offlineimap: add nixos module (#16842)

nixos/modules/module-list.nix

@@ -368,6 +368,7 @@
   ./services/networking/ntopng.nix
   ./services/networking/ntpd.nix
   ./services/networking/nylon.nix
+  ./services/networking/offlineimap.nix
   ./services/networking/oidentd.nix
   ./services/networking/openfire.nix
   ./services/networking/openntpd.nix

nixos/modules/services/networking/offlineimap.nix

@@ -0,0 +1,73 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.services.offlineimap;
+in {
+
+  options.services.offlineimap = {
+    enable = mkEnableOption "Offlineimap, a software to dispose your mailbox(es) as a local Maildir(s).";
+
+    install = mkOption {
+      type = types.bool;
+      default = false;
+      example = true;
+      description = ''
+        Whether to install a user service for Offlineimap. Once
+        the service is started, emails will be fetched automatically.
+
+        The service must be manually started for each user with
+        "systemctl --user start offlineimap" or globally through
+        <varname>services.offlineimap.enable</varname>.
+      '';
+    };
+
+    package = mkOption {
+      type = types.package;
+      default = pkgs.offlineimap;
+      defaultText = "pkgs.offlineimap";
+      description = "Offlineimap derivation to use.";
+    };
+
+    path = mkOption {
+      type = types.listOf types.path;
+      default = [];
+      example = literalExample "[ pkgs.pass pkgs.bash pkgs.notmuch ]";
+      description = "List of derivations to put in Offlineimap's path.";
+    };
+
+    onCalendar = mkOption {
+      type = types.str;
+      default = "*:0/3"; # every 3 minutes
+      description = "How often is offlineimap started. Default is '*:0/3' meaning every 3 minutes. See systemd.time(7) for more information about the format.";
+    };
+
+    timeoutStartSec = mkOption {
+      type = types.str;
+      default = "120sec"; # Kill if still alive after 2 minutes
+      description = "How long waiting for offlineimap before killing it. Default is '120sec' meaning every 2 minutes. See systemd.time(7) for more information about the format.";
+    };
+  };
+  config = mkIf (cfg.enable || cfg.install) {
+    systemd.user.services.offlineimap = {
+      description = "Offlineimap: a software to dispose your mailbox(es) as a local Maildir(s)";
+      serviceConfig = {
+        Type      = "oneshot";
+        ExecStart = "${cfg.package}/bin/offlineimap -u basic -o -1";
+        TimeoutStartSec = cfg.timeoutStartSec;
+      };
+      path = cfg.path;
+    };
+    environment.systemPackages = [ "${cfg.package}" ];
+    systemd.user.timers.offlineimap = {
+      description = "offlineimap timer";
+      timerConfig               = {
+        Unit = "offlineimap.service";
+        OnCalendar = cfg.onCalendar;
+        # start immediately after computer is started:
+        Persistent = "true";
+      };
+    } // optionalAttrs cfg.enable { wantedBy = [ "default.target" ]; };
+  };
+}