"""
Mission executor launch file.
Selects config based on env argument at launch time.

Usage:
  ros2 launch rov_mission mission.launch.py          # dev config (default)
  ros2 launch rov_mission mission.launch.py env:=field  # field config
"""
from launch import LaunchDescription
from launch.actions import DeclareLaunchArgument, OpaqueFunction
from launch.substitutions import LaunchConfiguration
from launch_ros.actions import Node
from ament_index_python.packages import get_package_share_directory
import os


def _launch_with_config(context, *args, **kwargs):
    """Resolve env argument and return node with correct config file."""
    pkg_dir = get_package_share_directory('rov_mission')

    # Evaluate env argument at launch time
    env = LaunchConfiguration('env').perform(context)

    config_file = os.path.join(pkg_dir, 'config', f'{env}.yaml')

    if not os.path.exists(config_file):
        raise FileNotFoundError(
            f'Config file not found: {config_file}. '
            f'Valid environments: dev, field'
        )

    return [
        Node(
            package='rov_mission',
            executable='mission_executor',
            name='mission_executor',
            output='screen',
            parameters=[config_file],
            respawn=True,
            respawn_delay=5.0,
        ),
        Node(
            package='rov_mission',
            executable='cockpit_bridge',
            name='cockpit_bridge',
            output='screen',
            respawn=True,
            respawn_delay=5.0,
        )
    ]


def generate_launch_description():
    """Launch mission executor with environment-specific config."""
    return LaunchDescription([
        DeclareLaunchArgument(
            'env',
            default_value='dev',
            description='Deployment environment: dev, field'
        ),
        OpaqueFunction(function=_launch_with_config),
    ])