#!/bin/sh
# Wipe /dev/sda, create partitions and filesystems
#
# Partition layout
# /dev/sda1 mounted at /var/media  ext4, size (remaining space)
# /dev/sda2 mounted at /var/backup ext4, size 512MB

# All sizes in blocks (1KB)
set -e
DEV_FILE=/dev/sda
BACKUP_PART_SIZE=$((512*1024))
MEDIA_PART_START=4 # Align to 4KB boundary
FORCE=0

[ -b $DEV_FILE ] || exit 1
[ "$1" = "-f" ] && FORCE=1

if [ $FORCE != 1 ]; then
  sdasha1sum=$(dd if=$DEV_FILE bs=1024 count=1024 2>/dev/null | sha1sum |
    while read a junk; do echo $a; done)
  if [ $sdasha1sum != 3b71f43ff30f4b15b5cd85dd9e95ebc7e84eb5a3 ]; then
    echo "$DEV_FILE is not an empty disk. Use -f to force wiping." 1>&2
    exit 1
  fi
fi

TOTAL_SIZE=$(sfdisk -s $DEV_FILE)
MEDIA_PART_SIZE=$(( (TOTAL_SIZE - BACKUP_PART_SIZE - 4) / 4 * 4 )) # Align to 4KB boundary
BACKUP_PART_START=$((MEDIA_PART_START + MEDIA_PART_SIZE))

echo Partitioning $DEV_FILE
sfdisk -q -L -u B $DEV_FILE <<EOF
$MEDIA_PART_START,$MEDIA_PART_SIZE
$BACKUP_PART_START,
EOF

create_fs() {
  echo Creating filesystem in $1
  mkfs.ext4 -b 4096 -i 16384 -O extent,flex_bg,large_file $1
}

create_fs ${DEV_FILE}1
create_fs ${DEV_FILE}2