# shellcheck shell=bash

export ZERO="$0"
HELP="$ZERO: tracker [-1] [-v [-v ...]] [q [-q ...]]
  -1     run once and exit
  -v     increase verbosity (default >= warn)
  -q     decrease verbosity
"
trap 'kill -15 $$' INT

trace() { (( LOG_LEVEL > 2 ))  && (exec 1>&2; builtin echo "$@"|grep .||true); }
debug() { (( LOG_LEVEL > 1 ))  && (exec 1>&2; builtin echo "$@"|grep .||true); }
info()  { (( LOG_LEVEL > 0 ))  && (exec 1>&2; builtin echo "$@"|grep .||true); }
warn()  { (( LOG_LEVEL > -1 )) && (exec 1>&2; builtin echo "$@"|grep .||true); }
error() { (( LOG_LEVEL > -2 )) && (exec 1>&2; builtin echo "$@"|grep .||true); }
fatal() {                         (exec 1>&2; builtin echo "$@"|grep .||true); exit 4; }
log()   { info "$@"; }

unbuf() { SCRIPT="$1"; shift ; stdbuf -oL -eL bash -c "$SCRIPT" - "$@" ; }

start() {
  if ! options="$(getopt vq1 -- "$@")";then
    fatal "$HELP"
  fi

  eval set "$options"                           

  while [ $# -gt 0 ];do                            
    case "$1" in                                  
      -1) ONCE=1 ;;
      -h) info "$HELP"; exit 0 ;;
      -v) LOG_LEVEL=$(( LOG_LEVEL + 1 )) ;;
      -q) LOG_LEVEL=$(( LOG_LEVEL - 1 )) ;;
      --) shift;break;;  # we're _explicitly_ done with options
      -*) error "invalid option $1"; fatal "$HELP" ;;
      *) break;;  # we're done with options.   
    esac                                                                       
    shift                                              
  done

  if [ "$VALIDATION" ];then
    # fix up the validation regex to not search.
    VALIDATION="${VALIDATION#^}"
    VALIDATION="${VALIDATION%'$'}"
    VALIDATION='^'"$VALIDATION"'$'
  fi

  info "Running with LOG_LEVEL=$LOG_LEVEL"

  debug "   VALIDATION: $VALIDATION"
  debug "   RATE_LIMIT: $RATE_LIMIT"
  debug "POLL_INTERVAL: $POLL_INTERVAL"
  debug "    watch_cmd: $watch_cmd"

  if [ "$(echo "$POLL_INTERVAL < $RATE_LIMIT"|bc)" = 1 ];then
    warn "POLL_INTERVAL cannot be less than RATE_LIMIT."
    info "increasing POLL_INTERVAL to $RATE_LIMIT."
    POLL_INTERVAL=$RATE_LIMIT
  fi

  while true;do
    _poll || exit $?
    (( ONCE )) && exit 0

    $watch_cmd | while sleep $RATE_LIMIT;do
      # read with a maximum of the poll interval minus the previous rate limit.
      # rounding _up_ to the nearest second.  (bc floors when scale is unset.)
      if read -r -t "$( echo "$POLL_INTERVAL - $RATE_LIMIT + .5 " | bc )";then
        debug "received poll.  removing other poll requests."
      else
        debug "reached the polling interval.  forcing poll."
      fi
      N=0
      while read -t 0;do read -r; N=$((N + 1));done
      debug "removed $N extra events"
      _poll
      debug "sleeping for $RATE_LIMIT"
    done
    warn "tracker died.  restarting after $RATE_LIMIT seconds."
    sleep $RATE_LIMIT
    done | unbuf "$_filter"
  info "bye"
}

_poll() {
  NEWVAL="$(poll | head -1)"
  local skipped=0
  echo "$NEWVAL" | while read -r LINE;do
    (( skipped )) && info "$LINE"
    skipped=1
  done

  local failed=0
  if [ "$JQ_VALIDATION" ];then
    echo "$NEWVAL" | jq -e "$JQ_VALIDATION" > /dev/null || failed=2
  fi
  if [ "$VALIDATION" ];then
    echo "$NEWVAL" | grep -qE "$VALIDATION" || failed=1
  fi
  if (( failed == 2 ));then
    warn "$NEWVAL failed jq validation"
  elif (( failed ));then
    warn "$NEWVAL failed validation"
  else
    echo "$NEWVAL"
  fi
}

# MODULE OPTIONS

RATE_LIMIT=.1
rate_limit() {
  RATE_LIMIT=$1
}

POLL_INTERVAL=60
poll_interval() {
  POLL_INTERVAL=$1
}

_filter="uniq"
filter() {
  _filter="$(printf " %q" "$@")"
}

# VALIDATORS

VALIDATION=
output_integer() {
  VALIDATION='^-?[0-9]+$'
}

output_boolean() {
  VALIDATION='^true|false$'
}

output_string() {
  VALIDATION="${1-.*}"
}

JQ_VALIDATION=
output_json() {
  JQ_VALIDATION="${1-.}"
}

# EVENT HANDLERS

# each event source needs to emit a single _EMPTY_ line per event.
# poll will be called for each line.
on_volume() { on _on_volume; }
_on_volume() {
  pactl subscribe | while read -r ;do
    case "$REPLY" in
      *change*) echo;;
    esac
  done
}

on_sway() { on _on_sway; }
_on_sway() {
  swaymsg -t subscribe -m '[ "workspace", "window" ]' |
    jq --unbuffered -c . |
    while read -r;do
      echo
    done
}

on_system_dbus() { on _on_system_dbus; }
_on_system_dbus() {
  unbuf dbus-monitor --system | while read -r;do
    case "$REPLY" in
      signal*) echo;;
    esac
  done
}

on() { watch_cmd="$1"; }