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

with lib;

let

  cfg = config.programs.gnupg;

  xserverCfg = config.services.xserver;

  defaultPinentryFlavor =
    if xserverCfg.desktopManager.lxqt.enable
    || xserverCfg.desktopManager.plasma5.enable
    || xserverCfg.desktopManager.deepin.enable then
      "qt"
    else if xserverCfg.desktopManager.xfce.enable then
      "gtk2"
    else if xserverCfg.enable || config.programs.sway.enable then
      "gnome3"
    else
      "curses";

in

{

  options.programs.gnupg = {
    package = mkOption {
      type = types.package;
      default = pkgs.gnupg;
      defaultText = literalExpression "pkgs.gnupg";
      description = lib.mdDoc ''
        The gpg package that should be used.
      '';
    };

    agent.enable = mkOption {
      type = types.bool;
      default = false;
      description = lib.mdDoc ''
        Enables GnuPG agent with socket-activation for every user session.
      '';
    };

    agent.enableSSHSupport = mkOption {
      type = types.bool;
      default = false;
      description = lib.mdDoc ''
        Enable SSH agent support in GnuPG agent. Also sets SSH_AUTH_SOCK
        environment variable correctly. This will disable socket-activation
        and thus always start a GnuPG agent per user session.
      '';
    };

    agent.enableExtraSocket = mkOption {
      type = types.bool;
      default = false;
      description = lib.mdDoc ''
        Enable extra socket for GnuPG agent.
      '';
    };

    agent.enableBrowserSocket = mkOption {
      type = types.bool;
      default = false;
      description = lib.mdDoc ''
        Enable browser socket for GnuPG agent.
      '';
    };

    agent.pinentryFlavor = mkOption {
      type = types.nullOr (types.enum pkgs.pinentry.flavors);
      example = "gnome3";
      default = defaultPinentryFlavor;
      defaultText = literalMD ''matching the configured desktop environment'';
      description = lib.mdDoc ''
        Which pinentry interface to use. If not null, the path to the
        pinentry binary will be set in /etc/gnupg/gpg-agent.conf.
        If not set at all, it'll pick an appropriate flavor depending on the
        system configuration (qt flavor for lxqt and plasma5, gtk2 for xfce
        4.12, gnome3 on all other systems with X enabled, ncurses otherwise).
      '';
    };

    dirmngr.enable = mkOption {
      type = types.bool;
      default = false;
      description = lib.mdDoc ''
        Enables GnuPG network certificate management daemon with socket-activation for every user session.
      '';
    };
  };

  config = mkIf cfg.agent.enable {
    environment.etc."gnupg/gpg-agent.conf".text =
      lib.optionalString (cfg.agent.pinentryFlavor != null) ''
      pinentry-program ${pkgs.pinentry.${cfg.agent.pinentryFlavor}}/bin/pinentry
    '';

    # This overrides the systemd user unit shipped with the gnupg package
    systemd.user.services.gpg-agent = {
      unitConfig = {
        Description = "GnuPG cryptographic agent and passphrase cache";
        Documentation = "man:gpg-agent(1)";
        Requires = [ "gpg-agent.socket" ];
      };
      serviceConfig = {
        ExecStart = "${cfg.package}/bin/gpg-agent --supervised";
        ExecReload = "${cfg.package}/bin/gpgconf --reload gpg-agent";
      };
    };

    systemd.user.sockets.gpg-agent = {
      unitConfig = {
        Description = "GnuPG cryptographic agent and passphrase cache";
        Documentation = "man:gpg-agent(1)";
      };
      socketConfig = {
        ListenStream = "%t/gnupg/S.gpg-agent";
        FileDescriptorName = "std";
        SocketMode = "0600";
        DirectoryMode = "0700";
      };
      wantedBy = [ "sockets.target" ];
    };

    systemd.user.sockets.gpg-agent-ssh = mkIf cfg.agent.enableSSHSupport {
      unitConfig = {
        Description = "GnuPG cryptographic agent (ssh-agent emulation)";
        Documentation = "man:gpg-agent(1) man:ssh-add(1) man:ssh-agent(1) man:ssh(1)";
      };
      socketConfig = {
        ListenStream = "%t/gnupg/S.gpg-agent.ssh";
        FileDescriptorName = "ssh";
        Service = "gpg-agent.service";
        SocketMode = "0600";
        DirectoryMode = "0700";
      };
      wantedBy = [ "sockets.target" ];
    };

    systemd.user.sockets.gpg-agent-extra = mkIf cfg.agent.enableExtraSocket {
      unitConfig = {
        Description = "GnuPG cryptographic agent and passphrase cache (restricted)";
        Documentation = "man:gpg-agent(1)";
      };
      socketConfig = {
        ListenStream = "%t/gnupg/S.gpg-agent.extra";
        FileDescriptorName = "extra";
        Service = "gpg-agent.service";
        SocketMode = "0600";
        DirectoryMode = "0700";
      };
      wantedBy = [ "sockets.target" ];
    };

    systemd.user.sockets.gpg-agent-browser = mkIf cfg.agent.enableBrowserSocket {
      unitConfig = {
        Description = "GnuPG cryptographic agent and passphrase cache (access for web browsers)";
        Documentation = "man:gpg-agent(1)";
      };
      socketConfig = {
        ListenStream = "%t/gnupg/S.gpg-agent.browser";
        FileDescriptorName = "browser";
        Service = "gpg-agent.service";
        SocketMode = "0600";
        DirectoryMode = "0700";
      };
      wantedBy = [ "sockets.target" ];
    };

    systemd.user.services.dirmngr = mkIf cfg.dirmngr.enable {
      unitConfig = {
        Description = "GnuPG network certificate management daemon";
        Documentation = "man:dirmngr(8)";
        Requires = "dirmngr.socket";
      };
      serviceConfig = {
        ExecStart = "${cfg.package}/bin/dirmngr --supervised";
        ExecReload = "${cfg.package}/bin/gpgconf --reload dirmngr";
      };
    };

    systemd.user.sockets.dirmngr = mkIf cfg.dirmngr.enable {
      unitConfig = {
        Description = "GnuPG network certificate management daemon";
        Documentation = "man:dirmngr(8)";
      };
      socketConfig = {
        ListenStream = "%t/gnupg/S.dirmngr";
        SocketMode = "0600";
        DirectoryMode = "0700";
      };
      wantedBy = [ "sockets.target" ];
    };

    services.dbus.packages = mkIf (cfg.agent.pinentryFlavor == "gnome3") [ pkgs.gcr ];

    environment.systemPackages = with pkgs; [ cfg.package ];

    environment.interactiveShellInit = ''
      # Bind gpg-agent to this TTY if gpg commands are used.
      export GPG_TTY=$(tty)
    '';

    programs.ssh.extraConfig = optionalString cfg.agent.enableSSHSupport ''
      # The SSH agent protocol doesn't have support for changing TTYs; however we
      # can simulate this with the `exec` feature of openssh (see ssh_config(5))
      # that hooks a command to the shell currently running the ssh program.
      Match host * exec "${pkgs.runtimeShell} -c '${cfg.package}/bin/gpg-connect-agent --quiet updatestartuptty /bye >/dev/null 2>&1'"
    '';

    environment.extraInit = mkIf cfg.agent.enableSSHSupport ''
      if [ -z "$SSH_AUTH_SOCK" ]; then
        export SSH_AUTH_SOCK=$(${cfg.package}/bin/gpgconf --list-dirs agent-ssh-socket)
      fi
    '';

    assertions = [
      { assertion = cfg.agent.enableSSHSupport -> !config.programs.ssh.startAgent;
        message = "You can't use ssh-agent and GnuPG agent with SSH support enabled at the same time!";
      }
    ];
  };

  # uses attributes of the linked package
  meta.buildDocsInSandbox = false;
}