#!/bin/bash

set -e  # exit on error

TARGET_FOLDER="./rpi_image"
VERSION="2020-02-13"

echo "This script downloads raspian lite, and modifies the image to  enable SSH and set hostname"

if [[ $EUID -ne 0 ]]; then
   echo "This script must be run as root"
   exit 1
fi

echo -n Hostname of new pi
read -p "Hostname of new pi [newrpi]: " RPI_HOSTNAME
RPI_HOSTNAME=${HOSTNAME:-newrpi}
SCRIPT_DIR=`pwd`
mkdir -p $TARGET_FOLDER
cd $TARGET_FOLDER


echo "Downloading image"
IMG_FILE_BASENAME=${VERSION}-raspbian-buster-lite.zip
wget http://downloads.raspberrypi.org/raspbian_lite/images/raspbian_lite-${VERSION}/${IMG_FILE_BASENAME}.zip
wget http://downloads.raspberrypi.org/raspbian_lite/images/raspbian_lite-${VERSION}/${IMG_FILE_BASENAME}.zip.sha256


echo "Checksum verification"
sha256sum -c ${IMG_FILE_BASENAME}.zip.sha256


echo "Unpack image"
unzip ${IMG_FILE_BASENAME}.zip
rm ${IMG_FILE_BASENAME}.zip


echo "Mounting image"
mkdir mounted_image
mkdir mounted_image/boot
mkdir mounted_image/system
losetup -P /dev/loop42 ${IMG_FILE_BASENAME}.img
mount /dev/loop42p1 mounted_image/boot
mount /dev/loop42p2 mounted_image/system


echo "Enabling SSH and writing hostname"
echo $RPI_HOSTNAME > mounted_image/system/etc/hostname
touch mounted_image/boot/ssh  # startup ssh
sed -i "/^#PermitRootLogin/ cPermitRootLogin prohibit-password" mounted_image/system/etc/ssh/sshd_config
mkdir -p mounted_image/system/root/.ssh
cat $SCRIPT_DIR/public_keys/*.pub > mounted_image/system/root/.ssh/authorized_keys
chmod 700 mounted_image/system/root/.ssh
chmod 600 mounted_image/system/root/.ssh/authorized_keys

echo "Unmounting image"
umount /dev/loop42p1
umount /dev/loop42p2
losetup -d /dev/loop42
rmdir mounted_image/boot
rmdir mounted_image/system


echo ""
echo ""
echo "The image is ready in folder ${TARGET_FOLDER}"
echo "copy to SD card with"
echo "  dd bs=4M status=progress if=the_image of=/dev/your/sdcard"
echo "  use e.g. /dev/sdb not /dev/sdb1"