#!/usr/bin/env bash

set -euo pipefail

usage() {
  echo "Usage: $0 -c COMMENT_SYMBOL [-e EXCLUDE_PATTERN]... TARGET"
  echo "  -c  Comment symbol (e.g., '#' or '//')"
  echo "  -e  Exclude pattern (can be specified multiple times)"
  echo "  TARGET  File or directory to process"
  exit 1
}

comment_sym=""
excludes=()

while getopts "c:e:h" opt; do
  case $opt in
  c) comment_sym="$OPTARG" ;;
  e) excludes+=("$OPTARG") ;;
  h) usage ;;
  *) usage ;;
  esac
done

shift $((OPTIND - 1))
[[ $# -ne 1 ]] && usage
[[ -z "$comment_sym" ]] && usage

target="$(realpath "$1")"
base_dir="$(pwd)"

should_exclude() {
  local path="$1"
  for pattern in "${excludes[@]}"; do
    if [[ "$path" == *"$pattern"* ]]; then
      return 0
    fi
  done
  return 1
}

process_file() {
  local file="$1"
  local rel_path="${file#"$base_dir"/}"

  should_exclude "$rel_path" && return

  local path_comment="$comment_sym path: $rel_path"

  # Read first two lines
  local line1 line2
  IFS= read -r line1 <"$file" 2>/dev/null || line1=""
  IFS= read -r line2 < <(tail -n +2 "$file") 2>/dev/null || line2=""

  # Check if path comment exists in first or second line
  [[ "$line1" == *"path: "* ]] && return
  [[ "$line2" == *"path: "* ]] && return

  # Insert after shebang if present, otherwise at top
  if [[ "$line1" =~ ^#! ]]; then
    {
      echo "$line1"
      echo "$path_comment"
      tail -n +2 "$file"
    } >"$file.tmp"
  else
    {
      echo "$path_comment"
      cat "$file"
    } >"$file.tmp"
  fi

  mv "$file.tmp" "$file"
}

if [[ -f "$target" ]]; then
  process_file "$target"
elif [[ -d "$target" ]]; then
  while IFS= read -r -d '' file; do
    process_file "$file"
  done < <(find "$target" -type f -print0)
else
  echo "Error: $target is not a file or directory" >&2
  exit 1
fi