Modified algorithm to stay awake and retry nightscout request to avoid missing last reading

NightscoutEInkClient.ino

@@ -20,8 +20,6 @@ ThinkInk_290_Tricolor_Z10 display(EPD_DC, EPD_RESET, EPD_CS, SRAM_CS, EPD_BUSY);
 #define COLOR1 EPD_BLACK
 #define COLOR2 EPD_RED
 
-const char* ssid     = "Breqtest";
-const char* password = "aidsaids";
 
 const char* nightscoutUrl = "http://nightscout.chrispr.org:8082/api/v1/entries?count=20";
 
@@ -58,38 +56,60 @@ void setup() {
   //turn EPD on
   pinMode(EPD_ENABLE, OUTPUT);
   digitalWrite(EPD_ENABLE, HIGH);
-  
-  String nightscoutResponse = httpGETRequest(nightscoutUrl);
-  //Serial.println(nightscoutResponse);
-  DynamicJsonDocument doc(8192);
-  DeserializationError error = deserializeJson(doc, nightscoutResponse);
-  
-   if (error) {
-    Serial.print(F("deserializeJson() failed: "));
-    Serial.println(error.f_str());
-    return;
-  }
 
-  JsonArray array = doc.as<JsonArray>();
+  int timeSinceLastSyncInSeconds = 0;
+  JsonArray jsonArray;
+  JsonVariant latestReading;
+  time_t lastSyncTime;
+  DynamicJsonDocument doc(8192);
   
+  while(timeSinceLastSyncInSeconds < (15 * 60))
+  { //break out of the loop if we haven't received a reading in 15 minutes to conserve battery
+    String nightscoutResponse = httpGETRequest(nightscoutUrl);
+    //Serial.println(nightscoutResponse);
+    
+    DeserializationError error = deserializeJson(doc, nightscoutResponse);
+    
+     if (error) {
+      Serial.print(F("deserializeJson() failed: "));
+      Serial.println(error.f_str());
+      return;
+    }
+
+    //Serial.println(nightscoutResponse);
   
+    jsonArray = doc.as<JsonArray>();
+    latestReading = jsonArray[0];
+    Serial.printf("Received %d sgv records\n", jsonArray.size());
+
+    SleepIfCGMWarmup(latestReading);
+
+    unsigned long long dateInt = latestReading["date"].as<unsigned long long>();
+    int correctedDateInt = dateInt / 1000;
+    lastSyncTime = (time_t)correctedDateInt;
+
+    timeSinceLastSyncInSeconds = GetLastSyncTimeDifference(lastSyncTime);
+    Serial.printf("timeSinceLastSyncInSeconds %d\n", timeSinceLastSyncInSeconds);
+    
+    if(timeSinceLastSyncInSeconds < 60)
+      break; //got the most recent reading, display it
+      
+    if(timeSinceLastSyncInSeconds < 300 && timeSinceLastSyncInSeconds > 120)
+      break; //we missed it, or came in between readings, so sleep until the next one
+      
+      //otherwise, try again in a few seconds
+      Serial.printf("timeSinceLastSyncInSeconds is %d, so trying again", timeSinceLastSyncInSeconds);
+      delay(1000);
+  }
   display.begin();
   display.clearBuffer();
 
-  JsonVariant latestReading = array[0];
+  RenderGraph(jsonArray);
-  
-  SleepIfCGMWarmup(latestReading);
-
-  RenderGraph(array);
   RenderRightPane(latestReading);
   RenderBatteryPercentage();
 
   display.display();
 
-  unsigned long long dateInt = latestReading["date"].as<unsigned long long>();
-  int correctedDateInt = dateInt / 1000;
-  time_t lastSyncTime = (time_t)correctedDateInt;
-
   SleepUntilNextReading(lastSyncTime);
 }
 
@@ -126,6 +146,7 @@ void initTime()
   tzset();
 }
 
+//Deprecated
 int GetLastSyncTimeInSecondsWithinHour(String dateString) {
   //"dateString":"2022-02-11T19:59:42.481-0500"
   int idx = dateString.indexOf("T");
@@ -141,6 +162,18 @@ void SleepIfCGMWarmup(JsonVariant latestReading) {
   }
 }
 
+int GetLastSyncTimeDifference(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);
+  return timeDiff;
+}
 void SleepUntilNextReading(time_t lastReading) {
   struct tm timeinfo;
   time_t localTime;
@@ -229,16 +262,25 @@ void RenderGraph(JsonArray sgvRecords) {
   //Get 46 minutes into the past, to filter out older records
   unsigned long timeCutoff = GetCurrentEpochTime() - (46 * 60);
 
-  for(int i=sgvRecords.size(); i >= 0; i--) {
+  for(int i=sgvRecords.size()-1; i >= 0; i--) {
     
     JsonObject obj = sgvRecords[i].as<JsonObject>(); //v.as<JsonObject>();
+    
+    if(&obj == NULL || obj["sgv"].as<String>() == NULL)
+      continue;
+    Serial.println("sgv");
     Serial.println(obj["sgv"].as<String>());
+    Serial.println("device");
+    Serial.println(obj["device"].as<String>());
+    
+    
     if(obj["device"].as<String>().indexOf("xDrip") == -1) {
       continue;
     }
     if(cnt > 0)
       continue;
     unsigned long readingTime = (unsigned long)(obj["date"].as<unsigned long long>() / 1000);
+
     Serial.printf("readingTime: %d\n", readingTime);
     if(readingTime < timeCutoff)
       continue;