feat: add fetchElasticMapping helper

* add fetchElasticMapping helper

* fix lint error

* fix return Promise type

* fix lint error

.gitignore

@@ -46,3 +46,4 @@ node_modules
 
 coverage
 .nyc_output
+package-lock.json

src/index.js

@@ -4,3 +4,4 @@ export { composeWithElastic } from './composeWithElastic';
 export { convertToSourceTC, inputPropertiesToGraphQLTypes } from './mappingConverter';
 export { default as ElasticApiParser } from './ElasticApiParser';
 export { elasticApiFieldConfig } from './elasticApiFieldConfig';
+export { fetchElasticMapping } from './utils';

src/utils.js

@@ -1,6 +1,7 @@
 /* @flow */
 
 import { TypeStorage } from 'graphql-compose';
+import type { ElasticMappingT } from './mappingConverter';
 
 const typeStorage = new TypeStorage();
 
@@ -29,3 +30,35 @@ export function reorderKeys<T: Object>(obj: T, names: string[]): T {
   });
   return { ...orderedFields, ...fields };
 }
+
+export type fetchElasticMappingOptsT = {
+  elasticIndex: string,
+  elasticType: string,
+  elasticMapping: ElasticMappingT,
+  elasticClient: Object,
+};
+
+export async function fetchElasticMapping(
+  opts: fetchElasticMappingOptsT
+): Promise<ElasticMappingT> {
+  if (!opts.elasticIndex || typeof opts.elasticIndex !== 'string') {
+    throw new Error('Must provide `elasticIndex` string parameter from your Elastic server.');
+  }
+
+  if (!opts.elasticType || typeof opts.elasticType !== 'string') {
+    throw new Error('Must provide `elasticType` string parameter from your Elastic server.');
+  }
+
+  if (!opts.elasticClient) {
+    throw new Error(
+      'Must provide `elasticClient` Object parameter connected to your Elastic server.'
+    );
+  }
+
+  const elasticMapping = (await opts.elasticClient.indices.getMapping({
+    index: opts.elasticIndex,
+    type: opts.elasticType,
+  }))[opts.elasticIndex].mappings[opts.elasticType];
+
+  return elasticMapping;
+}