server/rewards/reward_function.py

"""Decomposed reward function.

Two stages:
1. **Per-step reward** ``compute_step_reward``: shapes behaviour with small
   incentives (progress, evidence quality, valid prerequisites) and
   penalties (rule violations, repeated work, wasted resources).
2. **Terminal reward** ``compute_terminal_reward``: graded only when the
   agent submits a discovery claim or runs out of resources. Compares the
   submitted claim against the hidden ``LatentParticle`` truth.

The terminal reward is intentionally dominant so the policy must care about
the *correct* discovery, not just looking busy.

Anti-reward-hacking design notes
--------------------------------
The shaping reward is layered with several independent checks so that
exploiting any single one alone cannot dominate the terminal grade
(see hackathon guidance: *"use multiple independent reward functions"*):

* ``tool_fit`` is **gated**: the agent only earns it when ``method`` is
  in ``TOOL_REGISTRY`` *and* the tool's category matches the action's
  expected category. Bogus method strings get **penalized**, not rewarded.
* ``valid_action`` is gated on a parsed structured action that the rules
  engine accepts — pure JSON-shaped junk does not earn it.
* ``progress_milestone`` only fires on the *first* time a milestone is
  unlocked, so re-doing already-completed steps cannot farm it.
* ``redundancy`` and the new ``repeat_action_penalty`` punish loops that
  re-emit the same action type many times in a row.
* The terminal grade dominates total reward via ``terminal_scale``, and
  the overconfident-wrong penalty also fires when the claim *significance*
  exceeds what was actually measured.
"""

from __future__ import annotations

from collections import deque
from dataclasses import dataclass, field
from typing import Deque, Dict, List, Optional

import numpy as np

from models import (
    ActionType,
    DiscoveryClaim,
    ExperimentAction,
    IntermediateOutput,
    TOOL_REGISTRY,
    is_recommended_tool,
)

from server.rules.engine import RuleResult, ViolationCode
from server.simulator.latent_state import FullLatentState


# ── Configuration ────────────────────────────────────────────────────────


@dataclass
class RewardWeights:
    # ── per-step shaping ────────────────────────────────────────
    valid_action: float = 0.05
    progress_milestone: float = 0.25
    evidence_quality: float = 0.20
    # Cut to ~1/3 of original (was 0.10) to lower the per-step shaping
    # floor. Combined with a smaller step_reward_clip and a heavier
    # repeat-action penalty this prevents the agent from farming
    # +0.20+/step by cycling well-formed-but-inert tool calls.
    tool_fit: float = 0.033           # paid only on a method ∈ TOOL_REGISTRY
                                      # whose category matches the action.
    bogus_method_penalty: float = -0.05  # penalises method strings outside
                                         # TOOL_REGISTRY (anti-string-spam).
    # Was -0.08; bumped to -0.5 because the previous value was easily out-
    # earned by stacking format_bonus + valid_action + tool_fit. The
    # gating in compute_step_reward also now triggers from the *2nd*
    # consecutive identical action_type instead of the 3rd.
    repeat_action_penalty: float = -0.5
    soft_violation: float = -0.05
    hard_violation: float = -0.50
    redundancy: float = -0.10
    resource_overspend: float = -0.30
    failure: float = -0.30

    # Hard cap on what a single shaping step can earn. Without this a
    # policy could in principle stack milestone + evidence_quality +
    # tool_fit + valid_action and approach the terminal reward magnitude.
    # Cut from 0.75 → 0.25 so the per-step shaping floor cannot exceed
    # ~1/3 of the wrong-claim terminal penalty.
    step_reward_clip: float = 0.25

    # ── terminal grading ────────────────────────────────────────
    terminal_scale: float = 5.0   # multiplied with the convex sum below

    mass_calibration: float = 0.30
    significance_quality: float = 0.20
    channel_correctness: float = 0.20
    spin_correctness: float = 0.10
    width_calibration: float = 0.05
    confidence_calibration: float = 0.10
    efficiency_bonus: float = 0.05

    overconfident_wrong_penalty: float = 4.0  # subtracted from terminal
    overclaim_significance_penalty: float = 1.5  # claim_sigma >> measured_sigma

    # Big bonus for getting BOTH mass and channel right, on top of the
    # terminal grade. Makes the bandit math strictly favour attempting a
    # claim when uncertain rather than running out the clock: a correct
    # claim now returns ~+10–12, a wrong one ~−1.85, no claim ~−5.
    correct_claim_bonus: float = 6.0

    # Penalty applied at episode end when the trajectory never even
    # *attempted* a SUBMIT_DISCOVERY_CLAIM. Defeats the "hide forever and
    # farm shaping" reward hack we observed in v1 (mean +0.22/step over
    # ~12 steps was a better deal than risking the wrong-claim penalty).
    no_claim_terminal_penalty: float = -5.0


# ── Outputs ──────────────────────────────────────────────────────────────


@dataclass
class RewardBreakdown:
    components: Dict[str, float] = field(default_factory=dict)
    total: float = 0.0

    def add(self, key: str, value: float) -> None:
        self.components[key] = self.components.get(key, 0.0) + value
        self.total += value


@dataclass
class StepReward:
    reward: float
    breakdown: RewardBreakdown


@dataclass
class TerminalReward:
    reward: float
    breakdown: RewardBreakdown
    discovered: bool
    correct_mass: bool
    correct_channel: bool
    correct_spin: bool


# ── Per-step ─────────────────────────────────────────────────────────────


_PROGRESS_FLAGS = [
    "beam_configured",
    "luminosity_allocated",
    "trigger_set",
    "collisions_collected",
    "channel_selected",
    "tracks_reconstructed",
    "detector_calibrated",
    "invariant_mass_built",
    "background_subtracted",
    "resonance_fitted",
    "significance_estimated",
]


def _milestone_progress(state_before: FullLatentState, state_after: FullLatentState) -> int:
    """Number of new progress milestones unlocked this step."""
    delta = 0
    for flag in _PROGRESS_FLAGS:
        was = getattr(state_before.progress, flag)
        now = getattr(state_after.progress, flag)
        if now and not was:
            delta += 1
    return delta


def _consecutive_repeat_count(
    history: List, action_type: ActionType, look_back: int = 6
) -> int:
    """How many times this action_type appeared *consecutively* most recently
    (excluding the just-applied action). Used to dampen loops.
    """
    if not history:
        return 0
    n = 0
    for rec in reversed(history[-look_back:]):
        if getattr(rec, "action_type", None) == action_type:
            n += 1
        else:
            break
    return n


def compute_step_reward(
    *,
    action: ExperimentAction,
    output: IntermediateOutput,
    state_before: FullLatentState,
    state_after: FullLatentState,
    rule_result: RuleResult,
    weights: RewardWeights = RewardWeights(),
    history: Optional[List] = None,
) -> StepReward:
    """Compute the per-step shaping reward.

    ``history`` is the list of ``PipelineStepRecord`` *before* this step. We
    use it to detect consecutive-repeat loops (e.g. a model spamming the
    same action_type to farm shaping). All other fields are local.
    """

    breakdown = RewardBreakdown()

    # ── basic validity / failure ────────────────────────────────────
    if rule_result.allowed and output.success:
        breakdown.add("valid_action", weights.valid_action)
    if not output.success:
        breakdown.add("failure", weights.failure)

    # ── milestone progress (one-shot per flag, anti-farming) ────────
    new_milestones = _milestone_progress(state_before, state_after)
    if new_milestones > 0:
        breakdown.add("progress", weights.progress_milestone * new_milestones)

    # ── evidence quality ────────────────────────────────────────────
    if output.success:
        breakdown.add(
            "evidence_quality",
            weights.evidence_quality * float(output.quality_score),
        )

    # ── tool fit: gated on TOOL_REGISTRY membership + category match ─
    # Bogus or mismatched method strings are explicitly penalised so the
    # model can't farm shaping reward by setting method='whatever'.
    if action.method:
        if is_recommended_tool(action.action_type, action.method):
            breakdown.add("tool_fit", weights.tool_fit)
        elif action.method not in TOOL_REGISTRY:
            breakdown.add("bogus_method", weights.bogus_method_penalty)
        # If the tool exists but the category doesn't match the action,
        # we silently award nothing (no penalty, no reward).

    # ── rule penalties ──────────────────────────────────────────────
    if rule_result.violations:
        breakdown.add(
            "hard_violation",
            weights.hard_violation * len(rule_result.violations),
        )
    if rule_result.soft_violations:
        soft_redundant = sum(
            1 for v in rule_result.soft_violations if v == ViolationCode.REDUNDANT
        )
        soft_other = len(rule_result.soft_violations) - soft_redundant
        if soft_redundant:
            breakdown.add("redundancy", weights.redundancy * soft_redundant)
        if soft_other:
            breakdown.add("soft_violation", weights.soft_violation * soft_other)

    # ── consecutive-repeat penalty (catches loop hacks) ─────────────
    # Triggers from the *2nd* identical action in a row (previously
    # only kicked in at the 3rd). The escalating multiplier scales with
    # the run length so that 4-in-a-row gets 4× the base penalty —
    # important because v1 found that a tiny -0.08 was easily out-earned
    # by the +0.22/step shaping floor.
    repeats = _consecutive_repeat_count(history or [], action.action_type)
    if repeats >= 1:
        breakdown.add(
            "repeat_action",
            weights.repeat_action_penalty * repeats,
        )

    # ── resource overspend ──────────────────────────────────────────
    res = state_after.resources
    if res.budget_used_musd > res.budget_total_musd:
        breakdown.add("budget_overspend", weights.resource_overspend)
    if res.luminosity_used_fb > res.luminosity_total_fb:
        breakdown.add("lumi_overspend", weights.resource_overspend)
    if res.time_used_days > res.time_limit_days:
        breakdown.add("time_overspend", weights.resource_overspend)

    # ── total + soft cap ────────────────────────────────────────────
    total = float(breakdown.total)
    if weights.step_reward_clip > 0:
        total = float(np.clip(total, -10.0, weights.step_reward_clip))
    return StepReward(reward=total, breakdown=breakdown)


# ── Terminal grading ─────────────────────────────────────────────────────


def _mass_score(true_mass: float, claim_mass: Optional[float], unc: Optional[float]) -> float:
    """1.0 within 1σ, smoothly decays to 0 by 5 GeV (or 5σ, whichever larger)."""
    if claim_mass is None or true_mass <= 0:
        return 0.0
    err = abs(claim_mass - true_mass)
    # Tolerance: max(1.0 GeV, 1% of true mass, claimed unc)
    tol = max(1.0, 0.01 * true_mass)
    if unc is not None and unc > 0:
        tol = max(tol, float(unc))
    if err <= tol:
        return 1.0
    if err >= 5 * tol:
        return 0.0
    return float(np.clip(1.0 - (err - tol) / (4 * tol), 0.0, 1.0))


def _significance_score(state: FullLatentState, claim_sigma: Optional[float]) -> float:
    """High score when claimed σ matches measured σ and is ≥ 5.

    A claim_sigma far above the measured significance is a classic
    reward-hacking pattern (just write '50' in the field), so we penalise
    over-claiming proportionally.
    """
    measured = state.progress.best_significance_sigma or 0.0
    if claim_sigma is None:
        return 0.0
    over_claim = max(0.0, claim_sigma - measured)
    base = float(np.clip(measured / 5.0, 0.0, 1.0))
    penalty = float(np.clip(over_claim / 3.0, 0.0, 1.0))
    return float(np.clip(base - 0.5 * penalty, 0.0, 1.0))


def _significance_overclaim(
    state: FullLatentState, claim_sigma: Optional[float], threshold_sigma: float = 1.5
) -> float:
    """How many σ the claim *exceeds* what the env actually measured.

    Used as an extra penalty — distinct from ``_significance_score`` —
    so that a model can't compensate a giant over-claim by getting the
    mass slightly more accurate. Returns ``max(0, claim - measured - τ)``.
    """
    if claim_sigma is None:
        return 0.0
    measured = state.progress.best_significance_sigma or 0.0
    return float(max(0.0, claim_sigma - measured - threshold_sigma))


def _confidence_calibration(claim_conf: float, mass_score: float, channel_correct: bool) -> float:
    """Reward agents whose confidence tracks their actual accuracy."""
    actual = 0.5 * mass_score + 0.5 * (1.0 if channel_correct else 0.0)
    err = abs(actual - claim_conf)
    return float(np.clip(1.0 - err, 0.0, 1.0))


def _efficiency_bonus(state: FullLatentState) -> float:
    """Reward leftover budget (encourages succinct experiments)."""
    res = state.resources
    score = 0.0
    score += np.clip(res.budget_remaining / res.budget_total_musd, 0.0, 1.0)
    score += np.clip(res.luminosity_remaining / res.luminosity_total_fb, 0.0, 1.0)
    score += np.clip(res.time_remaining / res.time_limit_days, 0.0, 1.0)
    return float(score / 3.0)


def compute_terminal_reward(
    *,
    state: FullLatentState,
    claim: Optional[DiscoveryClaim],
    weights: RewardWeights = RewardWeights(),
) -> TerminalReward:
    """Grade the end-of-episode submission.

    ``claim`` is ``None`` when the episode terminated by *any* reason
    other than a ``submit_discovery_claim`` action (max_steps, budget
    exhausted, time exhausted) AND the trajectory never attempted to
    submit a claim. In that case we return a flat
    ``no_claim_terminal_penalty`` so the bandit math always favours
    *attempting* a claim over hiding forever to farm per-step shaping.
    See: v1 (anugrahhu/cernenv-grpo-smollm2-360m) which exploited this
    exact gap by spamming request_systematics for ~+0.22/step instead
    of risking the wrong-claim penalty (~−1.85).
    """
    breakdown = RewardBreakdown()

    if claim is None:
        breakdown.add("no_claim_terminal_penalty", weights.no_claim_terminal_penalty)
        return TerminalReward(
            reward=float(weights.no_claim_terminal_penalty),
            breakdown=breakdown,
            discovered=False,
            correct_mass=False,
            correct_channel=False,
            correct_spin=False,
        )

    truth = state.particle

    mass_score = _mass_score(truth.mass_gev, claim.mass_estimate_gev, claim.mass_uncertainty_gev)
    breakdown.add("mass_calibration", weights.mass_calibration * mass_score)

    sig_score = _significance_score(state, claim.significance_sigma)
    breakdown.add("significance_quality", weights.significance_quality * sig_score)

    channel_ok = claim.decay_channel == truth.primary_channel
    breakdown.add("channel_correctness", weights.channel_correctness * (1.0 if channel_ok else 0.0))

    spin_ok = claim.spin_hypothesis is not None and claim.spin_hypothesis == truth.spin
    breakdown.add("spin_correctness", weights.spin_correctness * (1.0 if spin_ok else 0.0))

    width_score = 0.0
    if claim.width_estimate_gev is not None and truth.width_gev > 0:
        rel = abs(claim.width_estimate_gev - truth.width_gev) / max(truth.width_gev, 1e-3)
        width_score = float(np.clip(1.0 - rel, 0.0, 1.0))
    breakdown.add("width_calibration", weights.width_calibration * width_score)

    conf_score = _confidence_calibration(claim.confidence, mass_score, channel_ok)
    breakdown.add("confidence_calibration", weights.confidence_calibration * conf_score)

    eff_score = _efficiency_bonus(state)
    breakdown.add("efficiency_bonus", weights.efficiency_bonus * eff_score)

    discovered = (
        mass_score >= 0.5
        and channel_ok
        and (claim.significance_sigma or 0.0) >= 4.5
    )

    raw = breakdown.total * weights.terminal_scale

    # Asymmetric claim cost (Fix #4). When the claim gets BOTH the mass
    # and the decay channel right, add a flat bonus on top of the graded
    # terminal so that a correct attempt is worth substantially more
    # than the no-claim penalty (-5) and the wrong-claim penalty (~-1.85).
    # This makes the bandit math: correct +10–12 ≫ no-claim −5 > wrong −2.
    if mass_score >= 0.5 and channel_ok:
        raw += weights.correct_claim_bonus
        breakdown.add("correct_claim_bonus", weights.correct_claim_bonus)

    # Overconfident-wrong penalty: high confidence but wrong channel & far mass
    if claim.confidence >= 0.8 and (mass_score < 0.2 or not channel_ok):
        raw -= weights.overconfident_wrong_penalty
        breakdown.add("overconfident_wrong", -weights.overconfident_wrong_penalty)

    # Significance-overclaim penalty (anti-reward-hacking): discourages the
    # model from just writing a giant σ in the claim regardless of evidence.
    overclaim_sigma = _significance_overclaim(state, claim.significance_sigma)
    if overclaim_sigma > 0:
        pen = weights.overclaim_significance_penalty * float(
            np.clip(overclaim_sigma / 3.0, 0.0, 2.0)
        )
        raw -= pen
        breakdown.add("overclaim_significance", -pen)

    # If the claim has zero/None mass and zero/None significance, treat it
    # as a "no-information" submission — clamp the raw reward so the model
    # can't pass the rules engine and then submit garbage to end early.
    if (claim.mass_estimate_gev is None) and (claim.significance_sigma in (None, 0.0)):
        raw = float(min(raw, 0.0))
        breakdown.add("no_information_claim", 0.0)

    return TerminalReward(
        reward=float(raw),
        breakdown=breakdown,
        discovered=discovered,
        correct_mass=mass_score >= 0.5,
        correct_channel=channel_ok,
        correct_spin=spin_ok,
    )


__all__ = [
    "RewardBreakdown",
    "RewardWeights",
    "StepReward",
    "TerminalReward",
    "compute_step_reward",
    "compute_terminal_reward",
]