Deduce pump timezone from data

README.md

@@ -27,7 +27,6 @@
 
 * `CARELINK_USERNAME` - your username for [CareLink][carelink]
 * `CARELINK_PASSWORD` - your password for [CareLink][carelink]
-* `CARELINK_PUMP_TIMEZONE` - a timezone offset string like `"-0700"` which represents the pump's offset from UTC (**TODO:** use time zone names like `America/Los_Angeles` instead, since offsets vary depending on DST)
 * `API_SECRET` - the value you use for `API_SECRET` on your Nightscout website
 * `WEBSITE_HOSTNAME` - the hostname for your Nightscout instance, which looks like `your.host.com`. If you are running this script in the same Azure environment as Nightscout, there is no need to set this, as it will [already be set by Azure][azure-environment]. If you set `NS` (see below), you do not need to set this.
 

nightscout.js

@@ -16,6 +16,27 @@ function addTimeToEntry(pumpTimeString, offset, entry) {
   return entry;
 }
 
+var guessPumpTimezone = (function() {
+  // From my observations, sMedicalDeviceTime is advanced by the server even when the app is
+  // not reporting data or the pump is not connected, so its difference from server time is
+  // always close to a whole number of hours, and can be used to guess the pump's timezone:
+  // https://gist.github.com/mddub/f673570e6427c93784bf
+
+  var lastGuess;
+
+  return function guessPumpTimezone(data) {
+    var timezoneNaivePumpTime = Date.parse(data['sMedicalDeviceTime'] + ' +0');
+    var serverTimeUTC = data['currentServerTime'];
+    var hours = Math.round((timezoneNaivePumpTime - serverTimeUTC) / (60*60*1000));
+    var offset = (hours >= 0 ? '+' : '-') + (Math.abs(hours) < 10 ? '0' : '') + Math.abs(hours) + '00';
+    if (offset !== lastGuess) {
+      logger.log('Guessed pump timezone ' + offset + ' (pump time: "' + data['sMedicalDeviceTime'] + '"; server time: ' + new Date(data['currentServerTime']) + ')');
+    }
+    lastGuess = offset;
+    return offset;
+  };
+})();
+
 function pumpStatusEntry(data, offset) {
   var entry = {'type': PUMP_STATUS_ENTRY_TYPE};
 
@@ -58,12 +79,13 @@ function sgvEntries(data, offset) {
   }
 }
 
-var transform = module.exports.transform = function(data, offset, sgvLimit) {
+var transform = module.exports.transform = function(data, sgvLimit) {
   if(sgvLimit === undefined) {
     sgvLimit = Infinity;
   }
 
-  var entries = [];
+  var entries = [],
+    offset = guessPumpTimezone(data);
 
   entries.push(pumpStatusEntry(data, offset));
 

run.js

@@ -16,7 +16,6 @@ function readEnv(key, defaultVal) {
 var config = {
   username: readEnv('CARELINK_USERNAME'),
   password: readEnv('CARELINK_PASSWORD'),
-  pumpTimezone: readEnv('CARELINK_PUMP_TIMEZONE'),
   nsHost: readEnv('WEBSITE_HOSTNAME'),
   nsBaseUrl: readEnv('NS'),
   nsSecret: readEnv('API_SECRET'),
@@ -25,12 +24,11 @@ var config = {
 };
 
 var client = carelink.Client({username: config.username, password: config.password});
-
 var endpoint = (config.nsBaseUrl ? config.nsBaseUrl : 'https://' + config.nsHost) + '/api/v1/entries.json';
 
 (function requestLoop() {
   client.fetch(function(data) {
-    var entries = nightscout.transform(data, config.pumpTimezone, config.sgvLimit);
+    var entries = nightscout.transform(data, config.sgvLimit);
     nightscout.upload(entries, endpoint, config.nsSecret, function(response) {
       setTimeout(requestLoop, config.interval);
     });