Attempt at generalizing the url requests

public/js/appChart.js

 "use strict";
 
-// Request parameters
+// DEBUG:
+// Observations WITHOUT data gap - Bau 225 / Datastream ID = 80
+// Observations WITH data gap - Bau 112 / Datastream ID = 78
 
-// Observations WITHOUT data gap - Bau 225
-const BASE_URL =
-  "http://193.196.39.91:8080/frost-icity-tp31/v1.1/Datastreams(80)/Observations";
+const BASE_URL = "http://193.196.39.91:8080/frost-icity-tp31/v1.1";
 
+/**
+ * Create URL to fetch the Observations corresponding to a provided Datastream
+ * @param {*} datastreamID - integer representing the Datastream ID
+ * @returns {String}
+ */
+const getObservationsUrl = function (datastreamID) {
+  if (!datastreamID) return;
+  const fullDatastreamURL = `${BASE_URL}/Datastreams(${datastreamID})/Observations`;
+  return fullDatastreamURL;
+};
+
+/**
+ * Create a temporal filter string for the fetched Observations
+ * @param {*} dateStart - start date in YYYY-MM-DD format
+ * @param {*} dateStop - stop date in YYYY-MM-DD format
+ * @returns {String}
+ */
+const createTemporalFilterString = function (dateStart, dateStop) {
+  if (!dateStart || !dateStop) return;
+  const filterString = `resultTime ge ${dateStart}T00:00:00.000Z and resultTime le ${dateStop}T00:00:00.000Z`;
+  return filterString;
+};
+
+const BASE_URL_OBSERVATIONS = getObservationsUrl(80);
 const PARAM_RESULT_FORMAT = "dataArray";
 const PARAM_ORDER_BY = "phenomenonTime asc";
-const PARAM_FILTER =
-  "resultTime ge 2020-01-01T00:00:00.000Z and resultTime le 2021-01-01T00:00:00.000Z";
+const PARAM_FILTER = createTemporalFilterString("2020-01-01", "2021-01-01");
 const PARAM_SELECT = "result,phenomenonTime";
 
-// Observations WITH data gap - Bau 112
-const BASE_URL2 =
-  "http://193.196.39.91:8080/frost-icity-tp31-v2/v1.1/Datastreams(78)/Observations";
-const PARAM_FILTER2 =
-  "resultTime ge 2020-06-01T00:00:00.000Z and resultTime le 2021-01-01T00:00:00.000Z";
+const axiosGetRequest = axios.get(BASE_URL_OBSERVATIONS, {
+  params: {
+    "$resultFormat": PARAM_RESULT_FORMAT,
+    "$orderBy": PARAM_ORDER_BY,
+    "$filter": PARAM_FILTER,
+    "$select": PARAM_SELECT,
+  },
+});
 
 /**
  * Format the response from SensorThings API to make it suitable for heatmap
@@ -216,16 +242,7 @@ const followNextLink = function (responsePromise) {
 };
 
 // Get "ALL" the Observations that satisfy our query
-followNextLink(
-  axios.get(BASE_URL, {
-    params: {
-      "$resultFormat": PARAM_RESULT_FORMAT,
-      "$orderBy": PARAM_ORDER_BY,
-      "$filter": PARAM_FILTER,
-      "$select": PARAM_SELECT,
-    },
-  })
-)
+followNextLink(axiosGetRequest)
   .then((success) => {
     const successValue = success.data.value;