feat(script): Implement retention for old snapshots (#1)

pacman-zfs-snapshot.sh

@@ -212,6 +212,22 @@ function get_snaps_in_cur_sev () {
     printf -- '%s' "${snaps_in_cur_sev}"
 }
 
+function do_retention () {
+    local snap_list snaps_done_by_us snaps_in_cur_sev snaps_limit oldest_snap
+    for successfully_snapped_dataset in "${successfully_snapped_datasets[@]}"; do        
+        snaps_in_cur_sev="$(get_snaps_in_cur_sev "${successfully_snapped_dataset}")"
+        if [[ "${severity}" == "${snaps_important_suffix}" ]]; then
+            snaps_limit="${snaps_important_keep}"
+        else
+            snaps_limit="${snaps_trivial_keep}"
+        fi
+        while [[ "$(get_snaps_in_cur_sev "${successfully_snapped_dataset}" | wc -l)" -gt "${snaps_limit}" ]]; do
+            oldest_snap="$(get_snaps_in_cur_sev "${successfully_snapped_dataset}" | head -n1)"
+            zfs destroy "${oldest_snap}"
+        done
+    done
+}
+
 function main () {
     local pkgs_in_transaction
     pkgs_in_transaction=("${@}")
@@ -245,7 +261,9 @@ function main () {
     local trimmed_pkg_list_oneline
     trim_pkg_list_oneline
 
+    local -a successfully_snapped_datasets
     do_snaps
+    do_retention
 }
 
 main "${pkgs[@]}"