import numpy as np


def get_data():
    with open('../data/sndata.txt', 'r') as f:
        lines = f.readlines()[5:]  # skip header
        z = []
        d_L = []
        sigma_d_L = []
        for line in lines:
            parts = line.split()
            z.append(float(parts[0]))
            d_L.append(float(parts[1]))       # Gpc
            sigma_d_L.append(float(parts[2])) # Gpc

    return z, d_L, sigma_d_L

def chi2(z_model, d_L_model, z_obs, d_L_obs, sigma_d_L):
    # Interpolate model at observed redshifts
    d_L_ipl_interp = np.interp(z_obs, z_model[::-1], d_L_model[::-1])

    return np.sum(((d_L_ipl_interp - d_L_obs) / sigma_d_L) ** 2)