Always create monthly and yearly archives (fixes #29) (#35)

Previously, the first day of the year would create a yearly archive,
the second day would create a monthly, and the third would create a
daily archive. With this change, yearly, monthly, and daily archives
always exist.

Daily archives are created every time acts is run. If monthly and/or
yearly archives don't exist, the new daily archive is copied to
the other(s).

Copies are based on metadata. That metadata must be read and parsed,
which causes some data transfer. However, that data is quite minimal
and should impose very little cost.

Copies do take some time to run. The time scales with the number of
files in the archive, not with the size of each file. And though
time scales, it scales very slowly. In my tests, copies are faster
than archive creation for all but the smallest archives of 1-5 files.
Copies are substantially faster for large archives.

acts

@@ -175,30 +175,48 @@ for dir in $backuptargets; do
     log_debug "message=\"Starting backup of $dir\""
     archive_starttime=$(date +%s)
     nicedirname=$(nicedirname "$dir")
-    # Determine the archive type to create
-    if echo "$archives" | grep -E -q "^$hostname-yearly-$year-.+$nicedirname$"; then
-        if echo "$archives" | grep -E -q "^$hostname-monthly-$year-$month-.+$nicedirname$"; then
-            # There's a yearly and monthly backup already
-            archivetype="daily"
-        else
-            # There was a yearly but no monthly backup
-            archivetype="monthly"
-        fi
-    else
-        # There's no yearly backup
-        archivetype="yearly"
-    fi
-    log_verbose "archive-type type=$archivetype"
-    archivename="$hostname-$archivetype-$today$nicedirname"
-    log_verbose "backup-start type=$archivetype dir=/$dir name=$archivename"
+
+    dailyarchive="$hostname-daily-$today$nicedirname"
+    monthlyarchive="$hostname-monthly-$today$nicedirname"
+    yearlyarchive="$hostname-yearly-$today$nicedirname"
+
+    log_verbose "backup-start  type=daily dir=/$dir name=$dailyarchive"
     # Uncontrolled expansion is bad, but we have little choice. See https://github.com/koalaman/shellcheck/wiki/Sc2086
     # shellcheck disable=SC2086
-    if ! output="$($tarsnap -c -f "$archivename" -C / $tarsnapbackupoptions "$dir" 2>&1)"; then
-        log_message "backup-error type=$archivetype dir=/$dir output=\"$(echo $output | tr '\n' " ")\""
+    if ! output="$($tarsnap -c -f "$dailyarchive" -C / $tarsnapbackupoptions "$dir" 2>&1)"; then
+        log_message "backup-error type=daily dir=/$dir output=\"$(echo $output | tr '\n' " ")\""
         backuprc=1
     fi
     archive_endtime=$(date +%s)
-    log_verbose "backup-finish type=$archivetype dir=/$dir duration=$((archive_endtime - archive_starttime))s"
+    log_verbose "backup-finish type=daily dir=/$dir duration=$((archive_endtime - archive_starttime))s"
+
+    # Determine whether other backup levels need to be created too
+    # If so, copy them from $dailyarchive
+    if ! echo "$archives" | grep -E -q "^$hostname-yearly-$year-.+$nicedirname$"; then
+        # No yearly backup
+        log_debug "message=\"Copying daily archive to yearly archive\""
+        archive_starttime=$(date +%s)
+        # shellcheck disable=SC2086
+        if ! output="$(tarsnap -c -f "$yearlyarchive" $tarsnapbackupoptions "@@$dailyarchive" 2>&1)"; then
+            log_message "copy-error  type=yearly output=\"$(echo $output | tr '\n' " ")\""
+            backuprc=1
+        fi
+        archive_endtime=$(date +%s)
+        log_verbose "copy-finish type=yearly dir=/$dir name=$yearlyarchive duration=$((archive_endtime - archive_starttime))s"
+    fi
+
+    if ! echo "$archives" | grep -E -q "^$hostname-monthly-$year-$month-.+$nicedirname$"; then
+        # No monthly backup
+        log_debug "message=\"Copying daily archive to monthly archive\""
+        archive_starttime=$(date +%s)
+        # shellcheck disable=SC2086
+        if ! output="$(tarsnap -c -f "$monthlyarchive" $tarsnapbackupoptions "@@$dailyarchive" 2>&1)"; then
+            log_message "copy-error  type=monthly output=\"$(echo $output | tr '\n' " ")\""
+            backuprc=1
+        fi
+        archive_endtime=$(date +%s)
+        log_verbose "copy-finish type=monthly dir=/$dir name=$monthlyarchive duration=$((archive_endtime - archive_starttime))s"
+    fi
 done
 # Update the archive listing
 archives=$($tarsnap --list-archives | sort -n)
@@ -213,7 +231,7 @@ prune_backups() {
 
     if [ "$max" -gt 0 ]; then
         backupslist=$(echo "$archives" | grep -E "$hostname-$backuplevel-.+$nicedirname$" | sort -rn)
-        numberofbackups=$(echo "$backupslist" | awk 'END{print NR}')
+        numberofbackups=$(printf '%s' "$backupslist" | awk 'END{print NR}')
         if [ "$numberofbackups" -gt "$max" ]; then
             log_debug "message=\"More than $max $backuplevel backups, deleting the oldest\""
             echo "$backupslist" | tail -n +"$(( max+1 ))" | while read -r archiveprefixtodel; do
@@ -224,7 +242,7 @@ prune_backups() {
                 done
             done
         else
-            log_debug "message=\"Found $numberofbackups $backuplevel backups, not deleting\""
+            log_debug "message=\"Found $numberofbackups $backuplevel backups; not deleting any\""
         fi
     else
         log_debug "message=\"Keeping all $backuplevel backups indefinitely; not deleting any\""