Improve calculator selected standards config cache coherency

apps/api/src/services/calculator.ts

@@ -49,19 +49,19 @@ class CalculatorStandardsService {
 
 class CalculatorStandardsConfigService {
     private cache = {
-        refreshInterval: 30_000,
-        lastRefreshedAt: 0,
-        isStale: function () {
-            return Date.now() - this.lastRefreshedAt >= this.refreshInterval;
-        },
-        isIncomplete: function () {
-            return !this.data.id || !this.data.datasetId || !this.data.config
-        },
         data: {
             id: null as string | null,
             datasetId: null as string | null,
             config: null as StandardsConfig | null
         },
+        isStale: async () => {
+            const { standards_config_id: selectedConfigId } = await db.selectFrom("calculators")
+                .select("standards_config_id")
+                .where("name", "=", this.name)
+                .executeTakeFirstOrThrow();
+            return selectedConfigId !== this.cache.data.id;
+        },
+        isComplete: () => Object.values(this.cache.data).every((v) => v !== null),
     }
 
     constructor(private name: string) { }
@@ -73,9 +73,10 @@ class CalculatorStandardsConfigService {
     }
 
     async refresh(opt: { onlyIfStale?: boolean } = {}): Promise<void> {
-        if (!this.cache.isIncomplete() && (opt.onlyIfStale && !this.cache.isStale())) return;
-
         try {
+            const cacheIsCoherent = this.cache.isComplete() && (opt.onlyIfStale && !(await this.cache.isStale()));
+            if (cacheIsCoherent) return;
+
             const result = await db.selectFrom("calculators")
                 .innerJoin("standards_configs", "standards_configs.id", "calculators.standards_config_id")
                 .innerJoin("standards_datasets", "standards_datasets.id", "standards_configs.dataset_id")
@@ -97,9 +98,6 @@ class CalculatorStandardsConfigService {
                 data: result.data,
                 params: result.params
             };
-            // only mark as refreshed once we've actually confirmed the selected
-            // config; a failed attempt must not make stale data look fresh
-            this.cache.lastRefreshedAt = Date.now();
         } catch (err) {
             throw new CalculatorUnavailableError("Unable to determine the calculator's standards configuration", { cause: err });
         }