#!/usr/bin/env bash

bats_run_under_flock() {
  flock "$BATS_SEMAPHORE_DIR" "$@"
}

bats_run_under_shlock() {
      local lockfile="$BATS_SEMAPHORE_DIR/shlock.lock"
      while ! shlock -p $$ -f "$lockfile"; do
        sleep 1
      done
      # we got the lock now, execute the command
      "$@"
      local status=$?
      # free the lock
      rm -f "$lockfile"
      return $status
    }

# setup the semaphore environment for the loading file
bats_semaphore_setup() {
  export -f bats_semaphore_get_free_slot_count
  export -f bats_semaphore_acquire_while_locked
  export BATS_SEMAPHORE_DIR="$BATS_RUN_TMPDIR/semaphores"

  if command -v flock >/dev/null; then
    BATS_LOCKING_IMPLEMENTATION=flock
  elif command -v shlock >/dev/null; then
    BATS_LOCKING_IMPLEMENTATION=shlock
  else
    printf "ERROR: flock/shlock is required for parallelization within files!\n" >&2
    exit 1
  fi
}

# $1 - output directory for stdout/stderr
# $@ - command to run
# run the given command in a semaphore
# block when there is no free slot for the semaphore
# when there is a free slot, run the command in background
# gather the output of the command in files in the given directory
bats_semaphore_run() {
  local output_dir=$1
  shift
  local semaphore_slot
  semaphore_slot=$(bats_semaphore_acquire_slot)
  bats_semaphore_release_wrapper "$output_dir" "$semaphore_slot" "$@" &
  printf "%d\n" "$!"
}

# $1 - output directory for stdout/stderr
# $@ - command to run
# this wraps the actual function call to install some traps on exiting
bats_semaphore_release_wrapper() {
  local output_dir="$1"
  local semaphore_name="$2"
  shift 2 # all other parameters will be use for the command to execute

  # shellcheck disable=SC2064 # we want to expand the semaphore_name right now!
  trap "status=$?; bats_semaphore_release_slot '$semaphore_name'; exit $status" EXIT

  mkdir -p "$output_dir"
  "$@" 2>"$output_dir/stderr" >"$output_dir/stdout"
  local status=$?

  # bash bug: the exit trap is not called for the background process
  bats_semaphore_release_slot "$semaphore_name"
  trap - EXIT # avoid calling release twice
  return $status
}

bats_semaphore_acquire_while_locked() {
  if [[ $(bats_semaphore_get_free_slot_count) -gt 0 ]]; then
    local slot=0
    while [[ -e "$BATS_SEMAPHORE_DIR/slot-$slot" ]]; do
      ((++slot))
    done
    if [[ $slot -lt $BATS_SEMAPHORE_NUMBER_OF_SLOTS ]]; then
      touch "$BATS_SEMAPHORE_DIR/slot-$slot" && printf "%d\n" "$slot" && return 0
    fi
  fi
  return 1
}

# block until a semaphore slot becomes free
# prints the number of the slot that it received
bats_semaphore_acquire_slot() {
  mkdir -p "$BATS_SEMAPHORE_DIR"
  # wait for a slot to become free
  # TODO: avoid busy waiting by using signals -> this opens op prioritizing possibilities as well
  while true; do
    # don't lock for reading, we are fine with spuriously getting no free slot
    if [[ $(bats_semaphore_get_free_slot_count) -gt 0 ]]; then
      bats_run_under_"$BATS_LOCKING_IMPLEMENTATION" \
        bash -c bats_semaphore_acquire_while_locked \
      && break
    fi
    sleep 1
  done
}

bats_semaphore_release_slot() {
  # we don't need to lock this, since only our process owns this file
  # and freeing a semaphore cannot lead to conflicts with others
  rm "$BATS_SEMAPHORE_DIR/slot-$1" # this will fail if we had not acquired a semaphore!
}

bats_semaphore_get_free_slot_count() {
  # find might error out without returning something useful when a file is deleted,
  # while the directory is traversed ->  only continue when there was no error
  until used_slots=$(find "$BATS_SEMAPHORE_DIR" -name 'slot-*' 2>/dev/null | wc -l); do :; done
  echo $((BATS_SEMAPHORE_NUMBER_OF_SLOTS - used_slots))
}