2 files changed, 23 insertions, 16 deletions

diff --git a/modules/zfssnap/default.nix b/modules/zfssnap/default.nix
index 86e7fdc0..27e5198d 100644
--- a/modules/zfssnap/default.nix
+++ b/modules/zfssnap/default.nix
@@ -77,7 +77,7 @@ in {
         ExecStart = let
           mkSectionName = name: strings.escape [ "[" "]" ] (strings.toUpper name);
           zfssnapConfig = generators.toINI { inherit mkSectionName; } cfg.config;
-        in "${zfssnap}/bin/zfssnap -v prune --config=${pkgs.writeText "zfssnap.ini" zfssnapConfig}";
+        in "${zfssnap}/bin/zfssnap -v prune --dry-run --config=${pkgs.writeText "zfssnap.ini" zfssnapConfig}";
       };
     };
 
diff --git a/modules/zfssnap/zfssnap.py b/modules/zfssnap/zfssnap.py
index 1c3e1f9a..cf6ab28c 100644
--- a/modules/zfssnap/zfssnap.py
+++ b/modules/zfssnap/zfssnap.py
@@ -53,8 +53,7 @@ def _get_items():
 
     return items
         
-def prune(config, dry_run):
-    
+def prune(config, dry_run, keep_newest):
     items = defaultdict(list)
 
     args = ['zfs', 'get', '-H', '-p', '-o', 'name,value', '-t', 'snapshot', 'creation']
@@ -116,21 +115,25 @@ def prune(config, dry_run):
         desired_count = config.getint('KEEP', rule, fallback=0)
 
         for base, snaps in items.items():
-            last_period = None
-            to_keep = desired_count
-
-            if to_keep == 0:
-                continue
+            periods = OrderedDict()
             
-            for snap in sorted(snaps, key=lambda snap: snap['creation'], reverse=True):
+            for snap in sorted(snaps, key=lambda snap: snap['creation'], reverse=keep_newest):
+                period = pattern(snap['creation'])
+                if period not in periods:
+                    periods[period] = deque()
+                periods[period].append(snap)
+
+            to_keep = desired_count
+            ordered_periods = reversed(periods.items()) if keep_newest else periods.items()
+            for period, period_snaps in ordered_periods:
                 if to_keep == 0:
                     break
 
-                period = pattern(snap['creation'])
-                if period != last_period:
-                    last_period = period
-                    keep_because(base, snap['name'], rule, period=period)
-                    to_keep -= 1
+                for snap in period_snaps:
+                    if snap['name'] not in keep:
+                        keep_because(base, snap['name'], rule, period=period)
+                        to_keep -= 1
+                        break
 
             if to_keep > 0:
                 logger.debug(f'Missing {to_keep} to fulfill {rule}={desired_count} for ‘{base}’')
@@ -147,7 +150,10 @@ def prune(config, dry_run):
         args += [snap]
         _log_cmd(*args)
         subprocess.run(args, check=True)
-        logger.info(f'Pruned ‘{snap}’')
+        if dry_run:
+            logger.info(f'Would have pruned ‘{snap}’')
+        else:
+            logger.info(f'Pruned ‘{snap}’')
     
 def rename(snapshots, destroy=False):
     args = ['zfs', 'get', '-H', '-p', '-o', 'name,value', 'creation', *snapshots]
@@ -269,6 +275,7 @@ def main():
     prune_parser = subparsers.add_parser('prune')
     prune_parser.add_argument('--config', '-c', dest='config_files', nargs='*', default=list())
     prune_parser.add_argument('--dry-run', '-n', action='store_true', default=False)
+    prune_parser.add_argument('--keep-newest', action='store_true', default=False)
     prune_parser.set_defaults(cmd=prune)
     args = parser.parse_args()
 
@@ -280,7 +287,7 @@ def main():
         logger.setLevel(logging.DEBUG)
 
     cmdArgs = {}
-    for copy in {'snapshots', 'dry_run', 'destroy'}:
+    for copy in {'snapshots', 'dry_run', 'destroy', 'keep_newest'}:
         if copy in vars(args):
             cmdArgs[copy] = vars(args)[copy]
     if 'config_files' in vars(args):