Module maven_iuvs.time

import datetime
import warnings

import numpy as np
import julian
import pytz
import spiceypy as spice
from astropy.io import fits

from maven_iuvs.search import get_files


def utc_to_sol(utc):
    """
    Converts a UTC datetime object into the equivalent Martian decimal sol and year.

    Parameters
    ----------
    utc : object
        UTC datetime object.

    Returns
    -------
    sol : float
        The decimal sol date.
    my : int
        The Mars year.
    """
    # constants
    ns = 668.6  # number of sols in a Mars year
    jdref = 2442765.667  # reference Julian date corresponding to Ls = 0
    myref = 12  # jdref is the beginning of Mars year 12

    # convert datetime object to Julian date
    jd = julian.to_jd(utc, fmt='jd')

    # calculate the sol
    sol = (jd - jdref) * (86400. / 88775.245) % ns

    # calculate the Mars year
    my = int((jd - jdref) * (86400. / 88775.245) / ns + myref)

    # return the decimal sol and Mars year
    return sol, my


def et2datetime(et):
    """
    Convert an input time from ephemeris seconds past J2000 to a standard Python datetime.
    This is supposed to be included in the SpiceyPy package, but didn't show up in my installation,
    so I copied it here and modified it.

    Parameters
    ----------
    et : float
        Input epoch in ephemeris seconds past J2000.

    Returns
    -------
    Output datetime object in UTC.
    """

    # convert to UTC using ISO calendar format with 6 digits of fractional precision
    result = spice.et2utc(et, 'ISOC', 6)

    # define the ISO calendar format for datetime
    isoformat = '%Y-%m-%dT%H:%M:%S.%f'

    # return the datetime object version of the input ephemeris time
    return datetime.datetime.strptime(result,
                                      isoformat).replace(tzinfo=pytz.utc)


def find_segment_et(orbit_number, data_directory, segment='apoapse'):
    """
    Calculates the ephemeris time at the moment of apoapsis or periapsis for an orbit. Requires data files exist for
    the choice of orbit and segment. If not, use the full-mission "find_maven_apsis" function available in the "data"
    sub-module. Also requires furnishing of all SPICE kernels.

    Parameters
    ----------
    orbit_number : int
        The MAVEN orbit number.
    data_directory : str
        Absolute system path to the location containing orbit block folders ("orbit01300", orbit01400", etc.)
    segment : str
        For which orbit segment you want to calculate the ephemeris time. Options are 'apoapse' and 'periapse." Default
        choice is 'apoapse'.

    Returns
    -------
    et : float
        The ephemeris time for the chosen segment/orbit number.
    """

    # load files
    files = get_files(orbit_number, data_directory, segment=segment)
    if len(files) == 0:
        raise Exception('No %s files for orbit %i.' % (segment, orbit_number))
    else:
        hdul = fits.open(files[0])
        et_start = hdul['integration'].data['et'][0]

    # do very complicated SPICE stuff
    target = 'Mars'
    abcorr = 'NONE'
    observer = 'MAVEN'
    relate = ''
    refval = 0.
    if segment == 'periapse':
        relate = 'LOCMIN'
        refval = 3396. + 500.
    elif segment == 'apoapse':
        relate = 'LOCMAX'
        refval = 3396. + 6200.
    adjust = 0.
    step = 60.
    et = [et_start, et_start + 4800]
    cnfine = spice.utils.support_types.SPICEDOUBLE_CELL(2)
    spice.wninsd(et[0], et[1], cnfine)
    ninterval = 100
    result = spice.utils.support_types.SPICEDOUBLE_CELL(100)
    spice.gfdist(target, abcorr, observer, relate, refval, adjust, step, ninterval, cnfine, result=result)
    et = spice.wnfetd(result, 0)[0]

    # return the ephemeris time of the orbit segment
    return et


class ScienceWeek:
    # TODO: Decide if I want to prohibit users from inputting negative
    #       science weeks, or dates that result in them

    # TODO: Decide how to handle future science week (should I warn if
    #       they request science week from a future date?)
    def __init__(self):
        """ A ScienceWeek object can convert dates into MAVEN science weeks.

        Properties
        ----------
        science_start_date: datetime.date
            The date when IUVS began performing science.
        """
        self.__science_start_date = datetime.date(2014, 11, 11)

    @property
    def science_start_date(self):
        return self.__science_start_date

    def get_science_week_from_date(self, some_date):
        """ Get the science week number at an input date.

        Parameters
        ----------
        some_date: datetime.date
            The date at which to get the science week.

        Returns
        -------
        science_week: int
            The science week at the input date.
        """
        try:
            science_week = (some_date - self.__science_start_date).days // 7
            return science_week
        except TypeError:
            raise TypeError('some_date should be of type datetime.date')

    def get_current_science_week(self):
        """ Get the science week number for today.

        Returns
        -------
        science_week: int
            The current science week.
        """
        science_week = self.get_science_week_from_date(datetime.date.today())
        return science_week

    def get_science_week_start_date(self, week):
        """ Get the date when the requested science week began.

        Parameters
        ----------
        week: int
            The science week.

        Returns
        -------
        science_week_start: datetime.date
            The date when the science week started.
        """
        try:
            rounded_week = int(np.floor(week))
            if week != rounded_week:
                warnings.warn('This is a non-integer week.'
                              ' Converting it to integer...')
            science_week_start = (self.__science_start_date
                                  + datetime.timedelta(days=rounded_week * 7))
            return science_week_start
        except TypeError:
            raise TypeError(f'week should be an int, not a {type(week)}.')

    def get_science_week_end_date(self, week):
        """ Get the date when the requested science week ended.

        Parameters
        ----------
        week: int
            The science week.

        Returns
        -------
        science_week_end: datetime.date
            The date when the science week ended.
        """
        return (self.get_science_week_start_date(week + 1)
                - datetime.timedelta(days=1))

    def get_science_week_date_range(self, week):
        """ Get the date range corresponding to the input science week.

        Parameters
        ----------
        week: int
            The science week.

        Returns
        -------
        date_range: tuple
            The start and end dates of the science week.
        """
        date_range = (self.get_science_week_start_date(week),
                      self.get_science_week_end_date(week))
        return date_range

    # TODO: Decide if I want a subclass to handle requests related to
    #       science week (ex. get_orbit_range_from_science_week)
    #
    #       Pro: It's easy to code after making the database and it'd
    #       be helpful
    #
    #       Con: It might be easier to make 1 utility for database
    #       searching and tell users to apply it to science week