fix-3809 race condition in Subscription extension fhir-path-criteria-…

…expression %previous value lookup (medplum#3810)

* fix-3809 race condition in Subscription extension fhir-path-criteria-expression %previous value lookup

* remove redundant check

packages/server/src/workers/utils.ts

@@ -114,20 +114,25 @@ export async function isFhirCriteriaMet(subscription: Subscription, currentResou
  if (!criteria?.valueString) {
  return true;
  }
- const history = await systemRepo.readHistory(currentResource.resourceType, currentResource?.id as string);
+ const previous = await getPreviousResource(currentResource);
  const evalInput = {
  '%current': toTypedValue(currentResource),
- '%previous': toTypedValue({}),
+ '%previous': toTypedValue(previous ?? {}),
  };
- const previousResource = history.entry?.[1]?.resource as Resource;
- if (previousResource) {
- evalInput['%previous'] = toTypedValue(previousResource);
- }
  const evalValue = evalFhirPathTyped(criteria.valueString, [toTypedValue(currentResource)], evalInput);
- if (evalValue?.[0]?.value === true) {
- return true;
- }
- return false;
+ return evalValue?.[0]?.value === true;
+}
+
+async function getPreviousResource(currentResource: Resource): Promise<Resource | undefined> {
+ const history = await systemRepo.readHistory(currentResource.resourceType, currentResource?.id as string);
+
+ return history.entry?.find((_, idx) => {
+ if (idx === 0) {
+ return false;
+ }
+
+ return history.entry?.[idx - 1]?.resource?.meta?.versionId === currentResource.meta?.versionId;
+ })?.resource;
 }
 
 export function isJobSuccessful(subscription: Subscription, status: number): boolean {