{ pkgs, lib
  # tzselect is your frind do find timezones
  , timeZones ? []
  , timeColor ? 9
  , timeZoneColor ? 10
  , calBackgroundColor ? 10
  , calWeekColor ? 13
  , calDayColor ? 9
  , enableIntelBacklight ? true
  , enableBattery ? true
  , ... }:

let
  hrule = ''
    hrule_cols=$(${pkgs.ncurses}/bin/tput cols)
    hrule_index=0
    while [ $hrule_index -lt $hrule_cols ]
    do
      echo -n '─'
      hrule_index=$(( 1 + $hrule_index ))
    done
    echo
  '';

  q-cal = let

    # Maximum width of cal's output.
    calwidth = 23;

    # Number of space characters between two calendars.
    hspace = 2;

    # Return number of columns required to print n calenders side by side.
    need_width = n:
      assert n >= 1;
      n * calwidth + (n - 1) * hspace;

    lpad = n: c: s:
      if lib.stringLength s < n
        then lpad n c (c + s)
        else s;

    pad = ''{
      ${pkgs.gnused}/bin/sed '
            # rtrim
            s/ *$//

            # delete last empty line
            ''${/^$/d}
          ' \
        | ${pkgs.gawk}/bin/awk '{printf "%-${toString calwidth}s\n", $0}' \
        | ${pkgs.gnused}/bin/sed "
              # colorize header
              1,2s/.*/[38;5;${toString calBackgroundColor}m&/

              # highlight current week
              s/^$(${pkgs.coreutils}/bin/date +%W)/[38;5;${toString calWeekColor}m&/

              # colorize week number
              s/^[ 1-9][0-9]/[38;5;${toString calBackgroundColor}m&/
            "
    }'';
  in ''
    cols=$(${pkgs.ncurses}/bin/tput cols)
    ${pkgs.coreutils}/bin/paste \
        <(if test $cols -ge ${toString (need_width 3)}; then
          ${pkgs.utillinux}/bin/cal -mw \
              $(${pkgs.coreutils}/bin/date +'%m %Y' -d 'last month') \
            | ${pad}
        fi) \
        <(if test $cols -ge ${toString (need_width 1)}; then
          ${pkgs.utillinux}/bin/cal -mw \
            | ${pkgs.gnused}/bin/sed '
                # colorize day of month
                s/\(^\| \)'"$(${pkgs.coreutils}/bin/date +%e)"'\>/[38;5;${toString calDayColor}m&/
              ' \
            | ${pad}
        fi) \
        <(if test $cols -ge ${toString (need_width 2)}; then
          ${pkgs.utillinux}/bin/cal -mw \
              $(${pkgs.coreutils}/bin/date +'%m %Y' -d 'next month') \
            | ${pad}
        fi) \
      | ${pkgs.gnused}/bin/sed '
          s/^\t//
          s/\t$//
          s/\t/${lpad hspace " " ""}/g
        '
  '';

  q-timeZoneDate = zone:
    let dateString = comment: '' '+%Y-%m-%dT[;38;5;${toString timeColor}m%H:%M:%S[;38;5;${toString timeZoneColor}m%:z ${comment}' '';
        timeZoneVariable = lib.optionalString (zone != null) "TZ=${zone}";
        comment = lib.optionalString (zone != null) " : ${zone}";
    in /* sh */ ''
      ${timeZoneVariable} ${pkgs.coreutils}/bin/date ${dateString comment}
    '';

  q-timeZoneDates = if timeZones == [] then
    q-timeZoneDate null
  else
    lib.concatMapStringsSep "\n" q-timeZoneDate timeZones;

  q-gitdir = ''
    if test -d .git; then
      #git status --porcelain
      branch=$(
        ${pkgs.git}/bin/git branch \
          | ${pkgs.gnused}/bin/sed -rn 's/^\* (.*)/\1/p'
      )
      echo "± $LOGNAME@''${HOSTNAME-$(${pkgs.nettools}/bin/hostname)}:$PWD .git $branch"
    fi
  '';

  q-intel_backlight = ''
    cd /sys/class/backlight/intel_backlight
    </dev/null exec ${pkgs.gawk}/bin/awk '
      END {
        getline actual_brightness < "actual_brightness"
        getline max_brightness < "max_brightness"
        getline brightness < "brightness"
        printf "%20s │ %d%% %d/%d\n" \
            , "intel_backlight" \
            , actual_brightness / max_brightness * 100 \
            , actual_brightness \
            , max_brightness
      }
    '
  '';

  q-power_supply = let
    power_supply = pkgs.writers.writeBash "power_supply" ''
      set -efu
      uevent=$1
      eval "$(${pkgs.gnused}/bin/sed -n '
        s/^\([A-Z_]\+=[0-9A-Za-z_-]*\)$/export \1/p
      ' $uevent)"
      case $POWER_SUPPLY_NAME in
        AC)
          exit # not battery
          ;;
      esac
      exec </dev/null
      exec ${pkgs.gawk}/bin/awk '
        function die(s) {
          printf "%20s │ %s\n", name, s
          exit 1
        }

        function print_hm(h, m) {
          m = (h - int(h)) * 60
          return sprintf("%dh%dm", h, m)
        }

        function print_bar(bar_size, charge, full_bars, empty_bars, full_color) {
          full_bars = int(charge * bar_size)
          empty_bars = bar_size - full_bars

          if (charge >= .42) full_color = "2"
          else if (charge >= .23) full_color = "3"
          else              full_color = "1"

          left_arrow = 1
          middle_arrow = 1
          right_arrow = 1
          if (full_bars == 0) {
            left_arrow = 0
            middle_arrow = 0
          }
          if (empty_bars == 0) {
            middle_arrow = 0
            right_arrow = 0
          }

          empty_color = "0";
          return sgr("38;5;" 8) sgr("48;5;" full_color) strdup("",left_arrow) strdup(" ", full_bars) sgr("48;5;" empty_color) sgr("38;5;" full_color) strdup("",middle_arrow) strdup(" ", empty_bars) sgr() sgr("38;5;" empty_color) strdup("",right_arrow) sgr()
        }

        function sgr(p) {
          return "\x1b[" p "m"
        }

        function strdup(s,n,t) {
          t = sprintf("%"n"s","")
          gsub(/ /,s,t)
          return t
        }

        END {
          name = ENVIRON["POWER_SUPPLY_NAME"]

          charge_unit = "Ah"
          charge_now = ENVIRON["POWER_SUPPLY_CHARGE_NOW"] / 10^6
          charge_full = ENVIRON["POWER_SUPPLY_CHARGE_FULL"] / 10^6

          current_unit = "A"
          current_now = ENVIRON["POWER_SUPPLY_CURRENT_NOW"] / 10^6

          energy_unit = "Wh"
          energy_now = ENVIRON["POWER_SUPPLY_ENERGY_NOW"] / 10^6
          energy_full = ENVIRON["POWER_SUPPLY_ENERGY_FULL"] / 10^6

          power_unit = "W"
          power_now = ENVIRON["POWER_SUPPLY_POWER_NOW"] / 10^6

          voltage_unit = "V"
          voltage_now = ENVIRON["POWER_SUPPLY_VOLTAGE_NOW"] / 10^6
          voltage_min_design = ENVIRON["POWER_SUPPLY_VOLTAGE_MIN_DESIGN"] / 10^6

          #printf "charge_now: %s\n", charge_now
          #printf "charge_full: %s\n", charge_full
          #printf "current_now: %s\n", current_now
          #printf "energy_now: %s\n", energy_now
          #printf "energy_full: %s\n", energy_full
          #printf "energy_full: %s\n", ENVIRON["POWER_SUPPLY_ENERGY_FULL"]
          #printf "energy_full: %s\n", ENVIRON["POWER_SUPPLY_ENERGY_FULL"] / 10^6
          #printf "power_now: %s\n", power_now
          #printf "voltage_now: %s\n", voltage_now

          if (current_now == 0 && voltage_now != 0) {
            current_now = power_now / voltage_now
          }
          if (power_now == 0) {
            power_now = current_now * voltage_now
          }
          if (charge_now == 0 && voltage_min_design != 0) {
            charge_now = energy_now / voltage_min_design
          }
          if (energy_now == 0) {
            energy_now = charge_now * voltage_min_design
          }
          if (charge_full == 0 && voltage_min_design != 0) {
            charge_full = energy_full / voltage_min_design
          }
          if (energy_full == 0) {
            energy_full = charge_full * voltage_min_design
          }

          if (charge_now == 0 || charge_full == 0) {
            die("unknown charge")
          }

          charge_ratio = charge_now / charge_full

          out = out sprintf("%20s │", name)
          out = out sprintf(" %s", print_bar(10, charge_ratio))
          out = out sprintf(" %d%", charge_ratio * 100)
          out = out sprintf(" %.2f%s", charge_now, charge_unit)
          if (current_now != 0) {
            out = out sprintf("/%.1f%s", current_now, current_unit)
          }
          out = out sprintf(" %d%s", energy_full, energy_unit)
          if (power_now != 0) {
            out = out sprintf("/%.1f%s", power_now, power_unit)
          }
          if (current_now != 0) {
            out = out sprintf(" %s", print_hm(charge_now / current_now))
          }

          print out
        }
      '
    '';
  in ''
    for uevent in /sys/class/power_supply/*/uevent; do
      ${power_supply} "$uevent" || :
    done
  '';

  q-virtualization = ''
    printf '%20s │ %s\n' "VT" \
      $(${pkgs.systemd}/bin/systemd-detect-virt)
  '';

  q-wireless = ''
    for dev in $(
      ${pkgs.iw}/bin/iw dev \
        | ${pkgs.gnused}/bin/sed -n 's/^\s*Interface\s\+\([0-9a-z]\+\)$/\1/p'
    ); do
      inet=$(${pkgs.iproute}/bin/ip addr show $dev \
        | ${pkgs.gnused}/bin/sed -n '
            s/.*inet \([0-9]\+\.[0-9]\+\.[0-9]\+\.[0-9]\+\).*/\1/p
          ') \
        || unset inet
      ssid=$(${pkgs.iw}/bin/iw dev $dev link \
        | ${pkgs.gnused}/bin/sed -n '
            s/.*\tSSID: \(.*\)/\1/p
          ') \
        || unset ssid
      printf '%20s │ %s %s\n' $dev ''${inet+ $inet} ''${ssid+ $ssid}
    done
  '';

  q-online = ''
    if ${pkgs.curl}/bin/curl -s google.com >/dev/null; then
      echo '             status  │ online'
    else
      echo '             status  │ offline '
    fi
  '';

  q-thermal_zone = ''
    for i in /sys/class/thermal/thermal_zone*; do
      type=$(${pkgs.coreutils}/bin/cat $i/type)
      temp=$(${pkgs.coreutils}/bin/cat $i/temp)
      printf '%20s │ %s°C\n' $type $(echo $temp / 1000 | ${pkgs.bc}/bin/bc)
    done
  '';

  q-task-active = ''
    ${pkgs.taskwarrior}/bin/task export  +ACTIVE status:pending | ${pkgs.jq}/bin/jq --raw-output '.[] | "⇒ \(.id) \(.description)"'
  '';

in

# bash needed for <(...)
pkgs.writers.writeBashBin "q" ''
  set -eu
  export PATH=/var/empty
  ${hrule}
  ${q-cal}
  ${hrule}
  ${q-timeZoneDates}
  ${hrule}
  ${lib.optionalString enableIntelBacklight "(${q-intel_backlight}) &"}
  ${lib.optionalString enableBattery "(${q-power_supply}) &"}
  (${q-virtualization}) &
  (${q-wireless}) &
  (${q-online}) &
  (${q-thermal_zone}) & wait
  ${hrule}
  ${q-task-active}
  ${hrule}
''