tasks/task4.py

"""Task 4: Fault Recovery with Degradation.

This 'Extra Hard' tier task evaluates the agent's ability to maintain plant 
stability under additive environmental stress. It introduces a major thermal 
shock (T-spike) at solar-noon (Step 4) while simultaneously modelling cumulative 
hardware degradation that reduces coolant effectiveness.
"""

from typing import Dict, Optional, Tuple, Any

from env.state import ThermalPlantState
from tasks.config import ThermalPlantTask, AgentPolicy
from utils.constants import T_BOUNDS, PR_BOUNDS, TASK_CODE

class ShockPolicy(AgentPolicy):
    """Heavy cooling strategy."""
    
    def get_action(self, observation: Dict[str, float]) -> Dict[str, float]:
        # Track power to load cautiously
        u_target = min(observation["U"] + 0.2 * (observation["L"] - observation["P"]), 0.8)
        
        # Heavy cooling
        f_target = 0.6
        if observation["T"] > 0.8 or observation["Pr"] > 0.8:
            f_target = 1.0
            u_target = 0.0 # Emergency shutdown
            
        return {"U_target": max(0.0, u_target), "F_target": f_target}


class Task4(ThermalPlantTask):
    task_id = "task4"
    name = "Fault Recovery with Degradation"
    description = "Recover from a major thermal spike at step 4 while managing ongoing system degradation."
    max_steps = 12

    def reset(self, episode_id: int) -> None:
        self._seed = int(episode_id)

    def apply_disturbance(self, state: ThermalPlantState, step: int) -> Tuple[Dict[str, float], Optional[Dict[str, Any]]]:
        """
        Inject non-linear disturbances into the plant state.
        
        At Step 4, a +0.5 normalised thermal spike is injected to simulate a 
        major equipment fault. The agent must perform emergency cooling to 
        prevent catastrophic system stress.
        """
        deltas = {}
        event = {"type": "constant_load"}

        target_L = 0.6
        if abs(state.L - target_L) > 1e-5:
            deltas["L"] = target_L - state.L

        if step == 4:
            deltas["T"] = 0.5
            event = {"type": "thermal_fault", "T_delta": deltas["T"]}
            
        # Constant hardware degradation to simulate reduced mechanical reliability
        deltas["D"] = 0.02

        return deltas, event

    def is_completed(self, state: ThermalPlantState, step_count: int) -> bool:
        # Task 4 has a major fault at step 4.
        # Don't end early before the fault has been processed and stabilized.
        if step_count < 6:
            return False
        return abs(state.P - 0.6) <= 0.02 and state.T < 0.8 and state.Pr < 0.8

    def get_baseline_policy(self) -> AgentPolicy:
        return ShockPolicy()