Forecasts from OpenWeatherMap do not show "Yesterday" during any portion of a day

AUTHORS

@@ -7,3 +7,4 @@ Simon Legner <Simon.Legner@gmail.com>,
 Mattia Meneguzzo <odysseus@fedoraproject.org>,
 Christian Metzler <neroth@xeked.com>,
 Jens Lody <jens@jenslody.de>
+Taylor Raack <taylor@raack.info>

README.md

@@ -99,6 +99,9 @@ Copyright © 2011 - 2013
 Copyright © 2013 - 2017
 * Jens Lody <openweather@jenslody.de>.
 
+Copyright &copy; 2018
+* Taylor Raack <taylor@raack.info>.
+
 
 This file is part of *gnome-shell-extension-openweather*.
 

src/openweathermap_org.js

@@ -17,6 +17,8 @@
  *     Jens Lody <jens@jenslody.de>
  * Copyright (C) 2014 -2015
  *     Jens Lody <jens@jenslody.de>,
+ * Copyright (C) 2018
+ *     Taylor Raack <taylor@raack.info>
  *
  *
  * This file is part of gnome-shell-extension-openweather.
@@ -428,10 +430,29 @@ function parseWeatherForecast() {
     let forecast = this.forecastWeatherCache;
     let beginOfDay = new Date(new Date().setHours(0, 0, 0, 0));
 
+    // OpenWeatherMap sometimes returns the previous day's forecast, especially in the early morning hours
+    // of the lat / lng being queried. To prevent the first forecast element in the UI from being the previous
+    // day's forecast, check for the returned forecast elements being for a previous day and maintain a
+    // forecast index advance counter to skip previous day forecasts.
+    let dateAdvanceIndex = 0;
+    for (let i = 0; i < this._days_forecast; i++) {
+        let forecastData = forecast[i];
+        if (forecastData === undefined)
+            continue;
+        let forecastDate = new Date(forecastData.dt * 1000).setHours(0,0,0,0);
+        if (forecastDate >= beginOfDay) {
+        	// forecast is at least at the beginning of the current day; no need to look any further
+        	break;
+        }
+        // forecast is behind the current day, so advance the increment index
+    	dateAdvanceIndex++;
+    }
+
     // Refresh forecast
     for (let i = 0; i < this._days_forecast; i++) {
         let forecastUi = this._forecast[i];
-        let forecastData = forecast[i];
+        // make sure to use the dateAdvanceIndex to skip any previous day forecasts
+        let forecastData = forecast[i + dateAdvanceIndex];
         if (forecastData === undefined)
             continue;