#!/bin/bash

# Check we have an appropriate tool available
which sha512sum >/dev/null 2>&1
if [ $? -eq 0 ]; then
  SUM=chksumDirect
else
  which openssl >/dev/null 2>&1
  if [ $? -eq 0 ]; then
    SUM=chksumOpenSSL
  else
    echo "No suitable SHA512 sum command available"
    exit 1
  fi
fi

function chksumDirect() {
  local F="$1"
  sha512sum $F | sed -e 's![^ ]*/!!' > "$F.sha512"
}

function chksumOpenSSL() {
  local F="$1"
  local SUM=$(openssl sha -sha512 $F | awk '{print $2}')
  echo "$SUM  $F" > "$F.sha512"
}

function chksum() {
    local F="$1"
    if [[ ! -e $F ]]
    then
	echo "Error: no such file: $F"
	exit 1
    fi
    if [[ ! -e "$F.sha512" ]]
    then
	## Basename only
	$SUM $F
        echo "Added SHA512 checksum for $F"
    else
	echo "Checksum already exists: $F"
    fi
}

FILES=$(find . -name \*.md5 -a ! -name \*.sha512.md5 )

for F in $FILES
do
    B="${F%.md5}"
 
    # Some OSes/find implementations may output paths relative to the current directory
    # thus resulting in ./ being prefixed to the filenames.  Therefore remove leading 
    # ./ if present so the hash file only contains the hash and the raw filename
    B=${B##\./}

    chksum "$B"
    # echo $B
done