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

with lib;

let
  cfg = config.services.opensnitch;
  format = pkgs.formats.json {};

  predefinedRules = flip mapAttrs cfg.rules (name: cfg: {
    file = pkgs.writeText "rule" (builtins.toJSON cfg);
  });

in {
  options = {
    services.opensnitch = {
      enable = mkEnableOption (mdDoc "Opensnitch application firewall");

      rules = mkOption {
        default = {};
        example = literalExpression ''
          {
            "tor" = {
              "name" = "tor";
              "enabled" = true;
              "action" = "allow";
              "duration" = "always";
              "operator" = {
                "type" ="simple";
                "sensitive" = false;
                "operand" = "process.path";
                "data" = "''${lib.getBin pkgs.tor}/bin/tor";
              };
            };
          };
        '';

        description = mdDoc ''
          Declarative configuration of firewall rules.
          All rules will be stored in `/var/lib/opensnitch/rules`.
          See [upstream documentation](https://github.com/evilsocket/opensnitch/wiki/Rules)
          for available options.
        '';

        type = types.submodule {
          freeformType = format.type;
        };
      };

      settings = mkOption {
        type = types.submodule {
          freeformType = format.type;

          options = {
            Server = {

              Address = mkOption {
                type = types.str;
                description = mdDoc ''
                  Unix socket path (unix:///tmp/osui.sock, the "unix:///" part is
                  mandatory) or TCP socket (192.168.1.100:50051).
                '';
              };

              LogFile = mkOption {
                type = types.path;
                description = mdDoc ''
                  File to write logs to (use /dev/stdout to write logs to standard
                  output).
                '';
              };

            };

            DefaultAction = mkOption {
              type = types.enum [ "allow" "deny" ];
              description = mdDoc ''
                Default action whether to block or allow application internet
                access.
              '';
            };

            DefaultDuration = mkOption {
              type = types.enum [
                "once" "always" "until restart" "30s" "5m" "15m" "30m" "1h"
              ];
              description = mdDoc ''
                Default duration of firewall rule.
              '';
            };

            InterceptUnknown = mkOption {
              type = types.bool;
              description = mdDoc ''
                Whether to intercept spare connections.
              '';
            };

            ProcMonitorMethod = mkOption {
              type = types.enum [ "ebpf" "proc" "ftrace" "audit" ];
              description = mdDoc ''
                Which process monitoring method to use.
              '';
            };

            LogLevel = mkOption {
              type = types.enum [ 0 1 2 3 4 ];
              description = mdDoc ''
                Default log level from 0 to 4 (debug, info, important, warning,
                error).
              '';
            };

            Firewall = mkOption {
              type = types.enum [ "iptables" "nftables" ];
              description = mdDoc ''
                Which firewall backend to use.
              '';
            };

            Stats = {

              MaxEvents = mkOption {
                type = types.int;
                description = mdDoc ''
                  Max events to send to the GUI.
                '';
              };

              MaxStats = mkOption {
                type = types.int;
                description = mdDoc ''
                  Max stats per item to keep in backlog.
                '';
              };

            };
          };
        };
        description = mdDoc ''
          opensnitchd configuration. Refer to [upstream documentation](https://github.com/evilsocket/opensnitch/wiki/Configurations)
          for details on supported values.
        '';
      };
    };
  };

  config = mkIf cfg.enable {

    # pkg.opensnitch is referred to elsewhere in the module so we don't need to worry about it being garbage collected
    services.opensnitch.settings = mapAttrs (_: v: mkDefault v) (builtins.fromJSON (builtins.unsafeDiscardStringContext (builtins.readFile "${pkgs.opensnitch}/etc/opensnitchd/default-config.json")));

    systemd = {
      packages = [ pkgs.opensnitch ];
      services.opensnitchd.wantedBy = [ "multi-user.target" ];
    };

    systemd.services.opensnitchd.preStart = mkIf (cfg.rules != {}) (let
      rules = flip mapAttrsToList predefinedRules (file: content: {
        inherit (content) file;
        local = "/var/lib/opensnitch/rules/${file}.json";
      });
    in ''
      # Remove all firewall rules from `/var/lib/opensnitch/rules` that are symlinks to a store-path,
      # but aren't declared in `cfg.rules` (i.e. all networks that were "removed" from
      # `cfg.rules`).
      find /var/lib/opensnitch/rules -type l -lname '${builtins.storeDir}/*' ${optionalString (rules != {}) ''
        -not \( ${concatMapStringsSep " -o " ({ local, ... }:
          "-name '${baseNameOf local}*'")
        rules} \) \
      ''} -delete
      ${concatMapStrings ({ file, local }: ''
        ln -sf '${file}' "${local}"
      '') rules}

      if [ ! -f /etc/opensnitch-system-fw.json ]; then
        cp "${pkgs.opensnitch}/etc/opensnitchd/system-fw.json" "/etc/opensnitchd/system-fw.json"
      fi
    '');

    environment.etc = mkMerge [ ({
      "opensnitchd/default-config.json".source = format.generate "default-config.json" cfg.settings;
    }) (mkIf (cfg.settings.ProcMonitorMethod == "ebpf") {
      "opensnitchd/opensnitch.o".source = "${config.boot.kernelPackages.opensnitch-ebpf}/etc/opensnitchd/opensnitch.o";
      "opensnitchd/opensnitch-dns.o".source = "${config.boot.kernelPackages.opensnitch-ebpf}/etc/opensnitchd/opensnitch-dns.o";
      "opensnitchd/opensnitch-procs.o".source = "${config.boot.kernelPackages.opensnitch-ebpf}/etc/opensnitchd/opensnitch-procs.o";
    })];

  };
}