From 719fb5fb7470df7f610fd190985765c71a2698e2 Mon Sep 17 00:00:00 2001
From: Axel Burri <axel@tty0.ch>
Date: Thu, 5 Apr 2018 16:42:26 +0200
Subject: [PATCH] btrbk: bugfix: correct scheduling of "first weekly backup in
 month/year"

In the scheduler, a month (or year) does not start at the first day,
but at the first `preserve_day_of_week`. Make sure that all days
before `preserve_day_of_week` in a month get delta_months+1.

Example (corner case):
  - `preserve_day_of_week  sunday`
  - `target_preserve  *m`
  - no backups in 2018-02
  - backup with timestamp 2018-03-01 (which is a thursday)
  - backup with timestamp 2018-03-04 (which is a sunday)

Without this patch, because there are no sunday backups in 2018-02,
the first backup is considered a weekly (+4d after sunday), and as
such "first weekly of month 2018-03", and the second one is discarded.

With this patch, the first item is considered "first weekly of month
2018-02", and the second gets "first weekly of month 2018-03".

NOTE: This change may result in (previously preserved) backups to be
deleted!
---
 ChangeLog |  3 +++
 btrbk     | 22 +++++++++++++++++-----
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index e17085a..b117093 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,6 +1,9 @@
 btrbk-0.27.0-dev
 
   * Add "preserve_hour_of_day" configuration option (close #202).
+  * Bugfix: correct scheduling of "first weekly backup in month/year"
+    (close #217). Note that this change may result in (previously
+    preserved) backups to be deleted!
 
 btrbk-0.26.1
 
diff --git a/btrbk b/btrbk
index 0c6f1e8..b164b23 100755
--- a/btrbk
+++ b/btrbk
@@ -3746,7 +3746,9 @@ sub schedule(@)
   # first, do our calendar calculations
   # - days start on $preserve_hour_of_day (or 00:00 if timestamp_format=short)
   # - weeks start on $preserve_day_of_week
-  # - leap hours are NOT taken into account for $delta_hours
+  # - months start on first $preserve_day_of_week of month
+  # - years start on first $preserve_day_of_week of year
+  # NOTE: leap hours are NOT taken into account for $delta_hours
   my $now_h = timegm_nocheck( 0, 0, $tm_now[2], $tm_now[3], $tm_now[4], $tm_now[5] ); # use timelocal() here (and below) if you want to honor leap hours
 
   foreach my $href (@sorted_schedule)
@@ -3762,13 +3764,23 @@ sub schedule(@)
     if($delta_days_from_eow < 0) {
       $delta_days_from_eow += 7;
     }
+    my $month_corr = $tm[4];  # [0..11]
+    my $year_corr = $tm[5];
+    if($tm[3] <= $delta_days_from_eow) {
+      # our month/year start on first $preserve_day_of_week, corrected value
+      $month_corr -= 1;
+      if($month_corr < 0) {
+        $month_corr = 11;
+        $year_corr -= 1;
+      }
+    }
 
     # check timegm: ignores leap hours
     my $delta_hours  = int(($now_h - timegm_nocheck( 0, 0, $tm[2], $tm[3], $tm[4], $tm[5] )  ) / (60 * 60));
     my $delta_days   = int(($delta_hours + $delta_hours_from_hod) / 24);  # days from beginning of day
     my $delta_weeks  = int(($delta_days + $delta_days_from_eow) / 7);  # weeks from beginning of week
-    my $delta_years  = ($tm_now[5] - $tm[5]);
-    my $delta_months = $delta_years * 12 + ($tm_now[4] - $tm[4]);
+    my $delta_years  = ($tm_now[5] - $year_corr);
+    my $delta_months = $delta_years * 12 + ($tm_now[4] - $month_corr);
 
     $href->{delta_hours}   = $delta_hours;
     $href->{delta_days}    = $delta_days;
@@ -3777,8 +3789,8 @@ sub schedule(@)
     $href->{delta_years}   = $delta_years;
 
     # these are only needed for text output (format_preserve_delta)
-    $href->{year} = $tm[5] + 1900;
-    $href->{month} = $tm[4] + 1;
+    $href->{year} = $year_corr + 1900;
+    $href->{month} = $month_corr + 1;
     $href->{delta_hours_from_hod} = $delta_hours_from_hod;
     $href->{delta_days_from_eow} = $delta_days_from_eow;
     $href->{real_hod} = $preserve_hour_of_day if($has_exact_time);