# file      : libbutl/manifest-parser.bash.in
# license   : MIT; see accompanying LICENSE file

if [ "$butl_manifest_parser" ]; then
  return 0
else
  butl_manifest_parser=true
fi

@import libbutl.bash/utility@

# Parse the manifest reading from stdin and writing the binary representation
# to stdout.
#
# Normally you would use the start/finish functions below. But if you don't
# care about errors, the following would be the typical usage:
#
# while IFS=: read -r -d '' n v; do
#   ...
# done < <(butl_parse_manifest)
#
function butl_parse_manifest ()
{
  "$(butl_path)/manifest" parse
}

# Start the manifest parsing co-process setting the following "return"
# variables:
#
#   butl_manifest_parser_ofd
#   butl_manifest_parser_ifd
#   butl_manifest_parser_pid
#
# If <file> is not specified, then read from stdin.
#
# The typical usage:
#
#   butl_manifest_parser_start
#
#   while IFS=: read -ru "$butl_manifest_parser_ofd" -d '' n v; do
#     ...
#   done
#
#   butl_manifest_parser_finish
#
function butl_manifest_parser_start () # [<file>]
{
  if [ "$#" -gt 0 ]; then
    exec {butl_manifest_parser_ifd}<"$1"
  else
    exec {butl_manifest_parser_ifd}<&0
  fi

  # Note that bash co-process facility is racy: as soon as the process
  # finishes, bash unsets COPROC/COPROC_PID (my guess would be it checks after
  # each command in the script). This specific sequence of steps (and the one
  # in *_finish()) seems to work reliably at least from bash 4.3.30 and
  # up. See the following resources for details:
  #
  # http://wiki.bash-hackers.org/syntax/keywords/coproc
  # http://tldp.org/LDP/abs/html/bashver4.html (coproc section)
  # https://lists.gnu.org/archive/html/bug-bash/2014-02/msg00017.html
  # https://lists.gnu.org/archive/html/bug-bash/2012-12/msg00069.html
  # https://lists.gnu.org/archive/html/bug-bash/2012-10/msg00027.html
  #
  # Also note that the bash bug (still present in 5.0) prevents running
  # multiple coprocesses at a time (see the BUGS section of bash(1) man page
  # for details).
  #
  # An update: it turns out that we still can end up with an unset COPROC if
  # the process finishes too early. To avoid that we suspend the subshell
  # before executing the parser process and resume it after querying the
  # COPROC value. Note that we need to be careful not to attempt to resume the
  # process that hasn't suspended itself (see butl_resume_process() for
  # details).
  #
  # Note that the suspend builtin doesn't work in subshells by default since
  # there is no job control enabled for them. Also when it is enabled (via
  # `set -m`), the builtin stops subshells recursively up to the command being
  # run from the interactive shell, which is not what we want. That's why we
  # use kill which is also a builtin and thus presumably is not slower than
  # suspend.
  #
  coproc { kill -SIGSTOP $BASHPID; exec "$(butl_path)/manifest" parse; } \
         <&"$butl_manifest_parser_ifd"

  exec {butl_manifest_parser_ofd}<&"${COPROC[0]}"
  butl_manifest_parser_pid="$COPROC_PID"

  butl_resume_process "$butl_manifest_parser_pid"
}

# Finish the manifest parsing co-process.
#
function butl_manifest_parser_finish ()
{
  exec {butl_manifest_parser_ofd}<&-
  wait "$butl_manifest_parser_pid"
  exec {butl_manifest_parser_ifd}<&-
}