from __future__ import (absolute_import, division, print_function)

from .extension import _pw, _tv, _tk

from .constants import Constants

from .util import extract_vars

from .metadecorators import copy_and_set_metadata

@copy_and_set_metadata(copy_varname="T", name="pw",

remove_dims=("bottom_top",),

description="precipitable water",

MemoryOrder="XY",

units="kg m-2")

def get_pw(wrfin, timeidx=0, method="cat", squeeze=True, cache=None,

meta=True, _key=None):

"""Return the preciptiable water.

This functions extracts the necessary variables from the NetCDF file

object in order to perform the calculation.

Args:

wrfin (:class:`netCDF4.Dataset`, :class:`Nio.NioFile`, or an \

iterable): WRF-ARW NetCDF

data as a :class:`netCDF4.Dataset`, :class:`Nio.NioFile`

or an iterable sequence of the aforementioned types.

timeidx (:obj:`int` or :data:`wrf.ALL_TIMES`, optional): The

desired time index. This value can be a positive integer,

negative integer, or

:data:`wrf.ALL_TIMES` (an alias for None) to return

all times in the file or sequence. The default is 0.

method (:obj:`str`, optional): The aggregation method to use for

sequences. Must be either 'cat' or 'join'.

'cat' combines the data along the Time dimension.

'join' creates a new dimension for the file index.

The default is 'cat'.

squeeze (:obj:`bool`, optional): Set to False to prevent dimensions

with a size of 1 from being automatically removed from the shape

of the output. Default is True.

cache (:obj:`dict`, optional): A dictionary of (varname, ndarray)

that can be used to supply pre-extracted NetCDF variables to the

computational routines. It is primarily used for internal

purposes, but can also be used to improve performance by

eliminating the need to repeatedly extract the same variables

used in multiple diagnostics calculations, particularly when using

large sequences of files.

Default is None.

meta (:obj:`bool`, optional): Set to False to disable metadata and

return :class:`numpy.ndarray` instead of

:class:`xarray.DataArray`. Default is True.

_key (:obj:`int`, optional): A caching key. This is used for internal

purposes only. Default is None.

Returns:

:class:`xarray.DataArray` or :class:`numpy.ndarray`: The preciptable

water. If xarray is

enabled and the *meta* parameter is True, then the result will be a

:class:`xarray.DataArray` object. Otherwise, the result will be a

:class:`numpy.ndarray` object with no metadata.

"""

varnames = ("T", "P", "PB", "PH", "PHB", "QVAPOR")

ncvars = extract_vars(wrfin, timeidx, varnames, method, squeeze, cache,

meta=False, _key=_key)

t = ncvars["T"]

p = ncvars["P"]

pb = ncvars["PB"]

ph = ncvars["PH"]

phb = ncvars["PHB"]

qv = ncvars["QVAPOR"]

full_p = p + pb

ht = (ph + phb)/Constants.G

full_t = t + Constants.T_BASE

tk = _tk(full_p, full_t)

tv = _tv(tk, qv)

return _pw(full_p, tv, qv, ht)