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

with lib;

let
  cfg = config.services.caddy;

  virtualHosts = attrValues cfg.virtualHosts;
  acmeVHosts = filter (hostOpts: hostOpts.useACMEHost != null) virtualHosts;

  mkVHostConf = hostOpts:
    let
      sslCertDir = config.security.acme.certs.${hostOpts.useACMEHost}.directory;
    in
      ''
        ${hostOpts.hostName} ${concatStringsSep " " hostOpts.serverAliases} {
          bind ${concatStringsSep " " hostOpts.listenAddresses}
          ${optionalString (hostOpts.useACMEHost != null) "tls ${sslCertDir}/cert.pem ${sslCertDir}/key.pem"}
          log {
            ${hostOpts.logFormat}
          }

          ${hostOpts.extraConfig}
        }
      '';

  configFile =
    let
      Caddyfile = pkgs.writeText "Caddyfile" ''
        {
          ${cfg.globalConfig}
        }
        ${cfg.extraConfig}
      '';

      Caddyfile-formatted = pkgs.runCommand "Caddyfile-formatted" { nativeBuildInputs = [ cfg.package ]; } ''
        ${cfg.package}/bin/caddy fmt ${Caddyfile} > $out
      '';
    in
      if pkgs.stdenv.buildPlatform == pkgs.stdenv.hostPlatform then Caddyfile-formatted else Caddyfile;

  acmeHosts = unique (catAttrs "useACMEHost" acmeVHosts);

  mkCertOwnershipAssertion = import ../../../security/acme/mk-cert-ownership-assertion.nix;
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><para>
          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.
        </para></note>
      '';
    };

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

        <note><para>
          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.
        </para></note>
      '';
    };

    package = mkOption {
      default = pkgs.caddy;
      defaultText = literalExpression "pkgs.caddy";
      type = types.package;
      description = ''
        Caddy package to use.
      '';
    };

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

        <note>
          <para>
            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.
          </para>
          <para>
            Caddy v2 replaced <literal>CADDYPATH</literal> with XDG directories.
            See <link xlink:href="https://caddyserver.com/docs/conventions#file-locations"/>.
          </para>
        </note>
      '';
    };

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

        <note><para>
          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.
        </para></note>
      '';
    };

    logFormat = mkOption {
      type = types.lines;
      default = ''
        level ERROR
      '';
      example = literalExpression ''
        mkForce "level INFO";
      '';
      description = ''
        Configuration for the default logger. See
        <link xlink:href="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 = "caddyfile";
      example = "nginx";
      type = types.str;
      description = ''
        Name of the config adapter to use.
        See <link xlink:href="https://caddyserver.com/docs/config-adapters"/>
        for the full list.

        <note><para>
          Any value other than <literal>caddyfile</literal> is only valid when
          providing your own <option>configFile</option>.
        </para></note>
      '';
    };

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

    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 <literal>Caddyfile</literal>.

        Refer to <link xlink:href="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 <literal>Caddyfile</literal>.
      '';
    };

    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 = "https://acme-v02.api.letsencrypt.org/directory";
      example = "https://acme-staging-v02.api.letsencrypt.org/directory";
      type = with types; nullOr str;
      description = ''
        The URL to the ACME CA's directory. It is strongly recommended to set
        this to Let's Encrypt's staging endpoint for testing or development.

        Set it to <literal>null</literal> if you want to write a more
        fine-grained configuration manually.
      '';
    };

    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.
      '';
    };

  };

  # implementation
  config = mkIf cfg.enable {

    assertions = [
      { assertion = cfg.adapter != "caddyfile" -> cfg.configFile != configFile;
        message = "Any value other than 'caddyfile' is only valid when providing your own `services.caddy.configFile`";
      }
    ] ++ map (name: mkCertOwnershipAssertion {
      inherit (cfg) group user;
      cert = config.security.acme.certs.${name};
      groups = config.users.groups;
    }) acmeHosts;

    services.caddy.extraConfig = concatMapStringsSep "\n" mkVHostConf virtualHosts;
    services.caddy.globalConfig = ''
      ${optionalString (cfg.email != null) "email ${cfg.email}"}
      ${optionalString (cfg.acmeCA != null) "acme_ca ${cfg.acmeCA}"}
      log {
        ${cfg.logFormat}
      }
    '';

    systemd.packages = [ cfg.package ];
    systemd.services.caddy = {
      wants = map (hostOpts: "acme-finished-${hostOpts.useACMEHost}.target") acmeVHosts;
      after = map (hostOpts: "acme-selfsigned-${hostOpts.useACMEHost}.service") acmeVHosts;
      before = map (hostOpts: "acme-${hostOpts.useACMEHost}.service") acmeVHosts;

      wantedBy = [ "multi-user.target" ];
      startLimitIntervalSec = 14400;
      startLimitBurst = 10;

      serviceConfig = {
        # https://www.freedesktop.org/software/systemd/man/systemd.service.html#ExecStart=
        # If the empty string is assigned to this option, the list of commands to start is reset, prior assignments of this option will have no effect.
        ExecStart = [ "" "${cfg.package}/bin/caddy run --config ${cfg.configFile} --adapter ${cfg.adapter} ${optionalString cfg.resume "--resume"}" ];
        ExecReload = [ "" "${cfg.package}/bin/caddy reload --config ${cfg.configFile} --adapter ${cfg.adapter} --force" ];

        ExecStartPre = "${cfg.package}/bin/caddy validate --config ${cfg.configFile} --adapter ${cfg.adapter}";
        User = cfg.user;
        Group = cfg.group;
        ReadWriteDirectories = cfg.dataDir;
        StateDirectory = mkIf (cfg.dataDir == "/var/lib/caddy") [ "caddy" ];
        LogsDirectory = mkIf (cfg.logDir == "/var/log/caddy") [ "caddy" ];
        Restart = "on-abnormal";
        SupplementaryGroups = mkIf (length acmeVHosts != 0) [ "acme" ];

        # TODO: attempt to upstream these options
        NoNewPrivileges = true;
        PrivateDevices = true;
        ProtectHome = true;
      };
    };

    users.users = optionalAttrs (cfg.user == "caddy") {
      caddy = {
        group = cfg.group;
        uid = config.ids.uids.caddy;
        home = cfg.dataDir;
      };
    };

    users.groups = optionalAttrs (cfg.group == "caddy") {
      caddy.gid = config.ids.gids.caddy;
    };

    security.acme.certs =
      let
        reloads = map (useACMEHost: nameValuePair useACMEHost { reloadServices = [ "caddy.service" ]; }) acmeHosts;
      in
        listToAttrs reloads;

  };
}