joint auto switching for postmodern ruby tools chruby and gem_home (ZSH)

ruby-switch.sh

source /usr/local/share/chruby/chruby.sh
source /usr/local/share/gem_home/gem_home.sh

unset RUBY_SWITCH_DEFAULT
unset RUBY_SWITCH_CURRENT
unset RUBY_SWITCH_GEMHOME

RUBY_SWITCH_DEFAULT=$(cat ~/.ruby-switch-default)

if [[ -z "$RUBY_SWITCH_DEFAULT" ]]; then
  RUBY_SWITCH_DEFAULT="system"
fi

chruby "$RUBY_SWITCH_DEFAULT"

function __ruby_switch_check_gemset() {
  if [ -f "$1/.ruby-gemset" ]; then
    local real
    if [ -d "$1/.gem" ]; then
      real=$(realpath "$1/.gem/..")
    else
      real=$(realpath "$1")
    fi
    if [[ "$real" != "$RUBY_SWITCH_GEMHOME" ]]; then
      __ruby_switch_revert_gemset
      RUBY_SWITCH_GEMHOME="$real"
      gem_home "$real"
    fi
  else
    __ruby_switch_revert_gemset
  fi
}

function __ruby_switch_revert_gemset() {
  if [[ -n "$RUBY_SWITCH_GEMHOME" ]]; then
    unset RUBY_SWITCH_GEMHOME
    gem_home -
  fi
}

function ruby_switch_auto() {
  local dir="$PWD/" version

  until [[ -z "$dir" ]]; do
    dir="${dir%/*}"

    if { read -r version <"$dir/.ruby-version"; } 2>/dev/null || [[ -n "$version" ]]; then
      version="${version%%[[:space:]]}"

      if [[ "$version" == "$RUBY_SWITCH_CURRENT" ]]; then
        __ruby_switch_check_gemset "$dir"
        return
      else
        __ruby_switch_revert_gemset
        RUBY_SWITCH_CURRENT="$version"
        chruby "$version"
        local retval=$?
        if (( $retval != 0 )); then return $retval; fi
        __ruby_switch_check_gemset "$dir"
        return $retval
      fi
    fi
  done

  if [[ -n "$RUBY_SWITCH_CURRENT" ]]; then
    __ruby_switch_revert_gemset
    unset RUBY_SWITCH_CURRENT
    chruby "$RUBY_SWITCH_DEFAULT"
    return $?
  fi
}

if [[ ! "$precmd_functions" == *ruby_switch_auto* ]]; then
  precmd_functions+=("ruby_switch_auto")
fi