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

SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
# shellcheck disable=SC1091
source "${SCRIPT_DIR}/load-env.sh"

camera_device="${OMNI_CAMERA_DEVICE}"
occupancy_policy="${OMNI_CAMERA_OCCUPANCY_POLICY:-check}"
release_service="${OMNI_CAMERA_RELEASE_SERVICE:-}"

die() {
  echo "[camera-preflight] $*" >&2
  exit 1
}

camera_pids() {
  fuser "${camera_device}" 2>/dev/null \
    | tr ' ' '\n' \
    | grep -E '^[0-9]+$' \
    | sort -nu \
    || true
}

pid_service() {
  local pid="$1"
  local service

  service="$(sed -nE 's#.*[/:]([^/:]+\.service)$#\1#p' "/proc/${pid}/cgroup" 2>/dev/null | head -1)"
  printf '%s' "${service:-unknown}"
}

report_owners() {
  local pid
  local comm
  local service
  local found=0

  while read -r pid; do
    [[ -n "${pid}" ]] || continue
    found=1
    comm="$(cat "/proc/${pid}/comm" 2>/dev/null || printf 'unknown')"
    service="$(pid_service "${pid}")"
    echo "[camera-preflight] owner pid=${pid} command=${comm} service=${service}" >&2
  done < <(camera_pids)

  if [[ "${found}" == "1" ]]; then
    return 0
  fi
  return 1
}

has_proc_manager_owner() {
  local pid

  while read -r pid; do
    [[ -n "${pid}" ]] || continue
    if [[ "$(pid_service "${pid}")" == "proc_manager.service" ]]; then
      return 0
    fi
  done < <(camera_pids)

  return 1
}

if [[ ! -e "${camera_device}" ]]; then
  die "camera device does not exist: ${camera_device}"
fi

if ! command -v fuser >/dev/null 2>&1; then
  die "missing required command: fuser (install the psmisc package)"
fi

resolved_device="$(readlink -f "${camera_device}" 2>/dev/null || printf '%s' "${camera_device}")"
echo "[camera-preflight] checking ${camera_device} (${resolved_device}) policy=${occupancy_policy}" >&2

if ! report_owners; then
  echo "[camera-preflight] ${camera_device} is free" >&2
  exit 0
fi

case "${occupancy_policy}" in
  check)
    die "${camera_device} is busy; no process was stopped"
    ;;
  release-known)
    if [[ -z "${release_service}" ]]; then
      die "OMNI_CAMERA_RELEASE_SERVICE is required when policy=release-known"
    fi

    echo "[camera-preflight] stopping known camera service ${release_service}" >&2
    systemctl stop "${release_service}"

    if ! report_owners; then
      echo "[camera-preflight] ${camera_device} was released by ${release_service}" >&2
      exit 0
    fi

    if has_proc_manager_owner; then
      die "${camera_device} is still owned by proc_manager.service; refusing to stop the whole process manager. Unload the owning ROS component explicitly."
    fi

    die "${camera_device} remains busy after stopping ${release_service}"
    ;;
  *)
    die "unsupported OMNI_CAMERA_OCCUPANCY_POLICY=${occupancy_policy}; expected check or release-known"
    ;;
esac