#!/bin/bash

# Backup info
export BACKUP_DRIVE_UUID={{ disk.uuid }}
export BACKUP_DRIVE={{ disk.name }}
export BACKUP_DRIVE_PASSWORD={{ disk.password }}

# For notifications
export DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/{{ notifications.user.uid }}/bus
export USER={{ notifications.user.name }}

export SOURCE_DIR=${SOURCE_DIR:=/}
# Fix basename / showing up as "/" -> change to "root"
if [ $(basename $SOURCE_DIR) = / ]; then
    export SNAPSHOT_PREFIX=${SNAPSHOT_PREFIX:=root}
else
    export SNAPSHOT_PREFIX=${SNAPSHOT_PREFIX:=$(basename $SOURCE_DIR)}
fi
# Set snapshot prefix based on basename
export SNAPSHOT_TIME=$(date +"%y_%m_%d-%H.%M")
export SNAPSHOT_NAME=$SNAPSHOT_PREFIX-$SNAPSHOT_TIME
export SNAPSHOT_DIR=${SNAPSHOT_DIR:=/.snapshots}
export LATEST=$SNAPSHOT_PREFIX-latest
export BACKUP_DRIVE=backup0
export BACKUP_DRIVE_MNT=${BACKUP_DRIVE_MNT:=/mnt/$BACKUP_DRIVE}
export BACKUP_DIR=${BACKUP_DIR:=/mnt/$BACKUP_DRIVE/$(hostname)}

# Show snapshot settings
echo "SOURCE_DIR: $SOURCE_DIR"
echo "SNAPSHOT_PREFIX: $SNAPSHOT_PREFIX"
echo "SNAPSHOT_TIME: $SNAPSHOT_TIME"
echo "SNAPSHOT_NAME: $SNAPSHOT_NAME"
echo "SNAPSHOT_DIR: $SNAPSHOT_DIR"
echo "LATEST: $LATEST"
echo "BACKUP_DRIVE_MNT: $BACKUP_DRIVE_MNT"
echo "BACKUP_DIR: $BACKUP_DIR"

# Create readonly snapshot
btrfs subvolume snapshot -r $SOURCE_DIR $SNAPSHOT_DIR/$SNAPSHOT_NAME

# Attempt to mount backup disk
# Check if backup disk is mounted
mountpoint $BACKUP_DRIVE_MNT
if [ $? != 0 ]; then
    cryptsetup luksClose $BACKUP_DRIVE
    cryptsetup luksOpen /dev/disk/by-uuid/$BACKUP_DRIVE_UUID $BACKUP_DRIVE --key-file=$BACKUP_DRIVE_PASSWORD
    mount $BACKUP_DRIVE_MNT
fi

# Check if backup disk is mounted
mountpoint $BACKUP_DRIVE_MNT
if [ $? = 0 ]; then # backup drive mounted
    if [ ! -d $BACKUP_DIR ]; then
        mkdir -p $BACKUP_DIR
    fi
    # Sync latest backups
    # The "latest" symlinks can get out of sync for a variety of reasons,
    # including backups run while the disk is unplugged.
    # They must be kept in sync so that snapshots are sent with a parent
    # that actually exists on the backup drive
    #
    # In order to keep them in sync we'll do the following:
    # 1. Check the <backup>-latest on the backup drive matches
    #    <backup>-latest in the snapshot directory
    # 2. If they don't match, assume the backup drive has the correct
    #    snapshot. Replace the <backup>-latest symlink in the snapshots
    #    directory with the one from the backup drive
    #
    # First check if the symlinks exist
    if [ -L $SNAPSHOT_DIR/$LATEST ] && [ -L $BACKUP_DIR/$LATEST ]; then
        # Get the actual name of the latest backup
        LATEST_SNAPSHOT=$(basename $(readlink $SNAPSHOT_DIR/$LATEST))
        LATEST_BACKUP=$(basename $(readlink $BACKUP_DIR/$LATEST))
        # If the latest backups don't match
        if [ $LATEST_SNAPSHOT != $LATEST_BACKUP ]
        then
            echo "Detected drift. Synchronizing latest snapshot with backup. Set to $LATEST_BACKUP."
            # Remove and replace the snapshot directory's latest
            rm $SNAPSHOT_DIR/$LATEST
            ln -s $SNAPSHOT_DIR/$LATEST_BACKUP $SNAPSHOT_DIR/$LATEST
        fi
    fi

    # If we have a latest, use it as the parent
    if [ -L $BACKUP_DIR/$LATEST ]; then
        btrfs send -p $SNAPSHOT_DIR/$LATEST $SNAPSHOT_DIR/$SNAPSHOT_NAME | btrfs receive $BACKUP_DIR
    else
        btrfs send $SNAPSHOT_DIR/$SNAPSHOT_NAME | btrfs receive $BACKUP_DIR
    fi

    # Update latest in backup dir
    rm -f $BACKUP_DIR/$LATEST
    ln -s $BACKUP_DIR/$SNAPSHOT_NAME $BACKUP_DIR/$LATEST
    sudo -E -u $USER notify-send "Backup complete" "Snapshot $SNAPSHOT_NAME completed successfully"
else
    sudo -E -u $USER notify-send "Backup failed" "$BACKUP_DRIVE_MNT not mounted. Snapshot $SNAPSHOT_NAME not synced" -u critical
fi

# Update latest in snapshot dir
rm -f $SNAPSHOT_DIR/$LATEST
ln -s $SNAPSHOT_DIR/$SNAPSHOT_NAME $SNAPSHOT_DIR/$LATEST