#!/usr/bin/env bash

set -euo pipefail

usage() {
  echo "Usage: $(basename "$0") <command> [options] TARGET"
  echo ""
  echo "Commands:"
  echo "  add   Add/update path comment in first 5 lines of each file"
  echo "  undo  Remove any path comment from first 5 lines of each file"
  echo ""
  echo "Options:"
  echo "  -c  Comment symbol (e.g., '#' or '//') [required for add]"
  echo "  -e  Exclude pattern (can be specified multiple times)"
  exit 1
}

[[ $# -lt 1 ]] && usage

cmd="$1"
shift

[[ "$cmd" != "add" && "$cmd" != "undo" ]] && usage

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

if [[ "$cmd" == "add" ]]; then
  [[ -z "$comment_sym" ]] && {
    echo "Error: -c is required for add" >&2
    usage
  }
fi

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

strip_path_comment() {
  local file="$1"
  awk 'NR <= 5 && /path: / { next } { print }' "$file" >"$file.tmp"
  mv "$file.tmp" "$file"
}

process_file() {
  local file="$1"
  # shellcheck disable=SC2295
  local rel_path="${file#$base_dir/}"
  local path_comment="$comment_sym path: $rel_path"

  strip_path_comment "$file"

  local line1
  IFS= read -r line1 <"$file" 2>/dev/null || line1=""

  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"
}

dispatch() {
  local file="$1"
  if [[ "$cmd" == "add" ]]; then
    process_file "$file"
  else
    strip_path_comment "$file"
  fi
}

if [[ -f "$target" ]]; then
  dispatch "$target"
elif [[ -d "$target" ]]; then
  find_cmd=(find "$target" \( -name ".*" -prune \))

  if [[ ${#excludes[@]} -gt 0 ]]; then
    find_cmd+=(-o \()
    for i in "${!excludes[@]}"; do
      [[ $i -gt 0 ]] && find_cmd+=(-o)
      find_cmd+=(-path "*/${excludes[$i]}" -prune)
      find_cmd+=(-o -path "*/${excludes[$i]}/*" -prune)
    done
    find_cmd+=(\))
  fi

  find_cmd+=(-o -type f -print0)

  while IFS= read -r -d '' file; do
    dispatch "$file"
  done < <("${find_cmd[@]}")
else
  echo "Error: $target is not a file or directory" >&2
  exit 1
fi