app/models/dosing/surrogate_pkpd.py

"""Surrogate PK/PD transition."""

from __future__ import annotations

from app.models.dosing.pkpd_state import PKPDState


def step_pkpd(
    state: PKPDState,
    dose_delta: float,
    organ_factor: float = 0.0,
    interaction_factor: float = 0.0,
) -> PKPDState:
    # Effect benefits modestly from dose increases, but toxicity amplifies with organ stress + interactions.
    effective_delta = dose_delta * (1.0 - min(0.6, organ_factor * 0.4))
    new_effect = max(0.0, min(1.0, state.effect_level + 0.28 * effective_delta - 0.05 * interaction_factor))
    toxicity_gain = max(0.0, dose_delta) * (0.35 + organ_factor * 0.25 + interaction_factor * 0.2)
    new_toxicity = max(0.0, min(1.0, (state.toxicity_level * 0.85) + toxicity_gain))
    new_underdose = max(0.0, min(1.0, 1.0 - new_effect + max(0.0, -dose_delta) * 0.15))
    return PKPDState(
        effect_level=new_effect,
        toxicity_level=new_toxicity,
        underdose_risk=new_underdose,
        organ_stress=max(0.0, min(1.0, organ_factor)),
        interaction_load=max(0.0, min(1.0, interaction_factor)),
    )