"""
Stream parsing of VOTables.

This module builds on a shallow wrapping of expat in utils.iterparse.
There is an "almost-tight" parsing loop in the parse method.  It
builds an xmlstan tree (mainly through the _processNodeDefault method).
"""

#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.


# To fiddle with the nodes as they are generated, define an
# _end_ELEMENTNAME method.  If you do this, you will have to do
# any adding of children to parents yourself (it happens in 
# _processNodeDefault, which is called when no custom handler is
# present.

import io

from gavo import utils
from gavo.utils import ElementTree
from gavo.votable import common
from gavo.votable import model
from gavo.votable import tableparser


DEFAULT_WATCHSET = []

# We treat all VOTable versions as equal.
VOTABLE_NAMESPACES = [
	"http://www.ivoa.net/xml/VOTable/v1.0",
	"http://www.ivoa.net/xml/VOTable/v1.1",
	"http://www.ivoa.net/xml/VOTable/v1.2",
	"http://www.ivoa.net/xml/VOTable/v1.3",
]


class IGNORE(object):
	"""this is a sentinel element used when an element is not known
	but robust parsing is requested.

	These should not end up in a DOM, but if they do, they're silent.

	They're designed to largely behave like stanxml Elements; it can't
	autoconstruct, though.
	"""
	def __init__(self):
		pass
	
	def __call__(self, **kwargs):
		return self
	
	def __getitem__(self, item):
		pass
	
	def isEmpty(self):
		return True
	
	def shouldBeSkipped(self):
		return True
	
	def apply(self, func):
		return


def _processNodeDefault(text, child, parent):
	"""the default node processor: Append child to parent, return child.
	"""
	assert not (text and text.strip()), (
		"Content '%s' in must-empty VOTable element %s"%(text, repr(child)))
	parent[child]
	return child


def _processNodeWithContent(text, child, parent):
	"""the node processor for nodes with text content.
	"""
	if text and text.strip():
		child[text]  # Attention: mixed content not supported
	parent[child]
	return child


_end_DESCRIPTION = _processNodeWithContent
_end_INFO = _processNodeWithContent
_end_MODEL = _processNodeWithContent
_end_URL = _processNodeWithContent
_end_LITERAL = _processNodeWithContent
_end_NAME = _processNodeWithContent
# STREAMs and TABLEDATA should ordinarily be processed by the table 
# iterator, so this really is only interesting for special applications:
_end_STREAM = _processNodeWithContent  
_end_TD = _processNodeWithContent
_end_IDREF = _processNodeWithContent
_end_LITERAL = _processNodeWithContent


def _end_VOTABLE(text, child, parent):
# VOTABLEs have no useful parents.
	return child


def _computeEndProcessorsImpl():
	"""returns a dictionary of tag names to end processors.

	Each processor as defined using _end_XXXX has an entry each for
	each namespace we're likely to encounter, and one non-namespaced.
	"""
	res, globs = {}, globals()
	for n, v in globs.items():
		if n.startswith("_end_"):
			elName = n[5:]
			res[elName] = v
			for ns in VOTABLE_NAMESPACES:
				res["%s:%s"%(ns, elName)] = v
	return res

computeEndProcessors = utils.CachedGetter(_computeEndProcessorsImpl)


def _computeElementsImpl():
	"""returns a dictionary of tag names to xmlstan elements building them.

	All elements are present for each VOTABLE_NAMESPACE, plus once non-namespaced.
	"""
	res = {}
	for n in dir(model.VOTable):
		if not n.startswith("_"):
			val = getattr(model.VOTable, n)
			res[n] = val
			for ns in VOTABLE_NAMESPACES:
				res[ElementTree.QName(ns, n)] = val
	return res

computeElements = utils.CachedGetter(_computeElementsImpl)


def _cleanAttributes(attrDict, element, raiseOnInvalid):
	"""returns a sanitised version of attDict for element.

	We force attribute keys to be byte strings (since they're being used
	as keyword arguments), and we drop everything that's namespace related 
	-- it's not necessary for VOTables and people mess it up anyway.  
	
	Also, we complain about or filter out attributes that element
	cannot deal with.
	"""
	cleaned = {}
	for key, value in attrDict.items():
		if ":" in key or key=="xmlns":
			continue
		key = str(key.replace("-", "_"))
		if not hasattr(element, "_a_"+key):
			if raiseOnInvalid:
				raise KeyError(key)
			else:
				continue
		cleaned[key] = value
	return cleaned


def parse(inFile, watchset=DEFAULT_WATCHSET, raiseOnInvalid=True):
	"""returns an iterator yielding items of interest.

	inFile is a something that supports read(bytes)

	watchset is a sequence of items of VOTable you want yielded.  By
	default, that's just VOTable.TABLE.  You may want to see INFO
	or PARAM of certain protocols.
	"""
# This parser has gotten a bit too fat.  Maybe move the whole thing
# to a class?  All this isn't terribly critical to performance...
	watchset = set(watchset)
	idmap = {}
	processors = computeEndProcessors()
	elements = computeElements()
	elementStack = [None]  # None is VOTABLE's parent
	iterator = utils.iterparse(inFile, common.VOTableParseError)
	content = []

	for type, tag, payload in iterator:
		if type=="data":
			content.append(payload)

		elif type=="start":
			# Element open: push new node on the stack...
			if tag not in elements:
				if raiseOnInvalid:
					raise iterator.getParseError("Unknown tag: %s"%tag)
				else:
					element = IGNORE()
			else:
				element = elements[tag]()

			if payload: 
				try:
					payload = _cleanAttributes(payload, element, raiseOnInvalid)
				except KeyError as msg:
					raise iterator.getParseError("Attribute %s invalid on %s"%(
						str(msg), element.name_))
			elementStack.append(element(**payload))

			# ...prepare for new content,...
			content = []

			# ...add the node to the id map if it has an ID...
			elId = payload.get("ID")
			if elId is not None:
				idmap[elId] = elementStack[-1]

			# ...and pass control to special iterator if DATA is coming in.
			if tag=="DATA":
				yield tableparser.Rows(elementStack[-2], iterator)

		elif type=="end":
			# Element close: process text content...
			if content:
				text = "".join(content)
				content = []
			else:
				text = None
			
			# ...see if we have any special procssing to do for the node type...
			nodeProc = processors.get(tag, _processNodeDefault)
			preChild = elementStack.pop()
			if not isinstance(preChild, IGNORE):
				# ...call handler with the current node and its future parent...
				child = nodeProc(text, preChild, elementStack[-1])
				
				# ...and let user do something with the element if she ordered it.
				if child is not None and child.__class__ in watchset:
					child.idmap = idmap
					yield child

		else:
			assert False


def readRaw(inFile):
	"""returns a V.VOTABLE instance with filled-in data for the input from
	inFile.
	"""
	for el in parse(inFile, [model.VOTable.TABLE, model.VOTable.VOTABLE]):
		if isinstance(el, tableparser.Rows):
			el.tableDefinition.rows = list(el)
	return el


def parseBytes(string, watchset=DEFAULT_WATCHSET, raiseOnInvalid=True):
	"""returns an iterator yielding pairs of (table definition, row iterator).

	string contains a VOTable literal as bytes (where we fall back to utf-8
	encoding strings if necessary).
	"""
	return parse(io.BytesIO(utils.bytify(string)), watchset, raiseOnInvalid)
