#!/bin/sh

pebkac() {
  [ "${*}" ] && printf "%s\n\n" "${*}"
  cat <<EOF
Usage: fixuser [-c|-i|-r] <user> [user ...]

 -c    Check symlinks for sanity
 -i    Install symlinks
 -r    Remove symlinks

This script will adjust the bash-config symlinks in the homedir of
the supplied user, or all users if unspecified.

This script will avoid tampering with files that it thinks are
manually added. Use -c to check, and verify the files manually
afterwards.

EOF
  exit "${#}"
}

files="bash_profile bashrc"

userlist() {
  # Ignore users with shell not in /etc/shells
  # Ignore users with invalid homedir
  # Ignore subsequent users with the same homedir (root, toor, daemon, etc)
  # List all remaining usernames
  local _home_cache
  getent passwd | while IFS=: read user pass uid gid gecos home shell extra
  do
    getent shells "${shell}" >&- || continue
    [ -d "${home}" ] || continue
    echo "${_home_cache}" | grep -q " ${home} " && continue
    _home_cache="${_home_cache} ${home} "
    echo "${user}"
  done
}

userdir() {
  [ "${1}" ] || return 1
  # This is a loop because read will not work after pipe due to subshell isolation
  getent passwd "${1}" | while IFS=: read user pass uid gid gecos home shell extra
  do
    echo "${home}"
    break
  done
}

mine() {
  [ "${1}" ] || return 1
  user="${1}"; shift
  [ "${#}" -eq 0 ] && set - ${files}
  while [ "${1}" ]
  do
    file="${1}"
    link="$(userdir "${user}")/.${file}"
    real="/usr/local/etc/bash-config/${file}"
    if [ ! -L "${link}" ] || [ "$(realpath "$(readlink "${link}")")" != "$(realpath "${real}")" ]
    then
      return 1
    fi
    shift
  done
  return 0
}

gone() {
  [ "${1}" ] || return 1
  user="${1}"; shift
  [ "${#}" -eq 0 ] && set - ${files}
  while [ "${1}" ]
  do
    file="${1}"
    link="$(userdir "${user}")/.${file}"
    [ -f "${link}" ] && return 1
    shift
  done
  return 0
}

check() {
  [ "${1}" ] || return 1
  user="${1}"; shift
  [ "${#}" -eq 0 ] && set - ${files}
  echo "Checking user ${user}..."
  while [ "${1}" ]
  do
    file="${1}"
    if gone "${user}" "${file}"
    then
      echo " File ${file} does not exist."
    else
      if mine "${user}" "${file}"
      then
        echo " File ${file} is mine."
      else
        echo " File ${file} exists, but is not mine."
      fi
    fi
    shift
  done
}

install() {
  [ "${1}" ] || return 1
  user="${1}"
  if mine "${user}"
  then
    echo "User symlinks appear to be correct"
    return 0
  fi
  
  if ! gone "${user}"
  then
    echo "User files (${files}) appear to exist, and are not mine"
    echo "Refusing to molest them"
    return 1
  fi
  
  for file in ${files}
  do
    link="$(userdir "${user}")/.${file}"
    real="/usr/local/etc/bash-config/${file}"
    [ "${link%%.${file}}" = "/" ] && return 1
    su "${user}" -c "ln -s '${real}' '${link}'" || return $?
  done
  return 0
}

remove() {
  [ "${1}" ] || return 1
  user="${1}"
  if gone "${user}"
  then
    echo "User symlinks already removed"
    return 0
  fi
  
  if ! mine "${user}"
  then
    echo "User files (${files}) appear to exist, and are not mine"
    echo "Refusing to molest them"
    return 1
  fi
  
  for file in ${files}
  do
    link="$(userdir "${user}")/.${file}"
    [ "${link%%.${file}}" = "/" ] && return 1
    rm -f "${link}" || return $?
  done
  return 0
}

state() {
  [ -z "${cmd}" ] || pebkac "Only specify one of -c -i -r"
  cmd="${1}"
}

cmd=""

while getopts "cir" opt
do
  case "${opt}" in
  c)  state check ;;
  i)  state install ;;
  r)  state remove ;;
  [?]) pebkac "Unrecognized option ${OPTARG}" ;;
  esac
done
shift $(( $OPTIND - 1 ))

[ "${cmd}" ] || pebkac

# Default to current user if not root
if [ "$(id -u)" -gt 0 ]
then
  if [ "${*}" -a "${*}" != "${USER}" ]
  then
    echo "Mortal users can only modify themselves" >&2
    exit 1
  fi
  [ "${#}" -eq 0 ] && set - ${USER}
else
  [ "${#}" -eq 0 ] && set - $(userlist)
fi

printf "Working on user(s) "
echo "${@}"

while [ "${1}" ]
do
  "${cmd}" "${1}"
  shift
done