#!/usr/bin/env bash
set -euo pipefail

app_name="git-stack"

die() {
  echo "$app_name: $*" >&2
  exit 1
}

in_repo() {
  git rev-parse --git-dir >/dev/null 2>&1
}

require_repo() {
  in_repo || die "not inside a Git repository"
}

git_path() {
  git rev-parse --git-path "$1"
}

stack_file() {
  local p
  p="$(git_path "$app_name/messages")"
  mkdir -p "$(dirname "$p")"
  touch "$p"
  printf '%s\n' "$p"
}

install_hook() {
  local hooks_dir hook tmp
  hooks_dir="$(git_path hooks)"
  hook="$hooks_dir/pre-commit"
  mkdir -p "$hooks_dir"

  if [ -f "$hook" ] && ! grep -Fq "# managed-by: $app_name" "$hook"; then
    return 0
  fi

  tmp="$(mktemp)"
  cat >"$tmp" <<'EOF'
#!/usr/bin/env bash
# managed-by: git-stack
set -euo pipefail

stack_file="$(git rev-parse --git-path git-stack/messages)"
if [ -f "$stack_file" ] && [ -s "$stack_file" ]; then
  echo "git-stack: commit blocked; message stack is not empty" >&2
  echo "git-stack: pending messages:" >&2
  nl -ba "$stack_file" >&2
  echo "git-stack: clear with: git stack pop / git stack clear" >&2
  exit 1
fi
EOF

  chmod +x "$tmp"
  mv "$tmp" "$hook"
}

ensure_ready() {
  require_repo
  install_hook
}

cmd_push() {
  ensure_ready
  [ "$#" -ge 1 ] || die 'usage: git stack push "message"'
  local file msg
  file="$(stack_file)"
  msg="$*"
  printf '%s\n' "$msg" >>"$file"
  echo "$msg"
}

cmd_peek() {
  ensure_ready
  local file
  file="$(stack_file)"
  [ -s "$file" ] || die "stack is empty"
  tail -n 1 "$file"
}

cmd_list() {
  ensure_ready
  local file
  file="$(stack_file)"
  [ -s "$file" ] || exit 0
  nl -ba "$file"
}

cmd_pop() {
  ensure_ready
  local file last tmp
  file="$(stack_file)"
  [ -s "$file" ] || die "stack is empty"

  last="$(tail -n 1 "$file")"
  echo "$last"

  tmp="$(mktemp)"
  sed '$d' "$file" >"$tmp" || true
  mv "$tmp" "$file"
}

cmd_clear() {
  ensure_ready
  : >"$(stack_file)"
}

cmd_install() {
  ensure_ready
  echo "hook installed in $(git_path hooks)/pre-commit"
}

usage() {
  cat <<'EOF'
Usage:
  git stack push "message"
  git stack peek
  git stack list
  git stack pop
  git stack clear
  git stack install
EOF
}

main() {
  [ "$#" -ge 1 ] || {
    usage
    exit 1
  }

  case "$1" in
    push)
      shift
      cmd_push "$@"
      ;;
    peek)
      shift
      cmd_peek "$@"
      ;;
    list)
      shift
      cmd_list "$@"
      ;;
    pop)
      shift
      cmd_pop "$@"
      ;;
    clear)
      shift
      cmd_clear "$@"
      ;;
    install)
      shift
      cmd_install "$@"
      ;;
    *)
      usage
      exit 1
      ;;
  esac
}

main "$@"