
+            this.instance = instance;
+        });
+    }
+
+    private _instancePk?: PKT;
+
+    @property({ attribute: false })
+    instance?: T;
+
+    constructor() {
+        super();
+        this.addEventListener(EVENT_REFRESH, () => {
+            if (!this._instancePk) return;
+            this.loadInstance(this._instancePk).then(instance => {
+                this.instance = instance;
+            });
+        });
+    }
+
+}