#!/usr/bin/env bash
set -e
[ -n "$RBENV_DEBUG" ] && set -x

SHIM_PATH="${RBENV_ROOT}/shims"
PROTOTYPE_SHIM_PATH="${SHIM_PATH}/.rbenv-shim"

# Create the shims directory if it doesn't already exist.
mkdir -p "$SHIM_PATH"

# Ensure only one instance of rbenv-rehash is running at a time by
# setting the shell's `noclobber` option and attempting to write to
# the prototype shim file. If the file already exists, print a warning
# to stderr and exit with a non-zero status.
set -o noclobber
{ echo > "$PROTOTYPE_SHIM_PATH"
} 2>/dev/null ||
{ echo "rbenv: cannot rehash: $PROTOTYPE_SHIM_PATH exists"
  exit 1
} >&2
set +o noclobber

# If we were able to obtain a lock, register a trap to clean up the
# prototype shim when the process exits.
trap remove_prototype_shim EXIT

remove_prototype_shim() {
  rm -f "$PROTOTYPE_SHIM_PATH"
}

# The prototype shim file is a script that re-execs itself, passing
# its filename and any arguments to `rbenv exec`. This file is
# hard-linked for every binary and then removed. The linking technique
# is fast, uses less disk space than unique files, and also serves as
# a locking mechanism.
create_prototype_shim() {
  cat > "$PROTOTYPE_SHIM_PATH" <<SH
#!/usr/bin/env bash
set -e
[ -n "\$RBENV_DEBUG" ] && set -x

program="\${0##*/}"
if [ "\$program" = "ruby" ]; then
  for arg; do
    case "\$arg" in
    -e* | -- ) break ;;
    */* )
      if [ -f "\$arg" ]; then
        export RBENV_DIR="\${arg%/*}"
        break
      fi
      ;;
    esac
  done
fi

export RBENV_ROOT="$RBENV_ROOT"
exec rbenv exec "\$program" "\$@"
SH
  chmod +x "$PROTOTYPE_SHIM_PATH"
}

# If the contents of the prototype shim file differ from the contents
# of the first shim in the shims directory, assume rbenv has been
# upgraded and the existing shims need to be removed.
remove_outdated_shims() {
  for shim in *; do
    if ! diff "$PROTOTYPE_SHIM_PATH" "$shim" >/dev/null 2>&1; then
      for shim in *; do rm -f "$shim"; done
    fi
    break
  done
}

# The basename of each argument passed to `make_shims` will be
# registered for installation as a shim. In this way, plugins may call
# `make_shims` with a glob to register many shims at once.
make_shims() {
  local shims="$@"

  for file in $shims; do
    local shim="${file##*/}"
    register_shim "$shim"
  done
}

# Create an empty array for the list of registered shims.
registered_shims=()

# We will keep track of shims registered for installation with the
# global `reigstered_shims` array and with a global variable for each
# shim. The array will let us iterate over all registered shims. The
# global variables will let us quickly check whether a shim with the
# given name has been registered or not.
register_shim() {
  local shim="$@"
  local var="$(shim_variable_name "$shim")"

  if [ -z "${!var}" ]; then
    registered_shims[${#registered_shims[*]}]="$shim"
    eval "${var}=1"
  fi
}

# To compute the global variable name for a given shim we must first
# escape any non-alphanumeric characters. If the shim name is
# alphanumeric (including a hyphen or underscore) we can take a
# shorter path. Otherwise, we must iterate over each character and
# escape the non-alphanumeric ones using `printf`.
shim_variable_name() {
  local shim="$1"
  local result="_shim_"

  if [[ ! "$shim" =~ [^[:alnum:]_-] ]]; then
    shim="${shim//_/_5f}"
    shim="${shim//-/_2d}"
    result="$result$shim"
  else
    local length="${#shim}"
    local char i

    for ((i=0; i<length; i++)); do
      char="${shim:$i:1}"
      if [[ "$char" =~ [[:alnum:]] ]]; then
        result="$result$char"
      else
        result="$result$(printf "_%02x" \'"$char")"
      fi
    done
  fi

  echo "$result"
}

# To install all the registered shims, we iterate over the
# `registered_shims` array and create a link if one does not already
# exist.
install_registered_shims() {
  for shim in "${registered_shims[@]}"; do
    [ -e "$shim" ] || ln -f "$PROTOTYPE_SHIM_PATH" "$shim"
  done
}

# Once the registered shims have been installed, we make a second pass
# over the contents of the shims directory. Any file that is present
# in the directory but has not been registered as a shim should be
# removed.
remove_stale_shims() {
  local var
  for shim in *; do
    var="$(shim_variable_name "$shim")"
    if [ -z "${!var}" ]; then
      rm -f "$shim" 
    fi
  done
}


# Change to the shims directory.
cd "$SHIM_PATH"
shopt -s nullglob

# Create the prototype shim, then register shims for all known binaries.
create_prototype_shim
remove_outdated_shims
make_shims ../versions/*/bin/*

# Restore the previous working directory.
cd "$OLDPWD"

# Allow plugins to register shims.
for script in $(rbenv-hooks rehash); do
  source "$script"
done

# Change back to the shims directory to install the registered shims
# and remove stale shims.
cd "$SHIM_PATH"
install_registered_shims
remove_stale_shims