#!/bin/bash
set -euo pipefail

SCRIPT_NAME=$(basename "$0")
log() {
  echo "[$(date '+%Y-%m-%d %H:%M:%S')] $SCRIPT_NAME: $*" >&2
}

cd / || exit 1

#UBUNTU_DEST="/mnt/Backup/Ubuntu"
UBUNTU_DEST="/mnt/Backup/Ubuntu/Backups"
CONTENT_SRC="/mnt/Content"
CONTENT_DEST="/mnt/Backup"

# helper wrapper: run rsync with low CPU and low I/O priority
run_rsync() {
  local label="$1"
  shift
  log "Starting low‑priority rsync ($label)"
  nice -n 19 ionice -c 3 rsync -avHAX --delete "$@"
}

# Helper function: Run a command with low CPU and I/O priority
run_low_priority() {
    local label="$1"
    shift
    log "Starting low-priority $label..."
    nice -n 19 ionice -c 3 "$@"
}

# Function to manage backup lifecycle - keep dailies for the past week, keep weeklies for the past month, keep montlies for 6 months.
manage_backups() {
    #local dir="/mnt/Backup/Ubuntu/Backups" - use UBUNTU_DEST
    log "Managing backups in $dir..."

    # Create the directory if it doesn't exist
    [ ! -d "$UBUNTU_DEST" ] && sudo mkdir -p "$UBUNTU_DEST"

    # List all .tgz files and sort them by modification time (oldest first)
    for backup_file in $(sudo ls -1 $UBUNTU_DEST/*.tgz | sort --key=1.2 --reverse); do
        filename=$(basename "$backup_file")
        timestamp=$(echo "$filename" | cut -d'-' -f3- | cut -d '.' -f1)

        # Calculate age in days
        mtime=$(stat -c %Y "$backup_file")
        age=$(( ($(date +%s) - $mtime) / (3600 * 24) ))

        # Extract day, month, and weekday from timestamp
        day=$(date -d "@$timestamp" +%d)
        month=$(date -d "@$timestamp" +%m)
        weekday=$(date -d "@$timestamp" +%w)

        # Check if backup is less than a week old (daily retention)
        if [ $age -lt 7 ]; then
            log "Backup $filename is less than a week old. Keeping."
            continue
        fi

        # Check for weekly backups on Sundays within the last month
        if [ $weekday == '0' ]; then
            current_month=$(date +%m)
            months_since=$(( (current_month - $month) % 12 ))
            if [ $months_since -lt 1 ]; then
                log "Backup $filename is a weekly backup on Sunday within the last month. Keeping."
                continue
            fi
        fi

        # Check for monthly backups on first day of the month within six months
        if [ $day == '01' ]; then
            current_month=$(date +%m)
            months_since=$(( (current_month - $month) % 12 ))
            if [ $months_since -lt 6 ]; then
                log "Backup $filename is a monthly backup on the first day within six months. Keeping."
                continue
            fi
        fi

        # Delete backups older than retention criteria
        log "Deleting backup: $filename"
        sudo rm "$backup_file"
    done
}

# --- 1. Backup / → /mnt/Backup/Ubuntu (fast, configs + Docker) ---

log "Starting tar backup of / → $UBUNTU_DEST (excluding /mnt and pseudo‑dirs)"

sudo mkdir -p "$UBUNTU_DEST"

# no longer using rsync to backup main filesystem as single file backup using compression works better with remote sync - does not interfere with syncthing state files and folders at the destination
#run_rsync "Ubuntu configs & Docker" \
#  --exclude-from=/etc/backup-excludes/ubuntu.exclude \
#  / "$UBUNTU_DEST"/

# Create a compressed tar backup with timestamp in the filename
timestamp=$(date +%Y%m%d-%H%M%S)
tar_output="$UBUNTU_DEST/backup-full-$timestamp.tgz"

log "Starting backup of /..."
run_low_priority "Ubuntu full backup" \
    tar -czf "$tar_output" --exclude-from=/etc/backup-excludes/ubuntu.exclude /


log "Finished / → $UBUNTU_DEST backup."

# --- 2. Backup /mnt/Content → /mnt/Backup (large media‑heavy sync) ---

if [ -d "$CONTENT_SRC" ]; then
  log "Starting rsync of $CONTENT_SRC → $CONTENT_DEST (with excludes)"

  # using --delete-before to ensure space is freed at destination for new and updated files
  run_rsync "Content -> Backup (media)" \
    --delete-before
    --exclude-from=/etc/backup-excludes/content.exclude \
    "$CONTENT_SRC"/ "$CONTENT_DEST"/

  log "Finished $CONTENT_SRC → $CONTENT_DEST backup."
else
  log "WARNING: $CONTENT_SRC not found or not a directory; skipping."
fi

log "All backups completed."