import math

from .health_bmi_types import Bmi, BmiCategory
from .math_round_float import round_float


def _check_range(name: str, value: float, low: float, high: float, unit: str) -> None:
    ok = not isinstance(value, bool) and isinstance(value, (int, float)) and math.isfinite(value)
    if not ok or value < low or value > high:
        raise ValueError("%s must be a number from %s to %s %s, received %r" % (name, low, high, unit, value))


def bmi(weight_kg: float, height_cm: float) -> Bmi:
    """Body mass index for an adult: weight over height squared, to one
    decimal place, and the band it falls in. The bands are published to one
    decimal place (18.5-24.9, 25-29.9, ...), so the category is read from the
    rounded index: 24.97 is reported as 25.0 and is overweight, not healthy."""
    _check_range("weightKg", weight_kg, 10, 650, "kg")
    # Height in metres (1.75) is the commonest unit slip; 50 cm is the floor.
    _check_range("heightCm", height_cm, 50, 272, "cm")
    metres = float(height_cm) / 100
    value = round_float(float(weight_kg) / (metres * metres), 1)
    category: BmiCategory
    if value < 18.5:
        category = "underweight"
    elif value <= 24.9:
        category = "healthy-weight"
    elif value <= 29.9:
        category = "overweight"
    elif value <= 34.9:
        category = "obesity-class-1"
    elif value <= 39.9:
        category = "obesity-class-2"
    else:
        category = "obesity-class-3"
    return Bmi(value=value, category=category)