nixos-module.nix

{self}: {
  config,
  pkgs,
  lib,
  ...
}:
with builtins; let
  std = pkgs.lib;
  nginx = config.services.nginx;
  mkRobotsTxt = robots: let
    agents = std.concatStringsSep "\n" (map (agent: "User-agent: ${agent}") robots);
  in
    pkgs.writeText "robots.txt" ''
      ${agents}
      Disallow: /
    '';
  regexEscapes = ["\"" "[" "]" "(" ")" "{" "}" "^" "$" "+" "*" "." "|" "?" "\\"];
  defaultBlockList = attrNames (fromJSON (readFile "${self.inputs.ai-robots-txt}/robots.json"));
in {
  options = with lib; {
    services.nginx = {
      virtualHostDefaults = mkOption {
        type = types.deferredModuleWith {
          staticModules = [];
        };
        description = "Default configuration merged into every virtual host.";
        default = {};
      };
      virtualHosts = mkOption {
        # type-merge the `virtualHosts` submodule so we can import `nginx.virtualHostDefaults` into every virtualHost
        type = types.attrsOf (types.submoduleWith {
          # avoid conflict with default submodule declaration
          shorthandOnlyDefinesConfig = true;
          modules = [
            nginx.virtualHostDefaults
            ({
              config,
              lib,
              ...
            }: {
              options = {
                blockAgents = {
                  enable = mkEnableOption "blocking a set of user agents from accessing this virtual host.";
                  agents = mkOption {
                    type = types.listOf types.str;
                    description = "User agent strings to block from accessing this virtual host.";
                    default = defaultBlockList;
                    defaultText = "The user agent list from [github:ai-robots-txt/ai.robots.txt](https://github.com/ai-robots-txt/ai.robots.txt).";
                    example = ["Amazonbot" "AI2Bot" "Applebot"];
                  };
                  robotsTxt = {
                    enable = mkEnableOption "robots.txt";
                  };
                  method = mkOption {
                    type = types.str;
                    description = "Method by which to block agents.";
                    default = "return 444";
                    defaultText = "`return 444`, dropping the connection.";
                    example = "return 307 https://ash-speed.hetzner.com/10GB.bin";
                  };
                };
              };
              config = lib.mkMerge [
                (lib.mkIf (config.blockAgents.enable && (length config.blockAgents.agents) > 0) {
                  locations."=/robots.txt" = lib.mkIf config.blockAgents.robotsTxt.enable {
                    alias = mkRobotsTxt config.blockAgents.agents;
                  };
                  extraConfig = let
                    agentRules = lib.concatStringsSep "|" (map (lib.strings.escape regexEscapes) config.blockAgents.agents);
                  in ''
                    if ($http_user_agent ~* "(${agentRules})") {
                      ${config.blockAgents.method};
                    }
                  '';
                })
              ];
            })
          ];
        });
      };
    };
  };
  disabledModules = [];
  imports = [];
  config = {};
  meta = {};
}