"""
SafetyRails: FvCB vs ML divergence guard for the SolarWine 2.0 control loop.

Position in the control loop (Phase 3, Step 7):
  After TradeoffEngine selects a minimum dose, SafetyRails validates that
  the FvCB and ML photosynthesis predictions are sufficiently consistent.

  If the two models disagree by more than DIVERGENCE_THRESHOLD (12%), the
  system cannot confidently predict that shading will help, so it falls back
  to full astronomical tracking (zero energy sacrifice, zero risk).

Rationale
---------
The FvCB mechanistic model and ML ensemble are calibrated on different
assumptions:
  - FvCB is reliable in standard conditions (T < 30°C, moderate VPD).
  - ML handles non-linear stress regimes better.

When both agree → high confidence → proceed with intervention.
When they disagree significantly → sensor fault, regime change, or edge
case not covered by calibration. The safe default is no intervention.
"""

from __future__ import annotations

from dataclasses import dataclass
from typing import Optional

from config.settings import DIVERGENCE_THRESHOLD


# ---------------------------------------------------------------------------
# Result dataclass
# ---------------------------------------------------------------------------

@dataclass
class SafetyCheckResult:
    """Outcome of a single FvCB vs ML divergence check."""

    passed: bool
    fvcb_a: float
    ml_a: float
    divergence_pct: float          # |fvcb_a - ml_a| / max(fvcb_a, ml_a) × 100
    fallback_needed: bool          # True when divergence > threshold
    reason: str                    # human-readable explanation

    def __str__(self) -> str:
        status = "PASS" if self.passed else "FAIL → fallback to θ_astro"
        return (
            f"SafetyRails [{status}] "
            f"FvCB={self.fvcb_a:.2f}  ML={self.ml_a:.2f}  "
            f"divergence={self.divergence_pct:.1f}%  "
            f"(threshold={DIVERGENCE_THRESHOLD * 100:.0f}%)"
        )


# ---------------------------------------------------------------------------
# SafetyRails
# ---------------------------------------------------------------------------

class SafetyRails:
    """
    Validates that FvCB and ML model outputs are consistent before any
    shading command is issued.

    Usage
    -----
    rails = SafetyRails()
    result = rails.check(fvcb_a=14.3, ml_a=14.8)
    if result.fallback_needed:
        # stay at θ_astro, log result
    """

    def __init__(self, threshold: Optional[float] = None) -> None:
        """
        Parameters
        ----------
        threshold : divergence fraction (0–1) that triggers fallback.
                    Defaults to DIVERGENCE_THRESHOLD (0.12) from settings.
        """
        self.threshold = threshold if threshold is not None else DIVERGENCE_THRESHOLD

    def check(
        self,
        fvcb_a: float,
        ml_a: float,
        context: Optional[str] = None,
    ) -> SafetyCheckResult:
        """
        Compare FvCB and ML photosynthesis outputs.

        Parameters
        ----------
        fvcb_a  : net A from FarquharModel (µmol CO₂ m⁻² s⁻¹)
        ml_a    : net A from ML ensemble (µmol CO₂ m⁻² s⁻¹)
        context : optional string for logging (e.g. "2025-07-15 13:00")

        Returns
        -------
        SafetyCheckResult
        """
        denominator = max(abs(fvcb_a), abs(ml_a), 1e-6)
        divergence = abs(fvcb_a - ml_a) / denominator
        divergence_pct = divergence * 100.0

        fallback_needed = divergence > self.threshold

        if fallback_needed:
            reason = (
                f"Models diverge by {divergence_pct:.1f}% "
                f"(FvCB={fvcb_a:.2f}, ML={ml_a:.2f}) — "
                f"exceeds {self.threshold * 100:.0f}% threshold. "
                f"Falling back to full astronomical tracking."
            )
        elif fvcb_a < 0 and ml_a < 0:
            reason = "Both models predict carbon loss (dark/night); no shading beneficial."
            fallback_needed = True
        else:
            reason = (
                f"Models agree within {self.threshold * 100:.0f}% threshold "
                f"(FvCB={fvcb_a:.2f}, ML={ml_a:.2f}, "
                f"divergence={divergence_pct:.1f}%). Proceeding."
            )

        return SafetyCheckResult(
            passed=not fallback_needed,
            fvcb_a=fvcb_a,
            ml_a=ml_a,
            divergence_pct=round(divergence_pct, 2),
            fallback_needed=fallback_needed,
            reason=reason,
        )

    def check_from_log(self, fvcb_a: Optional[float], ml_a: Optional[float]) -> SafetyCheckResult:
        """
        Variant that handles None inputs gracefully (e.g. ML model not loaded).

        If either value is None, defaults to passing with a warning — the
        calling code should use whichever model is available.
        """
        if fvcb_a is None or ml_a is None:
            available = fvcb_a if fvcb_a is not None else ml_a
            return SafetyCheckResult(
                passed=True,
                fvcb_a=fvcb_a or 0.0,
                ml_a=ml_a or 0.0,
                divergence_pct=0.0,
                fallback_needed=False,
                reason=(
                    f"Only one model available (value={available:.2f}). "
                    "Cannot check divergence; proceeding with available model."
                ),
            )
        return self.check(fvcb_a, ml_a)


# ---------------------------------------------------------------------------
# CLI smoke test
# ---------------------------------------------------------------------------

if __name__ == "__main__":
    rails = SafetyRails()

    cases = [
        (14.3, 14.8,  "Normal agreement (3.4%)"),
        (14.3, 16.5,  "Borderline (15.4% — over threshold)"),
        (14.3, 12.0,  "Below threshold (17.6% — over)"),
        (14.3, 14.3,  "Perfect agreement"),
        (14.3, None,  "ML unavailable"),
        (-2.0, -1.8,  "Carbon loss (night)"),
    ]

    print(f"SafetyRails — threshold={rails.threshold * 100:.0f}%\n")
    for fvcb, ml, label in cases:
        result = rails.check_from_log(fvcb, ml)
        status = "FALLBACK" if result.fallback_needed else "OK     "
        print(f"  [{status}] {label}")
        print(f"           {result.reason}")
        print()