"""
Base classes and common code for grammars.

NOTE: If you add grammars, you have to enter manually them in
rscdef.builtingrammars.GRAMMAR_REGISTRY (we don't want to import all
the mess in this package just to make that).
"""

#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.


import codecs
import io
import re
import os
import select
import subprocess

from gavo import base
from gavo import rscdef
from gavo import utils
from gavo.rscdef import procdef
from gavo.rscdef import rowtriggers


class REAttribute(base.UnicodeAttribute):
	"""is an attribute containing (compiled) RE
	"""
	def parse(self, value):
		if value is None or not value:
			return None
		try:
			return re.compile(value)
		except re.error as msg:
			raise base.ui.logOldExc(base.LiteralParseError(self.name_, value,
				hint="A python regular expression was expected here.  Compile"
					" complained: %s"%str(msg)))
	
	def unparse(self, value):
		if value is None:
			return ""
		else:
			return value.pattern


class FilteredInputFile(object):
	"""a pseudo-file that allows piping data thorugh a shell command.

	It supports read, readline, and close.  Close closes the original
	file, too.

	Warning: the command passed in will be shell-expanded (which is fair
	since you can pass in any command you want anyway).

	If you pass silent=True, stderr will be redirected to /dev/null.
	This is probably only attractive for unit tests and such.
	"""
	def __init__(self, filterCommand, origFile, silent=False):
		self.filterCommand, self.origFile = filterCommand, origFile

		processArgs = {"shell": True,
			"stdin": subprocess.PIPE, 
			"stdout": subprocess.PIPE, 
			"close_fds": True}
		if silent:
			processArgs["stderr"] = open("/dev/null", "w")
		self.process = subprocess.Popen([self.filterCommand], **processArgs)
		self.fromChild, self.toChild = self.process.stdout, self.process.stdin
		self.buffer = utils.StreamBuffer(2**14)
		self.PIPE_BUF = select.PIPE_BUF

		origClose = self.origFile.close
		self.origFile.close = self._makeCloser(origClose)
	
	def _makeCloser(self, origClose):
		def _():
			origClose()
			if self.process.returncode is None:
				self.process.terminate()
				# not checking the return code here; if the client closed
				# while the child was still running, an error from it would
				# not count as an error.
				self.process.wait()
			if self.fromChild:
				self.fromChild.close()
			if self.toChild:
				self.toChild.close()
		return _

	def _fillChildBuffer(self):
		"""feeds the child new data, closing the source file if all data
		has been fed.
		"""
		data = self.origFile.read(self.PIPE_BUF)
		if data==b"":
			# source file exhausted, tell child we're done
			self.toChild.close()
			self.toChild = None 
		else:
			self.toChild.write(data)

	def _readAll(self):
		allChunks = []
		while True:
			data = self.read(2**20)
			if data==b"":
				break
			allChunks.append(data)
		return b"".join(allChunks)

	def _fillBuffer(self):
		"""tries to obtain another chunk of data from the child, feeding
		it new data if possible.
		"""
		if self.toChild:
			writeList = [self.toChild]
		else:
			writeList = []
		readReady, writeReady, _ = select.select(
			[self.fromChild], writeList, [])
		
		if writeReady:
			self._fillChildBuffer()

		if readReady:
			data = self.fromChild.read(self.PIPE_BUF)
			if data==b"":
				self.buffer.doneWriting()
				if self.process.wait():
					raise IOError("Child exited with return code %s"%
						self.process.wait())
			self.buffer.add(data)

	def read(self, nBytes=None):
		if nBytes is None:
			return self._readAll()

		while self.buffer.curSize<nBytes and not self.buffer.finished:
			self._fillBuffer()

		return self.buffer.get(nBytes) or b""

	def readline(self):
		# let's do a quick one ourselves rather than inherit from file
		# just for this; this just works with unix line ends.
		while True:
			val = self.buffer.getToChar(b"\n")
			if val is None:
				if self.buffer.finished:
					return self.buffer.getRest()
				else:
					self._fillBuffer()
			else:
				return val

	def __iter__(self):
		while True:
			res = self.readline()
			if not res:
				break
			yield res

	def close(self):
		self.origFile.close()


class Rowfilter(procdef.ProcApp):
	"""A generator for rows coming from a grammar.

	Rowfilters receive rows (i.e., dictionaries) as yielded by a grammar
	under the name row.  Additionally, the embedding row iterator is
	available under the name rowIter.

	Macros are expanded within the embedding grammar.

	The procedure definition *must* result in a generator, i.e., there must
	be at least one yield; in general, this will typically be a ``yield row``,
	but a rowfilter may swallow or create as many rows as desired.

	If you forget to have a yield in the rowfilter source, you'll get a
	"NoneType is not iterable" error that's a bit hard to understand.

	Here, you can only access whatever comes from the grammar.  You can
	access grammar keys in late parameters as row[key] or, if key is 
	like an identifier, as @key.
	"""
	name_ = "rowfilter"
	requiredType="rowfilter"
	formalArgs = "row, rowIter"

	def getFuncCode(self):
		return rscdef.replaceProcDefAt(procdef.ProcApp.getFuncCode(self), "row")


def compileRowfilter(filters):
	"""returns an iterator that "pipes" the rowfilters in filters.

	This means that the output of filters[0] is used as arguments to
	filters[1] and so on.

	If filters is empty, None is returned.
	"""
	if not filters:
		return
	iters = [f.compile() for f in filters] #noflake: code gen
	src = [
		"def iterPipe(row, rowIter):",
		"  for item0 in iters[0](row, rowIter):"]
	for ind in range(1, len(filters)):
		src.append("%s  for item%d in iters[%d](item%d, rowIter):"%(
			"  "*ind, ind, ind, ind-1))
	src.append("%s  yield item%d"%("  "*len(filters), len(filters)-1))
	d = locals()
	exec("\n".join(src), d)
	return d["iterPipe"]


class SourceFieldApp(rscdef.ProcApp):
	"""A procedure application that returns a dictionary added to all 
	incoming rows.
	
	Use this to programmatically provide information that can be computed
	once but that is then added to all rows coming from a single source, usually
	a file.  This could be useful to add information on the source of a
	record or the like.

	The code must return a dictionary.  The source that is about to be parsed is
	passed in as sourceToken.  When parsing from files, this simply is the file
	name.  The data the rows will be delivered to is available as "data", which
	is useful for adding or retrieving meta information.
	"""
	name_ = "sourceFields"

	requriedType = "sourceFields"
	formalArgs = "sourceToken, data"


class MapKeys(base.Structure):
	"""Mapping of names, specified in long or short forms.

	mapKeys is necessary in grammars like keyValueGrammar or fitsProdGrammar.
	In these, the source files themselves give key names.  Within the GAVO
	DC, keys are required to be valid python identifiers (i.e., match
	``[A-Za-z\_][A-Za-z\_0-9]*``).  If keys coming in do not have this form, 
	mapping can force proper names.

	mapKeys could also be used to make incoming names more suitable for
	matching with shell patterns (like in rowmaker idmaps).
	"""
	name_ = "mapKeys"

	_content = base.DataContent(description="Simple mappings in the form"
		"<dest>:<src>{,<dest>:<src>}")
	_mappings = base.DictAttribute("maps", keyName="dest", description=
		"Map source names given in content to the name given in dest.", 
		itemAttD=base.UnicodeAttribute("map"), inverted=True,
		copyable=True)

	def _parseShortenedMap(self, literal):
		try:
			for dest, src in (p.split(":") for p in literal.split(",")):
				src = src.strip()
				if src not in self.maps:
					self.maps[src] = dest.strip()
				else:
					raise base.StructureError(
						"%s clobbers an existing source within the key map."%src)
		except ValueError:
			raise base.ui.logOldExc(base.LiteralParseError(self.name_, literal,
				hint="A key-value enumeration of the format k:v {,k:v}"
				" is expected here"))

	def onElementComplete(self):
		if self.content_:
			self._parseShortenedMap(self.content_)
		self._onElementCompleteNext(MapKeys)

	def doMap(self, aDict):
		"""returns dict with the keys mapped according to the defined mappings.
		"""
		if self.maps:
			newDict = {}
			for k, v in aDict.items():
				newDict[self.maps.get(k, k)] = v
			return newDict
		else:
			return aDict


class RowIterator(object):
	"""An object that encapsulates the a source being parsed by a
	grammar.

	RowIterators are returned by Grammars' parse methods.  Iterate
	over them to retrieve the rows contained in the source.

	You can also call getParameters on them to retrieve document-global
	values (e.g., the parameters of a VOTable, a global header of
	a FITS table).

	The getLocator method should return some string that aids the user
	in finding out why something went wrong (file name, line number, etc.)

	This default implementation works for when source is a sequence
	of dictionaries.  You will, in general, want to override 
	_iteRows and getLocator, plus probably __init__ (to prepare external
	resources) and getParameters (if you have them; make sure to update
	any parameters you have with self.sourceRow as shown in the default
	getParameters implementation).

	RowIterators are supposed to be self-destructing, i.e., they should 
	release any external resources they hold when _iterRows runs out of
	items.

	_iterRows should arrange for the instance variable recNo to be incremented
	by one for each item returned.
	"""
	notify = True

	def __init__(self, grammar, sourceToken, sourceRow=None):
		self.grammar, self.sourceToken = grammar, sourceToken
		self.sourceRow = sourceRow
		self.recNo = 0

	def __iter__(self):
		if self.notify:
			base.ui.notifyNewSource(self.sourceToken)
		if hasattr(self, "rowfilter"):
			baseIter = self._iterRowsProcessed()
		else:
			baseIter = self._iterRows()
		if self.grammar.ignoreOn:
			rowSource = self._filteredIter(baseIter)
		else:
			rowSource = baseIter

		try:
			try:
				for row in rowSource:
					# handle dispatched grammars here, too
					if isinstance(row, tuple):
						d = row[1]
					else:
						d = row

					if isinstance(d, dict):
						# else it could be a sentinel like FLUSH, which we leave alone
						if self.sourceRow:
							d.update(self.sourceRow)
						d["parser_"] = self

					yield row
			except Exception:
				base.ui.notifySourceError()
				raise

		finally:
			if self.notify:
				base.ui.notifySourceFinished()

	def _filteredIter(self, baseIter):
		for row in baseIter:
			if not self.grammar.ignoreOn(row):
				yield row

	def _iterRowsProcessed(self):
		if self.grammar.isDispatching:
			for dest, row in self._iterRows():
				for procRow in self.rowfilter(row, self):
					yield dest, procRow
		else:
			for row in self._iterRows():
				for procRow in self.rowfilter(row, self):
					yield procRow

	def _iterRows(self):
		if False:
			yield None
		self.grammar = None # don't wait for garbage collection

	def getParameters(self):
		res = {"parser_": self}
		if self.sourceRow:
			res.update(self.sourceRow)
		return res
	
	def getLocator(self):
		return "(unknown position -- locator missing)"


def wrapFileFor(fileobj, desiredMode, enc):
	"""wraps or unwraps fileobj so that it matches the open mode desiredMode.

	If there's a "b" in desiredMode, this will return fileobj.raw if it's
	there.  Otherwise, it'll wrap it into a codec.getreader for enc.
	"""
	# I guess there's no good way to figure out if fileobj is binary or
	# text; so let's have a bit of heuristics.
	if hasattr(fileobj, "mode"):
		foundMode = fileobj.mode
	elif isinstance(fileobj, io.BytesIO):
		foundMode = "rb"
	elif isinstance(fileobj, io.StringIO):
		foundMode = "r"
	else:
		foundMode = "r" if hasattr(fileobj, "raw") else "rb"

	if "b" in desiredMode:
		if "b" in foundMode:
			return fileobj
		else:
			return fileobj.raw
	
	else:
		if "b" in foundMode:
			return codecs.getreader(enc)(fileobj)
		else:
			return fileobj


class FileRowIterator(RowIterator):
	"""is a RowIterator base for RowIterators reading files.

	It analyzes the sourceToken to see if it's a string, in which case
	it opens it as a file name and leaves the file object in self.inputFile.

	Otherwise, it assumes sourceToken already is a file object and binds
	it to self.inputFile.  It then tries to come up with a sensible designation
	for sourceToken.

	It also inspects the parent grammar for a gunzip attribute.  If it is
	present and true, the input file will be unzipped transparently.  Don't
	add more features like this; preFilter is a lot more flexible.

	Classes using this reading binary data will want to set fileMode
	to rb.  If they don't what's returned is strings.
	"""
	fileMode = "r"

	def __init__(self, grammar, sourceToken, **kwargs):
		RowIterator.__init__(self, grammar, sourceToken, **kwargs)
		self.curLine = 1
		try:
			self._openFile()
		except IOError as ex:
			raise base.ui.logOldExc(
				base.SourceParseError("I/O operation failed (%s)"%str(ex),
					source=str(sourceToken), location="start"))
	
	def _openFile(self):
		preFilter = None
		# we'll use at the end to generate a sourceToken for disply purposes
		parsingFrom = self.sourceToken
		if hasattr(parsingFrom, "name"):
			# it' probably an open file
			parsingFrom = self.sourceToken.name
		if not isinstance(parsingFrom, str):
			parsingFrom = repr(parsingFrom)

		if hasattr(self.grammar, "gunzip") and self.grammar.gunzip:
			preFilter = "zcat"
		preFilter = preFilter or (
			hasattr(self.grammar, "preFilter") and self.grammar.preFilter)

		# need to handle preFilter first, as that needs a binary file.
		curSrc = self.sourceToken
		if preFilter:
			if isinstance(curSrc, str):
				curSrc = open(curSrc, "rb")
			else:
				curSrc = curSrc
			curSrc = FilteredInputFile(preFilter, curSrc)

		if isinstance(curSrc, str):
			curSrc = open(curSrc, "rb")

		# now curSrc is a binary file.  If a normal file mode
		# is requested, wrap it into a codec.
		if "b" not in self.fileMode:
			curSrc = wrapFileFor(
				curSrc, self.fileMode, self.grammar.enc or "ascii")

		self.inputFile = curSrc
		self.sourceToken = parsingFrom


class FileRowAttributes(object):
	"""A mixin for grammars with FileRowIterators.

	This provides some attributes that FileRowIterators interpret, e.g.,
	preFilter.
	"""
	_gunzip = base.BooleanAttribute("gunzip", description="Unzip sources"
		" while reading? (Deprecated, use preFilter='zcat')", default=False)
	_preFilter = base.UnicodeAttribute("preFilter", description="Shell"
		" command to pipe the input through before passing it on to the"
		" grammar.  Classical examples include zcat or bzcat, but you"
		" can commit arbitrary shell atrocities here.",
		copyable=True)

	def completeElement(self, ctx):
		if ctx.restricted:
			if self.preFilter is not None:
				raise base.RestrictedElement("preFilter")
		self._completeElementNext(FileRowAttributes, ctx)


class GrammarMacroMixin(base.StandardMacroMixin):
	"""A collection of macros available to rowfilters.

	NOTE: All macros should return only one single physical python line,
	or they will mess up the calculation of what constructs caused errors.
	"""
	def macro_inputRelativePath(self, liberalChars="True"):
		"""returns an expression giving the current source's path
		relative to inputsDir

		liberalChars can be a boolean literal (True, False, etc); if false,
		a value error is raised if characters that will result in trouble
		with the product mixin are within the result path.

		In rowmakers fed by grammars with //products#define, better use
		@prodtblAccref.
		"""
		return ('utils.getRelativePath(rowIter.sourceToken,'
			' base.getConfig("inputsDir"), liberalChars=%s)'%(
				base.parseBooleanLiteral(liberalChars)))

	def macro_fullDLURL(self, dlService):
		r"""returns a python expression giving a link to the full current data
		set retrieved through the datalink service.

		You would write \fullDLURL{dlsvc} here, and the macro will expand into
		something like http://yourserver/currd/dlsvc/dlget?ID=ivo://whatever.

		dlService is the id of the datalink service in the current RD.

		This is intended for "virtual" data where the dataset is generated
		on the fly through datalink.
		"""
		baseURL = self.rd.getById(dlService).getURL("dlget")
		return ("'%%s?ID=%%s'%%(%s,"
			" urllib.parse.quote_plus(getStandardPubDID(rowIter.sourceToken)))"%(
				repr(baseURL)))

	def macro_dlMetaURI(self, dlService):
		r"""like fullDLURL, except it points to the datalink metadata.

		This is intended for binding to //products#define's datalink
		parameter.

		If you need the value in a rowmaker, grab it from @prodtblDatalink.
		"""
		baseURL = self.rd.getById(dlService).getURL("dlmeta")
		return ("'%%s?ID=%%s'%%(%s,"
			" urllib.parse.quote_plus(getStandardPubDID(rowIter.sourceToken)))"%(
				repr(baseURL)))

	def macro_standardPreviewPath(self):
		"""returns an expression for the standard path for a custom preview.

		This consists of resdir, the name of the previewDir property on the
		embedding DD, and the flat name of the accref (which this macro
		assumes to see in its namespace as accref; this is usually the
		case in //products#define, which is where this macro would typically be
		used).

		As an alternative, there is the splitPreviewPath macro, which does not
		mogrify the file name.  In particular, do not use standardPreviewPath
		when you have more than a few 1e4 files, as it will have all these
		files in a single, flat directory, and that can become a chore.
		
		See the introduction to custom previews for details.
		"""
		constantPrefix = os.path.join(
			rscdef.getInputsRelativePath(self.parent.rd.resdir),
			self.parent.getProperty("previewDir"))+"/"
		return (repr(constantPrefix)
			+"+getFlatName(accref)")

	def macro_splitPreviewPath(self, ext):
		"""returns an expression for the split standard path for a custom 
		preview.

		As standardPreviewPath, except that the directory hierarchy of the data 
		files will be reproduced in previews.  For ext, you should typically pass
		the extension appropriate for the preview (like {.png} or {.jpeg}).
		
		See the introduction to custom previews for details.
		"""
		constantPrefix = os.path.join(
			rscdef.getInputsRelativePath(self.parent.rd.resdir),
			self.parent.getProperty("previewDir"))+"/"
		return (repr(constantPrefix)
			+"+accref+'%s'"%ext)

	def macro_sourceDate(self):
		"""returns an expression giving the timestamp of the current source.
		"""
		return ('datetime.datetime.utcfromtimestamp('
			'os.path.getmtime(rowIter.sourceToken))')
		
	def macro_srcstem(self):
		"""returns python code for the stem of the source file currently parsed in a rowmaker.
		
		Example: if you're currently parsing /tmp/foo.bar, the stem is foo.
		"""
		return 'getFileStem(rowIter.sourceToken)'

	def macro_rootlessPath(self):
		"""returns an expression giving the current source's path with
		the resource descriptor's root removed.
		"""
		return ('utils.getRelativePath(rowIter.sourceToken,'
			' rowIter.grammar.rd.resdir)')

	def macro_inputSize(self):
		"""returns an expression giving the size of the current source.
		"""
		return 'os.path.getsize(rowIter.sourceToken)'

	def macro_colNames(self, tableRef):
		"""returns a comma-separated list of column names for a table reference.

		This is convenient if an input file matches the table structure; you
		can then simply say things like <reGrammar names="\\\\colName{someTable}"/>.
		"""
		return ",".join(c.name for c in self.rd.getById(tableRef))

	def macro_property(self, property):
		"""returns the value of property on the parent DD.
		"""
		return self.parent.getProperty(property)


class Grammar(base.Structure, GrammarMacroMixin):
	"""An abstract grammar.

	Grammars are configured via their structure parameters.  Their 
	parse(sourceToken) method returns an object that iterates over rawdicts
	(dictionaries mapping keys to (typically) strings) that can then be fed
	through rowmakers; it also has a method getParameters that returns
	global properties of the whole document (like parameters in VOTables;
	this will be empty for many kinds of grammars).

	RowIterators will return a reference to themselves in the raw dicts in the
	parser_ key unless you override their _iterRowsProcessed method (which you
	shouldn't).  This is used by rowmaker macros.

	What exactly sourceToken is is up to the concrete grammar.  While
	typically it's a file name, it might be a sequence of dictionaries,
	a twisted web request, or whatever.
	
	To derive a concrete Grammar, define a RowIterator for your source
	and set the rowIterator class attribute to it.
	"""
	name_ = "grammar"

	_encoding = base.UnicodeAttribute("enc", default=None, description=
		"Encoding of strings coming in from source.", copyable=True)
	_rowfilters = base.StructListAttribute("rowfilters", 
		description="Row filters for this grammar.", 
		childFactory=Rowfilter, copyable=True)
	_ignoreOn = base.StructAttribute("ignoreOn", default=None, copyable=True,
		description="Conditions for ignoring certain input records.  These"
			" triggers drop an input record entirely.  If you feed multiple"
			" tables and just want to drop a row from a specific table, you"
			" can use ignoreOn in a rowmaker.",
		childFactory=rowtriggers.IgnoreOn)
	_sourceFields = base.StructAttribute("sourceFields", default=None,
		copyable=True, description="Code returning a dictionary of values"
		" added to all returned rows.", childFactory=SourceFieldApp)
	_properties = base.PropertyAttribute(copyable=True)
	_original = base.OriginalAttribute()
	_rd = rscdef.RDAttribute()

	# isDispatching is used by various special grammars to signify the
	# grammar returns rowdicts for multiple makers.  See those.
	# Here, we just fix it to false so clients can rely on the attribute's
	# existance.
	isDispatching = False

	rowIterator = RowIterator

	def getSourceFields(self, sourceToken, data):
		"""returns a dict containing user-defined fields to be added to
		all results.
		"""
		if self.sourceFields is None:
			return None
		if not hasattr(self, "_compiledSourceFields"):
			self._compiledSourceFields = self.sourceFields.compile()
		return self._compiledSourceFields(sourceToken, data)

	def parse(self, sourceToken, targetData=None):
		ri = self.rowIterator(self, sourceToken, 
			sourceRow=self.getSourceFields(sourceToken, targetData))
		if self.rowfilters:
			ri.rowfilter = compileRowfilter(self.rowfilters)
		return ri


class NullGrammar(Grammar):
	"""A grammar that never returns any rows.
	"""
	name_ = "nullGrammar"


class TransparentGrammar(Grammar):
	"""A grammar that returns its sourceToken as the row iterator.

	This only makes sense in extreme situations and never without custom
	code.  If you're not sure you need this, you don't want to know about
	it.
	"""
	name_ = "transparentGrammar"

	def parse(self, sourceToken, targetData=None):
		return sourceToken
