{
  config,
  lib,
  pkgs,
  ...
}:
with lib; let
  cfg = config.services.caddy;

  virtualHosts = attrValues cfg.virtualHosts;

  mkVHostConf = hostOpts: ''
    ${hostOpts.hostName} ${concatStringsSep " " hostOpts.serverAliases} {
      ${optionalString (
      hostOpts.listenAddresses != []
    ) "bind ${concatStringsSep " " hostOpts.listenAddresses}"}
      log {
        ${hostOpts.logFormat}
      }

      ${hostOpts.extraConfig}
    }
  '';

  settingsFormat = pkgs.formats.json {};

  configFile =
    if cfg.settings != {}
    then settingsFormat.generate "caddy.json" cfg.settings
    else let
      Caddyfile = pkgs.writeTextDir "Caddyfile" ''
        {
          ${cfg.globalConfig}
        }
        ${cfg.extraConfig}
        ${concatMapStringsSep "\n" mkVHostConf virtualHosts}
      '';

      Caddyfile-formatted = pkgs.runCommand "Caddyfile-formatted" {} ''
        mkdir -p $out
        cp --no-preserve=mode ${Caddyfile}/Caddyfile $out/Caddyfile
        ${lib.getExe cfg.package} fmt --overwrite $out/Caddyfile
      '';
    in "${
      if pkgs.stdenv.buildPlatform == pkgs.stdenv.hostPlatform
      then Caddyfile-formatted
      else Caddyfile
    }/Caddyfile";
in {
  imports = [
    (mkRemovedOptionModule [
      "services"
      "caddy"
      "agree"
    ] "this option is no longer necessary for Caddy 2")
    (mkRenamedOptionModule ["services" "caddy" "ca"] ["services" "caddy" "acmeCA"])
    (mkRenamedOptionModule ["services" "caddy" "config"] ["services" "caddy" "extraConfig"])
  ];

  # interface
  options.services.caddy = {
    enable = mkEnableOption "Caddy web server";

    user = mkOption {
      default = "caddy";
      type = types.str;
      description = ''
        User account under which caddy runs.

        ::: {.note}
        If left as the default value this user will automatically be created
        on system activation, otherwise you are responsible for
        ensuring the user exists before the Caddy service starts.
        :::
      '';
    };

    group = mkOption {
      default = "caddy";
      type = types.str;
      description = ''
        Group under which caddy runs.

        ::: {.note}
        If left as the default value this group will automatically be created
        on system activation, otherwise you are responsible for
        ensuring the group exists before the Caddy service starts.
        :::
      '';
    };

    package = mkPackageOption pkgs "caddy" {};

    dataDir = mkOption {
      type = types.path;
      default = "/usr/local/var/lib/caddy";
      description = ''
        The data directory for caddy.

        ::: {.note}
        If left as the default value this directory will automatically be created
        before the Caddy server starts, otherwise you are responsible for ensuring
        the directory exists with appropriate ownership and permissions.

        Caddy v2 replaced `CADDYPATH` with XDG directories.
        See <https://caddyserver.com/docs/conventions#file-locations>.
        :::
      '';
    };

    logDir = mkOption {
      type = types.path;
      default = "/usr/local/var/log/caddy";
      description = ''
        Directory for storing Caddy access logs.

        ::: {.note}
        If left as the default value this directory will automatically be created
        before the Caddy server starts, otherwise the sysadmin is responsible for
        ensuring the directory exists with appropriate ownership and permissions.
        :::
      '';
    };

    logFormat = mkOption {
      type = types.lines;
      default = ''
        level ERROR
      '';
      example = literalExpression ''
        mkForce "level INFO";
      '';
      description = ''
        Configuration for the default logger. See
        <https://caddyserver.com/docs/caddyfile/options#log>
        for details.
      '';
    };

    configFile = mkOption {
      type = types.path;
      default = configFile;
      defaultText = "A Caddyfile automatically generated by values from services.caddy.*";
      example = literalExpression ''
        pkgs.writeText "Caddyfile" '''
          example.com

          root * /var/www/wordpress
          php_fastcgi unix//run/php/php-version-fpm.sock
          file_server
        ''';
      '';
      description = ''
        Override the configuration file used by Caddy. By default,
        NixOS generates one automatically.
      '';
    };

    adapter = mkOption {
      default =
        if ((cfg.configFile != configFile) || (builtins.baseNameOf cfg.configFile) == "Caddyfile")
        then "caddyfile"
        else null;
      defaultText = literalExpression ''
        if ((cfg.configFile != configFile) || (builtins.baseNameOf cfg.configFile) == "Caddyfile") then "caddyfile" else null
      '';
      example = literalExpression "nginx";
      type = with types; nullOr str;
      description = ''
        Name of the config adapter to use.
        See <https://caddyserver.com/docs/config-adapters>
        for the full list.

        If `null` is specified, the `--adapter` argument is omitted when
        starting or restarting Caddy. Notably, this allows specification of a
        configuration file in Caddy's native JSON format, as long as the
        filename does not start with `Caddyfile` (in which case the `caddyfile`
        adapter is implicitly enabled). See
        <https://caddyserver.com/docs/command-line#caddy-run> for details.

        ::: {.note}
        Any value other than `null` or `caddyfile` is only valid when providing
        your own `configFile`.
        :::
      '';
    };

    resume = mkOption {
      default = false;
      type = types.bool;
      description = ''
        Use saved config, if any (and prefer over any specified configuration passed with `--config`).
      '';
    };

    globalConfig = mkOption {
      type = types.lines;
      default = "";
      example = ''
        debug
        servers {
          protocol {
            experimental_http3
          }
        }
      '';
      description = ''
        Additional lines of configuration appended to the global config section
        of the `Caddyfile`.

        Refer to <https://caddyserver.com/docs/caddyfile/options#global-options>
        for details on supported values.
      '';
    };

    extraConfig = mkOption {
      type = types.lines;
      default = "";
      example = ''
        example.com {
          encode gzip
          log
          root /srv/http
        }
      '';
      description = ''
        Additional lines of configuration appended to the automatically
        generated `Caddyfile`.
      '';
    };

    virtualHosts = mkOption {
      type = with types; attrsOf (submodule (import ./vhost-options.nix {inherit cfg;}));
      default = {};
      example = literalExpression ''
        {
          "hydra.example.com" = {
            serverAliases = [ "www.hydra.example.com" ];
            extraConfig = '''
              encode gzip
              root * /srv/http
            ''';
          };
        };
      '';
      description = ''
        Declarative specification of virtual hosts served by Caddy.
      '';
    };

    acmeCA = mkOption {
      default = null;
      example = "https://acme-v02.api.letsencrypt.org/directory";
      type = with types; nullOr str;
      description = ''
        ::: {.note}
        Sets the [`acme_ca` option](https://caddyserver.com/docs/caddyfile/options#acme-ca)
        in the global options block of the resulting Caddyfile.
        :::

        The URL to the ACME CA's directory. It is strongly recommended to set
        this to `https://acme-staging-v02.api.letsencrypt.org/directory` for
        Let's Encrypt's [staging endpoint](https://letsencrypt.org/docs/staging-environment/)
        while testing or in development.

        Value `null` should be prefered for production setups,
        as it omits the `acme_ca` option to enable
        [automatic issuer fallback](https://caddyserver.com/docs/automatic-https#issuer-fallback).
      '';
    };

    email = mkOption {
      default = null;
      type = with types; nullOr str;
      description = ''
        Your email address. Mainly used when creating an ACME account with your
        CA, and is highly recommended in case there are problems with your
        certificates.
      '';
    };

    settings = mkOption {
      type = settingsFormat.type;
      default = {};
      description = ''
        Structured configuration for Caddy to generate a Caddy JSON configuration file.
        See <https://caddyserver.com/docs/json/> for available options.

        ::: {.warning}
        Using a [Caddyfile](https://caddyserver.com/docs/caddyfile) instead of a JSON config is highly recommended by upstream.
        There are only very few exception to this.

        Please use a Caddyfile via {option}`services.caddy.configFile`, {option}`services.caddy.virtualHosts` or
        {option}`services.caddy.extraConfig` with {option}`services.caddy.globalConfig` instead.
        :::

        ::: {.note}
        Takes presence over most `services.caddy.*` options, such as {option}`services.caddy.configFile` and {option}`services.caddy.virtualHosts`, if specified.
        :::
      '';
    };

    environmentFile = mkOption {
      type = with types; nullOr path;
      default = null;
      example = "/run/secrets/caddy.env";
      description = ''
        Environment file as defined in {manpage}`launchd.plist(5)`.

        You can use environment variables to pass secrets to the service without adding
        them to the world-redable nix store.

        ```
        # in configuration.nix
        services.caddy.environmentFile = "/run/secrets/caddy.env";
        services.caddy.globalConfig = '''
          {
            acme_ca https://acme.zerossl.com/v2/DV90
            acme_eab {
              key_id {$EAB_KEY_ID}
              mac_key {$EAB_MAC_KEY}
            }
          }
        ''';
        ```

        ```
        # in /run/secrets/caddy.env
        EAB_KEY_ID=secret
        EAB_MAC_KEY=secret
        ```

        Find more examples
        [here](https://caddyserver.com/docs/caddyfile/concepts#environment-variables)
      '';
    };

    serviceConfig = mkOption {
      type = types.attrs;
      default = {};
      description = ''
        Additional launchd service configuration.
      '';
    };
  };

  # implementation
  config = mkIf cfg.enable {
    assertions = [
      {
        assertion = cfg.configFile == configFile -> cfg.adapter == "caddyfile" || cfg.adapter == null;
        message = "To specify an adapter other than 'caddyfile' please provide your own configuration via `services.caddy.configFile`";
      }
    ];

    services.caddy.globalConfig = ''
      ${optionalString (cfg.email != null) "email ${cfg.email}"}
      ${optionalString (cfg.acmeCA != null) "acme_ca ${cfg.acmeCA}"}
      log {
        ${cfg.logFormat}
      }
    '';

    launchd.user.agents.caddy = {
      path = [cfg.package];

      # Use script when environment file is provided, otherwise direct command
      script = mkIf (cfg.environmentFile != null) ''
        if [ -f "${cfg.environmentFile}" ]; then
          set -a
          source ${cfg.environmentFile}
          set +a
        fi
        exec ${lib.getExe cfg.package} run --config ${cfg.configFile} ${
          optionalString (cfg.adapter != null) "--adapter ${cfg.adapter}"
        } ${optionalString cfg.resume "--resume"}
      '';

      command = mkIf (cfg.environmentFile == null) "${lib.getExe cfg.package} run --config ${cfg.configFile} ${
        optionalString (cfg.adapter != null) "--adapter ${cfg.adapter}"
      } ${optionalString cfg.resume "--resume"}";

      serviceConfig =
        {
          KeepAlive = true;
          RunAtLoad = true;
          WorkingDirectory = cfg.dataDir;
          StandardOutPath = "${cfg.logDir}/caddy.log";
          StandardErrorPath = "${cfg.logDir}/caddy.error.log";
        }
        // cfg.serviceConfig
        // (optionalAttrs (cfg.user != "caddy") {
          UserName = cfg.user;
        });
    };

    # Note: User management is handled differently in Darwin
    # Users should be created manually or through other means

    system.activationScripts.caddy = mkIf cfg.enable ''
      # Create data directory
      if [ ! -d "${cfg.dataDir}" ]; then
        mkdir -p "${cfg.dataDir}"
        chown ${cfg.user}:${cfg.group} "${cfg.dataDir}"
        chmod 750 "${cfg.dataDir}"
      fi

      # Create log directory
      if [ ! -d "${cfg.logDir}" ]; then
        mkdir -p "${cfg.logDir}"
        chown ${cfg.user}:${cfg.group} "${cfg.logDir}"
        chmod 750 "${cfg.logDir}"
      fi
    '';
  };
}