#!/usr/bin/env bash

# Check for required argument
if [ $# -ne 1 ]; then
    echo "Usage: $(basename "$0") SNAPPER_CONFIG"
    echo "Example: $(basename "$0") root"
    exit 1
fi

# Configuration
SNAPPER_CONFIG="$1"
SOURCE_PATH="/.snapshots"
REMOTE_HOST="root@synology"
DEST_PATH="/volume1/backups/${SNAPPER_CONFIG}"  # Added config name to path
STATE_FILE="/var/lib/snapper-backup-${SNAPPER_CONFIG}.state"  # Made state file unique per config
LOG_FILE="/var/log/snapper-backup-${SNAPPER_CONFIG}.log"      # Made log file unique per config
KEEP_SNAPSHOTS=5

# Ensure we exit on any error
set -e

# Verify snapper config exists
if ! snapper -c "$SNAPPER_CONFIG" list &>/dev/null; then
    echo "ERROR: Snapper config '$SNAPPER_CONFIG' does not exist"
    exit 1
fi

# Logging function
log() {
    echo "$(date '+%Y-%m-%d %H:%M:%S') - $1" | tee -a "$LOG_FILE"
}

# Function to verify snapshot exists
verify_snapshot() {
    local snapshot_num="$1"
    if [ ! -d "$SOURCE_PATH/$snapshot_num/snapshot" ]; then
        log "ERROR: Snapshot $snapshot_num does not exist"
        return 1
    fi
    return 0
}

# Function to verify remote connectivity
verify_remote() {
    if ! ssh -q "$REMOTE_HOST" "exit"; then
        log "ERROR: Cannot connect to remote host"
        exit 1
    fi
}

# Function to get remote snapshots
get_remote_snapshots() {
    ssh "$REMOTE_HOST" "find '$DEST_PATH' -maxdepth 1 -type d -name 'snapshot*' | sort -n"
}

# Function to cleanup old remote snapshots
cleanup_remote_snapshots() {
    local snapshots=($(get_remote_snapshots))
    local count=${#snapshots[@]}

    if [ $count -gt $KEEP_SNAPSHOTS ]; then
        local to_delete=$((count - KEEP_SNAPSHOTS))
        log "Cleaning up $to_delete old snapshots on remote system"

        for ((i=0; i<$to_delete; i++)); do
            local snapshot="${snapshots[$i]}"
            log "Deleting remote snapshot: $snapshot"
            ssh "$REMOTE_HOST" "btrfs subvolume delete '$snapshot'" || \
                log "WARNING: Failed to delete snapshot $snapshot"
        done
    fi
}

# Start backup process
log "Starting backup for snapper config: $SNAPPER_CONFIG"

# Verify remote connectivity first
verify_remote

# Get latest successful transfer number
LAST_TRANSFERRED=$(cat "$STATE_FILE" 2>/dev/null || echo "")

# Get latest snapshot number from snapper
LATEST_SNAPSHOT=$(snapper -c "$SNAPPER_CONFIG" list | tail -n 1 | awk '{print $1}')

# Verify snapshots exist
verify_snapshot "$LATEST_SNAPSHOT" || exit 1
if [ -n "$LAST_TRANSFERRED" ]; then
    verify_snapshot "$LAST_TRANSFERRED" || exit 1
fi

# Exit if no new snapshots to transfer
if [ "$LAST_TRANSFERRED" = "$LATEST_SNAPSHOT" ]; then
    log "No new snapshots to transfer"
    exit 0
fi

# Create destination directory if it doesn't exist
ssh "$REMOTE_HOST" "mkdir -p '$DEST_PATH'"

# Perform the transfer
if [ -z "$LAST_TRANSFERRED" ]; then
    # First time backup - full send
    log "Performing full send of snapshot $LATEST_SNAPSHOT"
    sudo btrfs send "$SOURCE_PATH/$LATEST_SNAPSHOT/snapshot" | \
        pv -bytes | \
        ssh "$REMOTE_HOST" "btrfs receive '$DEST_PATH'" && {
            echo "$LATEST_SNAPSHOT" > "$STATE_FILE"
            log "Full send completed successfully"
        } || {
            log "ERROR: Full send failed"
            exit 1
        }
else
    # Incremental send
    log "Performing incremental send from $LAST_TRANSFERRED to $LATEST_SNAPSHOT"
    sudo btrfs send -p "$SOURCE_PATH/$LAST_TRANSFERRED/snapshot" \
        "$SOURCE_PATH/$LATEST_SNAPSHOT/snapshot" | \
        pv -bytes | \
        ssh "$REMOTE_HOST" "btrfs receive '$DEST_PATH'" && {
            echo "$LATEST_SNAPSHOT" > "$STATE_FILE"
            log "Incremental send completed successfully"
        } || {
            log "ERROR: Incremental send failed"
            exit 1
        }
fi

# Cleanup old snapshots if transfer was successful
cleanup_remote_snapshots

# Verify remote snapshots
log "Current remote snapshots:"
get_remote_snapshots | tee -a "$LOG_FILE"

# Final verification
if ! ssh "$REMOTE_HOST" "btrfs subvolume show '$DEST_PATH/snapshot'" &>/dev/null; then
    log "WARNING: Final verification failed"
    exit 1
fi

log "Backup completed successfully"