text: #!/usr/bin/env python
  # -*- coding: utf-8 -*-
  # Copyright (c) 2019 Satpy developers
  #
  # This file is part of satpy.
  #
  # satpy 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.
  #
  # satpy 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
  # satpy.  If not, see <http://www.gnu.org/licenses/>.
  r"""IASI L2 SO2 BUFR format reader.
  
  Introduction
  ------------
  The ``iasi_l2_so2_bufr`` reader reads IASI level2 SO2 data in BUFR format. The algorithm is described in the
  Theoretical Basis Document, linked below.
  
  Each BUFR file consists of a number of messages, one for each scan, each of which contains SO2 column amounts
  in Dobson units for retrievals performed with plume heights of 7, 10, 13, 16 and 25 km.
  
  Reader Arguments
  ----------------
  A list of retrieval files, fnames, can be opened as follows::
  
    Scene(reader="iasi_l2_so2_bufr", filenames=fnames)
  
  Example
  -------
  Here is an example how to read the data in satpy:
  
  .. code-block:: python
  
      from satpy import Scene
      import glob
  
      filenames = glob.glob(
          '/test_data/W_XX-EUMETSAT-Darmstadt,SOUNDING+SATELLITE,METOPA+IASI_C_EUMC_20200204091455_68984_eps_o_so2_l2.bin')
      scn = Scene(filenames=filenames, reader='iasi_l2_so2_bufr')
      scn.load(['so2_height_3', 'so2_height_4'])
      print(scn['so2_height_3'])
  
  
  Output:
  
  .. code-block:: none
  
      <xarray.DataArray 'so2_height_3' (y: 23, x: 120)>
      dask.array<where, shape=(23, 120), dtype=float64, chunksize=(1, 120), chunktype=numpy.ndarray>
      Coordinates:
          crs      object +proj=latlong +datum=WGS84 +ellps=WGS84 +type=crs
      Dimensions without coordinates: y, x
      Attributes:
          sensor:               IASI
          units:                dobson
          file_type:            iasi_l2_so2_bufr
          wavelength:           None
          modifiers:            ()
          platform_name:        METOP-2
          resolution:           12000
          fill_value:           -1e+100
          level:                None
          polarization:         None
          coordinates:          ('longitude', 'latitude')
          calibration:          None
          key:                  #3#sulphurDioxide
          name:                 so2_height_3
          start_time:           2020-02-04 09:14:55
          end_time:             2020-02-04 09:17:51
          area:                 Shape: (23, 120)\nLons: <xarray.DataArray 'longitud...
          ancillary_variables:  []
  
  References:
  Algorithm Theoretical Basis Document:
  https://acsaf.org/docs/atbd/Algorithm_Theoretical_Basis_Document_IASI_SO2_Jul_2016.pdf
  """
  
  
  # TDB: this reader is based on iasi_l2.py and seviri_l2_bufr.py
  
  import logging
  from datetime import datetime
  import numpy as np
  import xarray as xr
  import dask.array as da
  
  try:
      import eccodes as ec
  except ImportError as e:
      raise ImportError(
          """Missing eccodes-python and/or eccodes C-library installation. Use conda to install eccodes.
             Error: """, e)
  
  from satpy.readers.file_handlers import BaseFileHandler
  from satpy import CHUNK_SIZE
  
  logger = logging.getLogger('IASIL2SO2BUFR')
  
  data_center_dict = {3: 'METOP-1', 4: 'METOP-2', 5: 'METOP-3'}
  
  
  class IASIL2SO2BUFR(BaseFileHandler):
      """File handler for the IASI L2 SO2 BUFR product."""
  
      def __init__(self, filename, filename_info, filetype_info, **kwargs):
          """Initialise the file handler for the IASI L2 SO2 BUFR data."""
          super(IASIL2SO2BUFR, self).__init__(filename, filename_info, filetype_info)
  
          start_time, end_time = self.get_start_end_date()
  
          sc_id = self.get_attribute('satelliteIdentifier')
  
          self.metadata = {}
          self.metadata['start_time'] = start_time
          self.metadata['end_time'] = end_time
          self.metadata['SpacecraftName'] = data_center_dict[sc_id]
  
      @property
      def start_time(self):
          """Return the start time of data acqusition."""
          return self.metadata['start_time']
  
      @property
      def end_time(self):
          """Return the end time of data acquisition."""
          return self.metadata['end_time']
  
      @property
      def platform_name(self):
          """Return spacecraft name."""
          return '{}'.format(self.metadata['SpacecraftName'])
  
      def get_start_end_date(self):
          """Gets the first and last date from the bufr file."""
          fh = open(self.filename, "rb")
          i = 0
          while True:
              # get handle for message
              bufr = ec.codes_bufr_new_from_file(fh)
              if bufr is None:
                  break
              ec.codes_set(bufr, 'unpack', 1)
              year = ec.codes_get(bufr, 'year')
              month = ec.codes_get(bufr, 'month')
              day = ec.codes_get(bufr, 'day')
              hour = ec.codes_get(bufr, 'hour')
              minute = ec.codes_get(bufr, 'minute')
              second = ec.codes_get(bufr, 'second')
  
              obs_time = datetime(year=year, month=month, day=day, hour=hour, minute=minute, second=second)
  
              if i == 0:
                  start_time = obs_time
  
              ec.codes_release(bufr)
  
              i += 1
  
          end_time = obs_time
  
          fh.close()
  
          return start_time, end_time
  
      def get_attribute(self, key):
          """Get BUFR attributes."""
          # This function is inefficient as it is looping through the entire
          # file to get 1 attribute. It causes a problem though if you break
          # from the file early - dont know why but investigating - fix later
  
          fh = open(self.filename, "rb")
          while True:
              # get handle for message
              bufr = ec.codes_bufr_new_from_file(fh)
              if bufr is None:
                  break
              ec.codes_set(bufr, 'unpack', 1)
              attr = ec.codes_get(bufr, key)
              ec.codes_release(bufr)
  
          fh.close()
          return attr
  
      def get_array(self, key):
          """Get all data from file for the given BUFR key."""
          with open(self.filename, "rb") as fh:
              msgCount = 0
              while True:
  
                  bufr = ec.codes_bufr_new_from_file(fh)
                  if bufr is None:
                      break
  
                  ec.codes_set(bufr, 'unpack', 1)
  
                  values = ec.codes_get_array(
                          bufr, key, float)
  
                  if len(values) == 1:
                      values = np.repeat(values, 120)
  
                  # if is the first message initialise our final array
                  if (msgCount == 0):
  
                      arr = da.from_array([values], chunks=CHUNK_SIZE)
                  else:
                      tmpArr = da.from_array([values], chunks=CHUNK_SIZE)
  
                      arr = da.concatenate((arr, tmpArr), axis=0)
  
                  msgCount = msgCount+1
                  ec.codes_release(bufr)
  
          if arr.size == 1:
              arr = arr[0]
  
          return arr
  
      def get_dataset(self, dataset_id, dataset_info):
          """Get dataset using the BUFR key in dataset_info."""
          arr = self.get_array(dataset_info['key'])
          arr[arr == dataset_info['fill_value']] = np.nan
  
          xarr = xr.DataArray(arr, dims=["y", "x"], name=dataset_info['name'])
          xarr.attrs['sensor'] = 'IASI'
          xarr.attrs['platform_name'] = self.platform_name
          xarr.attrs.update(dataset_info)
  
          return xarr
  