# AST3220, Cosmo I, project 2 -- Big Bang Nucleosynthesis
# Jakob Borg, UiO, 2025
# Module providing the background cosmology for the BBN calculations.

# Imports:
...



class BackgroundBBN:
    def __init__(self, Omega_b0 = 0.05, N_eff = 3.0):
        """
        Initialize the background cosmology defined by input parameters.

        Parameters
        ----------
        Omega_b0 : float, optional
            The relative baryon density, by default 0.05
        N_eff : float, optional
            The effective number of neutrinos, by default 3.0
        """

        # Define constants and parameters:
        self.Omega_b0 = Omega_b0
        self.N_eff = N_eff
        self.H0 = ...
        self.rho_crit0 = ...
        self.Omega_r0 = ...

    def get_a(self, T):
        """
        Compute the scale factor as a function of temperature.

        Parameters
        ----------
        T : float or np.ndarray
            The temperature in Kelvin.

        Returns
        -------
        float or np.ndarray
            The scale factor.
        """
        a = ...
        return a

    def get_Hubble(self, T):
        """
        Compute the Hubble parameter as a function of temperature.

        Parameters
        ----------
        T : float or np.ndarray
            The temperature in Kelvin.

        Returns
        -------
        float or np.ndarray
            The Hubble parameter in 1/s.
        """
        H = ...
        return H

    def get_rho_b(self, T):
        """
        Compute the energy density of baryons as a function of temperature.

        Parameters
        ----------
        T : float or np.ndarray
            The temperature in Kelvin.

        Returns
        -------
        float or np.ndarray
            The energy density of baryons in g/cm^3.
        """
        rho_b = ...
        return rho_b