flexget nixos module: run the service and specify configuration

This module adds support for defining a flexget service.

Due to flexget insisting on being able to write all over where it finds
its configuration file, we use a ExecStartPre hook to copy the generated
configuration file into place under the user's home. It's fairly ugly
and I'm very open to suggestions

nixos/modules/module-list.nix

@@ -427,6 +427,7 @@
   ./services/system/nscd.nix
   ./services/system/uptimed.nix
   ./services/torrent/deluge.nix
+  ./services/torrent/flexget.nix
   ./services/torrent/peerflix.nix
   ./services/torrent/transmission.nix
   ./services/ttys/agetty.nix

nixos/modules/services/torrent/flexget.nix

@@ -0,0 +1,100 @@
+{ config, lib, pkgs, timezone, ... }:
+
+with lib;
+
+let
+  cfg = config.services.flexget;
+  pkg = pkgs.python27Packages.flexget;
+  ymlFile = pkgs.writeText "flexget.yml" ''
+    ${cfg.config}
+
+    ${optionalString cfg.systemScheduler "schedules: no"}
+'';
+  configFile = "${toString cfg.homeDir}/flexget.yml";
+in {
+  options = {
+    services.flexget = {
+      enable = mkEnableOption "Run FlexGet Daemon";
+
+      user = mkOption {
+        default = "deluge";
+        example = "some_user";
+        type = types.string;
+        description = "The user under which to run flexget.";
+      };
+
+      homeDir = mkOption {
+        default = /var/lib/deluge;
+        example = "/home/flexget";
+        type = types.path;
+        description = "Where files live.";
+      };
+
+      interval = mkOption {
+        default = "10m";
+        example = "1h";
+        type = types.string;
+        description = "When to perform a <command>flexget</command> run. See <command>man 7 systemd.time</command> for the format.";
+      };
+
+      systemScheduler = mkOption {
+        default = true;
+        example = "false";
+        type = types.bool;
+        description = "When true, execute the runs via the flexget-runner.timer. If false, you have to specify the settings yourself in the YML file.";
+      };
+
+      config = mkOption {
+        default = "";
+        type = types.lines;
+        description = "The YAML configuration for FlexGet.";
+      };
+    };
+  };
+
+  config = mkIf cfg.enable {
+
+    environment.systemPackages = [ pkgs.python27Packages.flexget ];
+
+    systemd.services = {
+      flexget = {
+        description = "FlexGet Daemon";
+        path = [ pkgs.pythonPackages.flexget ];
+        serviceConfig = {
+          User = cfg.user;
+          Environment = "TZ=${config.time.timeZone}";
+          ExecStartPre = "${pkgs.coreutils}/bin/install -m644 ${ymlFile} ${configFile}";
+          ExecStart = "${pkg}/bin/flexget -c ${configFile} daemon start";
+          ExecStop = "${pkg}/bin/flexget -c ${configFile} daemon stop";
+          ExecReload = "${pkg}/bin/flexget -c ${configFile} daemon reload";
+          Restart = "on-failure";
+          PrivateTmp = true;
+          WorkingDirectory = toString cfg.homeDir;
+        };
+        wantedBy = [ "multi-user.target" ];
+      };
+
+      flexget-runner = mkIf cfg.systemScheduler {
+        description = "FlexGet Runner";
+        after = [ "flexget.service" ];
+        wants = [ "flexget.service" ];
+        serviceConfig = {
+          User = cfg.user;
+          ExecStart = "${pkg}/bin/flexget -c ${configFile} execute";
+          PrivateTmp = true;
+          WorkingDirectory = toString cfg.homeDir;
+        };
+      };
+    };
+
+    systemd.timers.flexget-runner = mkIf cfg.systemScheduler {
+      description = "Run FlexGet every ${cfg.interval}";
+      wantedBy = [ "timers.target" ];
+      timerConfig = {
+        OnBootSec = "5m";
+        OnUnitInactiveSec = cfg.interval;
+        Unit = "flexget-runner.service";
+      };
+    };
+  };
+}