#!/bin/bash

# Stop on error
set -e

helpfn() {
  echo -e "USAGE: $(basename $0) FILE... [OPTION]..." >&2
  echo -e "Replace environment variables in file(s)." >&2
  echo -e "" >&2
  echo -e "OPTIONS:" >&2
  echo -e "  -e, --echo-only   Don't modify file in place, output result to stdout." >&2
  echo -e "  -h, --help        Show this help." >&2
  echo -e "  -o, --opening     Specify opening character sequence (default: #{{env: )." >&2
  echo -e "  -c, --closing     Specify closing character sequence (default: }} )." >&2
}

CRESET="\e[0m"
CRED="\e[31m"
CGREEN="\e[32m"
CBLUE="\e[34m"

echo -ne "${CRED}"
OPTS=`getopt -o ho:c:e --long help,opening:,closing:,debug,echo-only -n 'parse-options' -- "$@"`
echo -ne "${CRESET}"

if [ $? != 0 ]; then
  echo -e "${CRED}Failed parsing options.${CRESET}" >&2
  helpfn
  exit 1
fi

eval set -- "$OPTS"

OPENING='#{{env:'
CLOSING='}}'
HELP=false
ECHO_ONLY=false
DEBUG=false

while true; do
  case "$1" in
    -h | --help ) HELP=true; break ;;
    -o | --opening ) OPENING="$2"; shift 2 ;;
    -c | --closing ) CLOSING="$2"; shift 2 ;;
    -e | --echo-only ) ECHO_ONLY=true; shift ;;
    --debug ) DEBUG=true; shift ;;
    -- ) shift; break ;;
    * ) break ;;
  esac
done

if $HELP; then
  helpfn
  exit 0
fi

if [[ $# -lt 1 ]]; then
  echo -ne "${CRED}" >&2
  helpfn
  echo -ne "${CRESET}" >&2
  exit 1
fi

#============================================================

if $DEBUG; then set -x; fi

substenv_rep() {
  FILE="$1"

  # Find referenced variables
  vars=$(grep -oe "${OPENING}\([A-Za-z0-9_]*\)${CLOSING}" "$FILE" | \
    sort -u | \
    sed "s/${OPENING}\([A-Za-z0-9_]*\)${CLOSING}/\1/")

  echo -e "${CBLUE}$(echo $vars | wc -w) variables found: $(echo $vars).${CRESET}" >&2

  tmpfile="$(dirname $FILE)/.$(basename $FILE).substenv-ng~"
  cp "$FILE" "$tmpfile"

  for var in $vars; do
    value=$(printenv $var | sed 's/\//\\\//g')
    sed -i "s/${OPENING}${var}${CLOSING}/${value}/g" "$tmpfile"
  done

  cat "$tmpfile"
  rm "$tmpfile"
}

while [[ $# -ge 1 ]]; do
  FILE="$1"
  orig="$(dirname $FILE)/.$(basename $FILE).orig"

  if [[ ! -f "$orig" ]]; then
    if [[ ! -f "$FILE" ]]; then
      echo -e "${CRED}No file found: \"${FILE}\".${CRESET}" >&2
      exit 1
    fi
    cp "$FILE" "$orig"
  else
    echo -e "${CBLUE}Starting from \"$orig\".${CRESET}" >&2
  fi

  if $ECHO_ONLY; then
    substenv_rep "$orig" $OPENING $CLOSING
  else
    substenv_rep "$orig" $OPENING $CLOSING > "$FILE"
    echo -ne "${CGREEN}Replaced environment variables in \"$FILE\". " >&2
    echo -e "${CBLUE}Original backed up to \"$orig\".${CRESET}" >&2
  fi
  shift
done