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

SCRIPT_DIR=$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)
SOURCE_SCRIPT="${SCRIPT_DIR}/iptables-forward.sh"
TARGET_BIN=${INSTALL_TARGET:-/usr/local/bin/iptables-forward}

usage() {
  cat <<USAGE
用法:
  sudo ./install.sh
  sudo ./install.sh --uninstall

说明:
  - 仅创建符号链接，不复制源码。
  - 默认链接到 /usr/local/bin/iptables-forward。
  - 可通过 INSTALL_TARGET 自定义目标路径。
USAGE
}

require_root() {
  if (( EUID != 0 )); then
    printf '请使用 root 或 sudo 执行安装脚本。\n' >&2
    exit 2
  fi
}

target_is_current_link() {
  [[ -L ${TARGET_BIN} ]] || return 1
  [[ $(readlink -- "${TARGET_BIN}") == "${SOURCE_SCRIPT}" ]]
}

install_link() {
  [[ -f ${SOURCE_SCRIPT} ]] || {
    printf '未找到入口脚本: %s\n' "${SOURCE_SCRIPT}" >&2
    exit 1
  }
  mkdir -p "$(dirname -- "${TARGET_BIN}")"
  if [[ -e ${TARGET_BIN} || -L ${TARGET_BIN} ]]; then
    if target_is_current_link; then
      chmod 755 "${SOURCE_SCRIPT}"
      printf '链接已存在: %s -> %s\n' "${TARGET_BIN}" "${SOURCE_SCRIPT}"
      return 0
    fi
    printf '目标已存在且不是当前脚本的链接，拒绝覆盖: %s\n' "${TARGET_BIN}" >&2
    exit 1
  fi
  ln -s "${SOURCE_SCRIPT}" "${TARGET_BIN}"
  chmod 755 "${SOURCE_SCRIPT}"
  printf '已创建链接: %s -> %s\n' "${TARGET_BIN}" "${SOURCE_SCRIPT}"
}

uninstall_link() {
  if target_is_current_link; then
    rm -f "${TARGET_BIN}"
    printf '已删除链接: %s\n' "${TARGET_BIN}"
  elif [[ -L ${TARGET_BIN} || -e ${TARGET_BIN} ]]; then
    printf '目标不是当前脚本创建的链接，拒绝删除: %s\n' "${TARGET_BIN}" >&2
    exit 1
  else
    printf '未发现已安装链接: %s\n' "${TARGET_BIN}"
  fi
}

main() {
  case ${1:-install} in
    --help|-h)
      usage
      ;;
    install)
      require_root
      install_link
      ;;
    --uninstall|uninstall)
      require_root
      uninstall_link
      ;;
    *)
      usage >&2
      exit 1
      ;;
  esac
}

main "$@"