#!/usr/bin/env nix-shell
#!nix-shell -i bash

usage() {
  echo "usage: battery_estimate [options...]"
  echo
  echo "pretty-prints a battery estimate (icon to indicate state, and a duration estimate)"
  echo
  echo "options:"
  echo "  --debug: output additional information, to stderr"
}

# these icons come from sxmo; they only render in nerdfonts
bat_dis="󱊢"
bat_chg="󱊥"

log() {
  if [ "$BATTERY_ESTIMATE_DEBUG" = "1" ]; then
    printf "$@" >&2
    echo >&2
  fi
}

try_path() {
  # assigns output variables:
  # - perc, perc_left  (0-100)
  # - full, rate (pos means charging)
  if [ -f "$1/capacity" ]; then
    log "perc, perc_left from %s" "$1/capacity"
    perc=$(cat "$1/capacity")
    perc_left=$((100 - $perc))
  fi

  if [ -f "$1/charge_full_design" ] && [ -f "$1/current_now" ]; then
    log "full, rate from %s and %s" "$1/charge_full_design" "$1/current_now"
    # current is positive when charging
    full=$(cat "$1/charge_full_design")
    rate=$(cat "$1/current_now")
  elif [ -f "$1/energy_full" ] && [ -f "$1/power_now" ]; then
    log "full, rate from %s and %s" "$1/energy_full" "$1/power_now"
    # power_now is positive when discharging
    full=$(cat "$1/energy_full")
    rate=-$(cat "$1/power_now")
  elif [ -f "$1/energy_full" ] && [ -f "$1/energy_now" ]; then
    log "full, rate from %s and %s" "$1/energy_full" "$1/energy_now"
    log "  this is a compatibility path for legacy Thinkpad batteries which do not populate the 'power_now' field, and incorrectly populate 'energy_now' with power info"
    # energy_now is positive when discharging
    full=$(cat "$1/energy_full")
    rate=-$(cat "$1/energy_now")
  fi
}

try_all_paths() {
  try_path "/sys/class/power_supply/axp20x-battery"  # Pinephone
  try_path "/sys/class/power_supply/BAT0"  # Thinkpad
  log "perc: %d, left: %d" "$perc" "$perc_left"
  log "full: %f, rate: %f" "$full" "$rate"
  log "  rate > 0 means charging, else discharging"
}

fmt_minutes() {
  log "charge/discharge time: %f min" "$3"
  # args: <battery symbol> <text if ludicrous estimate> <estimated minutes to full/empty>
  if [[ $3 -gt 1440 ]]; then
    log "charge/discharge duration > 1d"
    printf "%s %s" "$1" "$2"  # more than 1d
  else
    hr=$(($3 / 60))
    hr_in_min=$(($hr * 60))
    min=$(($3 - $hr_in_min))
    printf "%s %dh%02dm" "$1" "$hr" "$min"
  fi
}

pretty_output() {
  if [[ $rate -lt 0 ]]; then
    log "discharging"
    fmt_minutes "$bat_dis" '∞' "$(($full * 60 * $perc / (-100 * $rate)))"
  elif [[ $rate -gt 0 ]]; then
    log "charging"
    fmt_minutes "$bat_chg" '100%' "$(($full * 60 * $perc_left / (100 * $rate)))"
  elif [[ "$perc" != "" ]]; then
    log "neither charging nor discharging"
    echo "$bat_dis $perc%"
  fi
}

while [ "$#" -gt 0 ]; do
  case "$1" in
    "--debug")
      shift
      BATTERY_ESTIMATE_DEBUG=1
      ;;
    *)
      usage
      exit 1
      ;;
  esac
done

try_all_paths
pretty_output