#!/bin/sh

set -e

# for debugging
[ -n "$DEBUG" ] && set -x

IMGFILE=$PWD/disk.img


# we want everything except the final result to stderr
( exec 1>&2;

ESP_FILE=$PWD/boot.img


mkdir -p /tmp/bios
cd /tmp/bios

# input is a tarball of filesystem on stdin with kernel in /boot
# output is an iso on stdout

# extract. BSD tar auto recognises compression, unlike GNU tar
# only if stdin is a tty, if so need files volume mounted...
[ -t 0 ] || bsdtar xzf -

INITRD="$(find . -name '*.img')"
KERNEL="./kernel"
CMDLINE_FILE="$(find . -name cmdline)"
CMDLINE="$(cat $CMDLINE_FILE )"


cat >> syslinux.cfg <<EOF
DEFAULT linux
LABEL linux
    KERNEL /kernel
    INITRD /initrd.img
    APPEND ${CMDLINE}
EOF

# now build an img file
KERNEL_FILE_SIZE=$(stat -c %s "$KERNEL")
INITRD_FILE_SIZE=$(stat -c %s "$INITRD")
# minimum headroom needed in ESP, in bytes
# 511KiB headroom seems to be enough
ESP_HEADROOM=$(( 1024 * 1024 ))


ESP_FILE_SIZE=$(( $KERNEL_FILE_SIZE + $INITRD_FILE_SIZE + $ESP_HEADROOM ))
# (x+1024)/1024*1024 rounds up to multiple of 1024KB, or 2048 sectors
# some firmwares get confused if the partitions are not aligned on 2048 blocks
# we will round up to the nearest multiple of 2048 blocks
# since each block is 512 bytes, we want the size to be a multiple of
# 2048 blocks * 512 bytes = 1048576 bytes = 1024KB
ESP_FILE_SIZE_KB=$(( ( ( ($ESP_FILE_SIZE+1024-1) / 1024 ) + 1024-1) / 1024 * 1024 ))
# and for sectors
ESP_FILE_SIZE_SECTORS=$(( $ESP_FILE_SIZE_KB * 2 ))

# create a raw disk with an EFI boot partition
# Stuff it into a FAT filesystem, making it as small as possible.
mkfs.vfat -v -C $ESP_FILE $(( $ESP_FILE_SIZE_KB )) > /dev/null
echo "mtools_skip_check=1" >> /etc/mtools.conf && \
mcopy -i $ESP_FILE syslinux.cfg ::/
mcopy -i $ESP_FILE $KERNEL ::/kernel
mcopy -i $ESP_FILE $INITRD ::/initrd.img

# install syslinux
syslinux --install $ESP_FILE

# now make our actual filesystem image
# how big an image do we want?
# it should be the size of our ESP file+1MB for BIOS boot + 1MB for MBR + 1MB for backup
ONEMB=$(( 1024 * 1024 ))
SIZE_IN_BYTES=$(( $(stat -c %s "$ESP_FILE") + 4*$ONEMB ))

# and make sure the ESP is bootable for BIOS mode
# settings
BLKSIZE=512
MB_BLOCKS=$(( $SIZE_IN_BYTES / $ONEMB ))

# make the image
dd if=/dev/zero of=$IMGFILE bs=1M count=$MB_BLOCKS


echo "w" | fdisk $IMGFILE || true
# format one large partition of the apprropriate size
echo ","$ESP_FILE_SIZE_SECTORS",;" | sfdisk $IMGFILE

# of course, "one large partition" means minus the 2048 at the beginning
ESP_SECTOR_START=2048

# copy in our EFI System Partition image
dd if=$ESP_FILE of=$IMGFILE bs=$BLKSIZE count=$ESP_FILE_SIZE_SECTORS conv=notrunc seek=$ESP_SECTOR_START

# install mbr
#dd if=/usr/share/syslinux/mbr.bin of="$IMGFILE" bs=440 count=1 conv=notrunc
dd if=/usr/share/syslinux/altmbr.bin bs=439 count=1 conv=notrunc of=$IMGFILE
printf '\1' | dd bs=1 count=1 seek=439 conv=notrunc of=$IMGFILE

sfdisk -A "$IMGFILE" 1

)

cat $IMGFILE