home/nix-index: init with db fetch timer

home/home.nix

@@ -18,6 +18,7 @@ in {
     ./programs/gpg
     ./programs/less.nix
     ./programs/neovim.nix
+    ./programs/nix-index
     ./programs/tmux.nix
     ./programs/zsh
 

home/programs/nix-index/default.nix

@@ -0,0 +1,9 @@
+{ ... }:
+{
+  imports = [ ./fetch-nix-index-database.nix ];
+
+  programs.nix-index = {
+    enable = true;
+    enableDatabaseFetcher = true;
+  };
+}

home/programs/nix-index/fetch-nix-index-database.nix

@@ -0,0 +1,58 @@
+{ config, pkgs, lib, ... }:
+let
+  cfg = config.programs.nix-index;
+in
+{
+  options.programs.nix-index.enableDatabaseFetcher = lib.mkEnableOption "timed unit that fetches an updated database of nixpkgs outputs";
+
+  config = {
+    systemd.user.timers.fetch-nix-index-database = lib.mkIf cfg.enableDatabaseFetcher {
+      Unit = {
+        Description = "Fetch nix-index database";
+        Documentation = [ "https://github.com/nix-community/nix-index-database" ];
+      };
+
+      Timer = {
+        Unit = "fetch-nix-index-database.service";
+        OnCalendar = "weekly";
+        Persistent = true;
+      };
+
+      Install = {
+        WantedBy = [ "timers.target" ];
+      };
+    };
+
+    systemd.user.services.fetch-nix-index-database = lib.mkIf cfg.enableDatabaseFetcher {
+      Unit = {
+        Description = "Fetch nix-index database";
+        Documentation = [ "https://github.com/nix-community/nix-index-database" ];
+      };
+
+      Service = {
+        Type = "oneshot";
+        ExecStart = lib.getExe (pkgs.writeShellApplication {
+          name = "fetch-nix-index-database";
+          runtimeInputs = with pkgs; [
+            gnused
+            wget
+          ];
+
+          # Source: https://github.com/nix-community/nix-index-database?tab=readme-ov-file#ad-hoc-download
+          # Slightly modified to satisfy shellcheck
+          text = ''
+            download_nixpkgs_cache_index () {
+              filename="index-$(uname -m | sed 's/^arm64$/aarch64/')-$(uname | tr '[:upper:]' '[:lower:]')"
+              mkdir -p "${config.home.homeDirectory}/.cache/nix-index" && cd "${config.home.homeDirectory}/.cache/nix-index"
+              # -N will only download a new version if there is an update.
+              wget -q -N "https://github.com/nix-community/nix-index-database/releases/latest/download/$filename"
+              ln -f "$filename" files
+            }
+
+            download_nixpkgs_cache_index
+          '';
+        });
+      };
+    };
+  };
+}