From dd50bf614cc9282ff1c3a2fd408e902912c00ab6 Mon Sep 17 00:00:00 2001
From: Christian Pointner <equinox@helsinki.at>
Date: Fri, 17 Jul 2015 02:50:47 +0200
Subject: week calculation works now...


diff --git a/src/helsinki.at/rhrdtime/rhrdtime.go b/src/helsinki.at/rhrdtime/rhrdtime.go
index 5a9f0d0..a5b47f5 100644
--- a/src/helsinki.at/rhrdtime/rhrdtime.go
+++ b/src/helsinki.at/rhrdtime/rhrdtime.go
@@ -27,6 +27,7 @@ package main
 import (
   "fmt"
   "time"
+  "math"
   "flag"
   "net/http"
   "encoding/json"
@@ -38,13 +39,41 @@ import (
 
 type timeUpdate struct {
   Timestamp int64 `json:"timestamp"`
+  TZOffset int `json:"tz-offset"`
   Week uint8 `json:"week"`
 }
 
 func getTimeUpdate() []byte {
-  now := time.Now()
+  //
+  // This computes the current Rivendell Week based on the number
+  // of weeks since epoch.
+  //
+  // Explanation:
+  //  epoch was at 01.01.1970 UTC which was a Thursday.
+  //  Monday in that week is (s-from-epoch + 3*24*60*60) seconds ago.
+  //  This needs to be adjusted by the timezone offset for Europe/Vienna
+  //  which is of course not constant (damn you daylight savings time)
+  //  Divide this by (7*24*60*60) and you get the number of
+  //  weeks since the Monday in the week of epoch adjusted for timezone offsets.
+  //  This week had week number 3 so add an offset of 2 and
+  //  get the modulo of 4. This rounded down gives you the current week
+  //  with 0 meaning Week 1. So add 1 to that number and you will get
+  //  the current RD week.
+  //
+
+  loc, err := time.LoadLocation("Europe/Vienna");
+  if err != nil {
+    fmt.Println(err)
+    return []byte{'{', '}'}
+  }
+
+  now := time.Now().In(loc);
+  _, offset := now.Zone()
+
+  sEpoch := now.Unix() + int64(offset)
+  week := uint8(math.Floor(math.Mod((((float64(sEpoch) + 259200)/604800) + 2), 4)) + 1)
 
-  update := timeUpdate{now.Unix(), 1}
+  update := timeUpdate{now.Unix(), offset, week}
   update_json, err := json.Marshal(update)
   if err != nil {
     fmt.Println(err)
-- 
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