"""
Routines for reading GCPEX D3R files.

"""

import datetime

import numpy as np
import netCDF4

from ..config import FileMetadata
from ..io.common import make_time_unit_str, _test_arguments
from ..core.radar import Radar


D3R_FIELD_NAMES = {
    # corrected reflectivity, horizontal
    'Reflectivity': 'reflectivity',
    # corrected reflectivity, vertical
    'DBZV': 'reflectivity',
    # differential reflectivity
    'DifferentialReflectivity': 'differential_reflectivity',
    'CrossPolCorrelation': 'cross_correlation_ratio',
    'ClutterPowerH': 'clutter_power_h',
    'ClutterPowerV': 'clutter_power_v',
    'DifferentialPhase': 'differential_phase',
    'KDP': 'specific_differential_phase',
    'NormalizedCoherentPower': 'normalized_coherent_power',
    'Signal+Clutter_toNoise_H': 'signal_to_noise_ratio',
    'Velocity': 'velocity',
    'SpectralWidth': 'spectrum_width',
    'SignalPower_H': 'signal_power_h',
}


def read_d3r_gcpex_nc(filename, field_names=None, additional_metadata=None,
                      file_field_names=False, exclude_fields=None,
                      include_fields=None, read_altitude_from_nc=False, **kwargs):
    """
    Read a D3R GCPEX netCDF file.

    Parameters
    ----------
    filename : str
        Name of the ODIM_H5 file to read.
    field_names : dict, optional
        Dictionary mapping ODIM_H5 field names to radar field names. If a
        data type found in the file does not appear in this dictionary or has
        a value of None it will not be placed in the radar.fields dictionary.
        A value of None, the default, will use the mapping defined in the
        Py-ART configuration file.
    additional_metadata : dict of dicts, optional
        Dictionary of dictionaries to retrieve metadata from during this read.
        This metadata is not used during any successive file reads unless
        explicitly included.  A value of None, the default, will not
        introduct any addition metadata and the file specific or default
        metadata as specified by the Py-ART configuration file will be used.
    file_field_names : bool, optional
        True to use the MDV data type names for the field names. If this
        case the field_names parameter is ignored. The field dictionary will
        likely only have a 'data' key, unless the fields are defined in
        `additional_metadata`.
    exclude_fields : list or None, optional
        List of fields to exclude from the radar object. This is applied
        after the `file_field_names` and `field_names` parameters. Set
        to None to include all fields specified by include_fields.
    include_fields : list or None, optional
        List of fields to include from the radar object. This is applied
        after the `file_field_names` and `field_names` parameters. Set
        to None to include all fields not specified by exclude_fields.
    read_altitude_from_nc : bool, optional
        True if you want the altitude value to be read from the provider netCDF file.
        False will default to the value np.array([295.], dtype='float64')

    Returns
    -------
    radar : Radar
        Radar object containing data from ODIM_H5 file.

    """
    # TODO before moving to pyart.io
    # * unit test
    # * add default field mapping, etc to default config
    # * auto-detect file type with pyart.io.read function
    # * instrument parameters
    # * add additional checks for HOW attributes
    # * support for other objects (SCAN, XSEC)

    # test for non empty kwargs
    _test_arguments(kwargs)

    # create metadata retrieval object
    if field_names is None:
        field_names = D3R_FIELD_NAMES
    filemetadata = FileMetadata('cfradial', field_names, additional_metadata,
                                file_field_names, exclude_fields,
                                include_fields)

    # read the data
    ncobj = netCDF4.Dataset(filename)
    ncvars = ncobj.variables

    # One sweep per file
    nsweeps = 1

    # latitude, longitude and altitude
    latitude = filemetadata('latitude')
    longitude = filemetadata('longitude')
    altitude = filemetadata('altitude')

    latitude['data'] = np.array([ncobj.Latitude], dtype='float64')
    longitude['data'] = np.array([ncobj.Longitude], dtype='float64')
    altitude_list = [ncobj.Altitude] if read_altitude_from_nc else [295.]
    altitude['data'] = np.array(altitude_list, dtype='float64')

    # metadata
    metadata = filemetadata('metadata')
    metadata['source'] = "Colorado State EE - chandrasekar"
    metadata['original_container'] = 'D3R_gcpex_nc'
    metadata['nc_conventions'] = ncobj.NetCDFRevision

    metadata['version'] = ncobj.NetCDFRevision
    metadata['source'] = "Chandra"

    metadata['system'] = ncobj.RadarName
    metadata['software'] = ncobj.NetCDFRevision
    metadata['sw_version'] = ncobj.NetCDFRevision

    # sweep_start_ray_index, sweep_end_ray_index
    sweep_start_ray_index = filemetadata('sweep_start_ray_index')
    sweep_end_ray_index = filemetadata('sweep_end_ray_index')

    rays_per_sweep = np.shape(ncvars['Azimuth'][:])
    ssri = np.cumsum(np.append([0], rays_per_sweep[:-1])).astype('int32')
    seri = np.cumsum(rays_per_sweep).astype('int32') - 1
    sweep_start_ray_index['data'] = ssri
    sweep_end_ray_index['data'] = seri

    # sweep_number
    sweep_number = filemetadata('sweep_number')
    sweep_number['data'] = np.arange(nsweeps, dtype='int32')

    # sweep_mode
    sweep_mode = filemetadata('sweep_mode')
    sweep_mode['data'] = np.array(nsweeps * ['azimuth_surveillance'])

    # scan_type
    if ncobj.ScanType == 2:
        scan_type = 'ppi'
    else:
        scan_type = 'rhi'

    # fixed_angle
    fixed_angle = filemetadata('fixed_angle')
    if ncobj.ScanType == 2:
        sweep_el = ncvars['Elevation'][0]
    else:
        sweep_el = ncvars['Azimuth'][0]
    fixed_angle['data'] = np.array([sweep_el], dtype='float32')

    # elevation
    elevation = filemetadata('elevation')
    elevation['data'] = ncvars['Elevation']

    # range
    _range = filemetadata('range')
    # check that the gate spacing is constant between sweeps
    rstart = ncvars['StartRange'][:]
    if any(rstart != rstart[0]):
        raise ValueError('range start changes between sweeps')
    rscale = ncvars['GateWidth'][:]/1000.
    if any(rscale != rscale[0]):
        raise ValueError('range scale changes between sweeps')

    nbins = ncobj.NumGates
    _range['data'] = (np.arange(nbins, dtype='float32') * rscale[0] +
                      rstart[0] * 1000.)
    _range['meters_to_center_of_first_gate'] = rstart[0]
    _range['meters_between_gates'] = float(rscale[0])

    # azimuth
    azimuth = filemetadata('azimuth')
    azimuth['data'] = ncvars['Azimuth'][:]

    # time
    _time = filemetadata('time')
    start_time = datetime.datetime.utcfromtimestamp(ncobj.Time)
    _time['units'] = make_time_unit_str(start_time)
    _time['data'] = (ncvars['Time']-ncobj.Time).astype('float32')

    # fields
    # all variables with dimensions of 'Radial', 'Gate' are fields
    keys = [k for k, v in ncvars.items()
            if v.dimensions == ('Radial', 'Gate')]

    fields = {}
    for key in keys:
        field_name = filemetadata.get_field_name(key)
        if field_name is None:
            if exclude_fields is not None and key in exclude_fields:
                continue
            if include_fields is not None:
                if not key in include_fields:
                    continue
            field_name = key
        fields[field_name] = _ncvar_to_dict(ncvars[key])

    # instrument_parameters
    instrument_parameters = None

    return Radar(
        _time, _range, fields, metadata, scan_type,
        latitude, longitude, altitude,
        sweep_number, sweep_mode, fixed_angle, sweep_start_ray_index,
        sweep_end_ray_index,
        azimuth, elevation,
        instrument_parameters=instrument_parameters)


def _ncvar_to_dict(ncvar):
    """ Convert a NetCDF Dataset variable to a dictionary. """
    # copy all attribute except for scaling parameters
    d = dict((k, getattr(ncvar, k)) for k in ncvar.ncattrs()
             if k not in ['scale_factor', 'add_offset'])
    d['data'] = ncvar[:]
    if np.isscalar(d['data']):
        # netCDF4 1.1.0+ returns a scalar for 0-dim array, we always want
        # 1-dim+ arrays with a valid shape.
        d['data'] = np.array(d['data'])
        d['data'].shape = (1, )
    return d
