io

#!/bin/bash
set -eu

: ${IO_RUNNING_FILE:=.io_running}
: ${IO_STDIN_FILE:=.io_stdin}
: ${IO_STDOUT_FILE:=.io_stdout}

io.help() {
  cat <<EOT
Usage: io <command> [<args>]

Commands:
  run <command and args>
  info
  quit
  echo <any echo args>
  cat <any cat args>
  tail <any tail args>
  stdin
  stdout
EOT
}

is_running() {
  [[ -f "$IO_RUNNING_FILE" || -f "$IO_STDIN_FILE" || -f "$IO_STDOUT_FILE" ]]
}

cleanup() {
  rm -f "$IO_RUNNING_FILE" "$IO_STDIN_FILE" "$IO_STDOUT_FILE"
}

abort_if_running() {
  if is_running; then
    >&2 echo "ERROR: Command has already been running by io."
    return 1
  fi
}

abort_if_not_running() {
  if ! is_running; then
    >&2 echo "ERROR: No command is running by io."
    return 1
  fi
}

io.run() {
  abort_if_running
  if (($# == 0)); then
    >&2 echo "ERROR: No command is specified."
    return 1
  fi
  if ! type "$1" >/dev/null 2>&1; then
    >&2 echo "ERROR: Command '$1' is not found."
    return 1
  fi
  echo "$*" >"$IO_RUNNING_FILE"
  mkfifo "$IO_STDIN_FILE"
  (while [[ -f "$IO_RUNNING_FILE" ]]; do sleep 1; done) >"$IO_STDIN_FILE" &
  "$@" <"$IO_STDIN_FILE" >"$IO_STDOUT_FILE" &
}

io.info() {
  if is_running; then
    echo -n "Running: "
    cat "$IO_RUNNING_FILE"
  else
    echo "Not running."
  fi
}

io.quit() {
  abort_if_not_running
  cleanup
}

io.echo() {
  abort_if_not_running
  echo "$@" >"$IO_STDIN_FILE"
}

io.cat() {
  abort_if_not_running
  cat "$@" >"$IO_STDIN_FILE"
}

io.tail() {
  abort_if_not_running
  tail "$@" "$IO_STDOUT_FILE"
}

io.stdin() {
  abort_if_not_running
  echo "$IO_STDIN_FILE"
}

io.stdout() {
  abort_if_not_running
  echo "$IO_STDOUT_FILE"
}

main() {
  if (($# == 0)); then
    >&2 io.help
    return 1
  fi
  local cmd="$1"; shift
  local io_cmd="io.${cmd}"
  if type "$io_cmd" >/dev/null 2>&1; then
    "$io_cmd" "$@"
  else
    >&2 echo -e "ERROR: Unknown command '${cmd}'\n"
    >&2 io.help
    return 1
  fi
}

main "$@"