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

let
  cfg = config.services.vmagent;
  settingsFormat = pkgs.formats.yaml {};

  startCLIList =
    [
      "${cfg.package}/bin/vmagent"
    ]
    ++ lib.optionals (cfg.remoteWrite.url != null) [
      "-remoteWrite.url=${cfg.remoteWrite.url}"
      "-remoteWrite.tmpDataPath=%C/vmagent/remote_write_tmp"
    ]
    ++ lib.optional (
      cfg.remoteWrite.basicAuthUsername != null
    ) "-remoteWrite.basicAuth.username=${cfg.remoteWrite.basicAuthUsername}"
    ++ lib.optional (
      cfg.remoteWrite.basicAuthPasswordFile != null
    ) "-remoteWrite.basicAuth.passwordFile=\${CREDENTIALS_DIRECTORY}/remote_write_basic_auth_password"
    ++ cfg.extraArgs;
  prometheusConfigYml = checkedConfig (
    settingsFormat.generate "prometheusConfig.yaml" cfg.prometheusConfig
  );

  checkedConfig = file:
    pkgs.runCommand "checked-config" {nativeBuildInputs = [cfg.package];} ''
      ln -s ${file} $out
      ${lib.escapeShellArgs startCLIList} -promscrape.config=${file} -dryRun
    '';
in {
  imports = [
    (lib.mkRemovedOptionModule [ "services" "vmagent" "dataDir" ] "dataDir has been deprecated in favor of systemd provided CacheDirectory")
    (lib.mkRemovedOptionModule [ "services" "vmagent" "user" ] "user has been deprecated in favor of systemd DynamicUser")
    (lib.mkRemovedOptionModule [ "services" "vmagent" "group" ] "group has been deprecated in favor of systemd DynamicUser")
    (lib.mkRenamedOptionModule [ "services" "vmagent" "remoteWriteUrl" ] [ "services" "vmagent" "remoteWrite" "url" ])
  ];

  options.services.vmagent = {
    enable = lib.mkOption {
      type = lib.types.bool;
      default = false;
      description = ''
        Whether to enable VictoriaMetrics's `vmagent`.

        `vmagent` efficiently scrape metrics from Prometheus-compatible exporters
      '';
    };

    package = lib.mkPackageOption pkgs "vmagent" { };

    remoteWrite = {
      url = lib.mkOption {
        default = null;
        type = lib.types.nullOr lib.types.str;
        description = ''
          Endpoint for prometheus compatible remote_write
        '';
      };
      basicAuthUsername = lib.mkOption {
        default = null;
        type = lib.types.nullOr lib.types.str;
        description = ''
          Basic Auth username used to connect to remote_write endpoint
        '';
      };
      basicAuthPasswordFile = lib.mkOption {
        default = null;
        type = lib.types.nullOr lib.types.str;
        description = ''
          File that contains the Basic Auth password used to connect to remote_write endpoint
        '';
      };
    };

    prometheusConfig = lib.mkOption {
      type = lib.types.submodule { freeformType = settingsFormat.type; };
      description = ''
        Config for prometheus style metrics
      '';
    };

    openFirewall = lib.mkOption {
      type = lib.types.bool;
      default = false;
      description = ''
        Whether to open the firewall for the default ports.
      '';
    };

    extraArgs = lib.mkOption {
      type = lib.types.listOf lib.types.str;
      default = [];
      description = ''
        Extra args to pass to `vmagent`. See the docs:
        <https://docs.victoriametrics.com/vmagent.html#advanced-usage>
        or {command}`vmagent -help` for more information.
      '';
    };
  };

  config = lib.mkIf cfg.enable {
    networking.firewall.allowedTCPPorts = lib.mkIf cfg.openFirewall [ 8429 ];

    systemd.services.vmagent = {
      wantedBy = [ "multi-user.target" ];
      after = [ "network.target" ];
      description = "vmagent system service";
      serviceConfig = {
        DynamicUser = true;
        User = "vmagent";
        Group = "vmagent";
        Type = "simple";
        Restart = "on-failure";
        CacheDirectory = "vmagent";
        ExecStart = lib.escapeShellArgs (
          startCLIList
          ++ lib.optionals (cfg.prometheusConfig != null) ["-promscrape.config=${prometheusConfigYml}"]
        );
        LoadCredential = lib.optional (cfg.remoteWrite.basicAuthPasswordFile != null) [
          "remote_write_basic_auth_password:${cfg.remoteWrite.basicAuthPasswordFile}"
        ];
      };
    };
  };
}