import numpy as np

# constants depending on source models
K_BRUNE = 0.37
K_MADARIAGA_P = 0.32
K_MADARIAGA_S = 0.21
# averages of  radiation coefficients
G_P = 0.52
G_S = 0.63


def spectrum2moment(spectral_level, density, velocity, distance, g):
    return spectral_level * 4.0 * np.pi * density * velocity ** 3 * distance / g


def damping(q_factor, frequencies, travel_time):
    """Exponential damping"""
    return np.exp(np.pi * frequencies * travel_time / q_factor)


def mm(mo):
    """Calculate moment magnitude from the spectral level (Mo)
    :return moment magnitude (float):
    """
    return (np.log10(mo) - 9.1) / 1.5


def m0(mw):
    """Calculate the spectral level (Mo) from the moment magnitude (Mw)
    :return spectral level (float):
    """
    return 10 ** (mw * 1.5 + 9.1)


def calc_source_size(s_vel, corner_freq, k):
    """Calculate source radius"""
    return k * s_vel / corner_freq


def calc_stress_drop(seismic_moment, source_radius):
    """Calculate stress drop"""
    return 7 / 16 * seismic_moment / source_radius ** 3