"""
Common code for generation of various data formats.

The main function here is formatData.  It receives a string format id, a data
instance and a destination file (binary mode).  It dispatches this to
formatters previously registred using registerDataWriter.

The data writers must take a data instance and a file instance; their
effect must be that a serialized representation of data, or, if the format
does not support this, the data's primary table is written to the file 
instance.
"""

#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 cgi
import io
import os
import mimetypes

from gavo import base
from gavo import utils


# used in guessMediaType
EXTENSION_FALLBACKS = {
	".vot": base.votableType,
	".fits": "application/fits",
	".fz": "image/fits",
}

# image/fits is probably not quite legal (it's not in Debian's
# /etc/mime.types), but it's too handy to pass up
mimetypes.add_type("image/fits", ".fits")


class CannotSerializeIn(base.Error):
	def __init__(self, format):
		self.format = format
		base.Error.__init__(self, format,
			hint="Either you gave an invalid format id or a known format"
			" did not get registred for some reason.  Format codes"
			" known at this point: %s.  You can also try common MIME types"%(
				", ".join(FORMATS_REGISTRY.writerRegistry)))
		self.args = [format]
	
	def __str__(self):
		return "Cannot serialize in '%s'."%self.format


def getMIMEKey(contentType):
	"""makes a DaCHS mime key from a content-type string.

	This is used for retrieving matching mime types and is a triple
	of major and minor mime type and a set of parameter pairs.

	contentType is a string-serialized mime type.

	We also normalise everything to lower case.  I don't think that's
	quite standards-compliant, but with all the other case-insensitivity
	nonsense, anything else will get really ugly.
	"""
	contentType = contentType.lower()
	media_type, paramdict = cgi.parse_header(contentType)
	try:
		major, minor = media_type.split("/")
	except (ValueError, TypeError):
		raise CannotSerializeIn(contentType)
	return (major, minor, 
			frozenset(iter(paramdict.items())))


class FORMATS_REGISTRY(object):
	"""a registry for data formats that can be produced by DaCHS.

	This works by self-registration of the respective modules on their
	input; hence, if you want to rely on some entry here, be sure
	there's an import somewhere.
	"""
	# format key -> writer function
	writerRegistry = {}
	# format key -> mime type
	formatToMIME = {}
	# format key -> human-readable label
	formatToLabel = {}
	# (major, minor, param pair set) -> format key
	mimeToKey = {}
	extensionToKey = utils.CaseSemisensitiveDict()
	keyToExtension = {}
	# Formats TAPRegExt standard ids have an entry here
	keyToTAPId = {}
	# main format key to aliases also accepted
	keyToAliases = {}

	@classmethod
	def registerDataWriter(cls, 
			key, writer, mainMime, label, extension, *aliases, tapId=None):
		"""adds a writer to the formats registry.

		Key is a short, unique handle for the format, writer is a writer
		function(data, outputFile) -> None (where data can be an rsc.Data
		or an rsc.Table instance), mainMime is the preferred media type,
		label is a human-readable designation for the format (shown in
		selection widgets and the like), extension is a suggested extension
		for the format (lower-case only), and aliases are other strings 
		that can be used to select the format in DALI FORMAT or similar.

		Where keys, mainMime, and aliases clash, previous entries are
		silently overwritten.  For extensions, the first registred format
		wins.
		"""
		cls.writerRegistry[key] = writer
		cls.formatToMIME[key] = mainMime
		cls.formatToLabel[key] = label

		cls.mimeToKey[getMIMEKey(mainMime)] = key
		for mime in aliases:
			cls.mimeToKey[getMIMEKey(mime)] = key
		if extension not in cls.extensionToKey:
			cls.extensionToKey[extension] = key
			cls.keyToExtension[key] = extension

		if tapId is not None:
			cls.keyToTAPId[key] = tapId
		cls.keyToAliases[key] = list(aliases)
		if mainMime!=key:
			cls.keyToAliases[key].append(key)

	@classmethod
	def getMIMEFor(cls, formatName, orderedFormat=None):
		"""returns a simple MIME type for our formatName (some incoming MIME 
		or an alias).

		Some magic, reserved mimes that need to be preserved from
		the input are recognised and returned in orderedFormat.  This
		is for TAP and related DALI hacks.
		"""
		# TAP Spec, 2.7.1, similar in DALI, wants us to keep some 
		# media types.  It's not quite clear which these actually are,
		# but I'd guess something like:
		if (orderedFormat
				and (orderedFormat.startswith("text/xml")
					or orderedFormat.startswith("application/x-votable+xml")
					or orderedFormat.startswith("text/plain"))):
			return orderedFormat

		if formatName in cls.formatToMIME:
			return cls.formatToMIME[formatName]

		# if it looks like a mime type, return it, otherwise assume it's
		# an unimported format and return a generic mime
		if "/" in formatName:
			return formatName
		else:
			return "application/octet-stream"

	@classmethod
	def getWriterFor(cls, formatName):
		"""returns a writer for formatName.

		writers are what's registred via registerDataWriter; formatName is
		a MIME type or a format alias.  This raises CannotSerializeIn
		if no writer is available.
		"""
		return cls.writerRegistry[cls.getKeyFor(formatName)]

	@classmethod
	def getLabelFor(cls, formatName):
		"""returns a label for formatName (DaCHS key or MIME type).
		"""
		return cls.formatToLabel[cls.getKeyFor(formatName)]

	@classmethod
	def getKeyFor(cls, formatName):
		"""returns a DaCHS format key for formatName (DaCHS key or MIME).

		If formatName is a mime type with parameters, we'll also try
		to get a format with the parameters stripped and silently succeed
		if that works.
		"""
		formatName = formatName.lower()
		if formatName in cls.writerRegistry:
			return formatName

		parsed = getMIMEKey(formatName)
		if parsed in cls.mimeToKey:
			return cls.mimeToKey[parsed]
		parsed = (parsed[0], parsed[1], frozenset())
		if parsed in cls.mimeToKey:
			return cls.mimeToKey[parsed]

		raise CannotSerializeIn(formatName)

	@classmethod
	def getAliasesFor(cls, formatName):
		"""returns alternate names for a DaCHS format key.

		Don't modify what you get back.  This will return the DaCHS format
		key if it is not the mime itself.
		"""
		return cls.keyToAliases[formatName]
	
	@classmethod
	def getTAPIdFor(cls, formatName):
		"""returns a TAPRegExt ivoid for a DaCHS format key.

		This will return None if TAPRegExt does not prescribe such a key.
		"""
		return cls.keyToTAPId.get(formatName)

	@classmethod
	def getTypeForExtension(cls, extension):
		"""returns the media type first registered for extension.

		extension must begin with a dot.  None is returned for extensions
		no format has (yet) claimed.
		"""
		key = cls.extensionToKey.get(extension.lower())
		if key is None:
			return None
		return cls.formatToMIME[key]

	@classmethod
	def iterFormats(cls):
		"""iterates over the short names of the available formats.
		"""
		return iter(cls.writerRegistry)


registerDataWriter = FORMATS_REGISTRY.registerDataWriter
getMIMEFor = FORMATS_REGISTRY.getMIMEFor
getKeyFor = FORMATS_REGISTRY.getKeyFor
getWriterFor = FORMATS_REGISTRY.getWriterFor
getLabelFor = FORMATS_REGISTRY.getLabelFor
getAliasesFor = FORMATS_REGISTRY.getAliasesFor
getTAPIdFor = FORMATS_REGISTRY.getTAPIdFor
iterFormats = FORMATS_REGISTRY.iterFormats


def formatData(
		formatName, 
		table, 
		outputFile, 
		acquireSamples=True,
		**moreFormatterArgs):
	"""writes a table to outputFile in the format given by key.

	Table may be a table or a ``Data`` instance.   ``formatName`` is a format 
	shortcut (``formats.iterFormats()`` gives keys available) or a media type.
	If you pass None, the default VOTable format will be selected.

	This raises a ``CannotSerializeIn`` exception if ``formatName`` is 
	not recognized.  Note that you have to import the serialising modules
	from the format package to make the formats available (fitstable,
	csvtable, geojson, jsontable, texttable, votable; api itself already
	imports the more popular of these).

	If a client knows a certain formatter understands additional arguments,
	it can hand them in as keywords arguments.  This will raise an error
	if another formatter that doesn't understand the argument is being used.
	"""
	if formatName is None:
		formatName = base.votableType
	getWriterFor(formatName)(
		table, 
		outputFile, 
		acquireSamples=acquireSamples,
		**moreFormatterArgs)


def getFormatted(formatName, table, acquireSamples=False):
	"""returns a string containing a representation of table in the
	format given by formatName.

	This is just wrapping the `function formatData`_; se there for formatName.
	This function will use large amounts of memory for large data.
	"""
	buffer = io.BytesIO()
	formatData(formatName, table, buffer, acquireSamples)
	return buffer.getvalue()


def guessMediaType(fName):
	"""returns a media type plausible for a file named fName.

	This first uses the extension map inferred by our formats registry, 
	has some built-in safety catches in case the formatters haven't 
	been imported, and then falls back to built-in python 
	mimetypes.guess_type  If nothing matches, it returns
	application/octet-stream.

	Extensions are used case-insensitively.  We don't do any encoding
	inference (yet).  We may, though, so by all means shout if you're using
	this in DaCHS-external code.
	"""
	extension = os.path.splitext(fName)[-1].lower()
	res = FORMATS_REGISTRY.getTypeForExtension(extension)

	if res is None:
		res = EXTENSION_FALLBACKS.get(extension)

	if res is None:
		res, _ = mimetypes.guess_type(fName)
	
	if res is None:
		res = "application/octet-stream"
	
	return res


def getExtensionFor(mediaType):
	"""returns a suggested extension for files of mediaType.

	mediaType can be an RFC 2045 media type, or one of DaCHS' internal format
	codes.

	As a fallback, .dat will be returned.
	"""
	try:
		return FORMATS_REGISTRY.keyToExtension[
			FORMATS_REGISTRY.getKeyFor(mediaType)]
	except (CannotSerializeIn, KeyError):
		return mimetypes.guess_extension(mediaType) or ".dat"
