#!/usr/bin/env bash
set -euo pipefail

BIN_ROOT="/opt/selective-vpn/bin"
COMPONENTS_RAW=""
DRY_RUN=0

usage() {
  cat <<'EOF'
Usage:
  rollback.sh [--bin-root DIR] [--component NAME[,NAME...]] [--dry-run]

Description:
  Rolls back transport companion binaries by one history step.
  Uses history files created by update.sh in BIN_ROOT/.packaging/*.history.

Examples:
  ./scripts/transport-packaging/rollback.sh --component singbox
  ./scripts/transport-packaging/rollback.sh --bin-root /tmp/svpn-bin --dry-run
EOF
}

require_cmd() {
  local cmd="$1"
  if ! command -v "$cmd" >/dev/null 2>&1; then
    echo "[transport-rollback] missing required command: ${cmd}" >&2
    exit 1
  fi
}

collect_components() {
  local state_dir="$1"
  local out=()
  if [[ -n "$COMPONENTS_RAW" ]]; then
    IFS=',' read -r -a out <<< "$COMPONENTS_RAW"
  else
    if [[ -d "$state_dir" ]]; then
      while IFS= read -r file; do
        local base
        base="$(basename "$file")"
        out+=("${base%.history}")
      done < <(find "$state_dir" -maxdepth 1 -type f -name '*.history' | sort)
    fi
  fi
  printf '%s\n' "${out[@]}"
}

rollback_component() {
  local component="$1"
  local state_dir="$2"
  local history_file="${state_dir}/${component}.history"

  if [[ ! -f "$history_file" ]]; then
    echo "[transport-rollback] ${component}: history file not found (${history_file})" >&2
    return 1
  fi

  mapfile -t lines < "$history_file"
  if [[ "${#lines[@]}" -lt 2 ]]; then
    echo "[transport-rollback] ${component}: not enough history entries to rollback" >&2
    return 1
  fi

  local current_line prev_line
  current_line="${lines[${#lines[@]}-1]}"
  prev_line="${lines[${#lines[@]}-2]}"

  IFS='|' read -r _ts_curr bin_curr version_curr target_curr <<< "$current_line"
  IFS='|' read -r _ts_prev bin_prev version_prev target_prev <<< "$prev_line"
  local binary_name="${bin_curr:-$bin_prev}"
  local active_link="${BIN_ROOT}/${binary_name}"

  if [[ -z "$binary_name" || -z "$target_prev" ]]; then
    echo "[transport-rollback] ${component}: invalid history lines" >&2
    return 1
  fi

  if [[ ! -e "$target_prev" ]]; then
    echo "[transport-rollback] ${component}: previous target does not exist: ${target_prev}" >&2
    return 1
  fi

  echo "[transport-rollback] ${component}: ${binary_name} ${version_curr} -> ${version_prev}"
  if [[ "$DRY_RUN" -eq 1 ]]; then
    echo "[transport-rollback] DRY-RUN ${component}: switch ${active_link} -> ${target_prev}"
    return 0
  fi

  ln -sfn "$target_prev" "$active_link"

  if [[ "${#lines[@]}" -eq 2 ]]; then
    printf '%s\n' "${lines[0]}" > "$history_file"
  else
    printf '%s\n' "${lines[@]:0:${#lines[@]}-1}" > "$history_file"
  fi
  echo "[transport-rollback] ${component}: active -> ${target_prev}"
}

while [[ $# -gt 0 ]]; do
  case "$1" in
    --bin-root)
      BIN_ROOT="${2:-}"
      shift 2
      ;;
    --component)
      COMPONENTS_RAW="${2:-}"
      shift 2
      ;;
    --dry-run)
      DRY_RUN=1
      shift
      ;;
    -h|--help)
      usage
      exit 0
      ;;
    *)
      echo "[transport-rollback] unknown argument: $1" >&2
      usage >&2
      exit 1
      ;;
  esac
done

require_cmd ln
require_cmd find
require_cmd basename

state_dir="${BIN_ROOT}/.packaging"
mapfile -t components < <(collect_components "$state_dir")

if [[ "${#components[@]}" -eq 0 ]]; then
  echo "[transport-rollback] no components selected/found" >&2
  exit 1
fi

echo "[transport-rollback] bin_root=${BIN_ROOT}"
if [[ -n "$COMPONENTS_RAW" ]]; then
  echo "[transport-rollback] components=${COMPONENTS_RAW}"
fi
if [[ "$DRY_RUN" -eq 1 ]]; then
  echo "[transport-rollback] mode=dry-run"
fi

for component in "${components[@]}"; do
  component="$(echo "$component" | xargs)"
  if [[ -z "$component" ]]; then
    continue
  fi
  rollback_component "$component" "$state_dir"
done

echo "[transport-rollback] done"