###############################################################################
# This file is part of SWIFT.
# Copyright (c) 2017 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/>.
#
##############################################################################

# Generates a distorted 1D grid with a density profile that balances out the
# external sine wave potential if run with an isothermal equation of state.

import numpy as np
import h5py

# constant thermal energy
# the definition below assumes the same thermal energy is defined in const.h,
# and also that the code was configured with an adiabatic index of 5./3.
uconst = 20.2615290634
cs2 = 2.0 * uconst / 3.0
A = 10.0

fileName = "sineWavePotential.hdf5"
numPart = 1000
boxSize = 1.0

coords = np.zeros((numPart, 3))
v = np.zeros((numPart, 3))
m = np.zeros(numPart) + 1000.0 / numPart
h = np.zeros(numPart) + 2.0 / numPart
u = np.zeros(numPart) + uconst
ids = np.arange(numPart, dtype="L")
rho = np.zeros(numPart)

# first set the positions, as we try to do a reasonable volume estimate to
# set the masses
for i in range(numPart):
    coords[i, 0] = (i + np.random.random()) / numPart

for i in range(numPart):
    # reasonable mass estimate (actually not really good, but better than assuming
    # a constant volume)
    if i == 0:
        V = 0.5 * (coords[1, 0] - coords[-1, 0] + 1.0)
    elif i == numPart - 1:
        V = 0.5 * (coords[0, 0] + 1.0 - coords[-2, 0])
    else:
        V = 0.5 * (coords[i + 1, 0] - coords[i - 1, 0])
    rho[i] = 1000.0 * np.exp(
        -0.5 * A / np.pi / cs2 * np.cos(2.0 * np.pi * coords[i, 0])
    )
    m[i] = rho[i] * V

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

# Header
grp = file.create_group("/Header")
grp.attrs["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"] = 1

# Units
grp = file.create_group("/Units")
grp.attrs["Unit length in cgs (U_L)"] = 1.0
grp.attrs["Unit mass in cgs (U_M)"] = 1.0
grp.attrs["Unit time in cgs (U_t)"] = 1.0
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")
grp.create_dataset("Density", data=rho, dtype="f")

file.close()
