#!/usr/bin/env bash
# Refresh the USB disk (sda) as a live boot-fallback clone of the
# running root filesystem. Run manually after a push:
#   sudo ./failover/sync-usb-backup.sh
#
# EEPROM BOOT_ORDER falls back to the SD card, then this USB disk, if the
# primary boot disk (NVMe) doesn't come up. /etc/fstab, /etc/machine-id,
# and /var/log are excluded from the sync so the clone keeps its own
# partition identity (PARTUUIDs differ per disk) and boot/journal history
# instead of inheriting the source disk's — see failover/README or repo
# memory "sd-fallback-fstab-clobber" for what breaks if those leak across.
set -euo pipefail

[ "$(id -u)" -eq 0 ] || { echo "Run as root (sudo)." >&2; exit 1; }

USB_ROOT_PART=/dev/sda2
MOUNT_POINT=/mnt/usb-backup-root

root_src=$(findmnt -no SOURCE /)
if [ "$root_src" = "$USB_ROOT_PART" ]; then
    echo "Currently booted from $USB_ROOT_PART — refusing to sync USB onto itself." >&2
    exit 1
fi

mkdir -p "$MOUNT_POINT"
mounted_here=0
if ! mountpoint -q "$MOUNT_POINT"; then
    mount "$USB_ROOT_PART" "$MOUNT_POINT"
    mounted_here=1
else
    mount -o remount,rw "$MOUNT_POINT"
fi

cleanup() {
    if [ "$mounted_here" -eq 1 ]; then
        umount "$MOUNT_POINT"
    fi
}
trap cleanup EXIT

rsync -aHAX --numeric-ids --delete \
    --info=progress2 \
    --exclude=/proc/* --exclude=/sys/* --exclude=/dev/* --exclude=/run/* \
    --exclude=/tmp/* --exclude=/mnt/* --exclude=/media/* --exclude=/lost+found \
    --exclude=/boot/firmware/* --exclude=/swapfile \
    --exclude=/etc/fstab --exclude=/etc/machine-id --exclude=/var/log/* \
    --stats / "$MOUNT_POINT/"

echo "USB backup ($USB_ROOT_PART) synced from $root_src."