{ 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 = "${pkgs.terminal-tools}/bin/hrule";

  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 = size: 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)
        " : ${lib.fixedWidthString size " " zone}";
      # sh
    in ''
      ${timeZoneVariable} ${pkgs.coreutils}/bin/date ${
        dateString comment
      } | ${pkgs.terminal-tools}/bin/center
    '';

  q-timeZoneDates = if timeZones == [ ] then
    q-timeZoneDate 0 null
  else
    let size = lib.foldr lib.max 0 (map builtins.stringLength timeZones);
    in lib.concatMapStringsSep "\n" (q-timeZoneDate size) timeZones;

  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-show-users = ''
    ${pkgs.procps}/bin/ps aux \
     | ${pkgs.gawk}/bin/awk '{ print $1 }' \
     | ${pkgs.gnused}/bin/sed '1 d' \
     | ${pkgs.coreutils}/bin/sort  \
     | ${pkgs.coreutils}/bin/uniq \
     | ${pkgs.utillinux}/bin/column
  '';

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

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

  # bash needed for <(...)
in 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}
  ${q-task-checklist}
  ${hrule}
  ${q-show-users}
''