#!/usr/bin/env bash

USAGE="
USAGE: avdd [<mod_list>='cpu mem bl vol-amixer bat dt'|-h|-[-]help]
            [<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 vol-amixer bat dt'
DEFAULT_PRE=' '
DEFAULT_SEP_L='| '
DEFAULT_SEP_R=' '
DEFAULT_SUF=' '
DIR="$(dirname "$0")"
MOD_DIR="${DIR}/mod"
DAEMON="$(basename "$0")"
FIFO="/tmp/${DAEMON}-fifo-$("${DIR}/rpid" $$)"

mod_list="${1-${DEFAULT_MOD_LIST}}"

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

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//-/_}"
}

# 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

# Process a list of mods. If a mod is in the status cache, call the module
# function to get the new value for that section of the status bar. If any
# of the new values are different from the cached ones, update the cache
# and redraw the status bar once after all the mods are processed.
process_mods() {
  local mod new_val is_changed
  for mod in "$@"; do
    if [[ -v stat_cache[${mod}] ]]; then
      new_val="$(eval "$(mod_to_fn "${mod}")")"
      if [[ "${new_val}" != stat_cache["${mod}"] ]]; then
        stat_cache["${mod}"]="${new_val}"
        is_changed=1
      fi
    fi
  done
  if [[ -v is_changed ]]; then draw_status; fi
}

# Setup the named pipe to receive commands
if [[ ! -p "${FIFO}" ]]; then mkfifo "${FIFO}"; fi
# shellcheck disable=SC2064
trap "rm -f ${FIFO}" EXIT

# Each time the pipe is emptied out, the inner while loop will finish, so
# wrap it in an infinte loop to keep blocking until there is data on the pipe
while :; do
  while read -r fifo_mod_list; do
    case "${fifo_mod_list}" in
      daem_all)
        process_mods "${mods[@]}"
        ;;
      daem_quit)
        exit 0
        ;;
      daem_*)
        ;;
      *)
        IFS=', ' read -r -a fifo_mods <<< "${fifo_mod_list}"
        process_mods "${fifo_mods[@]}"
        ;;
    esac
  done < "${FIFO}"
done