#!/usr/bin/env bash
set -Eeuo pipefail
shopt -s inherit_errexit nullglob

# -----------------------------------------------------------------------------
# CONFIGURATION — adjust to taste
# -----------------------------------------------------------------------------
readonly RETENTION_DAYS=7
readonly BACKUP_BASE=/media/extension/backup/ubuntu
readonly MOUNT_POINT=/media/extension

# timestamp format — no spaces
#readonly NOW=$(date +'%Y-%m-%d_%H-%M-%S')
readonly NOW=$(date +'%Y-%m-%d')
readonly THIS_RUN=${BACKUP_BASE}/${NOW}
readonly LATEST=${BACKUP_BASE}/latest

# directories (or files) to back up:
declare -a SOURCE_ITEMS=(
  "/home/oster/server"
  "/home/oster/photo-lib"
)

# rsync exclusions — add your own
declare -a EXCLUDES=(
  --exclude='.cache'
  --exclude='node_modules'
  --exclude='*.tmp'
)

# rsync niceties
RSYNC_OPTS=(
  -aAXHv                # archive, preserve ACLs/xattrs, human-readable, verbose
  --delete              # mirror deletions
  --partial             # keep partials if interrupted
  --stats               # give stats at end
  "${EXCLUDES[@]}"
)

# Dry-run? set to "--dry-run" to test without writing
DRY_RUN=""

# -----------------------------------------------------------------------------
# LOGGING & LOCKING / CLEANUP
# -----------------------------------------------------------------------------
log()   { echo "[$(date +'%F %T')] $*"; }
die()   { log "FATAL: $*"; exit 1; }
lockfile="${BACKUP_BASE}/.backup.lock"

#trap 'rm -rf "$lockfile"' EXIT
#if ! touch "$lockfile" 2>/dev/null; then
#  die "Another backup is running (lockfile exists)."
#fi

# -----------------------------------------------------------------------------
# FUNCTIONS
# -----------------------------------------------------------------------------
check_mount() {
  if ! mountpoint -q "$MOUNT_POINT"; then
    die "Backup mountpoint $MOUNT_POINT is not mounted."
  fi
}

rotate_old() {
  log "Rotating backups older than ${RETENTION_DAYS} days."
  find "$BACKUP_BASE" -maxdepth 1 -mindepth 1 -type d \
       ! -name 'latest' ! -name "$(basename "$THIS_RUN")" \
       -mtime +${RETENTION_DAYS} \
       -print -exec rm -rf {} \;
}

# -----------------------------------------------------------------------------
# MAIN
# -----------------------------------------------------------------------------
log "=== Starting backup run: $NOW ==="
check_mount

mkdir -p "$BACKUP_BASE"
mkdir -p "$THIS_RUN"

# Determine if we can do a hardlink-incremental snapshot
if [ -d "$LATEST" ]; then
  LINK_DEST="--link-dest=$(readlink -f $LATEST)"
  log "Using link‐dest for incremental snapshot → $LATEST"
else
  LINK_DEST=""
  log "No previous backup; doing full snapshot."
fi

for src in "${SOURCE_ITEMS[@]}"; do
  base=$(basename "$src")
  dst="${THIS_RUN}/${base}"
  log "Backing up $src → $dst"

  nice -n 10 ionice -c2 -n7 \
    rsync "${RSYNC_OPTS[@]}" $LINK_DEST $DRY_RUN \
      "$src"/ "$dst"/
done

# update the "latest" symlink atomically
tmp_latest="${BACKUP_BASE}/.latest.tmp"
rm -f "$tmp_latest"
ln -sfn "$(basename "$THIS_RUN")" "$tmp_latest"
mv -T "$tmp_latest" "$LATEST"

rotate_old
log "=== Backup completed successfully ==="