#!/bin/bash

# this will take read-only btrfs snapshots and make it available in /srv/snapshots

# variables
SUBVOLUMES="/"
DESTINATION_ROOT=/srv/snapshots
TIMESTAMP=$(date +%Y%m%d%H%M) #add %S if you want sub-minute snapshots
PREFIX="snapshot-"
NAME="$PREFIX$TIMESTAMP"
MAX_SNAPSHOTS=28 #how many snapshots should be kept?

# preflight checks
if [ $(whoami) != "root" ]; then
    echo "error: you need to be root"
    exit 1
fi

# take the snapshots
for SUBVOLUME in $SUBVOLUMES; do
    if [ -z ${SUBVOLUME#/} ]; then
        SNAPSHOT_PATH="$DESTINATION_ROOT"
    else
	PATH="$DESTINATION_ROOT/${SUBVOLUME#/}"
    fi
    if [ ! -d $SNAPSHOT_PATH ]; then
        echo "warning: snapshot path ($SNAPSHOT_PATH) does not yet exist. creating."
        mkdir -p $SNAPSHOT_PATH
    fi
    if [ -d $SNAPSHOT_PATH/$NAME ]; then
        echo "warning: snapshots with same name already exists. skipping."
    else
	#TODO: handle failed snapshots and failed link creations
        btrfs -q subvolume snapshot -r $SUBVOLUME $SNAPSHOT_PATH/$NAME
	if [ -h $SNAPSHOT_PATH/latest ]; then
	    rm $SNAPSHOT_PATH/latest
	fi
        ln -sf $SNAPSHOT_PATH/$NAME $SNAPSHOT_PATH/latest
    fi
done

# prune old snapshots
SNAPSHOTS=$(ls -r $SNAPSHOT_PATH | grep $PREFIX)
i=0
for SNAPSHOT in $SNAPSHOTS; do
    if [ $i -ge $MAX_SNAPSHOTS ]; then
	#TODO: handle failed snapshot deletions
	btrfs -q subvolume delete $SNAPSHOT_PATH/$SNAPSHOT
    fi
    i=$((i+1))
done

# end script successfully
exit 0