"""
A grammar wrapping spacepy to parse files in the Common Data Format (CDF),
http://cdf.gsfc.nasa.gov.
"""

#c Copyright 2008-2021, the GAVO project <gavo@ari.uni-heidelberg.de>
#c
#c This program is free software, covered by the GNU GPL.  See the
#c COPYING file in the source distribution.


from gavo import base
from gavo.grammars.common import Grammar, RowIterator, MapKeys


class CDFHeaderIterator(RowIterator):
	"""an iterator for headers of CDF files.
	"""
	def _iterRows(self):
		try:
			from spacepy import pycdf
		except ImportError:
			raise base.ui.logOldExc(
				base.ReportableError("cdfHeaderGrammar needs the external"
					" spacepy package.  You can obtain it from"
					" http://spacepy.lanl.gov."))
		
		cdfStruct = pycdf.CDF(self.sourceToken)

		res = {}
		for key, value in cdfStruct.attrs.items():
			if self.grammar.autoAtomize and value.max_idx()==0:
				res[key] = value[0]
			else:
				res[key] = value[:]
		yield res


class CDFHeaderGrammar(Grammar):
	"""A grammar that returns the header dictionary of a CDF file
	(global attributes).

	This grammar yields a single dictionary per file, which corresponds
	to the global attributes.  The values in this dictionary may have
	complex structure; in particular, sequences are returned as lists.

	To use this grammar, additional software is required that (by 2014)
	is not packaged for Debian.  See
	https://pythonhosted.org/SpacePy/install.html
	for installation 
	instructions.  Note that you must install the CDF library itself as
	described further down on that page; the default installation 
	instructions do not install the library in a public place, so if
	you use these, you'll have to set CDF_LIB to the right value, too,
	before running dachs imp.
	"""
	name_ = "cdfHeaderGrammar"

	_mapKeys = base.StructAttribute("mapKeys", childFactory=MapKeys,
		default=None, copyable=True, description="Prescription for how to"
		" map labels keys to grammar dictionary keys")
	_autoAtomize = base.BooleanAttribute("autoAtomize",
		default=False, copyable=True, description="Unpack 1-element"
		" lists to their first value.")


	rowIterator = CDFHeaderIterator

	def onElementComplete(self):
		if self.mapKeys is None:
			self.mapKeys = base.makeStruct(MapKeys)
		self._onElementCompleteNext(CDFHeaderGrammar)
