#!/usr/bin/env bash
set -euo pipefail

KEYFILE="/root/.ssh/backup"
DATASET="{{ backup_zfs_dataset }}"
USER="{{ backup_ssh_user }}"
HOST="{{ backup_ssh_host }}"
KEEP=10

# END OF CONFIG

HOST_DIR=backup
DATE="$(date +%Y-%m-%d-%H-%M-%S%z | tr '+' '-')"
SNAPSHOT="${DATASET}@${DATE}"
TARGET="${HOST}/${HOST_DIR}/${SNAPSHOT}.enc"

echo "Taking snapshot \"$SNAPSHOT\""
(set -x; zfs snapshot "$SNAPSHOT")

echo "Snapshot created"
echo "Encrypting snapshot and backing up to target \"${TARGET}\""

(set -x; zfs send "$SNAPSHOT" | age -e -i "$KEYFILE" | curl --key "$KEYFILE" -u ${USER}: -T - "sftp://${TARGET}")

echo "Getting listing of existing backups"
# Note: sorting only produces a time-ordered list inside one timezone
# This is fine because we're only taking a snapshot every day, so the timezone issue is not relevant
BACKUPS=$(set -x; echo "ls ${HOST_DIR}" | sftp -i "${KEYFILE}" "${USER}@${HOST}" 2>/dev/null | tail -n +2 | sort)
COUNT=$(set -x; echo $BACKUPS | wc -w | awk '{print $1}')

if [ ! "$COUNT" -gt "$KEEP" ]; then
    echo "Acceptable number of backups on remote, no need to prune"
    echo "Done"
    exit 0
fi

echo "Pruning old backups, keeping latest ${KEEP}"
for BACKUP in $BACKUPS; do
    if [ ! "$COUNT" -gt "$KEEP" ]; then
        echo "Acceptable number of backups on remote, no need to prune"
        break
    fi

    (set -x; echo "rm ${BACKUP}" | sftp -i "${KEYFILE}" "${USER}@${HOST}")
    COUNT=$((COUNT - 1))
done

echo "Done"