move garbage collect logic to nix module

modules/common.nix

@@ -164,12 +164,20 @@
   nix = {
     settings.experimental-features = ["nix-command" "flakes"]; # Enable modern Nix features (flakes and new CLI)
 
+    # Optimise the Nix store automatically to recover space
     optimise = {
-      # Optimise the Nix store automatically to recover space
       automatic = true;
-      dates = ["03:45"]; # Optional; allows customizing optimisation schedule
+      dates = ["03:45"];
       persistent = true; # Run missed optimisations
     };
+
+    # Garbage collect the Nix store automatically to recover space
+    gc = {
+      automatic = true;
+      dates = "weekly";
+      options = "--delete-older-than 60d";
+      persistent = true; # Run missed GC
+    };
   };
 
   # ================================

rebuild-nix-system.sh

@@ -2,13 +2,6 @@
 
 set -e
 
-# Days of nix generations to keep
-KEEP_DAYS=60
-# extra buffer before we trigger a GC
-BUFFER_DAYS=30
-# minimum number of generations to keep
-KEEP_MIN=5
-
 # Check for force flag
 FORCE_REBUILD=false
 if [[ "$1" == "-f" || "$1" == "--force" ]]; then
@@ -67,18 +60,3 @@ current=$(nixos-rebuild list-generations | grep current)
 
 # Commit all changes witih the generation metadata
 git commit -am "$NIXOS_HOST: $current"
-
-# Clean up old generations if conditions are met
-gens=$(nixos-rebuild list-generations | tail -n +2)
-# If there are less than KEEP_MIN generations, exit
-(( $(wc -l <<<"$gens") <= KEEP_MIN )) && exit 0
-
-# Get the oldest generation
-old=$(awk 'END{print $2" "$3}' <<<"$gens")
-# Calculate the age of the oldest generation in days
-age=$(( ( $(date +%s) - $(date -d "$old" +%s) )/86400 ))
-# If the age is greater than KEEP_DAYS+BUFFER_DAYS, delete the oldest generation
-(( age > KEEP_DAYS+BUFFER_DAYS )) || exit 0
-sudo nix-collect-garbage --delete-older-than ${KEEP_DAYS}d &>logs/nixos-gc.log || (cat logs/nixos-gc.log | grep --color error && exit 1)
-
-