Add menu conditions.

src/card-condition.ts

@@ -0,0 +1,68 @@
+import type { FrigateCardCondition } from './types';
+import { View } from './view';
+
+export interface ConditionState {
+  view?: View;
+  fullscreen?: boolean;
+}
+
+class ConditionStateRequestEvent extends Event {
+  public conditionState?: ConditionState;
+}
+
+export function evaluateCondition(
+  condition?: FrigateCardCondition,
+  state?: ConditionState,
+): boolean {
+  let result = true;
+  if (condition?.view?.length && state?.view) {
+    result &&= condition?.view.includes(state?.view.view);
+  }
+  if (condition?.fullscreen !== undefined && state?.fullscreen !== undefined) {
+    result &&= condition?.fullscreen == state?.fullscreen;
+  }
+  return result;
+}
+
+/**
+ * Evaluate whether a frigateCardCondition is met using an event to fetch state.
+ * @returns A boolean indicating whether the condition is met.
+ */
+export function fetchStateAndEvaluateCondition(
+  node: HTMLElement,
+  condition?: FrigateCardCondition,
+): boolean {
+  if (!condition) {
+    return true;
+  }
+
+  const stateEvent = new ConditionStateRequestEvent(
+    `frigate-card:condition-state-request`,
+    {
+      bubbles: true,
+      composed: true,
+    },
+  );
+
+  /* Special note on what's going on here:
+   *
+   * Some parts of the card (e.g. <frigate-card-elements>) may have arbitrary
+   * complexity and layers (that this card doesn't control) between that master
+   * element and the element that needs to evaluate the condition. In these
+   * cases there's no clean way to pass state from the rest of card down
+   * through these layers. Instead, an event is dispatched as a "request for
+   * state" (StateRequestEvent) upwards which is caught by the outer card
+   * and state added to the event object. Because event propagation is handled
+   * synchronously, the state will be added to the event before the flow
+   * proceeds.
+   */
+  node.dispatchEvent(stateEvent);
+  return evaluateCondition(condition, stateEvent.conditionState);
+}
+
+export function conditionStateRequestHandler(
+  ev: ConditionStateRequestEvent,
+  conditionState?: ConditionState,
+): void {
+  ev.conditionState = conditionState;
+}