{ config, lib, pkgs, ... }:
let
  cfg = config.virtualisation.podman;
  toml = pkgs.formats.toml { };
  json = pkgs.formats.json { };

  inherit (lib) mkOption types;

  podmanPackage = (pkgs.podman.override {
    extraPackages = cfg.extraPackages
      ++ lib.optional (builtins.elem "zfs" config.boot.supportedFilesystems) config.boot.zfs.package;
  });

  # Provides a fake "docker" binary mapping to podman
  dockerCompat = pkgs.runCommand "${podmanPackage.pname}-docker-compat-${podmanPackage.version}" {
    outputs = [ "out" "man" ];
    inherit (podmanPackage) meta;
  } ''
    mkdir -p $out/bin
    ln -s ${podmanPackage}/bin/podman $out/bin/docker

    mkdir -p $man/share/man/man1
    for f in ${podmanPackage.man}/share/man/man1/*; do
      basename=$(basename $f | sed s/podman/docker/g)
      ln -s $f $man/share/man/man1/$basename
    done
  '';

  net-conflist = pkgs.runCommand "87-podman-bridge.conflist" {
    nativeBuildInputs = [ pkgs.jq ];
    extraPlugins = builtins.toJSON cfg.defaultNetwork.extraPlugins;
    jqScript = ''
      . + { "plugins": (.plugins + $extraPlugins) }
    '';
  } ''
    jq <${cfg.package}/etc/cni/net.d/87-podman-bridge.conflist \
      --argjson extraPlugins "$extraPlugins" \
      "$jqScript" \
      >$out
  '';

in
{
  imports = [
    ./dnsname.nix
    ./network-socket.nix
    (lib.mkRenamedOptionModule [ "virtualisation" "podman" "libpod" ] [ "virtualisation" "containers" "containersConf" ])
  ];

  meta = {
    maintainers = lib.teams.podman.members;
  };

  options.virtualisation.podman = {

    enable =
      mkOption {
        type = types.bool;
        default = false;
        description = ''
          This option enables Podman, a daemonless container engine for
          developing, managing, and running OCI Containers on your Linux System.

          It is a drop-in replacement for the <command>docker</command> command.
        '';
      };

    dockerSocket.enable = mkOption {
      type = types.bool;
      default = false;
      description = ''
        Make the Podman socket available in place of the Docker socket, so
        Docker tools can find the Podman socket.

        Podman implements the Docker API.

        Users must be in the <literal>podman</literal> group in order to connect. As
        with Docker, members of this group can gain root access.
      '';
    };

    dockerCompat = mkOption {
      type = types.bool;
      default = false;
      description = ''
        Create an alias mapping <command>docker</command> to <command>podman</command>.
      '';
    };

    enableNvidia = mkOption {
      type = types.bool;
      default = false;
      description = ''
        Enable use of NVidia GPUs from within podman containers.
      '';
    };

    extraPackages = mkOption {
      type = with types; listOf package;
      default = [ ];
      example = lib.literalExpression ''
        [
          pkgs.gvisor
        ]
      '';
      description = ''
        Extra packages to be installed in the Podman wrapper.
      '';
    };

    package = lib.mkOption {
      type = types.package;
      default = podmanPackage;
      internal = true;
      description = ''
        The final Podman package (including extra packages).
      '';
    };

    defaultNetwork.extraPlugins = lib.mkOption {
      type = types.listOf json.type;
      default = [];
      description = ''
        Extra CNI plugin configurations to add to podman's default network.
      '';
    };

  };

  config = lib.mkIf cfg.enable (lib.mkMerge [
    {
      environment.systemPackages = [ cfg.package ]
        ++ lib.optional cfg.dockerCompat dockerCompat;

      environment.etc."cni/net.d/87-podman-bridge.conflist".source = net-conflist;

      virtualisation.containers = {
        enable = true; # Enable common /etc/containers configuration
        containersConf.settings = lib.optionalAttrs cfg.enableNvidia {
          engine = {
            conmon_env_vars = [ "PATH=${lib.makeBinPath [ pkgs.nvidia-podman ]}" ];
            runtimes.nvidia = [ "${pkgs.nvidia-podman}/bin/nvidia-container-runtime" ];
          };
        };
      };

      systemd.packages = [ cfg.package ];

      systemd.services.podman.serviceConfig = {
        ExecStart = [ "" "${cfg.package}/bin/podman $LOGGING system service" ];
      };

      systemd.sockets.podman.wantedBy = [ "sockets.target" ];
      systemd.sockets.podman.socketConfig.SocketGroup = "podman";

      systemd.user.services.podman.serviceConfig = {
        ExecStart = [ "" "${cfg.package}/bin/podman $LOGGING system service" ];
      };

      systemd.user.sockets.podman.wantedBy = [ "sockets.target" ];

      systemd.tmpfiles.packages = [
        # The /run/podman rule interferes with our podman group, so we remove
        # it and let the systemd socket logic take care of it.
        (pkgs.runCommand "podman-tmpfiles-nixos" { package = cfg.package; } ''
          mkdir -p $out/lib/tmpfiles.d/
          grep -v 'D! /run/podman 0700 root root' \
            <$package/lib/tmpfiles.d/podman.conf \
            >$out/lib/tmpfiles.d/podman.conf
        '') ];

      systemd.tmpfiles.rules =
        lib.optionals cfg.dockerSocket.enable [
          "L! /run/docker.sock - - - - /run/podman/podman.sock"
        ];

      users.groups.podman = {};

      assertions = [
        {
          assertion = cfg.dockerCompat -> !config.virtualisation.docker.enable;
          message = "Option dockerCompat conflicts with docker";
        }
        {
          assertion = cfg.dockerSocket.enable -> !config.virtualisation.docker.enable;
          message = ''
            The options virtualisation.podman.dockerSocket.enable and virtualisation.docker.enable conflict, because only one can serve the socket.
          '';
        }
      ];
    }
  ]);
}