1 files changed, 106 insertions, 0 deletions
diff --git a/app/assets/javascripts/lib/utils/apollo_startup_js_link.js b/app/assets/javascripts/lib/utils/apollo_startup_js_link.js
new file mode 100644
index 00000000000..5c120dd532f
--- /dev/null
+++ b/app/assets/javascripts/lib/utils/apollo_startup_js_link.js
@@ -0,0 +1,106 @@
+import { ApolloLink, Observable } from 'apollo-link';
+import { parse } from 'graphql';
+import { isEqual, pickBy } from 'lodash';
+
+/**
+ * Remove undefined values from object
+ * @param obj
+ * @returns {Dictionary<unknown>}
+ */
+const pickDefinedValues = obj => pickBy(obj, x => x !== undefined);
+
+/**
+ * Compares two set of variables, order independent
+ *
+ * Ignores undefined values (in the top level) and supports arrays etc.
+ */
+const variablesMatch = (var1 = {}, var2 = {}) => {
+  return isEqual(pickDefinedValues(var1), pickDefinedValues(var2));
+};
+
+export class StartupJSLink extends ApolloLink {
+  constructor() {
+    super();
+    this.startupCalls = new Map();
+    this.parseStartupCalls(window.gl?.startup_graphql_calls || []);
+  }
+
+  // Extract operationNames from the queries and ensure that we can
+  // match operationName => element from result array
+  parseStartupCalls(calls) {
+    calls.forEach(call => {
+      const { query, variables, fetchCall } = call;
+      const operationName = parse(query)?.definitions?.find(x => x.kind === 'OperationDefinition')
+        ?.name?.value;
+
+      if (operationName) {
+        this.startupCalls.set(operationName, {
+          variables,
+          fetchCall,
+        });
+      }
+    });
+  }
+
+  static noopRequest = (operation, forward) => forward(operation);
+
+  disable() {
+    this.request = StartupJSLink.noopRequest;
+    this.startupCalls = null;
+  }
+
+  request(operation, forward) {
+    // Disable StartupJSLink in case all calls are done or none are set up
+    if (this.startupCalls && this.startupCalls.size === 0) {
+      this.disable();
+      return forward(operation);
+    }
+
+    const { operationName } = operation;
+
+    // Skip startup call if the operationName doesn't match
+    if (!this.startupCalls.has(operationName)) {
+      return forward(operation);
+    }
+
+    const { variables: startupVariables, fetchCall } = this.startupCalls.get(operationName);
+    this.startupCalls.delete(operationName);
+
+    // Skip startup call if the variables values do not match
+    if (!variablesMatch(startupVariables, operation.variables)) {
+      return forward(operation);
+    }
+
+    return new Observable(observer => {
+      fetchCall
+        .then(response => {
+          // Handle HTTP errors
+          if (!response.ok) {
+            throw new Error('fetchCall failed');
+          }
+          operation.setContext({ response });
+          return response.json();
+        })
+        .then(result => {
+          if (result && (result.errors || !result.data)) {
+            throw new Error('Received GraphQL error');
+          }
+
+          // we have data and can send it to back up the link chain
+          observer.next(result);
+          observer.complete();
+        })
+        .catch(() => {
+          forward(operation).subscribe({
+            next: result => {
+              observer.next(result);
+            },
+            error: error => {
+              observer.error(error);
+            },
+            complete: observer.complete.bind(observer),
+          });
+        });
+    });
+  }
+}