{config, pkgs, ...}:

###### interface
let
  inherit (pkgs.lib) mkOption mapAttrs fold
    mergeListOption mergeTypedOption mergeAttrsWithFunc;

  options = {
    services = {
      extraJobs = mkOption {
        default = [];
        example = [
             { name = "test-job";
               job = ''
                 description "nc"
                 start on started network-interfaces
                 respawn
                 env PATH=/var/run/current-system/sw/bin
                 exec sh -c "echo 'hello world' | ${pkgs.netcat}/bin/nc -l -p 9000"
                 '';
             } ];
        # should have some checks to verify the syntax
        merge = pkgs.lib.mergeListOption;
        description = "
          Additional Upstart jobs.
        ";
      };

      tools = {
        upstartJobs = mkOption {
          default = {};
          description = "
            List of functions which can be used to create upstart-jobs.
          ";
        };
      };
    };

    tests = {
      upstartJobs = mkOption {
        internal = true;
        default = {};
        description = "
          Make it easier to build individual Upstart jobs. (e.g.,
          <command>nix-build /etc/nixos/nixos -A
          tests.upstartJobs.xserver</command>).
        ";
      };
    };
  };
in

###### implementation
let
  makeJob = import ./make-job.nix {
    inherit (pkgs) runCommand;
  };

  optional = cond: service: pkgs.lib.optional cond (makeJob service);

  requiredTTYs = config.requiredTTYs;

  jobs = map makeJob []

  # User-defined events.
  ++ (map makeJob (config.services.extraJobs));

  
  # Create an etc/event.d directory containing symlinks to the
  # specified list of Upstart job files.
  command = pkgs.runCommand "upstart-jobs" {inherit jobs;}
    ''
      ensureDir $out/etc/event.d
      for i in $jobs; do
        if ln -s $i . ; then
          if test -d $i; then
            ln -s $i/etc/event.d/* $out/etc/event.d/
          fi
        else
          echo Duplicate entry: $i;
        fi;
      done
    '';

in 

{
  require = [
    options
    ./tools.nix # !!! doesn't seem to be used anywhere
  ];

  environment = {
    etc = [{ # The Upstart events defined above.
      source = command + "/etc/event.d";
      target = "event.d";
    }]
    ++ pkgs.lib.concatLists (map (job: job.extraEtc) jobs);

    extraPackages =
      pkgs.lib.concatLists (map (job: job.extraPath) jobs);
  };

  users = {
    extraUsers =
      pkgs.lib.concatLists (map (job: job.users) jobs);

    extraGroups =
      pkgs.lib.concatLists (map (job: job.groups) jobs);
  };

  services = {
    extraJobs = [
      # For the built-in logd job.
      { jobDrv = pkgs.upstart; }
    ];
  };

  tests = {
    # see test/test-upstart-job.sh
    upstartJobs = { recurseForDerivations = true; } //
      builtins.listToAttrs (map (job:
        { name = if job ? jobName then job.jobName else job.name; value = job; }
      ) jobs);
  };
}