"""
ITU-R P.1546 model for point-to-area predictions.

Valid for:
- Frequency: 30-3000 MHz
- Distance: 1-1000 km
- Time percentages: 1%, 10%, 50%

Best for: VHF/UHF broadcasting and land mobile services.
Reference: ITU-R P.1546-6 (2019)
"""

import math
from app.propagation.base import PropagationModel, PropagationInput, PropagationOutput


class ITUR_P1546Model(PropagationModel):
    """
    Simplified P.1546 implementation.

    Full implementation would include terrain clearance angle,
    mixed path (land/sea), and time variability.
    """

    @property
    def name(self) -> str:
        return "ITU-R-P.1546"

    @property
    def frequency_range(self) -> tuple:
        return (30, 3000)

    @property
    def distance_range(self) -> tuple:
        return (1000, 1000000)  # 1-1000 km

    def calculate(self, input: PropagationInput) -> PropagationOutput:
        f = input.frequency_mhz
        d = max(input.distance_m / 1000, 1.0)  # km
        h1 = max(input.tx_height_m, 1.0)

        # Nominal frequency bands
        if f < 100:
            f_nom = 100
        elif f < 600:
            f_nom = 600
        else:
            f_nom = 2000

        # Basic field strength at 1 kW ERP (from curves, simplified regression)
        E_ref = 106.9 - 20 * math.log10(d)  # dBuV/m at 1kW

        # Height gain for transmitter
        delta_h1 = 20 * math.log10(h1 / 10) if h1 > 10 else 0

        # Frequency correction
        delta_f = 20 * math.log10(f / f_nom)

        # Convert field strength to path loss
        # L = 139.3 - E + 20*log10(f) (for 50 Ohm)
        E = E_ref + delta_h1 - delta_f
        L = 139.3 - E + 20 * math.log10(f)

        return PropagationOutput(
            path_loss_db=L,
            model_name=self.name,
            is_los=d < 5,
            breakdown={
                "reference_field": E_ref,
                "height_gain": delta_h1,
                "frequency_correction": delta_f,
                "path_loss": L,
            },
        )