Total overhaul!

src/cover-controller.js

@@ -0,0 +1,40 @@
+import {Controller} from "./controller.js";
+
+export class CoverController extends Controller {
+
+  get _value() {
+    return this.stateObj.state === "open"
+    ? this.stateObj.attributes.current_position
+    : 0;
+  }
+
+  set _value(value) {
+    this._hass.callService("cover", "set_cover_position", {
+      entity_id: this.stateObj.entity_id,
+      position: value,
+    });
+  }
+
+  get string() {
+    if (!this.hasSlider)
+      return "";
+    if (this.stateObj.state === "closed")
+      return this._hass.localize("state.cover.closed");
+    return `${this.value} %`
+  }
+
+  get hasToggle() {
+    return false;
+  }
+
+  get hasSlider() {
+    if ("current_position" in this.stateObj.attributes) return true;
+    if (("supported_features" in this.stateObj.attributes) &&
+      (this.stateObj.attributes.supported_features & 4)) return true;
+    return false;
+  }
+
+  get _step() {
+    return 10;
+  }
+}