text: /*
   * Copyright © 2011,2012  Google, Inc.
   *
   *  This is part of HarfBuzz, a text shaping library.
   *
   * Permission is hereby granted, without written agreement and without
   * license or royalty fees, to use, copy, modify, and distribute this
   * software and its documentation for any purpose, provided that the
   * above copyright notice and the following two paragraphs appear in
   * all copies of this software.
   *
   * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
   * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
   * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
   * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
   * DAMAGE.
   *
   * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
   * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
   * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
   * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
   * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
   *
   * Google Author(s): Behdad Esfahbod
   */
  
  #include "hb-ot-shape-normalize.hh"
  #include "hb-ot-shape-complex.hh"
  #include "hb-ot-shape.hh"
  
  
  /*
   * HIGHLEVEL DESIGN:
   *
   * This file exports one main function: _hb_ot_shape_normalize().
   *
   * This function closely reflects the Unicode Normalization Algorithm,
   * yet it's different.
   *
   * Each shaper specifies whether it prefers decomposed (NFD) or composed (NFC).
   * The logic however tries to use whatever the font can support.
   *
   * In general what happens is that: each grapheme is decomposed in a chain
   * of 1:2 decompositions, marks reordered, and then recomposed if desired,
   * so far it's like Unicode Normalization.  However, the decomposition and
   * recomposition only happens if the font supports the resulting characters.
   *
   * The goals are:
   *
   *   - Try to render all canonically equivalent strings similarly.  To really
   *     achieve this we have to always do the full decomposition and then
   *     selectively recompose from there.  It's kinda too expensive though, so
   *     we skip some cases.  For example, if composed is desired, we simply
   *     don't touch 1-character clusters that are supported by the font, even
   *     though their NFC may be different.
   *
   *   - When a font has a precomposed character for a sequence but the 'ccmp'
   *     feature in the font is not adequate, use the precomposed character
   *     which typically has better mark positioning.
   *
   *   - When a font does not support a combining mark, but supports it precomposed
   *     with previous base, use that.  This needs the itemizer to have this
   *     knowledge too.  We need to provide assistance to the itemizer.
   *
   *   - When a font does not support a character but supports its canonical
   *     decomposition, well, use the decomposition.
   *
   *   - The complex shapers can customize the compose and decompose functions to
   *     offload some of their requirements to the normalizer.  For example, the
   *     Indic shaper may want to disallow recomposing of two matras.
   */
  
  static bool
  decompose_unicode (const hb_ot_shape_normalize_context_t *c,
  		   hb_codepoint_t  ab,
  		   hb_codepoint_t *a,
  		   hb_codepoint_t *b)
  {
    return (bool) c->unicode->decompose (ab, a, b);
  }
  
  static bool
  compose_unicode (const hb_ot_shape_normalize_context_t *c,
  		 hb_codepoint_t  a,
  		 hb_codepoint_t  b,
  		 hb_codepoint_t *ab)
  {
    return (bool) c->unicode->compose (a, b, ab);
  }
  
  static inline void
  set_glyph (hb_glyph_info_t &info, hb_font_t *font)
  {
    (void) font->get_nominal_glyph (info.codepoint, &info.glyph_index());
  }
  
  static inline void
  output_char (hb_buffer_t *buffer, hb_codepoint_t unichar, hb_codepoint_t glyph)
  {
    buffer->cur().glyph_index() = glyph;
    buffer->output_glyph (unichar); /* This is very confusing indeed. */
    _hb_glyph_info_set_unicode_props (&buffer->prev(), buffer);
  }
  
  static inline void
  next_char (hb_buffer_t *buffer, hb_codepoint_t glyph)
  {
    buffer->cur().glyph_index() = glyph;
    buffer->next_glyph ();
  }
  
  static inline void
  skip_char (hb_buffer_t *buffer)
  {
    buffer->skip_glyph ();
  }
  
  /* Returns 0 if didn't decompose, number of resulting characters otherwise. */
  static inline unsigned int
  decompose (const hb_ot_shape_normalize_context_t *c, bool shortest, hb_codepoint_t ab)
  {
    hb_codepoint_t a = 0, b = 0, a_glyph = 0, b_glyph = 0;
    hb_buffer_t * const buffer = c->buffer;
    hb_font_t * const font = c->font;
  
    if (!c->decompose (c, ab, &a, &b) ||
        (b && !font->get_nominal_glyph (b, &b_glyph)))
      return 0;
  
    bool has_a = (bool) font->get_nominal_glyph (a, &a_glyph);
    if (shortest && has_a) {
      /* Output a and b */
      output_char (buffer, a, a_glyph);
      if (likely (b)) {
        output_char (buffer, b, b_glyph);
        return 2;
      }
      return 1;
    }
  
    unsigned int ret;
    if ((ret = decompose (c, shortest, a))) {
      if (b) {
        output_char (buffer, b, b_glyph);
        return ret + 1;
      }
      return ret;
    }
  
    if (has_a) {
      output_char (buffer, a, a_glyph);
      if (likely (b)) {
        output_char (buffer, b, b_glyph);
        return 2;
      }
      return 1;
    }
  
    return 0;
  }
  
  static inline void
  decompose_current_character (const hb_ot_shape_normalize_context_t *c, bool shortest)
  {
    hb_buffer_t * const buffer = c->buffer;
    hb_codepoint_t u = buffer->cur().codepoint;
    hb_codepoint_t glyph = 0;
  
    if (shortest && c->font->get_nominal_glyph (u, &glyph))
    {
      next_char (buffer, glyph);
      return;
    }
  
    if (decompose (c, shortest, u))
    {
      skip_char (buffer);
      return;
    }
  
    if (!shortest && c->font->get_nominal_glyph (u, &glyph))
    {
      next_char (buffer, glyph);
      return;
    }
  
    if (_hb_glyph_info_is_unicode_space (&buffer->cur()))
    {
      hb_codepoint_t space_glyph;
      hb_unicode_funcs_t::space_t space_type = buffer->unicode->space_fallback_type (u);
      if (space_type != hb_unicode_funcs_t::NOT_SPACE && c->font->get_nominal_glyph (0x0020u, &space_glyph))
      {
        _hb_glyph_info_set_unicode_space_fallback_type (&buffer->cur(), space_type);
        next_char (buffer, space_glyph);
        buffer->scratch_flags |= HB_BUFFER_SCRATCH_FLAG_HAS_SPACE_FALLBACK;
        return;
      }
    }
  
    if (u == 0x2011u)
    {
      /* U+2011 is the only sensible character that is a no-break version of another character
       * and not a space.  The space ones are handled already.  Handle this lone one. */
      hb_codepoint_t other_glyph;
      if (c->font->get_nominal_glyph (0x2010u, &other_glyph))
      {
        next_char (buffer, other_glyph);
        return;
      }
    }
  
    next_char (buffer, glyph); /* glyph is initialized in earlier branches. */
  }
  
  static inline void
  handle_variation_selector_cluster (const hb_ot_shape_normalize_context_t *c,
  				   unsigned int end,
  				   bool short_circuit HB_UNUSED)
  {
    /* TODO Currently if there's a variation-selector we give-up, it's just too hard. */
    hb_buffer_t * const buffer = c->buffer;
    hb_font_t * const font = c->font;
    for (; buffer->idx < end - 1 && buffer->successful;) {
      if (unlikely (buffer->unicode->is_variation_selector (buffer->cur(+1).codepoint))) {
        if (font->get_variation_glyph (buffer->cur().codepoint, buffer->cur(+1).codepoint, &buffer->cur().glyph_index()))
        {
  	hb_codepoint_t unicode = buffer->cur().codepoint;
  	buffer->replace_glyphs (2, 1, &unicode);
        }
        else
        {
          /* Just pass on the two characters separately, let GSUB do its magic. */
  	set_glyph (buffer->cur(), font);
  	buffer->next_glyph ();
  	set_glyph (buffer->cur(), font);
  	buffer->next_glyph ();
        }
        /* Skip any further variation selectors. */
        while (buffer->idx < end && unlikely (buffer->unicode->is_variation_selector (buffer->cur().codepoint)))
        {
  	set_glyph (buffer->cur(), font);
  	buffer->next_glyph ();
        }
      } else {
        set_glyph (buffer->cur(), font);
        buffer->next_glyph ();
      }
    }
    if (likely (buffer->idx < end)) {
      set_glyph (buffer->cur(), font);
      buffer->next_glyph ();
    }
  }
  
  static inline void
  decompose_multi_char_cluster (const hb_ot_shape_normalize_context_t *c, unsigned int end, bool short_circuit)
  {
    hb_buffer_t * const buffer = c->buffer;
    for (unsigned int i = buffer->idx; i < end && buffer->successful; i++)
      if (unlikely (buffer->unicode->is_variation_selector (buffer->info[i].codepoint))) {
        handle_variation_selector_cluster (c, end, short_circuit);
        return;
      }
  
    while (buffer->idx < end && buffer->successful)
      decompose_current_character (c, short_circuit);
  }
  
  
  static int
  compare_combining_class (const hb_glyph_info_t *pa, const hb_glyph_info_t *pb)
  {
    unsigned int a = _hb_glyph_info_get_modified_combining_class (pa);
    unsigned int b = _hb_glyph_info_get_modified_combining_class (pb);
  
    return a < b ? -1 : a == b ? 0 : +1;
  }
  
  
  void
  _hb_ot_shape_normalize (const hb_ot_shape_plan_t *plan,
  			hb_buffer_t *buffer,
  			hb_font_t *font)
  {
    if (unlikely (!buffer->len)) return;
  
    _hb_buffer_assert_unicode_vars (buffer);
  
    hb_ot_shape_normalization_mode_t mode = plan->shaper->normalization_preference;
    if (mode == HB_OT_SHAPE_NORMALIZATION_MODE_AUTO)
    {
      if (plan->has_gpos_mark)
        // https://github.com/harfbuzz/harfbuzz/issues/653#issuecomment-423905920
        //mode = HB_OT_SHAPE_NORMALIZATION_MODE_DECOMPOSED;
        mode = HB_OT_SHAPE_NORMALIZATION_MODE_COMPOSED_DIACRITICS;
      else
        mode = HB_OT_SHAPE_NORMALIZATION_MODE_COMPOSED_DIACRITICS;
    }
  
    const hb_ot_shape_normalize_context_t c = {
      plan,
      buffer,
      font,
      buffer->unicode,
      plan->shaper->decompose ? plan->shaper->decompose : decompose_unicode,
      plan->shaper->compose   ? plan->shaper->compose   : compose_unicode
    };
  
    bool always_short_circuit = mode == HB_OT_SHAPE_NORMALIZATION_MODE_NONE;
    bool might_short_circuit = always_short_circuit ||
  			     (mode != HB_OT_SHAPE_NORMALIZATION_MODE_DECOMPOSED &&
  			      mode != HB_OT_SHAPE_NORMALIZATION_MODE_COMPOSED_DIACRITICS_NO_SHORT_CIRCUIT);
    unsigned int count;
  
    /* We do a fairly straightforward yet custom normalization process in three
     * separate rounds: decompose, reorder, recompose (if desired).  Currently
     * this makes two buffer swaps.  We can make it faster by moving the last
     * two rounds into the inner loop for the first round, but it's more readable
     * this way. */
  
  
    /* First round, decompose */
  
    bool all_simple = true;
    {
      buffer->clear_output ();
      count = buffer->len;
      buffer->idx = 0;
      do
      {
        unsigned int end;
        for (end = buffer->idx + 1; end < count; end++)
  	if (unlikely (HB_UNICODE_GENERAL_CATEGORY_IS_MARK (_hb_glyph_info_get_general_category (&buffer->info[end]))))
  	  break;
  
        if (end < count)
  	end--; /* Leave one base for the marks to cluster with. */
  
        /* From idx to end are simple clusters. */
        if (might_short_circuit)
        {
          unsigned int done = font->get_nominal_glyphs (end - buffer->idx,
  						      &buffer->cur().codepoint,
  						      sizeof (buffer->info[0]),
  						      &buffer->cur().glyph_index(),
  						      sizeof (buffer->info[0]));
  	buffer->next_glyphs (done);
        }
        while (buffer->idx < end && buffer->successful)
  	decompose_current_character (&c, might_short_circuit);
  
        if (buffer->idx == count || !buffer->successful)
  	break;
  
        all_simple = false;
  
        /* Find all the marks now. */
        for (end = buffer->idx + 1; end < count; end++)
  	if (!HB_UNICODE_GENERAL_CATEGORY_IS_MARK (_hb_glyph_info_get_general_category (&buffer->info[end])))
  	  break;
  
        /* idx to end is one non-simple cluster. */
        decompose_multi_char_cluster (&c, end, always_short_circuit);
      }
      while (buffer->idx < count && buffer->successful);
      buffer->swap_buffers ();
    }
  
  
    /* Second round, reorder (inplace) */
  
    if (!all_simple)
    {
      count = buffer->len;
      for (unsigned int i = 0; i < count; i++)
      {
        if (_hb_glyph_info_get_modified_combining_class (&buffer->info[i]) == 0)
  	continue;
  
        unsigned int end;
        for (end = i + 1; end < count; end++)
  	if (_hb_glyph_info_get_modified_combining_class (&buffer->info[end]) == 0)
  	  break;
  
        /* We are going to do a O(n^2).  Only do this if the sequence is short. */
        if (end - i > HB_OT_SHAPE_COMPLEX_MAX_COMBINING_MARKS) {
  	i = end;
  	continue;
        }
  
        buffer->sort (i, end, compare_combining_class);
  
        if (plan->shaper->reorder_marks)
  	plan->shaper->reorder_marks (plan, buffer, i, end);
  
        i = end;
      }
    }
    if (buffer->scratch_flags & HB_BUFFER_SCRATCH_FLAG_HAS_CGJ)
    {
      /* For all CGJ, check if it prevented any reordering at all.
       * If it did NOT, then make it skippable.
       * https://github.com/harfbuzz/harfbuzz/issues/554
       */
      for (unsigned int i = 1; i + 1 < buffer->len; i++)
        if (buffer->info[i].codepoint == 0x034Fu/*CGJ*/ &&
  	  info_cc(buffer->info[i-1]) <= info_cc(buffer->info[i+1]))
        {
  	_hb_glyph_info_unhide (&buffer->info[i]);
        }
    }
  
  
    /* Third round, recompose */
  
    if (!all_simple &&
        (mode == HB_OT_SHAPE_NORMALIZATION_MODE_COMPOSED_DIACRITICS ||
         mode == HB_OT_SHAPE_NORMALIZATION_MODE_COMPOSED_DIACRITICS_NO_SHORT_CIRCUIT))
    {
      /* As noted in the comment earlier, we don't try to combine
       * ccc=0 chars with their previous Starter. */
  
      buffer->clear_output ();
      count = buffer->len;
      unsigned int starter = 0;
      buffer->next_glyph ();
      while (buffer->idx < count && buffer->successful)
      {
        hb_codepoint_t composed, glyph;
        if (/* We don't try to compose a non-mark character with it's preceding starter.
  	   * This is both an optimization to avoid trying to compose every two neighboring
  	   * glyphs in most scripts AND a desired feature for Hangul.  Apparently Hangul
  	   * fonts are not designed to mix-and-match pre-composed syllables and Jamo. */
  	  HB_UNICODE_GENERAL_CATEGORY_IS_MARK (_hb_glyph_info_get_general_category (&buffer->cur())))
        {
  	if (/* If there's anything between the starter and this char, they should have CCC
  	     * smaller than this character's. */
  	    (starter == buffer->out_len - 1 ||
  	     info_cc (buffer->prev()) < info_cc (buffer->cur())) &&
  	    /* And compose. */
  	    c.compose (&c,
  		       buffer->out_info[starter].codepoint,
  		       buffer->cur().codepoint,
  		       &composed) &&
  	    /* And the font has glyph for the composite. */
  	    font->get_nominal_glyph (composed, &glyph))
  	{
  	  /* Composes. */
  	  buffer->next_glyph (); /* Copy to out-buffer. */
  	  if (unlikely (!buffer->successful))
  	    return;
  	  buffer->merge_out_clusters (starter, buffer->out_len);
  	  buffer->out_len--; /* Remove the second composable. */
  	  /* Modify starter and carry on. */
  	  buffer->out_info[starter].codepoint = composed;
  	  buffer->out_info[starter].glyph_index() = glyph;
  	  _hb_glyph_info_set_unicode_props (&buffer->out_info[starter], buffer);
  
  	  continue;
  	}
        }
  
        /* Blocked, or doesn't compose. */
        buffer->next_glyph ();
  
        if (info_cc (buffer->prev()) == 0)
  	starter = buffer->out_len - 1;
      }
      buffer->swap_buffers ();
    }
  }
  