#!/bin/bash

# 2021 Dave Bechtel
# Generate a (hopefully) unique AWS S3 bucket name with arbitrary padding length up to limit
# REQUIRES: sha1sum, sha256sum, tr, cut, wc
# Will use 'aws' if installed and in PATH to check bucket existence, but not required

echo "$0 - arg1=prefix + [optional] arg2 = # of pad chars (limit 63)"
arg="$1"
prefix="${arg,,}" # LC 

# int
declare -i pad=30 # chars, limit 63
[ "$2" = "" ] || pad=$2
[ $pad -gt 63 ] && pad=63

# must consist of lowercase letters, numbers, periods, and hyphens

out1=$(echo "$(date)$prefix" |sha1sum) 
sleep 1 
#out2=$(echo "$prefix$(date)" |sha1sum)
out2=$(echo "$out1$((1 + $RANDOM % 99))$(date)" |sha256sum)
# include random number from 1-99 to try and prevent collisions

# fix for https://www.cloudconformity.com/knowledge-base/aws/S3/dns-compliant-buckets-names.html
result=$(echo "$prefix-rbn-$out2" |tr ' ' '-' |cut -c 1-$pad)

echo '         1         2         3         4         5         6  6'
echo '123456789012345678901234567890123456789012345678901234567890123'
echo "$result"

# Is aws commandline installed? query existence
if [ $(which aws |wc -l) -ge 1 ]; then
  echo "$(date) - Checking for preexisting bucket"
  time aws s3api wait bucket-not-exists --bucket "$result"
  rc=$?
  
  if [ "$rc" = "0" ]; then
    echo "Bucket does not exist! Somebody tell Charlie!" 
    exit 0
  else
    echo "! Preexisting bucket detected Mr. Wonka, please run again"
    exit $rc
  fi
fi

exit;


# e.g. give me a Random Bucket Name with 40 chars, pad as needed

$ s3-bucket-unique-name.sh testberferd1 40
s3-bucket-unique-name.sh - arg1=prefix + [optional] arg2 = # of pad chars (limit 63)
         1         2         3         4         5         6  6
123456789012345678901234567890123456789012345678901234567890123
testberferd1-rbn-f9d0ee0c77beb5a769fdd1b

^ Running the same command twice with same parms should always generate a different result

vv This means the bucket already exists, should exit within (2) seconds if it doesn't
Waiter BucketNotExists failed: Max attempts exceeded
real    1m39.380s
^^ RC=255

Faster method: ' aws s3 ls |grep $result ' but depends on being configured and only applies to current account