#!/usr/bin/env bash

# on NixOS: -U
# on macOS: -p
UNIV_OPT=$(if echo '' | shasum -U > /dev/null 2>&1; then echo '-U'; elif echo '' | shasum -p > /dev/null 2>&1; then echo '-p'; else echo ''; fi);

check_file_in=$(echo "$@" | awk -v RS=' -' '/(c|-check) / {print $2}')
# TODO: right now, we are only accepting input on stdin.
# If we parse all the command line args, we could use something
# like the following, except the file wouldn't necessarily be $1.
#shasum "$UNIV_OPT" -a 1 -c "$check_file_out" < "${1:-/dev/stdin}"

if [ -f "$check_file_in" ]; then
  check_file_out=$(mktemp -q)
  hash_value=$(awk '{print $1}' "$check_file_in")
  if [[ "$UNIV_OPT" -eq "-U" ]]; then
    echo "$hash_value U-" > "$check_file_out"
  elif [[ "$UNIV_OPT" -eq "-p" ]]; then
    echo "$hash_value ?-" > "$check_file_out"
  else
    echo "$hash_value  -" > "$check_file_out"
  fi

  shasum "$UNIV_OPT" -a 1 -c "$check_file_out" < /dev/stdin
else
  shasum "$UNIV_OPT" -a 1 | sed 's/\ .-/ ?-/' < /dev/stdin
fi