# -*- coding: utf-8 -*-
# Copyright (C) Duncan Macleod (2014-2020)
#
# This file is part of GWpy.
#
# GWpy is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# GWpy 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 General Public License
# along with GWpy.  If not, see <http://www.gnu.org/licenses/>.

"""This module provides methods to calculate the astrophysical sensitive
distance of an instrumental power-spectral density.
"""

import warnings

from functools import wraps
from math import pi

from scipy.integrate import trapz

from astropy import (
    units,
    constants,
)

from ..spectrogram import Spectrogram
from ..timeseries import TimeSeries
from ..utils import round_to_power
from ..utils.decorators import deprecated_function

__author__ = 'Duncan Macleod <duncan.macleod@ligo.org>'
__credits__ = 'Alex Urban <alexander.urban@ligo.org>'

DEFAULT_FFT_METHOD = "median"


def _get_isco_frequency(mass1, mass2):
    """Determine the innermost stable circular orbit (ISCO) frequency

    Parameters
    ----------
    mass1 : `float`
        the mass (in solar masses) of the first binary component

    mass2 : `float`
        the mass (in solar masses) of the second binary component

    Returns
    -------
    fisco : `~astropy.units.Quantity`
        linear frequency (Hz) of the innermost stable circular orbit
    """
    mtotal = units.Quantity(mass1 + mass2, 'solMass').to('kg')
    return (
        constants.c ** 3 / (constants.G * 6**1.5 * pi * mtotal)
    ).to('Hz')


def _get_spectrogram(hoft, **kwargs):
    """Check that the input is a spectrogram, or compute one if compatible

    Parameters
    ----------
    hoft : `~gwpy.timeseries.TimeSeries` or `~gwpy.spectrogram.Spectrogram`
        record of gravitational-wave strain output from a detector

    **kwargs : `dict`, optional
        additional keyword arguments to
        `~gwpy.timeseries.TimeSeries.spectrogram`

    Returns
    -------
    hoft : `~gwpy.spectrogram.Spectrogram`
        a time-frequency `Spectrogram` of the input
    """
    if not isinstance(hoft, Spectrogram):
        try:
            hoft = hoft.spectrogram(**kwargs)
        except (AttributeError, TypeError):
            msg = ('Could not produce a spectrogram from the input, please '
                   'pass an instance of gwpy.timeseries.TimeSeries or '
                   'gwpy.spectrogram.Spectrogram')
            raise TypeError(msg)
    return hoft


def _preformat_psd(func):
    @wraps(func)
    def decorated_func(psd, *args, **kwargs):
        if psd.unit != 1/units.Hz:  # force PSD to have the right units
            psd = psd.view()
            psd.override_unit('1/Hz')
        return func(psd, *args, **kwargs)
    return decorated_func


@_preformat_psd
def sensemon_range_psd(psd, snr=8, mass1=1.4, mass2=1.4, horizon=False):
    """Approximate the inspiral sensitive distance PSD from a GW strain PSD

    This method returns the power spectral density (in ``Mpc**2 / Hz``) to
    which a compact binary inspiral with the given component masses would
    be detectable given the instrumental PSD. The calculation is defined in:

    https://dcc.ligo.org/LIGO-T030276/public

    Parameters
    ----------
    psd : `~gwpy.frequencyseries.FrequencySeries`
        the instrumental power-spectral-density data

    snr : `float`, optional
        the signal-to-noise ratio for which to calculate range,
        default: `8`

    mass1 : `float`, `~astropy.units.Quantity`, optional
        the mass (`float` assumed in solar masses) of the first binary
        component, default: `1.4`

    mass2 : `float`, `~astropy.units.Quantity`, optional
        the mass (`float` assumed in solar masses) of the second binary
        component, default: `1.4`

    horizon : `bool`, optional
        if `True`, return the maximal 'horizon' sensitive distance, otherwise
        return the angle-averaged range, default: `False`

    Returns
    -------
    rspec : `~gwpy.frequencyseries.FrequencySeries`
        the calculated inspiral sensitivity PSD [Mpc^2 / Hz]
    """
    frange = (psd.frequencies > 0)
    # compute total mass and chirp mass
    mass1 = units.Quantity(mass1, 'solMass').to('kg')
    mass2 = units.Quantity(mass2, 'solMass').to('kg')
    mtotal = mass1 + mass2
    mchirp = (mass1 * mass2) ** (3/5.) / mtotal ** (1/5.)
    # calculate integrand with pre-factor
    prefactor = (
        (  # numerator
            (16 if horizon else 1.77**2)
            * 5
            * constants.c ** (1/3.)
            * (mchirp * constants.G / constants.c ** 2) ** (5/3.)
        )  # denominator
        / (
            96
            * pi ** (4/3.)
            * snr ** 2
        )
    )
    return (  # inspiral range PSD, avoiding DC value
        1 / psd[frange] * psd.frequencies[frange] ** (-7/3.) * prefactor
    ).to('Mpc^2 / Hz')


def sensemon_range(psd, snr=8, mass1=1.4, mass2=1.4, fmin=None, fmax=None,
                   horizon=False):
    """Approximate the inspiral sensitive distance from a GW strain PSD

    This method returns the distance (in megaparsecs) to which a compact
    binary inspiral with the given component masses would be detectable
    given the instrumental PSD. The calculation is as defined in:

    https://dcc.ligo.org/LIGO-T030276/public

    Parameters
    ----------
    psd : `~gwpy.frequencyseries.FrequencySeries`
        the instrumental power-spectral-density data

    snr : `float`, optional
        the signal-to-noise ratio for which to calculate range,
        default: `8`

    mass1 : `float`, `~astropy.units.Quantity`, optional
        the mass (`float` assumed in solar masses) of the first binary
        component, default: `1.4`

    mass2 : `float`, `~astropy.units.Quantity`, optional
        the mass (`float` assumed in solar masses) of the second binary
        component, default: `1.4`

    fmin : `float`, optional
        the lower frequency cut-off of the integral, default: `psd.df`

    fmax : `float`, optional
        the maximum frequency limit of the integral, defaults to
        innermost stable circular orbit (ISCO) frequency

    horizon : `bool`, optional
        if `True`, return the maximal 'horizon' sensitive distance, otherwise
        return the angle-averaged range, default: `False`

    Returns
    -------
    range : `~astropy.units.Quantity`
        the calculated inspiral range [Mpc]

    Examples
    --------
    Grab some data for LIGO-Livingston around GW150914 and generate a PSD:

    >>> from gwpy.timeseries import TimeSeries
    >>> hoft = TimeSeries.fetch_open_data('H1', 1126259446, 1126259478)
    >>> hoff = hoft.psd(fftlength=4)

    Now we can calculate the :func:`inspiral_range`:

    >>> from gwpy.astro import sensemon_range
    >>> r = sensemon_range(hoff, fmin=30)
    >>> print(r)
    70.4612102889 Mpc
    """
    fisco = _get_isco_frequency(mass1, mass2)
    # format frequency limits
    fmin = units.Quantity(fmin or psd.df, 'Hz')  # avoid DC value
    fmax = units.Quantity(fmax or fisco, 'Hz')
    if fmax > fisco:
        warnings.warn("Upper frequency bound greater than %s-%s ISCO "
                      "frequency of %s, using ISCO" % (mass1, mass2, fisco))
        fmax = fisco
    # integrate and return
    f = psd.frequencies.to('Hz')
    frange = (f >= fmin) & (f < fmax)
    integrand = sensemon_range_psd(psd[frange], snr=snr, mass1=mass1,
                                   mass2=mass2, horizon=horizon)
    return (units.Quantity(
        trapz(integrand.value, f.value[frange]),
        unit=integrand.unit * units.Hertz,
    ) ** (1/2.)).to('Mpc')


_DEPRECATED_SENSEMON_MESSAGE = (
    "the {} function currently uses the LIGO SenseMon (LIGO-T030276) "
    "estimation, but will be upgraded in gwpy-2.2.0 to use a model "
    "with cosmological corrections; to keep using the SenseMon "
    "estimation, please modify your usage to call "
    "gwpy.astro.{{0.__name__}}."
)
inspiral_range_psd = deprecated_function(
    sensemon_range_psd,
    _DEPRECATED_SENSEMON_MESSAGE.format("inspiral_range_psd"),
)


inspiral_range = deprecated_function(
    sensemon_range,
    _DEPRECATED_SENSEMON_MESSAGE.format("inspiral_range"),
)


@_preformat_psd
def burst_range_spectrum(psd, snr=8, energy=1e-2):
    """Calculate the frequency-dependent GW burst range from a strain PSD

    Parameters
    ----------
    psd : `~gwpy.frequencyseries.FrequencySeries`
        the instrumental power-spectral-density data

    snr : `float`, optional
        the signal-to-noise ratio for which to calculate range,
        default: `8`

    energy : `float`, optional
        the relative energy output of the GW burst,
        default: `0.01` (GRB-like burst)

    Returns
    -------
    rangespec : `~gwpy.frequencyseries.FrequencySeries`
        the burst range `FrequencySeries` [Mpc (default)]
    """
    frange = (psd.frequencies > 0)
    # calculate frequency dependent range in parsecs
    a = (
        constants.G * energy * constants.M_sun * 0.4
        / (pi**2 * constants.c)
    ) ** (1/2.)
    return (  # burst range spectrum, avoiding DC value
        psd[frange] ** (-1/2.) * a / (snr * psd.frequencies[frange])
    ).to('Mpc')


def burst_range(psd, snr=8, energy=1e-2, fmin=100, fmax=500):
    """Calculate the integrated GRB-like GW burst range from a strain PSD

    Parameters
    ----------
    psd : `~gwpy.frequencyseries.FrequencySeries`
        the instrumental power-spectral-density data

    snr : `float`, optional
        the signal-to-noise ratio for which to calculate range,
        default: ``8``

    energy : `float`, optional
        the relative energy output of the GW burst, defaults to ``1e-2``
        for a GRB-like burst

    fmin : `float`, optional
        the lower frequency cutoff of the burst range integral,
        default: ``100 Hz``

    fmax : `float`, optional
        the upper frequency cutoff of the burst range integral,
        default: ``500 Hz``

    Returns
    -------
    range : `~astropy.units.Quantity`
        the GRB-like-burst sensitive range [Mpc (default)]

    Examples
    --------
    Grab some data for LIGO-Livingston around GW150914 and generate a PSD

    >>> from gwpy.timeseries import TimeSeries
    >>> hoft = TimeSeries.fetch_open_data('H1', 1126259446, 1126259478)
    >>> hoff = hoft.psd(fftlength=4)

    Now we can calculate the :func:`burst_range`:

    >>> from gwpy.astro import burst_range
    >>> r = burst_range(hoff, fmin=30)
    >>> print(r)
    42.5055584195 Mpc
    """
    f = psd.frequencies.to('Hz').value
    # restrict integral
    fmin = fmin or psd.df.to('Hz').value
    fmax = fmax or f[-1].value
    frange = (f >= fmin) & (f < fmax)
    # calculate integrand and integrate
    integrand = burst_range_spectrum(
        psd[frange], snr=snr, energy=energy) ** 3
    out = trapz(integrand.value, f[frange])
    # normalize and return
    return (units.Quantity(
        out / (fmax - fmin),
        unit=integrand.unit,
    ) ** (1/3.)).to('Mpc')


def range_timeseries(hoft, stride=None, fftlength=None, overlap=None,
                     window='hann', method=DEFAULT_FFT_METHOD, nproc=1,
                     **rangekwargs):
    """Measure timeseries trends of astrophysical detector range (Mpc)
    directly from strain

    Parameters
    ----------
    hoft : `~gwpy.timeseries.TimeSeries` or `~gwpy.spectrogram.Spectrogram`
        record of gravitational-wave strain output from a detector

    stride : `float`, optional
        desired step size (seconds) of range timeseries, required if
        `hoft` is an instance of `TimeSeries`

    fftlength : `float`, optional
        number of seconds in a single FFT

    overlap : `float`, optional
        number of seconds of overlap between FFTs, defaults to the
        recommended overlap for the given window (if given), or 0

    window : `str`, `numpy.ndarray`, optional
        window function to apply to timeseries prior to FFT, see
        :func:`scipy.signal.get_window` for details on acceptable
        formats

    method : `str`, optional
        FFT-averaging method, defaults to median averaging, see
        :meth:`~gwpy.timeseries.TimeSeries.spectrogram` for
        more details

    nproc : `int`, optional
        number of CPUs to use in parallel processing of FFTs, default: 1

    **rangekwargs : `dict`, optional
        additional keyword arguments to :func:`burst_range` or
        :func:`inspiral_range` (see "Notes" below), defaults to
        inspiral range with `mass1 = mass2 = 1.4` solar masses

    Returns
    -------
    out : `~gwpy.timeseries.TimeSeries`
        timeseries trends of astrophysical range

    Notes
    -----
    This method is designed to quantify a gravitational-wave detector's
    sensitive range as a function of time. It supports the range to
    compact binary inspirals and to unmodelled GW bursts, each a class
    of transient event.

    See also
    --------
    gwpy.timeseries.TimeSeries.spectrogram
        for the underlying power spectral density estimator
    inspiral_range
        for the function that computes inspiral range
    burst_range
        for the function that computes burst range
    range_spectrogram
        for a `~gwpy.spectrogram.Spectrogram` of the range integrand
    """
    rangekwargs = rangekwargs or {'mass1': 1.4, 'mass2': 1.4}
    range_func = (burst_range if 'energy' in rangekwargs
                  else inspiral_range)
    hoft = _get_spectrogram(
        hoft, stride=stride, fftlength=fftlength, overlap=overlap,
        window=window, method=method, nproc=nproc)
    # loop over time bins
    out = TimeSeries(
        [range_func(psd, **rangekwargs).value for psd in hoft],
    )
    # finalise output
    out.__array_finalize__(hoft)
    out.override_unit('Mpc')
    return out


def range_spectrogram(hoft, stride=None, fftlength=None, overlap=None,
                      window='hann', method=DEFAULT_FFT_METHOD, nproc=1,
                      **rangekwargs):
    """Calculate the average range or range power spectrogram (Mpc or
    Mpc^2 / Hz) directly from strain

    Parameters
    ----------
    hoft : `~gwpy.timeseries.TimeSeries`  or `~gwpy.spectrogram.Spectrogram`
        record of gravitational-wave strain output from a detector

    stride : `float`, optional
        number of seconds in a single PSD (i.e., step size of spectrogram),
        required if `hoft` is an instance of `TimeSeries`

    fftlength : `float`, optional
        number of seconds in a single FFT

    overlap : `float`, optional
        number of seconds of overlap between FFTs, defaults to the
        recommended overlap for the given window (if given), or 0

    window : `str`, `numpy.ndarray`, optional
        window function to apply to timeseries prior to FFT, see
        :func:`scipy.signal.get_window` for details on acceptable
        formats

    method : `str`, optional
        FFT-averaging method, defaults to median averaging, see
        :meth:`~gwpy.timeseries.TimeSeries.spectrogram` for
        more details

    nproc : `int`, optional
        number of CPUs to use in parallel processing of FFTs, default: 1

    fmin : `float`, optional
        low frequency cut-off (Hz), defaults to `1/fftlength`

    fmax : `float`, optional
        high frequency cut-off (Hz), defaults to Nyquist frequency of `hoft`

    **rangekwargs : `dict`, optional
        additional keyword arguments to :func:`burst_range_spectrum` or
        :func:`inspiral_range_psd` (see "Notes" below), defaults to
        inspiral range with `mass1 = mass2 = 1.4` solar masses

    Returns
    -------
    out : `~gwpy.spectrogram.Spectrogram`
        time-frequency spectrogram of astrophysical range

    Notes
    -----
    This method is designed to show the contribution to a
    gravitational-wave detector's sensitive range across frequency bins
    as a function of time. It supports the range to compact binary
    inspirals and to unmodelled GW bursts, each a class of transient
    event.

    If inspiral range is requested and `fmax` exceeds the frequency of the
    innermost stable circular orbit (ISCO), the output will extend only up
    to the latter.

    See also
    --------
    gwpy.timeseries.TimeSeries.spectrogram
        for the underlying power spectral density estimator
    inspiral_range_psd
        for the function that computes inspiral range integrand
    burst_range_spectrum
        for the function that computes burst range integrand
    range_timeseries
        for `TimeSeries` trends of the astrophysical range
    """
    rangekwargs = rangekwargs or {'mass1': 1.4, 'mass2': 1.4}
    range_func = (burst_range_spectrum if 'energy' in rangekwargs
                  else inspiral_range_psd)
    hoft = _get_spectrogram(
        hoft, stride=stride, fftlength=fftlength, overlap=overlap,
        window=window, method=method, nproc=nproc)
    # set frequency limits
    f = hoft.frequencies.to('Hz')
    fmin = units.Quantity(
        rangekwargs.pop('fmin', hoft.df),
        'Hz',
    )
    fmax = units.Quantity(
        rangekwargs.pop(
            'fmax',
            round_to_power(f[-1].value, which='lower'),
        ),
        'Hz',
    )
    frange = (f >= fmin) & (f < fmax)
    # loop over time bins
    out = Spectrogram(
        [range_func(psd[frange], **rangekwargs).value for psd in hoft],
    )
    # finalise output
    out.__array_finalize__(hoft)
    out.override_unit('Mpc' if 'energy' in rangekwargs
                      else 'Mpc^2 / Hz')
    out.f0 = fmin
    return out
