feat: Add support for templates in actions (#1891)

- Closes #1878

src/card-controller/templates/index.ts

@@ -0,0 +1,80 @@
+import { HomeAssistant } from '@dermotduffy/custom-card-helpers';
+import { HASS, renderTemplate } from 'ha-nunjucks/dist';
+import { ConditionsEvaluationData, ConditionState } from '../../conditions/types';
+import { ActionType } from '../../config/types';
+
+interface TemplateContextInternal {
+  camera?: string;
+  view?: string;
+  trigger?: ConditionsEvaluationData;
+}
+
+interface TemplateContext {
+  advanced_camera_card: TemplateContextInternal;
+
+  // Convenient alias.
+  acc: TemplateContextInternal;
+}
+
+export class TemplateRenderer {
+  public renderRecursively = (
+    hass: HomeAssistant,
+    data: unknown,
+    options?: {
+      conditionState?: ConditionState;
+      triggerData?: ConditionsEvaluationData;
+    },
+  ): ActionType => {
+    return this._renderTemplateRecursively(
+      hass,
+      data,
+      this._conditionStateToTemplateContext(
+        options?.conditionState,
+        options?.triggerData,
+      ),
+    );
+  };
+
+  protected _conditionStateToTemplateContext(
+    conditionState?: ConditionState,
+    triggerData?: ConditionsEvaluationData,
+  ): TemplateContext | undefined {
+    if (!conditionState?.camera && !conditionState?.view && !triggerData) {
+      return;
+    }
+
+    const advancedCameraCardContext: TemplateContextInternal = {
+      ...(conditionState?.camera && { camera: conditionState.camera }),
+      ...(conditionState?.view && { view: conditionState.view }),
+      ...(triggerData && { trigger: triggerData }),
+    };
+
+    return {
+      acc: advancedCameraCardContext,
+      advanced_camera_card: advancedCameraCardContext,
+    };
+  }
+
+  protected _renderTemplateRecursively(
+    hass: HomeAssistant,
+    data: unknown,
+    templateContext?: TemplateContext,
+  ): ActionType {
+    if (typeof data === 'string') {
+      // ha-nunjucks has a more complete model of the Home Assistant object, but
+      // does not export it as a type.
+      return renderTemplate(hass as unknown as typeof HASS, data, templateContext);
+    } else if (Array.isArray(data)) {
+      return data.map((item) =>
+        this._renderTemplateRecursively(hass, item, templateContext),
+      );
+    } else if (typeof data === 'object' && data !== null) {
+      const result = {};
+      for (const key in data) {
+        result[key] = this._renderTemplateRecursively(hass, data[key], templateContext);
+      }
+      return result;
+    }
+    return data;
+  }
+}