## Busybox
## =======
##
## Busybox provides stripped-down versions of many usual
## Linux/Unix tools, and may be configured to include only
## the commands (termed "applets") required by the user or
## by other included modules.

{ lib, pkgs, config, ...}:
let
  inherit (lib) mkOption mkEnableOption types mapAttrsToList;
  inherit (pkgs.pseudofile) dir symlink;
  inherit (lib.strings) toUpper;

  attrs = { options, applets } :
    let
      extraOptions = builtins.concatStringsSep "\n"
        (mapAttrsToList (n: v: "CONFIG_${toUpper n} ${toString v}") options);
      appletOptions = builtins.concatStringsSep "\n"
        (map (n: "CONFIG_${toUpper n} y") applets);
    in {
      enableMinimal = true;
      extraConfig = ''
        ${extraOptions}
        ${appletOptions}
      '';
    };
  cfg = config.programs.busybox;
  busybox = pkgs.busybox.override (attrs { inherit (cfg) applets options; });
  makeLinks = lib.attrsets.genAttrs
    cfg.applets
    (a: symlink "${busybox}/bin/busybox");
  minimalApplets = [
    # this is probably less minimal than it could be
    "arch" "ash" "base64" "basename" "bc" "brctl" "bunzip2" "bzcat" "bzip2"
    "cal" "cat" "chattr" "chgrp" "chmod" "chown" "chpst" "chroot" "clear" "cmp"
    "comm" "cp" "cpio" "cut" "date" "dhcprelay" "dd" "df" "dirname" "dmesg"
    "du" "echo" "egrep" "env" "expand" "expr" "false" "fdisk" "fgrep" "find"
    "free" "fuser" "grep" "gunzip" "gzip" "head" "hexdump" "hostname" "hwclock"
    "ifconfig" "ipneigh" "kill"
    "killall" "killall5" "less" "ln" "ls" "lsattr" "lsof" "md5sum" "mkdir"
    "mknod" "mktemp" "mount" "mv" "nc" "netstat" "nohup" "od" "pgrep" "pidof"
    "ping" "ping6" "pkill" "pmap" "printenv" "printf" "ps" "pwd" "readlink"
    "realpath" "reset" "rm" "rmdir" "route" "sed" "seq" "setsid" "sha1sum"
    "sha256sum" "sha512sum" "sleep" "sort" "stat" "strings" "stty" "su" "sum"
    "swapoff" "swapon" "sync" "tail" "tee" "test" "time" "touch" "tr"
    "traceroute" "traceroute6" "true" "truncate" "tty" "udhcpc" "umount"
    "uname" "unexpand" "uniq" "unlink" "unlzma" "unxz" "unzip" "uptime" "watch"
    "wc" "whoami" "xargs" "xxd" "xz" "xzcat" "yes" "zcat"
  ];
in {
  options = {
    programs.busybox = {
      applets =  mkOption {
        type = types.listOf types.str;
        description = "Applets required";
        default = [];
        example = ["sh" "getty" "login"];
      };
      options = mkOption {
        # mostly the values are y n or m, but sometimes
        # other strings are also used
        description = "Other busybox config flags that do not map directly to applet names (often prefixed FEATURE_)";
        type = types.attrsOf types.nonEmptyStr;
        default =  { };
        example =  { FEATURE_DD_IBS_OBS = "y"; };
      };
    };
  };
  config = {
    programs.busybox = {
      applets = minimalApplets;
      options = {
        ASH_ECHO = "y";
        # ASH_OPTIMIZE_FOR_SIZE = "y";
        BASH_IS_NONE = "y";
        SH_IS_ASH = "y";
        ASH_BASH_COMPAT = "y";
        FEATURE_EDITING = "y"; # readline-ish command editing
        FEATURE_EDITING_HISTORY = "128";
        FEATURE_EDITING_MAX_LEN = "1024";
        FEATURE_TAB_COMPLETION = "y";
        FEATURE_EDITING_WINCH = "y";
        FEATURE_IPV6 = "y";
      };
    };
    filesystem = dir {
      bin = dir ({
        busybox = symlink "${busybox}/bin/busybox";
        sh = symlink "${busybox}/bin/busybox";
      } // makeLinks);
    };
  };
}