physix/server/environment.py

"""OpenEnv :class:`Environment` subclass for PhysiX-Live.

Owns one episode's lifecycle (state + budget + termination) and orchestrates
the parser/simulator/metrics/reward modules. No scoring logic lives here.
"""

from __future__ import annotations

import logging
import uuid
from typing import Any, Optional

import numpy as np
from openenv.core.env_server import Environment

from physix.models import (
    CONVERGENCE_THRESHOLD,
    DEFAULT_MAX_TURNS,
    HistoryEntry,
    PhysiXAction,
    PhysiXObservation,
    PhysiXState,
    RewardBreakdown,
)
from physix.systems import PhysicalSystem, SystemTier, get_system, list_systems_by_tier
from physix.systems.base import TrajectoryData
from physix.verifier import (
    ParseError,
    SimulationError,
    compute_match,
    compute_reward,
    parse_equation,
    residual_summary,
    simulate_hypothesis,
    summarize_mismatch,
)


_log = logging.getLogger(__name__)


class PhysiXEnvironment(Environment[PhysiXAction, PhysiXObservation, PhysiXState]):
    """OpenEnv environment that drives one episode of equation discovery."""

    def __init__(
        self,
        *,
        max_turns: int = DEFAULT_MAX_TURNS,
        train_tiers: tuple[SystemTier, ...] = (SystemTier.TIER_1, SystemTier.TIER_2),
        seed: Optional[int] = None,
    ) -> None:
        super().__init__()
        self._max_turns = max_turns
        self._train_tiers = train_tiers
        self._rng = np.random.default_rng(seed)

        self._state = PhysiXState(max_turns=max_turns)
        self._system: Optional[PhysicalSystem] = None
        self._trajectory: Optional[TrajectoryData] = None
        self._history: list[HistoryEntry] = []

    def reset(
        self,
        seed: Optional[int] = None,
        episode_id: Optional[str] = None,
        **kwargs: Any,
    ) -> PhysiXObservation:
        """Start a new episode. Pass ``system_id=`` to force a specific system."""
        if seed is not None:
            self._rng = np.random.default_rng(seed)

        forced_id = kwargs.get("system_id")
        chosen_id = forced_id or self._sample_training_system_id()

        self._system = get_system(chosen_id)
        self._trajectory = self._system.simulate(self._rng)
        self._history = []

        self._state = PhysiXState(
            episode_id=episode_id or str(uuid.uuid4()),
            step_count=0,
            system_id=chosen_id,
            ground_truth_equation=self._system.ground_truth_equation(),
            ground_truth_params=dict(self._system.parameters),
            last_reward_total=0.0,
            converged=False,
            max_turns=self._max_turns,
        )

        return self._build_observation(
            mismatch_summary="",
            reward_breakdown=RewardBreakdown(),
        )

    def step(
        self,
        action: PhysiXAction,
        timeout_s: Optional[float] = None,
        **kwargs: Any,
    ) -> PhysiXObservation:
        del timeout_s, kwargs  # accepted for OpenEnv API conformance, unused

        if self._system is None or self._trajectory is None:
            raise RuntimeError("step() called before reset(); call reset() first.")

        self._state.step_count = self._state.step_count + 1

        breakdown, mismatch_text = self._score_hypothesis(action)
        self._record_history(action, breakdown, mismatch_text)

        self._state.last_reward_total = breakdown.total
        self._state.last_r_match = breakdown.match
        if breakdown.match >= CONVERGENCE_THRESHOLD:
            self._state.converged = True

        return self._build_observation(
            mismatch_summary=mismatch_text,
            reward_breakdown=breakdown,
        )

    @property
    def state(self) -> PhysiXState:
        return self._state

    def current_observation(self) -> Optional[PhysiXObservation]:
        """Re-render the observation an external driver should feed to the
        agent for the *next* turn (i.e. before calling :meth:`step`).

        Used by the interactive HTTP router to build prompts mid-session.
        Returns ``None`` before :meth:`reset` has been called.
        """
        if self._system is None or self._trajectory is None:
            return None
        last = self._history[-1] if self._history else None
        breakdown = (
            RewardBreakdown(**last.reward_components)
            if last is not None
            else RewardBreakdown()
        )
        mismatch = last.mismatch_summary if last is not None else ""
        return self._build_observation(
            mismatch_summary=mismatch,
            reward_breakdown=breakdown,
        )

    @property
    def current_trajectory(self) -> Optional[TrajectoryData]:
        return self._trajectory

    @property
    def current_system(self) -> Optional[PhysicalSystem]:
        return self._system

    def _is_done(self) -> bool:
        if self._state.converged:
            return True
        return self._state.step_count >= self._max_turns

    def _score_hypothesis(
        self,
        action: PhysiXAction,
    ) -> tuple[RewardBreakdown, str]:
        assert self._system is not None
        assert self._trajectory is not None

        parameter_names = frozenset(action.params or {})

        try:
            parsed = parse_equation(
                action.equation,
                state_variables=self._system.state_variables,
                parameter_names=parameter_names,
            )
        except ParseError as exc:
            _log.debug("parse_equation failed: %s", exc)
            breakdown = compute_reward(
                parse_succeeded=False,
                r_match=0.0,
                operator_count=0,
                previous_r_match=self._state.last_r_match,
            )
            return breakdown, f"Parse error: {exc}"

        try:
            predicted = simulate_hypothesis(
                parsed,
                state_variables=self._system.state_variables,
                parameters=dict(action.params or {}),
                initial_conditions=self._trajectory.initial_conditions,
                timestamps=self._trajectory.timestamps,
            )
        except SimulationError as exc:
            _log.debug("simulate_hypothesis failed: %s", exc)
            breakdown = compute_reward(
                parse_succeeded=True,
                simulation_succeeded=False,
                r_match=0.0,
                operator_count=parsed.operator_count,
                previous_r_match=self._state.last_r_match,
            )
            return breakdown, f"Simulation error: {exc}"

        r_match = compute_match(
            observed=self._trajectory.states,
            predicted=predicted,
            state_variables=self._system.state_variables,
        )
        residuals = residual_summary(
            timestamps=self._trajectory.timestamps,
            observed=self._trajectory.states,
            predicted=predicted,
            state_variables=self._system.state_variables,
        )
        mismatch_text = summarize_mismatch(
            observed=self._trajectory.states,
            predicted=predicted,
            state_variables=self._system.state_variables,
            timestamps=self._trajectory.timestamps,
            summary=residuals,
        )

        breakdown = compute_reward(
            parse_succeeded=True,
            simulation_succeeded=True,
            r_match=r_match,
            operator_count=parsed.operator_count,
            previous_r_match=self._state.last_r_match,
        )
        return breakdown, mismatch_text

    def _record_history(
        self,
        action: PhysiXAction,
        breakdown: RewardBreakdown,
        mismatch_text: str,
    ) -> None:
        entry = HistoryEntry(
            turn=self._state.step_count,
            equation=action.equation,
            params=dict(action.params or {}),
            reward_total=breakdown.total,
            reward_components=breakdown.as_dict(),
            mismatch_summary=mismatch_text,
        )
        self._history.append(entry)

    def _build_observation(
        self,
        *,
        mismatch_summary: str,
        reward_breakdown: RewardBreakdown,
    ) -> PhysiXObservation:
        assert self._system is not None
        assert self._trajectory is not None

        return PhysiXObservation(
            done=self._is_done(),
            reward=reward_breakdown.total,
            trajectory=self._trajectory.to_observation_samples(),
            state_variables=list(self._system.state_variables),
            hint=self._system.hint(self._state.ground_truth_params),
            history=[entry.as_dict() for entry in self._history],
            mismatch_summary=mismatch_summary,
            turn=self._state.step_count,
            turn_remaining=max(0, self._max_turns - self._state.step_count),
            system_id=self._state.system_id,
            stats=self._trajectory.stats(),
            reward_breakdown=reward_breakdown.as_dict(),
        )

    def _sample_training_system_id(self) -> str:
        candidates: list[str] = []
        for tier in self._train_tiers:
            candidates.extend(list_systems_by_tier(tier))
        if not candidates:
            raise RuntimeError(
                f"No training systems found for tiers {self._train_tiers!r}."
            )
        idx = int(self._rng.integers(0, len(candidates)))
        return candidates[idx]