atuin: configure daemon using systemd and launchd

This configures the atuin daemon for Linux and Darwin systems using
systemd and launchd, respectively. For systemd, a socket is also
automatically configured to exist at atuin's default socket location.

modules/programs/atuin.nix

@@ -8,6 +8,7 @@ let
 
   tomlFormat = pkgs.formats.toml { };
 
+  inherit (pkgs.stdenv) isLinux isDarwin;
 in {
   meta.maintainers = [ maintainers.hawkw ];
 
@@ -94,49 +95,109 @@ in {
         Whether to enable Nushell integration.
       '';
     };
+
+    daemon.enable = mkEnableOption "atuin daemon";
   };
 
   config = let flagsStr = escapeShellArgs cfg.flags;
-  in mkIf cfg.enable {
+  in mkIf cfg.enable (mkMerge [
+    {
+      # Always add the configured `atuin` package.
+      home.packages = [ cfg.package ];
 
-    # Always add the configured `atuin` package.
-    home.packages = [ cfg.package ];
+      # If there are user-provided settings, generate the config file.
+      xdg.configFile."atuin/config.toml" = mkIf (cfg.settings != { }) {
+        source = tomlFormat.generate "atuin-config" cfg.settings;
+      };
 
-    # If there are user-provided settings, generate the config file.
-    xdg.configFile."atuin/config.toml" = mkIf (cfg.settings != { }) {
-      source = tomlFormat.generate "atuin-config" cfg.settings;
-    };
-
-    programs.bash.initExtra = mkIf cfg.enableBashIntegration ''
-      if [[ :$SHELLOPTS: =~ :(vi|emacs): ]]; then
-        source "${pkgs.bash-preexec}/share/bash/bash-preexec.sh"
-        eval "$(${lib.getExe cfg.package} init bash ${flagsStr})"
-      fi
-    '';
-
-    programs.zsh.initExtra = mkIf cfg.enableZshIntegration ''
-      if [[ $options[zle] = on ]]; then
-        eval "$(${lib.getExe cfg.package} init zsh ${flagsStr})"
-      fi
-    '';
-
-    programs.fish.interactiveShellInit = mkIf cfg.enableFishIntegration ''
-      ${lib.getExe cfg.package} init fish ${flagsStr} | source
-    '';
-
-    programs.nushell = mkIf cfg.enableNushellIntegration {
-      extraEnv = ''
-        let atuin_cache = "${config.xdg.cacheHome}/atuin"
-        if not ($atuin_cache | path exists) {
-          mkdir $atuin_cache
-        }
-        ${
-          lib.getExe cfg.package
-        } init nu ${flagsStr} | save --force ${config.xdg.cacheHome}/atuin/init.nu
+      programs.bash.initExtra = mkIf cfg.enableBashIntegration ''
+        if [[ :$SHELLOPTS: =~ :(vi|emacs): ]]; then
+          source "${pkgs.bash-preexec}/share/bash/bash-preexec.sh"
+          eval "$(${lib.getExe cfg.package} init bash ${flagsStr})"
+        fi
       '';
-      extraConfig = ''
-        source ${config.xdg.cacheHome}/atuin/init.nu
+
+      programs.zsh.initExtra = mkIf cfg.enableZshIntegration ''
+        if [[ $options[zle] = on ]]; then
+          eval "$(${lib.getExe cfg.package} init zsh ${flagsStr})"
+        fi
       '';
-    };
-  };
+
+      programs.fish.interactiveShellInit = mkIf cfg.enableFishIntegration ''
+        ${lib.getExe cfg.package} init fish ${flagsStr} | source
+      '';
+
+      programs.nushell = mkIf cfg.enableNushellIntegration {
+        extraEnv = ''
+          let atuin_cache = "${config.xdg.cacheHome}/atuin"
+          if not ($atuin_cache | path exists) {
+            mkdir $atuin_cache
+          }
+          ${
+            lib.getExe cfg.package
+          } init nu ${flagsStr} | save --force ${config.xdg.cacheHome}/atuin/init.nu
+        '';
+        extraConfig = ''
+          source ${config.xdg.cacheHome}/atuin/init.nu
+        '';
+      };
+    }
+
+    (mkIf cfg.daemon.enable (mkMerge [
+      {
+        assertions = [{
+          assertion = isLinux || isDarwin;
+          message =
+            "The atuin daemon can only be configured on either Linux or macOS.";
+        }];
+
+        programs.atuin.settings = { daemon = { enabled = true; }; };
+      }
+      (mkIf isLinux {
+        programs.atuin.settings = { daemon = { systemd_socket = true; }; };
+
+        systemd.user.services.atuin-daemon = {
+          Unit = {
+            Description = "atuin daemon";
+            Requires = [ "atuin-daemon.socket" ];
+          };
+          Install = {
+            Also = [ "atuin-daemon.socket" ];
+            WantedBy = [ "default.target" ];
+          };
+          Service = {
+            ExecStart = "${lib.getExe cfg.package} daemon";
+            Environment = [ "ATUIN_LOG=info" ];
+            Restart = "on-failure";
+            RestartSteps = 3;
+            RestartMaxDelaySec = 6;
+          };
+        };
+
+        systemd.user.sockets.atuin-daemon = {
+          Unit = { Description = "atuin daemon socket"; };
+          Install = { WantedBy = [ "sockets.target" ]; };
+          Socket = {
+            ListenStream = "%h/.local/share/atuin/atuin.sock";
+            SocketMode = "0600";
+            RemoveOnStop = true;
+          };
+        };
+      })
+      (mkIf isDarwin {
+        launchd.agents.atuin-daemon = {
+          enable = true;
+          config = {
+            ProgramArguments = [ "${lib.getExe cfg.package}" "daemon" ];
+            EnvironmentVariables = { ATUIN_LOG = "info"; };
+            KeepAlive = {
+              Crashed = true;
+              SuccessfulExit = false;
+            };
+            ProcessType = "Background";
+          };
+        };
+      })
+    ]))
+  ]);
 }