feat(refactor): WIP refactor server modules

modules/server/infra/postgres/postgres-upgrade.nix

@@ -0,0 +1,48 @@
+# taken from @jtojnar
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}: let
+  inherit (lib) types mkOption;
+
+  cfg = config.server.infra.postgresql;
+in {
+  options = {
+    server.infra.postgresql = {
+      upgradeTargetPackage = mkOption {
+        type = types.nullOr types.package;
+        default = null;
+        description = "PostgreSQL package that we want to upgrade to. When set, an update script will be installed.";
+      };
+    };
+  };
+
+  config = {
+    # https://nixos.org/manual/nixos/unstable/#module-services-postgres-upgrading
+    environment.systemPackages = lib.mkIf (cfg.upgradeTargetPackage != null) [
+      (pkgs.writeScriptBin "upgrade-pg-cluster" ''
+        set -eux
+        # XXX it's perhaps advisable to stop all services that depend on postgresql
+        systemctl stop postgresql
+
+        export NEWDATA="/var/lib/postgresql/${cfg.upgradeTargetPackage.psqlSchema}"
+
+        export NEWBIN="${cfg.upgradeTargetPackage}/bin"
+
+        export OLDDATA="${config.services.postgresql.dataDir}"
+        export OLDBIN="${config.services.postgresql.package}/bin"
+
+        install -d -m 0700 -o postgres -g postgres "$NEWDATA"
+        cd "$NEWDATA"
+        sudo -u postgres $NEWBIN/initdb -D "$NEWDATA"
+
+        sudo -u postgres $NEWBIN/pg_upgrade \
+          --old-datadir "$OLDDATA" --new-datadir "$NEWDATA" \
+          --old-bindir $OLDBIN --new-bindir $NEWBIN \
+          "$@"
+      '')
+    ];
+  };
+}