#!/bin/sh

# mktemp [-d] [template]
mktemp() (
  set -C
  umask 077
  OPTIND=1 dir=
  while getopts :d opt ; do
    case $opt in
      (d) dir=1 ;;
      ('?') 
        printf >&2 'mktemp: Invalid option -%s\n' "$OPTARG"
        return 2
      ;;
    esac
  done
  shift "$(( OPTIND - 1 ))"
  
  template=${1-${TMPDIR:-/tmp}/tmp.XXXXXXXXXX}
  case $template in
    (*XXXXXX) ;;
    (*)
      printf >&2 'mktemp: Template must end with at least 6 X characters\n'
      return 2
    ;;
  esac

  placeholder=${template##*[!X]}
  base=${template%"$placeholder"}
  retries=64
  while [ "$retries" -gt 0 ] ; do 
    placeholder=$(printf "$(
        awk -v n="$placeholder" -v i="$retries" '
          BEGIN {
            srand();
            srand(srand() * i);
            for (i = 0; i < length(n); ++i) {
              r = int(62 * rand());
              if (r < 10) printf("%s", r); # 0-9
              else if (r < 36) printf("\\%03o", r - 10 + 97); # a-z
              else printf("\\%03o", r - 36 + 65); # A-Z
            }
          }
        '
      )"
    )
    if [ "$dir" = 1 ] ; then
      if mkdir "$base$placeholder" 2>/dev/null ; then
        printf '%s\n' "$base$placeholder"
        return 0
      fi
    else
      if 2>/dev/null >"$base$placeholder" ; then
        printf '%s\n' "$base$placeholder"
        return 0
      fi
    fi
    retries=$(( retries - 1 ))
  done
  if [ "$dir" = 1 ] ; then
    printf >&2 'mktemp: Failed to create directory via template %s\n' "$template"
  else
    printf >&2 'mktemp: Failed to create file via template %s\n' "$template"
  fi
  return 1
)