{ config, lib, pkgs, ... }:

with lib;

let
  cfg = config.services.taskserver;

  taskd = "${pkgs.taskserver}/bin/taskd";

  mkVal = val:
    if val == true then "true"
    else if val == false then "false"
    else if isList val then concatStringsSep ", " val
    else toString val;

  mkConfLine = key: val: let
    result = "${key} = ${mkVal val}";
  in optionalString (val != null && val != []) result;

  mkManualPkiOption = desc: mkOption {
    type = types.nullOr types.path;
    default = null;
    description = desc + ''
      <note><para>
      Setting this option will prevent automatic CA creation and handling.
      </para></note>
    '';
  };

  manualPkiOptions = {
    ca.cert = mkManualPkiOption ''
      Fully qualified path to the CA certificate.
    '';

    server.cert = mkManualPkiOption ''
      Fully qualified path to the server certificate.
    '';

    server.crl = mkManualPkiOption ''
      Fully qualified path to the server certificate revocation list.
    '';

    server.key = mkManualPkiOption ''
      Fully qualified path to the server key.
    '';
  };

  mkAutoDesc = preamble: ''
    ${preamble}

    <note><para>
    This option is for the automatically handled CA and will be ignored if any
    of the <option>services.taskserver.pki.manual.*</option> options are set.
    </para></note>
  '';

  mkExpireOption = desc: mkOption {
    type = types.nullOr types.int;
    default = null;
    example = 365;
    apply = val: if isNull val then -1 else val;
    description = mkAutoDesc ''
      The expiration time of ${desc} in days or <literal>null</literal> for no
      expiration time.
    '';
  };

  autoPkiOptions = {
    bits = mkOption {
      type = types.int;
      default = 4096;
      example = 2048;
      description = mkAutoDesc "The bit size for generated keys.";
    };

    expiration = {
      ca = mkExpireOption "the CA certificate";
      server = mkExpireOption "the server certificate";
      client = mkExpireOption "client certificates";
      crl = mkExpireOption "the certificate revocation list (CRL)";
    };
  };

  needToCreateCA = let
    notFound = path: let
      dotted = concatStringsSep "." path;
    in throw "Can't find option definitions for path `${dotted}'.";
    findPkiDefinitions = path: attrs: let
      mkSublist = key: val: let
        newPath = path ++ singleton key;
      in if isOption val
         then attrByPath newPath (notFound newPath) cfg.pki.manual
         else findPkiDefinitions newPath val;
    in flatten (mapAttrsToList mkSublist attrs);
  in all isNull (findPkiDefinitions [] manualPkiOptions);

  configFile = pkgs.writeText "taskdrc" (''
    # systemd related
    daemon = false
    log = -

    # logging
    ${mkConfLine "debug" cfg.debug}
    ${mkConfLine "ip.log" cfg.ipLog}

    # general
    ${mkConfLine "ciphers" cfg.ciphers}
    ${mkConfLine "confirmation" cfg.confirmation}
    ${mkConfLine "extensions" cfg.extensions}
    ${mkConfLine "queue.size" cfg.queueSize}
    ${mkConfLine "request.limit" cfg.requestLimit}

    # client
    ${mkConfLine "client.allow" cfg.allowedClientIDs}
    ${mkConfLine "client.deny" cfg.disallowedClientIDs}

    # server
    server = ${cfg.listenHost}:${toString cfg.listenPort}
    ${mkConfLine "trust" cfg.trust}

    # PKI options
    ${if needToCreateCA then ''
      ca.cert = ${cfg.dataDir}/keys/ca.cert
      server.cert = ${cfg.dataDir}/keys/server.cert
      server.key = ${cfg.dataDir}/keys/server.key
      server.crl = ${cfg.dataDir}/keys/server.crl
    '' else ''
      ca.cert = ${cfg.pki.ca.cert}
      server.cert = ${cfg.pki.server.cert}
      server.key = ${cfg.pki.server.key}
      server.crl = ${cfg.pki.server.crl}
    ''}
  '' + cfg.extraConfig);

  orgOptions = { name, ... }: {
    options.users = mkOption {
      type = types.uniq (types.listOf types.str);
      default = [];
      example = [ "alice" "bob" ];
      description = ''
        A list of user names that belong to the organization.
      '';
    };

    options.groups = mkOption {
      type = types.listOf types.str;
      default = [];
      example = [ "workers" "slackers" ];
      description = ''
        A list of group names that belong to the organization.
      '';
    };
  };

  mkShellStr = val: "'${replaceStrings ["'"] ["'\\''"] val}'";

  certtool = "${pkgs.gnutls}/bin/certtool";

  nixos-taskserver = pkgs.buildPythonPackage {
    name = "nixos-taskserver";
    namePrefix = "";

    src = pkgs.runCommand "nixos-taskserver-src" {} ''
      mkdir -p "$out"
      cat "${pkgs.substituteAll {
        src = ./helper-tool.py;
        inherit taskd certtool;
        inherit (cfg) dataDir user group fqdn;
        certBits = cfg.pki.auto.bits;
        clientExpiration = cfg.pki.auto.expiration.client;
        crlExpiration = cfg.pki.auto.expiration.crl;
      }}" > "$out/main.py"
      cat > "$out/setup.py" <<EOF
      from setuptools import setup
      setup(name="nixos-taskserver",
            py_modules=["main"],
            install_requires=["Click"],
            entry_points="[console_scripts]\\nnixos-taskserver=main:cli")
      EOF
    '';

    propagatedBuildInputs = [ pkgs.pythonPackages.click ];
  };

  withMeta = meta: defs: mkMerge [ defs { inherit meta; } ];

in {
  options = {
    services.taskserver = {
      enable = mkOption {
        type = types.bool;
        default = false;
        example = true;
        description = ''
          Whether to enable the Taskwarrior server.

          More instructions about NixOS in conjuction with Taskserver can be
          found in the NixOS manual at
          <olink targetdoc="manual" targetptr="module-taskserver"/>.
        '';
      };

      user = mkOption {
        type = types.str;
        default = "taskd";
        description = "User for Taskserver.";
      };

      group = mkOption {
        type = types.str;
        default = "taskd";
        description = "Group for Taskserver.";
      };

      dataDir = mkOption {
        type = types.path;
        default = "/var/lib/taskserver";
        description = "Data directory for Taskserver.";
      };

      ciphers = mkOption {
        type = types.nullOr (types.separatedString ":");
        default = null;
        example = "NORMAL:-VERS-SSL3.0";
        description = let
          url = "https://gnutls.org/manual/html_node/Priority-Strings.html";
        in ''
          List of GnuTLS ciphers to use. See the GnuTLS documentation about
          priority strings at <link xlink:href="${url}"/> for full details.
        '';
      };

      organisations = mkOption {
        type = types.attrsOf (types.submodule orgOptions);
        default = {};
        example.myShinyOrganisation.users = [ "alice" "bob" ];
        example.myShinyOrganisation.groups = [ "staff" "outsiders" ];
        example.yetAnotherOrganisation.users = [ "foo" "bar" ];
        description = ''
          An attribute set where the keys name the organisation and the values
          are a set of lists of <option>users</option> and
          <option>groups</option>.
        '';
      };

      confirmation = mkOption {
        type = types.bool;
        default = true;
        description = ''
          Determines whether certain commands are confirmed.
        '';
      };

      debug = mkOption {
        type = types.bool;
        default = false;
        description = ''
          Logs debugging information.
        '';
      };

      extensions = mkOption {
        type = types.nullOr types.path;
        default = null;
        description = ''
          Fully qualified path of the Taskserver extension scripts.
          Currently there are none.
        '';
      };

      ipLog = mkOption {
        type = types.bool;
        default = false;
        description = ''
          Logs the IP addresses of incoming requests.
        '';
      };

      queueSize = mkOption {
        type = types.int;
        default = 10;
        description = ''
          Size of the connection backlog, see <citerefentry>
            <refentrytitle>listen</refentrytitle>
            <manvolnum>2</manvolnum>
          </citerefentry>.
        '';
      };

      requestLimit = mkOption {
        type = types.int;
        default = 1048576;
        description = ''
          Size limit of incoming requests, in bytes.
        '';
      };

      allowedClientIDs = mkOption {
        type = with types; loeOf (either (enum ["all" "none"]) str);
        default = [];
        example = [ "[Tt]ask [2-9]+" ];
        description = ''
          A list of regular expressions that are matched against the reported
          client id (such as <literal>task 2.3.0</literal>).

          The values <literal>all</literal> or <literal>none</literal> have
          special meaning. Overidden by any entry in the option
          <option>services.taskserver.client.deny</option>.
        '';
      };

      disallowedClientIDs = mkOption {
        type = with types; loeOf (either (enum ["all" "none"]) str);
        default = [];
        example = [ "[Tt]ask [2-9]+" ];
        description = ''
          A list of regular expressions that are matched against the reported
          client id (such as <literal>task 2.3.0</literal>).

          The values <literal>all</literal> or <literal>none</literal> have
          special meaning. Any entry here overrides these in
          <option>services.taskserver.client.allow</option>.
        '';
      };

      listenHost = mkOption {
        type = types.str;
        default = "localhost";
        description = ''
          The address (IPv4, IPv6 or DNS) to listen on.
        '';
      };

      listenPort = mkOption {
        type = types.int;
        default = 53589;
        description = ''
          Port number of the Taskserver.
        '';
      };

      fqdn = mkOption {
        type = types.str;
        default = "localhost";
        description = ''
          The fully qualified domain name of this server, which is also used
          as the common name in the certificates.
        '';
      };

      trust = mkOption {
        type = types.enum [ "allow all" "strict" ];
        default = "strict";
        description = ''
          Determines how client certificates are validated.

          The value <literal>allow all</literal> performs no client
          certificate validation. This is not recommended. The value
          <literal>strict</literal> causes the client certificate to be
          validated against a CA.
        '';
      };

      pki.manual = manualPkiOptions;
      pki.auto = autoPkiOptions;

      extraConfig = mkOption {
        type = types.lines;
        default = "";
        example = "client.cert = /tmp/debugging.cert";
        description = ''
          Extra lines to append to the taskdrc configuration file.
        '';
      };
    };
  };

  config = withMeta {
    doc = ./taskserver.xml;
  } (mkIf cfg.enable {

    environment.systemPackages = [ pkgs.taskserver nixos-taskserver ];

    users.users = optional (cfg.user == "taskd") {
      name = "taskd";
      uid = config.ids.uids.taskd;
      description = "Taskserver user";
      group = cfg.group;
    };

    users.groups = optional (cfg.group == "taskd") {
      name = "taskd";
      gid = config.ids.gids.taskd;
    };

    systemd.services.taskserver-ca = mkIf needToCreateCA {
      requiredBy = [ "taskserver.service" ];
      after = [ "taskserver-init.service" ];
      description = "Initialize CA for TaskServer";
      serviceConfig.Type = "oneshot";
      serviceConfig.UMask = "0077";

      script = ''
        silent_certtool() {
          if ! output="$("${certtool}" "$@" 2>&1)"; then
            echo "GNUTLS certtool invocation failed with output:" >&2
            echo "$output" >&2
          fi
        }

        mkdir -m 0700 -p "${cfg.dataDir}/keys"
        chown root:root "${cfg.dataDir}/keys"

        if [ ! -e "${cfg.dataDir}/keys/ca.key" ]; then
          silent_certtool -p \
            --bits ${toString cfg.pki.auto.bits} \
            --outfile "${cfg.dataDir}/keys/ca.key"
          silent_certtool -s \
            --template "${pkgs.writeText "taskserver-ca.template" ''
              cn = ${cfg.fqdn}
              expiration_days = ${toString cfg.pki.auto.expiration.ca}
              cert_signing_key
              ca
            ''}" \
            --load-privkey "${cfg.dataDir}/keys/ca.key" \
            --outfile "${cfg.dataDir}/keys/ca.cert"

          chgrp "${cfg.group}" "${cfg.dataDir}/keys/ca.cert"
          chmod g+r "${cfg.dataDir}/keys/ca.cert"
        fi

        if [ ! -e "${cfg.dataDir}/keys/server.key" ]; then
          silent_certtool -p \
            --bits ${toString cfg.pki.auto.bits} \
            --outfile "${cfg.dataDir}/keys/server.key"

          silent_certtool -c \
            --template "${pkgs.writeText "taskserver-cert.template" ''
              cn = ${cfg.fqdn}
              expiration_days = ${toString cfg.pki.auto.expiration.server}
              tls_www_server
              encryption_key
              signing_key
            ''}" \
            --load-ca-privkey "${cfg.dataDir}/keys/ca.key" \
            --load-ca-certificate "${cfg.dataDir}/keys/ca.cert" \
            --load-privkey "${cfg.dataDir}/keys/server.key" \
            --outfile "${cfg.dataDir}/keys/server.cert"

          chgrp "${cfg.group}" \
            "${cfg.dataDir}/keys/server.key" \
            "${cfg.dataDir}/keys/server.cert"

          chmod g+r \
            "${cfg.dataDir}/keys/server.key" \
            "${cfg.dataDir}/keys/server.cert"
        fi

        if [ ! -e "${cfg.dataDir}/keys/server.crl" ]; then
          silent_certtool --generate-crl \
            --template "${pkgs.writeText "taskserver-crl.template" ''
              expiration_days = ${toString cfg.pki.auto.expiration.crl}
            ''}" \
            --load-ca-privkey "${cfg.dataDir}/keys/ca.key" \
            --load-ca-certificate "${cfg.dataDir}/keys/ca.cert" \
            --outfile "${cfg.dataDir}/keys/server.crl"

          chgrp "${cfg.group}" "${cfg.dataDir}/keys/server.crl"
          chmod g+r "${cfg.dataDir}/keys/server.crl"
        fi

        chmod go+x "${cfg.dataDir}/keys"
      '';
    };

    systemd.services.taskserver-init = {
      requiredBy = [ "taskserver.service" ];
      description = "Initialize Taskserver Data Directory";

      preStart = ''
        mkdir -m 0770 -p "${cfg.dataDir}"
        chown "${cfg.user}:${cfg.group}" "${cfg.dataDir}"
      '';

      script = ''
        ${taskd} init
        echo "include ${configFile}" > "${cfg.dataDir}/config"
        touch "${cfg.dataDir}/.is_initialized"
      '';

      environment.TASKDDATA = cfg.dataDir;

      unitConfig.ConditionPathExists = "!${cfg.dataDir}/.is_initialized";

      serviceConfig.Type = "oneshot";
      serviceConfig.User = cfg.user;
      serviceConfig.Group = cfg.group;
      serviceConfig.PermissionsStartOnly = true;
    };

    systemd.services.taskserver = {
      description = "Taskwarrior Server";

      wantedBy = [ "multi-user.target" ];
      after = [ "network.target" ];

      environment.TASKDDATA = cfg.dataDir;

      preStart = let
        jsonOrgs = builtins.toJSON cfg.organisations;
        jsonFile = pkgs.writeText "orgs.json" jsonOrgs;
      in "${nixos-taskserver}/bin/nixos-taskserver process-json '${jsonFile}'";

      serviceConfig = {
        ExecStart = "@${taskd} taskd server";
        ExecReload = "${pkgs.coreutils}/bin/kill -USR1 $MAINPID";
        PermissionsStartOnly = true;
        User = cfg.user;
        Group = cfg.group;
      };
    };
  });
}