#!/usr/bin/env bash
# Archive exactly three legacy filesystem sessions before optionally deleting them.
# This helper is deliberately inert unless --delete is supplied after archive verification.
set -euo pipefail

usage() {
  echo "usage: $0 [--delete] SOURCE_SESSIONS_DIR BACKUP.tar SESSION_ID SESSION_ID SESSION_ID" >&2
  exit 2
}

delete_after_backup=false
if [[ ${1:-} == "--delete" ]]; then
  delete_after_backup=true
  shift
fi
[[ $# -eq 5 ]] || usage

source_dir=$1
backup=$2
shift 2
ids=("$@")

[[ -d $source_dir ]] || { echo "legacy session root is not a directory" >&2; exit 1; }
[[ ! -e $backup ]] || { echo "backup already exists; refusing to overwrite it" >&2; exit 1; }
[[ ${ids[0]} != "${ids[1]}" && ${ids[0]} != "${ids[2]}" && ${ids[1]} != "${ids[2]}" ]] \
  || { echo "exactly three distinct legacy session IDs are required" >&2; exit 1; }

paths=()
for id in "${ids[@]}"; do
  [[ $id =~ ^[A-Za-z0-9][A-Za-z0-9._-]{0,127}$ ]] \
    || { echo "invalid legacy session ID: $id" >&2; exit 1; }
  [[ -f "$source_dir/$id/session_manifest.yaml" ]] \
    || { echo "legacy session manifest is missing: $id" >&2; exit 1; }
  paths+=("$id")
done

tar --create --file "$backup" --directory "$source_dir" -- "${paths[@]}"
tar --list --file "$backup" >/dev/null
sha256sum "$backup" >"$backup.sha256"
echo "verified backup: $backup"
echo "checksum: $backup.sha256"

if ! $delete_after_backup; then
  echo "no legacy sessions deleted; review the archive, then rerun with --delete during maintenance" >&2
  exit 0
fi

for id in "${ids[@]}"; do
  rm -rf -- "$source_dir/$id"
done
echo "deleted exactly three archived legacy sessions"