"""Radio propagation model."""

import math
import random
from sim import config


def calculate_distance(x1: float, y1: float, x2: float, y2: float) -> float:
    """Calculate Euclidean distance between two points."""
    return math.sqrt((x2 - x1) ** 2 + (y2 - y1) ** 2)


def calculate_rssi(tx_power: float, distance: float) -> float:
    """
    Calculate RSSI using free-space path loss model.

    RSSI = TX_POWER - 10*n*log10(d) + Gaussian_noise

    Args:
        tx_power: Transmit power in dBm
        distance: Distance in meters

    Returns:
        RSSI in dBm
    """
    if distance < 1.0:
        distance = 1.0  # Avoid log(0)

    # Path loss
    path_loss = 10 * config.PATH_LOSS_EXPONENT * math.log10(distance)

    # Gaussian noise
    noise = random.gauss(0, config.NOISE_SIGMA)

    rssi = tx_power - path_loss + noise
    return rssi


def can_receive(rssi: float) -> bool:
    """Check if packet can be received based on RSSI threshold."""
    return rssi >= config.RSSI_THRESHOLD


def calculate_link_penalty(rssi: float) -> float:
    """
    Calculate link penalty for routing.

    penalty = max(0, (RSSI_THRESHOLD - RSSI) / SCALE)

    Args:
        rssi: Received signal strength

    Returns:
        Link penalty (higher = worse link)
    """
    return max(0.0, (config.RSSI_THRESHOLD - rssi) / config.LINK_PENALTY_SCALE)


def is_link_viable(rssi: float) -> bool:
    """Check if link is viable for communication."""
    return can_receive(rssi)