################################################################################
# This file is part of SWIFT.
# Copyright (c) 2018 Bert Vandenbroucke (bert.vandenbroucke@gmail.com)
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License as published
# by the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
################################################################################

import h5py
from numpy import *

# Generates a swift IC file for the 1D Zeldovich pancake

# Parameters
T_i = 100.0  # Initial temperature of the gas (in K)
z_c = 1.0  # Redshift of caustic formation (non-linear collapse)
z_i = 100.0  # Initial redshift
gamma = 5.0 / 3.0  # Gas adiabatic index
numPart_1D = 32  # Number of particles along each dimension
fileName = "zeldovichPancake.hdf5"


# Some units
Mpc_in_m = 3.08567758e22
Msol_in_kg = 1.98848e30
Gyr_in_s = 3.08567758e19
mH_in_kg = 1.6737236e-27

# Some constants
kB_in_SI = 1.38064852e-23
G_in_SI = 6.67408e-11

# Some useful variables in h-full units
H_0 = 1.0 / Mpc_in_m * 10 ** 5  # h s^-1
rho_0 = 3.0 * H_0 ** 2 / (8 * math.pi * G_in_SI)  # h^2 kg m^-3
lambda_i = 64.0 / H_0 * 10 ** 5  # h^-1 m (= 64 h^-1 Mpc)
x_min = -0.5 * lambda_i
x_max = 0.5 * lambda_i

# SI system of units
unit_l_in_si = Mpc_in_m
unit_m_in_si = Msol_in_kg * 1.0e10
unit_t_in_si = Gyr_in_s
unit_v_in_si = unit_l_in_si / unit_t_in_si
unit_u_in_si = unit_v_in_si ** 2

# Total number of particles
numPart = numPart_1D ** 3

# ---------------------------------------------------

# Get the frequency of the initial perturbation
k_i = 2.0 * pi / lambda_i

# Get the redshift prefactor for the initial positions
zfac = (1.0 + z_c) / (1.0 + z_i)

# Set box size and interparticle distance
boxSize = x_max - x_min
delta_x = boxSize / numPart_1D

# Get the particle mass
a_i = 1.0 / (1.0 + z_i)
m_i = boxSize ** 3 * rho_0 / numPart

# Build the arrays
coords = zeros((numPart, 3))
v = zeros((numPart, 3))
ids = linspace(1, numPart, numPart)
m = zeros(numPart)
h = zeros(numPart)
u = zeros(numPart)

# Set the particles on the left
for i in range(numPart_1D):
    for j in range(numPart_1D):
        for k in range(numPart_1D):
            index = i * numPart_1D ** 2 + j * numPart_1D + k
            q = x_min + (i + 0.5) * delta_x
            coords[index, 0] = q - zfac * sin(k_i * q) / k_i - x_min
            coords[index, 1] = (j + 0.5) * delta_x
            coords[index, 2] = (k + 0.5) * delta_x
            T = T_i * (1.0 / (1.0 - zfac * cos(k_i * q))) ** (2.0 / 3.0)
            u[index] = kB_in_SI * T / (gamma - 1.0) / mH_in_kg
            h[index] = 1.2348 * delta_x
            m[index] = m_i
            v[index, 0] = -H_0 * (1.0 + z_c) / sqrt(1.0 + z_i) * sin(k_i * q) / k_i
            v[index, 1] = 0.0
            v[index, 2] = 0.0

# Unit conversion
coords /= unit_l_in_si
v /= unit_v_in_si
m /= unit_m_in_si
h /= unit_l_in_si
u /= unit_u_in_si

boxSize /= unit_l_in_si

# File
file = h5py.File(fileName, "w")

# Header
grp = file.create_group("/Header")
grp.attrs["BoxSize"] = [boxSize, boxSize, boxSize]
grp.attrs["NumPart_Total"] = [numPart, 0, 0, 0, 0, 0]
grp.attrs["NumPart_Total_HighWord"] = [0, 0, 0, 0, 0, 0]
grp.attrs["NumPart_ThisFile"] = [numPart, 0, 0, 0, 0, 0]
grp.attrs["Time"] = 0.0
grp.attrs["NumFilesPerSnapshot"] = 1
grp.attrs["MassTable"] = [0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
grp.attrs["Flag_Entropy_ICs"] = 0
grp.attrs["Dimension"] = 3

# Units
grp = file.create_group("/Units")
grp.attrs["Unit length in cgs (U_L)"] = 100.0 * unit_l_in_si
grp.attrs["Unit mass in cgs (U_M)"] = 1000.0 * unit_m_in_si
grp.attrs["Unit time in cgs (U_t)"] = 1.0 * unit_t_in_si
grp.attrs["Unit current in cgs (U_I)"] = 1.0
grp.attrs["Unit temperature in cgs (U_T)"] = 1.0

# Particle group
grp = file.create_group("/PartType0")
grp.create_dataset("Coordinates", data=coords, dtype="d")
grp.create_dataset("Velocities", data=v, dtype="f")
grp.create_dataset("Masses", data=m, dtype="f")
grp.create_dataset("SmoothingLength", data=h, dtype="f")
grp.create_dataset("InternalEnergy", data=u, dtype="f")
grp.create_dataset("ParticleIDs", data=ids, dtype="L")

file.close()

# import pylab as pl

# pl.plot(coords[:,0], v[:,0], "k.")
# pl.show()