Round dates when making heatmap api requests

Changelog.md

@@ -1,13 +1,15 @@
 The data displayed has been produced by low-cost devices developed by [Connected Humber](https://www.connectedhumber.org/) members as part of a community driven effort to build a network of smart sensors in the Humber Region.
 # Changelog
 
-
 This is the changelog for the air quality web interface and its associated HTTP API.
 
  - `[API]` refers to changes to the [HTTP API](https://aq.connectedhumber.org/__nightdocs/05-API-Docs.html).
  - `[Code]` refers to internal changes to the code that have no direct impact on the web interface or the HTTP API, but are significant enough to warrant note.
  - `[Docs]` refers to changes to the [documentation](https://aq.connectedhumber.org/__nightdocs/00-Welcome.html).
 
+## v0.13
+ - Round dates before making API requests to improve caching potential
+
 ## v0.12
  - Added loading animation while the map is loading
  - Added device sensor information to the device info tab in the popup

client_src/js/Config.mjs

@@ -10,6 +10,10 @@ export default {
 	// The default zoom level to use when loading the page.
 	default_zoom: 12,
 	
+	// The number of minutes to round dates to when making time-based HTTP API requests.
+	// Very useful for improving cache hit rates.
+	date_rounding_interval: 6,
+	
 	heatmap: {
 		// The radius fo blobs on the heatmap
 		blob_radius: 0.02

client_src/js/Helpers/DateHelper.mjs

@@ -46,7 +46,23 @@ function human_time(seconds)
 	}
 }
 
+/**
+ * Rounds a Date to match the specified number of minutes.
+ * Useful when making API requests to improve caching.
+ * @param	{Date}	date				The date to round.
+ * @param	{int}	interval_minutes	The number of minutes to round it to. Should be less than 60.
+ * @return	{void}	Doesn't return anything - it mutates the original Date object instead.
+ */
+function round_date_interval(date, interval_minutes) {
+	date.setSeconds(0);
+	date.setMilliseconds(0);
+	date.setMinutes(
+		Math.floor(date.getMinutes() / interval_minutes) * interval_minutes
+	);
+}
+
 export {
 	human_duration_unit,
-	human_time_since, human_time
+	human_time_since, human_time,
+	round_date_interval
 };

client_src/js/Overlay/VoronoiManager.mjs

@@ -12,6 +12,7 @@ import Specs from './OverlaySpecs.mjs';
 
 import Vector2 from '../Helpers/Vector2.mjs';
 import GetFromUrl from '../Helpers/GetFromUrl.mjs';
+import { round_date_interval } from '../Helpers/DateHelper.mjs';
 
 class VoronoiManager {
 	
@@ -52,6 +53,8 @@ class VoronoiManager {
 		this.last_datetime = datetime;
 		this.last_reading_type = reading_type;
 		
+		round_date_interval(this.last_datetime, Config.date_rounding_interval);
+		
 		this.spec = Specs[reading_type] || Specs["unknown"];
 		if(typeof this.spec.chroma == "undefined")
 			this.spec.chroma = chroma.scale(Object.values(this.spec.gradient))