from __future__ import annotations

from dataclasses import dataclass
from math import exp

from app.config import get_settings


@dataclass(frozen=True)
class P833Coefficients:
    gamma_db_per_m: float
    max_attenuation_db: float


WORLDCOVER_P833: dict[str, P833Coefficients] = {
    "tree_cover": P833Coefficients(gamma_db_per_m=0.20, max_attenuation_db=30.0),
    "mangroves": P833Coefficients(gamma_db_per_m=0.22, max_attenuation_db=32.0),
    "shrubland": P833Coefficients(gamma_db_per_m=0.10, max_attenuation_db=12.0),
    "grassland": P833Coefficients(gamma_db_per_m=0.05, max_attenuation_db=6.0),
    "cropland": P833Coefficients(gamma_db_per_m=0.04, max_attenuation_db=5.0),
    "herbaceous_wetland": P833Coefficients(gamma_db_per_m=0.08, max_attenuation_db=10.0),
    "unknown": P833Coefficients(gamma_db_per_m=0.15, max_attenuation_db=25.0),
}


def p833_coefficients_for_class(class_name: str) -> P833Coefficients:
    if class_name in WORLDCOVER_P833:
        return WORLDCOVER_P833[class_name]
    settings = get_settings()
    return P833Coefficients(
        gamma_db_per_m=settings.p833_gamma_db_per_m,
        max_attenuation_db=settings.p833_max_attenuation_db,
    )


def p833_attenuation(
    depth_m: float,
    freq_hz: float,
    forest_type: str,
    coefficients: P833Coefficients | None = None,
) -> float:
    if depth_m <= 0:
        return 0.0
    if freq_hz <= 0:
        raise ValueError("freq_hz must be positive")

    coeff = coefficients or p833_coefficients_for_class(forest_type)
    if coeff.max_attenuation_db <= 0:
        raise ValueError("max_attenuation_db must be positive")
    return coeff.max_attenuation_db * (
        1 - exp(-(depth_m * coeff.gamma_db_per_m) / coeff.max_attenuation_db)
    )