feat(@data-point/fetch): adds new Fetch reducer

closes ViacomInc#426

packages/data-point-fetch/Fetch.js

@@ -0,0 +1,145 @@
+const { URL, URLSearchParams } = require("url");
+
+const fetch = require("node-fetch");
+
+const ReducerEntity = require("@data-point/core/ReducerEntity");
+const createReducer = require("@data-point/core/createReducer");
+
+function appendSearchParams(currentSearch, query) {
+  const newSearchParams = new URLSearchParams(query);
+
+  if (!currentSearch) {
+    return newSearchParams;
+  }
+
+  const existingSearchParams = new URLSearchParams(currentSearch);
+
+  newSearchParams.forEach((value, key) => {
+    existingSearchParams.append(key, value);
+  });
+
+  return existingSearchParams;
+}
+
+/**
+ * @param {string} initialUrl request url.
+ * @param {Object} query query string object.
+ * @returns {string} url with query string appended
+ */
+function createRequestUrl(initialUrl, query) {
+  if (!query) {
+    return initialUrl;
+  }
+
+  const url = new URL(initialUrl);
+
+  url.search = appendSearchParams(url.search, query);
+
+  return url.href;
+}
+
+/**
+ * @param {string} url request url.
+ * @param {options} options fetch [options](https://github.com/bitinn/node-fetch#fetch-options).
+ * @returns {Response} [Response](https://github.com/bitinn/node-fetch#class-response) from fetch.
+ * @throws Will throw error if `response.ok` is not `true`.
+ */
+async function makeFetch(url, options) {
+  const response = await fetch(url, options);
+
+  if (!response.ok) {
+    const error = new Error(`${response.status} - ${response.statusText}`);
+    error.response = response;
+    throw error;
+  }
+
+  return response;
+}
+
+/**
+ * DataPoint Reducer to interface with [node-fetch](https://github.com/bitinn/node-fetch)
+ *  module.
+ *
+ * By default it will return the value of `response.json()`, set
+ *  `Fetch.response` to have full control over the result of the
+ *  [Response](https://github.com/bitinn/node-fetch#class-response) object.
+ *
+ * @alias Fetch
+ */
+class Fetch extends ReducerEntity {
+  /**
+   * @param {Object} spec
+   * @param {Reducer} spec.url Resolves to the URL for fetching
+   * @param {Reducer} spec.query Resolves to a query string object to
+   *  append to the url
+   * @param {Reducer} spec.options [Options](https://github.com/bitinn/node-fetch#fetch-options)
+   *  for the http(s) request.
+   * @param {Reducer} spec.response Handles the response of the fetch
+   *  operation. It will execute only if [response.ok](https://github.com/bitinn/node-fetch#responseok)
+   *  is `true`.
+   *  The input value passed to this reducer is the [Response](https://github.com/bitinn/node-fetch#class-response).
+   */
+  constructor(spec = {}) {
+    super(spec);
+
+    if (!spec.url) {
+      throw new Error("fetch.url:Reducer must be provided");
+    }
+
+    this.url = createReducer(spec.url);
+
+    if (spec.query) {
+      this.query = createReducer(spec.query);
+    }
+
+    if (spec.options) {
+      this.options = createReducer(spec.options);
+    }
+
+    if (spec.response) {
+      this.response = createReducer(spec.response);
+    }
+  }
+
+  static create(spec) {
+    return new Fetch(spec);
+  }
+
+  /**
+   * @param {Accumulator} accumulator
+   * @param {Function} resolveReducer
+   * @returns {Promise}
+   */
+  async resolve(accumulator, resolveReducer) {
+    const request = await resolveReducer(accumulator, this.url);
+
+    const options = this.options
+      ? await resolveReducer(accumulator, this.options)
+      : undefined;
+
+    const query = this.query
+      ? await resolveReducer(accumulator, this.query)
+      : undefined;
+
+    const url = createRequestUrl(request, query);
+
+    const responseObject = await makeFetch(url, options);
+
+    // by default if this.response is not set then res.json() is assumed
+    if (!this.response) {
+      return responseObject.json();
+    }
+
+    return resolveReducer(
+      accumulator.set("value", responseObject),
+      this.response
+    );
+  }
+}
+
+module.exports = {
+  appendSearchParams,
+  createRequestUrl,
+  makeFetch,
+  Fetch
+};