nsHebrewProber.h

/*  -*- C++ -*-
    SPDX-FileCopyrightText: 1998 Netscape Communications Corporation <developer@mozilla.org>
 
    SPDX-License-Identifier: MIT
*/
 
#ifndef nsHebrewProber_h__
#define nsHebrewProber_h__
 
#include "nsSBCharSetProber.h"
namespace kencodingprober
{
// This prober doesn't actually recognize a language or a charset.
// It is a helper prober for the use of the Hebrew model probers
class KCODECS_NO_EXPORT nsHebrewProber : public nsCharSetProber
{
public:
    nsHebrewProber(void)
        : mLogicalProb(nullptr)
        , mVisualProb(nullptr)
    {
        Reset();
    }
 
    ~nsHebrewProber(void) override
    {
    }
    nsProbingState HandleData(const char *aBuf, unsigned int aLen) override;
    const char *GetCharSetName() override;
    void Reset(void) override;
 
    nsProbingState GetState(void) override;
 
    float GetConfidence(void) override
    {
        return (float)0.0;
    }
    void SetOpion() override
    {
    }
 
    void SetModelProbers(nsCharSetProber *logicalPrb, nsCharSetProber *visualPrb)
    {
        mLogicalProb = logicalPrb;
        mVisualProb = visualPrb;
    }
 
#ifdef DEBUG_PROBE
    void DumpStatus() override;
#endif
 
protected:
    static bool isFinal(char c);
    static bool isNonFinal(char c);
 
    int mFinalCharLogicalScore, mFinalCharVisualScore;
 
    // The two last characters seen in the previous buffer.
    char mPrev, mBeforePrev;
 
    // These probers are owned by the group prober.
    nsCharSetProber *mLogicalProb, *mVisualProb;
};
}
 
/**
 * ** 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 nsSBCharSetProbers and an nsHebrewProber,
 * all of which are managed, created, fed data, inquired and deleted by the
 * nsSBCSGroupProber. The two nsSBCharSetProbers 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 nsHebrewProber by combining final-letter scores
 * with the scores of the two nsSBCharSetProbers to produce a final answer.
 *
 * The nsSBCSGroupProber 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 nsSBCharSetProbers (model probers) share the same language model:
 * Win1255Model.
 * The first nsSBCharSetProber uses the model normally as any other
 * nsSBCharSetProber does, to recognize windows-1255, upon which this model was
 * built. The second nsSBCharSetProber 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 nsHebrewProber 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 nsHebrewProber
 * alone are meaningless. nsHebrewProber always returns 0.00 as confidence
 * since it never identifies a charset by itself. Instead, the pointer to the
 * nsHebrewProber 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
 * nsHebrewProber to make the final decision. In the nsHebrewProber, 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".
 *
 */
#endif /* nsHebrewProber_h__ */