#!/usr/bin/env bash
# rename_postfix.sh [-n|--dry-run] [-v] POSTFIX REPLACEMENT
set -o errexit -o pipefail
set -o nounset

dry_run=0
verbose=0

# ---- Parse flags
while [[ $# -gt 0 ]]; do
  case "$1" in
    -n|--dry-run) dry_run=1; shift ;;
    -v|--verbose) verbose=1; shift ;;
    --) shift; break ;;
    -*) echo "Unknown option: $1" >&2; exit 2 ;;
    *)  break ;;
  esac
done

if [[ $# -lt 2 ]]; then
  echo "Usage: ${0##*/} [-n|--dry-run] [-v] old_extension new_extension" >&2
  echo "Example: $0 .env .sh"
  exit 2
fi

old_ext="$1"
new_ext="$2"

if [[ -z "$new_ext" ]]; then
  echo "Refusing to run: new_ext cannot be empty." >&2
  exit 2
fi

# Match files in current dir whose names start with $postfix
# nullglob: if no matches, the glob expands to nothing (prevents literal)
shopt -s nullglob

# Include dotfiles if the postfix starts with a dot (like .env)
# (Bash already matches dotfiles when the pattern itself starts with a dot.)
# Handle spaces safely by quoting $f everywhere.
for file in *"$old_ext"; do
  [[ -e "$file" ]] || continue

  base="${file%$old_ext}"   # strip the old extension
  new_file="${base}${new_ext}"

  # Skip if nothing changes
  [[ "$file" == "$new_file" ]] && continue

  if (( dry_run )); then
    printf '[DRY-RUN] mv -- %q %q\n' "$file" "$new_file"
  else
    # -n: don't overwrite existing files accidentally
    # Add -v if requested
    if (( verbose )); then
      mv -vn -- "$file" "$new_file"
    else
      mv -n  -- "$file" "$new_file"
    fi
  fi
done