#!/bin/sh

doy=$(date +%j | sed 's/^0*//')
y=$(date +%y)

letters="ABCDEFGHIJKLMNOPQRSTUVWXYZ"

if [ "$doy" -eq 365 ]; then
  printf "%s+00\n" "$y"
elif [ "$doy" -eq 366 ]; then
  printf "%s+01\n" "$y"
else
  mIndex=$(( (doy - 1) / 14 ))
  dom=$(( (doy - 1) % 14 + 1 ))
  mChar=$(echo "$letters" | cut -c $((mIndex + 1)))
  printf "%s%s%02d\n" "$y" "$mChar" "$dom"
fi