######################## BEGIN LICENSE BLOCK ########################
# The Original Code is Mozilla Universal charset detector code.
#
# The Initial Developer of the Original Code is
#		  Shy Shalom
# Portions created by the Initial Developer are Copyright (C) 2005
# the Initial Developer. All Rights Reserved.
#
# Contributor(s):
#   Mark Pilgrim - port to Python
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# This library 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
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
# 02110-1301  USA
######################### END LICENSE BLOCK #########################

from charsetprober import CharSetProber
import constants

# This prober doesn't actually recognize a language or a charset.
# It is a helper prober for the use of the Hebrew model probers

### General ideas of the Hebrew charset recognition ###
#
# Four main charsets exist in Hebrew:
# "ISO-8859-8" - Visual Hebrew
# "windows-1255" - Logical Hebrew
# "ISO-8859-8-I" - Logical Hebrew
# "x-mac-hebrew" - ?? Logical Hebrew ??
#
# Both "ISO" charsets use a completely identical set of code points, whereas
# "windows-1255" and "x-mac-hebrew" are two different proper supersets of
# these code points. windows-1255 defines additional characters in the range
# 0x80-0x9F as some misc punctuation marks as well as some Hebrew-specific
# diacritics and additional 'Yiddish' ligature letters in the range 0xc0-0xd6.
# x-mac-hebrew defines similar additional code points but with a different
# mapping.
#
# As far as an average Hebrew text with no diacritics is concerned, all four
# charsets are identical with respect to code points. Meaning that for the
# main Hebrew alphabet, all four map the same values to all 27 Hebrew letters
# (including final letters).
#
# The dominant difference between these charsets is their directionality.
# "Visual" directionality means that the text is ordered as if the renderer is
# not aware of a BIDI rendering algorithm. The renderer sees the text and
# draws it from left to right. The text itself when ordered naturally is read
# backwards. A buffer of Visual Hebrew generally looks like so:
# "[last word of first line spelled backwards] [whole line ordered backwards
# and spelled backwards] [first word of first line spelled backwards]
# [end of line] [last word of second line] ... etc' "
# adding punctuation marks, numbers and English text to visual text is
# naturally also "visual" and from left to right.
#
# "Logical" directionality means the text is ordered "naturally" according to
# the order it is read. It is the responsibility of the renderer to display
# the text from right to left. A BIDI algorithm is used to place general
# punctuation marks, numbers and English text in the text.
#
# Texts in x-mac-hebrew are almost impossible to find on the Internet. From
# what little evidence I could find, it seems that its general directionality
# is Logical.
#
# To sum up all of the above, the Hebrew probing mechanism knows about two
# charsets:
# Visual Hebrew - "ISO-8859-8" - backwards text - Words and sentences are
#	backwards while line order is natural. For charset recognition purposes
#	the line order is unimportant (In fact, for this implementation, even
#	word order is unimportant).
# Logical Hebrew - "windows-1255" - normal, naturally ordered text.
#
# "ISO-8859-8-I" is a subset of windows-1255 and doesn't need to be
#	specifically identified.
# "x-mac-hebrew" is also identified as windows-1255. A text in x-mac-hebrew
#	that contain special punctuation marks or diacritics is displayed with
#	some unconverted characters showing as question marks. This problem might
#	be corrected using another model prober for x-mac-hebrew. Due to the fact
#	that x-mac-hebrew texts are so rare, writing another model prober isn't
#	worth the effort and performance hit.
#
#### The Prober ####
#
# The prober is divided between two SBCharSetProbers and a HebrewProber,
# all of which are managed, created, fed data, inquired and deleted by the
# SBCSGroupProber. The two SBCharSetProbers identify that the text is in
# fact some kind of Hebrew, Logical or Visual. The final decision about which
# one is it is made by the HebrewProber by combining final-letter scores
# with the scores of the two SBCharSetProbers to produce a final answer.
#
# The SBCSGroupProber is responsible for stripping the original text of HTML
# tags, English characters, numbers, low-ASCII punctuation characters, spaces
# and new lines. It reduces any sequence of such characters to a single space.
# The buffer fed to each prober in the SBCS group prober is pure text in
# high-ASCII.
# The two SBCharSetProbers (model probers) share the same language model:
# Win1255Model.
# The first SBCharSetProber uses the model normally as any other
# SBCharSetProber does, to recognize windows-1255, upon which this model was
# built. The second SBCharSetProber is told to make the pair-of-letter
# lookup in the language model backwards. This in practice exactly simulates
# a visual Hebrew model using the windows-1255 logical Hebrew model.
#
# The HebrewProber is not using any language model. All it does is look for
# final-letter evidence suggesting the text is either logical Hebrew or visual
# Hebrew. Disjointed from the model probers, the results of the HebrewProber
# alone are meaningless. HebrewProber always returns 0.00 as confidence
# since it never identifies a charset by itself. Instead, the pointer to the
# HebrewProber is passed to the model probers as a helper "Name Prober".
# When the Group prober receives a positive identification from any prober,
# it asks for the name of the charset identified. If the prober queried is a
# Hebrew model prober, the model prober forwards the call to the
# HebrewProber to make the final decision. In the HebrewProber, the
# decision is made according to the final-letters scores maintained and Both
# model probers scores. The answer is returned in the form of the name of the
# charset identified, either "windows-1255" or "ISO-8859-8".

# windows-1255 / ISO-8859-8 code points of interest
FINAL_KAF = '\xea'
NORMAL_KAF = '\xeb'
FINAL_MEM = '\xed'
NORMAL_MEM = '\xee'
FINAL_NUN = '\xef'
NORMAL_NUN = '\xf0'
FINAL_PE = '\xf3'
NORMAL_PE = '\xf4'
FINAL_TSADI = '\xf5'
NORMAL_TSADI = '\xf6'

# Minimum Visual vs Logical final letter score difference.
# If the difference is below this, don't rely solely on the final letter score distance.
MIN_FINAL_CHAR_DISTANCE = 5

# Minimum Visual vs Logical model score difference.
# If the difference is below this, don't rely at all on the model score distance.
MIN_MODEL_DISTANCE = 0.01

VISUAL_HEBREW_NAME = "ISO-8859-8"
LOGICAL_HEBREW_NAME = "windows-1255"

class HebrewProber(CharSetProber):
	def __init__(self):
		CharSetProber.__init__(self)
		self._mLogicalProber = None
		self._mVisualProber = None
		self.reset()

	def reset(self):
		self._mFinalCharLogicalScore = 0
		self._mFinalCharVisualScore = 0
		# The two last characters seen in the previous buffer,
		# mPrev and mBeforePrev are initialized to space in order to simulate a word
		# delimiter at the beginning of the data
		self._mPrev = ' '
		self._mBeforePrev = ' '
		# These probers are owned by the group prober.

	def set_model_probers(self, logicalProber, visualProber):
		self._mLogicalProber = logicalProber
		self._mVisualProber = visualProber

	def is_final(self, c):
		return c in [FINAL_KAF, FINAL_MEM, FINAL_NUN, FINAL_PE, FINAL_TSADI]

	def is_non_final(self, c):
		# The normal Tsadi is not a good Non-Final letter due to words like
		# 'lechotet' (to chat) containing an apostrophe after the tsadi. This
		# apostrophe is converted to a space in FilterWithoutEnglishLetters causing
		# the Non-Final tsadi to appear at an end of a word even though this is not
		# the case in the original text.
		# The letters Pe and Kaf rarely display a related behavior of not being a
		# good Non-Final letter. Words like 'Pop', 'Winamp' and 'Mubarak' for
		# example legally end with a Non-Final Pe or Kaf. However, the benefit of
		# these letters as Non-Final letters outweighs the damage since these words
		# are quite rare.
		return c in [NORMAL_KAF, NORMAL_MEM, NORMAL_NUN, NORMAL_PE]

	def feed(self, aBuf):
		# Final letter analysis for logical-visual decision.
		# Look for evidence that the received buffer is either logical Hebrew or
		# visual Hebrew.
		# The following cases are checked:
		# 1) A word longer than 1 letter, ending with a final letter. This is an
		#	indication that the text is laid out "naturally" since the final letter
		#	really appears at the end. +1 for logical score.
		# 2) A word longer than 1 letter, ending with a Non-Final letter. In normal
		#	Hebrew, words ending with Kaf, Mem, Nun, Pe or Tsadi, should not end with
		#	the Non-Final form of that letter. Exceptions to this rule are mentioned
		#	above in isNonFinal(). This is an indication that the text is laid out
		#	backwards. +1 for visual score
		# 3) A word longer than 1 letter, starting with a final letter. Final letters
		#	should not appear at the beginning of a word. This is an indication that
		#	the text is laid out backwards. +1 for visual score.
		#
		# The visual score and logical score are accumulated throughout the text and
		# are finally checked against each other in GetCharSetName().
		# No checking for final letters in the middle of words is done since that case
		# is not an indication for either Logical or Visual text.
		#
		# We automatically filter out all 7-bit characters (replace them with spaces)
		# so the word boundary detection works properly. [MAP]

		if self.get_state() == constants.eNotMe:
			# Both model probers say it's not them. No reason to continue.
			return constants.eNotMe

		aBuf = self.filter_high_bit_only(aBuf)

		for cur in aBuf:
			if cur == ' ':
				# We stand on a space - a word just ended
				if self._mBeforePrev != ' ':
					# next-to-last char was not a space so self._mPrev is not a 1 letter word
					if self.is_final(self._mPrev):
						# case (1) [-2:not space][-1:final letter][cur:space]
						self._mFinalCharLogicalScore += 1
					elif self.is_non_final(self._mPrev):
						# case (2) [-2:not space][-1:Non-Final letter][cur:space]
						self._mFinalCharVisualScore += 1
			else:
				# Not standing on a space
				if (self._mBeforePrev == ' ') and (self.is_final(self._mPrev)) and (cur != ' '):
					# case (3) [-2:space][-1:final letter][cur:not space]
					self._mFinalCharVisualScore += 1
			self._mBeforePrev = self._mPrev
			self._mPrev = cur

		# Forever detecting, till the end or until both model probers return eNotMe (handled above)
		return constants.eDetecting

	def get_charset_name(self):
		# Make the decision: is it Logical or Visual?
		# If the final letter score distance is dominant enough, rely on it.
		finalsub = self._mFinalCharLogicalScore - self._mFinalCharVisualScore
		if finalsub >= MIN_FINAL_CHAR_DISTANCE:
			return LOGICAL_HEBREW_NAME
		if finalsub <= -MIN_FINAL_CHAR_DISTANCE:
			return VISUAL_HEBREW_NAME

		# It's not dominant enough, try to rely on the model scores instead.
		modelsub = self._mLogicalProber.get_confidence() - self._mVisualProber.get_confidence()
		if modelsub > MIN_MODEL_DISTANCE:
			return LOGICAL_HEBREW_NAME
		if modelsub < -MIN_MODEL_DISTANCE:
			return VISUAL_HEBREW_NAME

		# Still no good, back to final letter distance, maybe it'll save the day.
		if finalsub < 0.0:
			return VISUAL_HEBREW_NAME

		# (finalsub > 0 - Logical) or (don't know what to do) default to Logical.
		return LOGICAL_HEBREW_NAME

	def get_state(self):
		# Remain active as long as any of the model probers are active.
		if (self._mLogicalProber.get_state() == constants.eNotMe) and \
		   (self._mVisualProber.get_state() == constants.eNotMe):
			return constants.eNotMe
		return constants.eDetecting
