feat: added $capabilities() function (#62)

src/helpers/fhirFunctions/capabilities.ts

@@ -0,0 +1,27 @@
+/**
+ * © Copyright Outburn Ltd. 2022-2024 All Rights Reserved
+ *   Project name: FUME-COMMUNITY
+ */
+import { getFhirClient } from '../fhirServer';
+import thrower from '../thrower';
+
+// cached copy of the capability statement resource
+let capabilityStatement: Record<string, any | any[]> = {};
+
+export const capabilities = async (): Promise<Record<string, any> | undefined> => {
+  // check if capability statement cached copy is empty
+  if (Object.keys(capabilityStatement).length === 0) {
+    // try to fetch from server
+    try {
+      capabilityStatement = await getFhirClient().read('metadata');
+    } catch (error) {
+      return thrower.throwRuntimeError(`Failed to fetch CapabilityStatement from FHIR server. ${JSON.stringify(error)}`);
+    }
+  };
+  // check that the object is actually a capability statement
+  if (!capabilityStatement?.resourceType || typeof capabilityStatement.resourceType !== 'string' || capabilityStatement.resourceType !== 'CapabilityStatement') {
+    return thrower.throwRuntimeError('Invalid response from FHIR server: The \'/metadata\' endpoint did not return a CapabilityStatement resource');
+  };
+  // return the cached capability statement
+  return capabilityStatement;
+};

src/helpers/fhirFunctions/index.ts

@@ -2,6 +2,7 @@
  * © Copyright Outburn Ltd. 2022-2024 All Rights Reserved
  *   Project name: FUME-COMMUNITY
  */
+import { capabilities } from './capabilities';
 import { fhirVersionToMinor } from './fhirVersionToMinor';
 import { literal } from './literal';
 import { reference } from './reference';
@@ -21,5 +22,6 @@ export default {
   translateCoding,
   translateCode,
   fhirVersionToMinor,
-  reference
+  reference,
+  capabilities
 };

src/helpers/jsonataFunctions/transform.ts

@@ -90,6 +90,7 @@ export const transform = async (input, expression: string, extraBindings: Record
     bindings.v2parse = v2.v2parse;
     bindings.v2json = v2.v2json;
     bindings.isNumeric = stringFuncs.isNumeric;
+    bindings.capabilities = fhirFuncs.capabilities;
 
     const { aliases } = getCache();
     // these are debug functions, should be removed in production versions