A lot of changes to get RTC clock synced and do accurate lastReading math to avoid missed readings

NightscoutEInkClient.ino

@@ -39,13 +39,25 @@ void setup() {
   while (!Serial) { delay(10); }
   Serial.println("Nightscout CGM BS Monitor starting...");
 
+  ConnectToWifi();
+
+  struct tm timeinfo;
+  initTime();
+  
+  if(!getLocalTime(&timeinfo)){
+    Serial.println("Failed to obtain time");
+  }
+  else {
+    Serial.println(&timeinfo, "%A, %B %d %Y %H:%M:%S");
+  }
+
   //turn EPD on
   pinMode(EPD_ENABLE, OUTPUT);
   digitalWrite(EPD_ENABLE, HIGH);
   
-  ConnectToWifi();
+  //ConnectToWifi();
   String nightscoutResponse = httpGETRequest(nightscoutUrl);
-  Serial.println(nightscoutResponse);
+  //Serial.println(nightscoutResponse);
   DynamicJsonDocument doc(8192);
   DeserializationError error = deserializeJson(doc, nightscoutResponse);
   
@@ -68,16 +80,39 @@ void setup() {
   display.display();
 
   String dateString = array[0]["dateString"].as<String>();
+  unsigned long long dateInt = array[0]["date"].as<unsigned long long>();
+  int correctedDateInt = dateInt / 1000;
+  time_t lastSyncTime = (time_t)correctedDateInt;
+  /*
+  Serial.println(dateInt);
+  Serial.println(correctedDateInt);
+  struct tm *lastSync;
+  //Serial.println(lastSync);
+  
+  lastSync = localtime(&lastSyncTime);
+  Serial.print("Last Sync Time ");
+  Serial.println(lastSync, "%A, %B %d %Y %H:%M:%S");
   int lastReadInSecondsWithinTheHour = GetLastSyncTimeInSecondsWithinHour(dateString);
   Serial.print("lastReadInSecondsWithinTheHour: ");
   Serial.println(lastReadInSecondsWithinTheHour);
   
-  randomSeed(analogRead(0));
-  //re-sync every 5th time or so
-  if(random(5) == 0)
-    SleepWithTimeSync(lastReadInSecondsWithinTheHour);
-  else
-    SleepFiveMins();
+  SleepWithTimeSync(lastReadInSecondsWithinTheHour);
+  */
+  SleepUntilNextReading(lastSyncTime);
+}
+
+void initTime()
+{
+  struct tm timeinfo;
+  if(!getLocalTime(&timeinfo))
+    configTime(0, 0, ntpServer);
+  while(!getLocalTime(&timeinfo)){
+    Serial.println("Sleeping until time is set..");    
+    delay(100);
+  }
+  //Setting EST timezone
+  setenv("TZ", "EST+5EDT,M3.2.0/2,M11.1.0/2",1);
+  tzset();
 }
 
 int GetLastSyncTimeInSecondsWithinHour(String dateString) {
@@ -87,9 +122,38 @@ int GetLastSyncTimeInSecondsWithinHour(String dateString) {
   int secondsInTheHour = dateString.substring(idx+7, idx+9).toInt();
   return (minutesInTheHour * 60) + secondsInTheHour;
 }
+
+void SleepUntilNextReading(time_t lastReading) {
+  struct tm timeinfo;
+  time_t localTime;
+  
+  if(!getLocalTime(&timeinfo)){
+    Serial.println("Error getting local time");
+  }
+  localTime = mktime(&timeinfo);
+
+  double timeDiff = difftime(localTime, lastReading);
+  Serial.print(timeDiff);
+  Serial.println(" seconds diff between lastReading and current time");
+  int secondsToSleep = 300 - (int)timeDiff;
+  //Add one more to not jump the gun
+  secondsToSleep += 3;
+  if(secondsToSleep > 0 && secondsToSleep < 300) {
+    //secondsToSleep = secondsToSleep + 7;
+    Serial.print("Sleeping ");
+    Serial.println(secondsToSleep);
+    esp_sleep_enable_timer_wakeup(secondsToSleep * uS_TO_S_FACTOR);
+    Serial.flush(); 
+    TurnOffEPD();
+    esp_deep_sleep_start();
+  }
+  else {
+    SleepFiveMins();
+  }
+}
 void SleepWithTimeSync(int lastReadingInSeconds) {
   
-  configTime(gmtOffset_sec, daylightOffset_sec, ntpServer);
+  //configTime(gmtOffset_sec, daylightOffset_sec, ntpServer);
   struct tm timeinfo;
   if(!getLocalTime(&timeinfo)){
     Serial.println("Failed to obtain time");
@@ -274,12 +338,21 @@ void ConnectToWifi() {
   //WiFi.mode(WIFI_STA);
   //WiFi.disconnect();
   WiFi.begin(ssid, password);
+  int cnt=0;
   Serial.println("Connecting to WiFi...");
     while(WiFi.status() != WL_CONNECTED) {
     delay(500);
-    Serial.print("status:" );
-    Serial.println(WiFi.status());
-    Serial.println(WiFi.localIP());
+    Serial.print('.');
+    //Serial.print("status:" );
+    //Serial.println(WiFi.status());
+    //Serial.println(WiFi.localIP());
+    cnt++;
+    if(cnt > 50){
+      Serial.println("Cycling wifi");
+      WiFi.disconnect();
+      WiFi.begin(ssid, password);
+      cnt = 0;
+    }
   }
   Serial.println("");
   Serial.print("Connected to WiFi network with IP Address: ");