#!/bin/bash

USAGE="
USAGE: avdd [<mod_list>='cpu mem bl vol-amixer bat dt']
            [<pre>=' '] [<sep_l>='| '] [<sep_r>=' '] [<suf>=' ']

        mod_list
                A comma or space separated list of modules that define both
                the order and the content of the status bar.

        pre     The prefix prepended to the beginning of the status bar.

        sep_l   The left separator between status bar sections.

        sep_r   The right separator between status bar sections.

        suf     The suffix appended to the end of the status bar.

EXAMPLES:

        Any of these will display this help message.

                avdd -h
                avdd -help
                avdd --help

        Run the daemon in the background to create a status bar with the
        default sections, prefix, separators, and suffix.

                avdd &

        Run the daemon in the background to create a status with only the
        volume and date/time sections, with the entire status between square
        brackets, and each section surrounded by angle brackets. Note that
        the first left separator and the last right separator are stripped
        from the output, so if you want them, simply include them in the
        prefix and suffix as shown here.

                avdd 'vol-amixer dt' '[<' '<' '>' '>]' &
"
DEFAULT_MOD_LIST='cpu mem bl vol-amixer bat dt'
DEFAULT_PRE=' '
DEFAULT_SEP_L='| '
DEFAULT_SEP_R=' '
DEFAULT_SUF=' '
MOD_DIR="$(dirname "$0")"/mod
ACTION_DIR=/tmp/avdd
ACTION_DIR_LEN=${#ACTION_DIR}

mod_list="${1-${DEFAULT_MOD_LIST}}"
pre="${2-${DEFAULT_PRE}}"
sep_l="${3-${DEFAULT_SEP_L}}"
sep_r="${4-${DEFAULT_SEP_R}}"
suf="${5-${DEFAULT_SUF}}"

# Map the module file name to the module function
mod_to_fn() {
  printf 'mod_%s' "${1//-/_}"
}

# Check if the user needs help
if [[ "${mod_list}" =~ ^(-h|-(-)?help)$ ]]; then
  printf '%s' "${USAGE}" 1>&2
  exit 0
fi

# For each module in the list, if the module file exists then source it,
# add its name to the ordered array, and call its function and cache the value
declare -A stat_cache
IFS=', ' read -r -a mods <<< "${mod_list}"
for mod in "${mods[@]}"; do
  mod_file="${MOD_DIR}/${mod}"
  if [[ -r "${mod_file}" ]]; then
    # shellcheck source=/dev/null
    source "${mod_file}"
    stat_cache_ordered_mods+=("${mod}")
    stat_cache["${mod}"]="$(eval "$(mod_to_fn "${mod}")")"
  fi
done

# Construct and display the status by looping over the cached values in  order
draw_status() {
  local mod stat
  for mod in "${stat_cache_ordered_mods[@]}"; do
    printf -v stat '%b%b%b%b' \
      "${stat}" "${sep_l}" "${stat_cache[${mod}]}" "${sep_r}"
  done

  # Trim the leading left separator and trailing right separator, and display
  # the status
  local -ri offset=${#sep_l}
  local -ri len=$((${#stat} - offset - ${#sep_r}))
  xsetroot -name "${pre}${stat:${offset}:${len}}${suf}"
}

# Draw the initial status
draw_status

# For each file in the action directory, remove the file, and if a module
# for the action is cached, call the module function and update the cache. If
# any cache entries were updated, redraw the status.
process_signal () {
  local -a action_paths
  local action_path mod is_changed
  readarray -d '' action_paths< \
    <(find "${ACTION_DIR}" -maxdepth 1 -type f -exec rm -f {} + -print0)
  for action_path in "${action_paths[@]}"; do
    mod="${action_path:$((ACTION_DIR_LEN + 1))}"
    if [[ -v stat_cache[${mod}] ]]; then
      stat_cache["${mod}"]="$(eval "$(mod_to_fn "${mod}")")"
      is_changed=1
    fi
  done
  if [[ -v is_changed ]]; then draw_status; fi
}

# Begin trapping signals
mkdir -p "${ACTION_DIR}"
trap process_signal SIGUSR1

# Wait for signals efficiently. In a loop begin a long-running sleep command
# in the background, then wait on it. If we trap a signal before the wait is
# over and sleep is still running, trap will call process_signal, then code
# execution will resume at the line after the wait statement. So on that line
# we kill the (probably) still running sleep command so they don't pile up,
# and loop to sleep and wait for the next signal. If we don't trap a signal
# during the long running sleep, then the wait ends, we try to kill the
# sleep command that has already exited, so it doesn't matter, and loop to
# sleep and wait again. Note that we don't make the sleep too long because
# if the daemon is killed, the sleep will become an orphaned process until
# the sleep period elapses.
while :; do
  sleep 30m &
  sleep_pid="$!"
  wait "${sleep_pid}"
  kill "${sleep_pid}" 2>/dev/null
done