# Licensed under a 3-clause BSD style license - see LICENSE.rst
import warnings

import numpy as np

from astropy.io import registry, fits
from astropy.table import Table
from astropy.time import Time, TimeDelta

from astropy.timeseries.sampled import TimeSeries

__all__ = ["kepler_fits_reader"]


def kepler_fits_reader(filename):
    """
    This serves as the FITS reader for KEPLER or TESS files within
    astropy-timeseries.

    This function should generally not be called directly, and instead this
    time series reader should be accessed with the
    :meth:`~astropy.timeseries.TimeSeries.read` method::

        >>> from astropy.timeseries import TimeSeries
        >>> ts = TimeSeries.read('kplr33122.fits', format='kepler.fits')  # doctest: +SKIP

    Parameters
    ----------
    filename : `str` or `pathlib.Path`
        File to load.

    Returns
    -------
    ts : `~astropy.timeseries.TimeSeries`
        Data converted into a TimeSeries.
    """
    hdulist = fits.open(filename)
    # Get the lightcurve HDU
    telescope = hdulist[0].header['telescop'].lower()

    if telescope == 'tess':
        hdu = hdulist['LIGHTCURVE']
    elif telescope == 'kepler':
        hdu = hdulist[1]
    else:
        raise NotImplementedError("{} is not implemented, only KEPLER or TESS are "
                                  "supported through this reader".format(hdulist[0].header['telescop']))

    if hdu.header['EXTVER'] > 1:
        raise NotImplementedError("Support for {} v{} files not yet "
                                  "implemented".format(hdu.header['TELESCOP'], hdu.header['EXTVER']))

    # Check time scale
    if hdu.header['TIMESYS'] != 'TDB':
        raise NotImplementedError("Support for {} time scale not yet "
                                  "implemented in {} reader".format(hdu.header['TIMESYS'], hdu.header['TELESCOP']))

    tab = Table.read(hdu, format='fits')

    # Some KEPLER files have a T column instead of TIME.
    if "T" in tab.colnames:
        tab.rename_column("T", "TIME")

    for colname in tab.colnames:
        # Fix units
        if tab[colname].unit == 'e-/s':
            tab[colname].unit = 'electron/s'
        if tab[colname].unit == 'pixels':
            tab[colname].unit = 'pixel'

        # Rename columns to lowercase
        tab.rename_column(colname, colname.lower())

    # Filter out NaN rows
    nans = np.isnan(tab['time'].data)
    if np.any(nans):
        warnings.warn('Ignoring {} rows with NaN times'.format(np.sum(nans)))
    tab = tab[~nans]

    # Time column is dependent on source and we correct it here
    reference_date = Time(hdu.header['BJDREFI'], hdu.header['BJDREFF'],
                          scale=hdu.header['TIMESYS'].lower(), format='jd')
    time = reference_date + TimeDelta(tab['time'].data)
    time.format = 'isot'

    # Remove original time column
    tab.remove_column('time')

    return TimeSeries(time=time, data=tab)


registry.register_reader('kepler.fits', TimeSeries, kepler_fits_reader)
registry.register_reader('tess.fits', TimeSeries, kepler_fits_reader)
