/*

 * Copyright © 2010,2012  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.hh"

#ifndef HB_NO_OT_SHAPE

#include "hb-ot-shaper-arabic.hh"

#include "hb-ot-shape.hh"

/* buffer var allocations */

#define arabic_shaping_action() ot_shaper_var_u8_auxiliary() /* arabic shaping action */

#define HB_BUFFER_SCRATCH_FLAG_ARABIC_HAS_STCH HB_BUFFER_SCRATCH_FLAG_SHAPER0

/* See:

 * https://github.com/harfbuzz/harfbuzz/commit/6e6f82b6f3dde0fc6c3c7d991d9ec6cfff57823d#commitcomment-14248516 */

#define HB_ARABIC_GENERAL_CATEGORY_IS_WORD(gen_cat) \

  (FLAG_UNSAFE (gen_cat) & \

   (FLAG (HB_UNICODE_GENERAL_CATEGORY_UNASSIGNED) | \

    FLAG (HB_UNICODE_GENERAL_CATEGORY_PRIVATE_USE) | \

    /*FLAG (HB_UNICODE_GENERAL_CATEGORY_LOWERCASE_LETTER) |*/ \

    FLAG (HB_UNICODE_GENERAL_CATEGORY_MODIFIER_LETTER) | \

    FLAG (HB_UNICODE_GENERAL_CATEGORY_OTHER_LETTER) | \

    /*FLAG (HB_UNICODE_GENERAL_CATEGORY_TITLECASE_LETTER) |*/ \

    /*FLAG (HB_UNICODE_GENERAL_CATEGORY_UPPERCASE_LETTER) |*/ \

    FLAG (HB_UNICODE_GENERAL_CATEGORY_SPACING_MARK) | \

    FLAG (HB_UNICODE_GENERAL_CATEGORY_ENCLOSING_MARK) | \

    FLAG (HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK) | \

    FLAG (HB_UNICODE_GENERAL_CATEGORY_DECIMAL_NUMBER) | \

    FLAG (HB_UNICODE_GENERAL_CATEGORY_LETTER_NUMBER) | \

    FLAG (HB_UNICODE_GENERAL_CATEGORY_OTHER_NUMBER) | \

    FLAG (HB_UNICODE_GENERAL_CATEGORY_CURRENCY_SYMBOL) | \

    FLAG (HB_UNICODE_GENERAL_CATEGORY_MODIFIER_SYMBOL) | \

    FLAG (HB_UNICODE_GENERAL_CATEGORY_MATH_SYMBOL) | \

    FLAG (HB_UNICODE_GENERAL_CATEGORY_OTHER_SYMBOL)))

/*

 * Joining types:

 */

/*

 * Bits used in the joining tables

 */

enum hb_arabic_joining_type_t {

  JOINING_TYPE_U    = 0,

  JOINING_TYPE_L    = 1,

  JOINING_TYPE_R    = 2,

  JOINING_TYPE_D    = 3,

  JOINING_TYPE_C    = JOINING_TYPE_D,

  JOINING_GROUP_ALAPH   = 4,

  JOINING_GROUP_DALATH_RISH = 5,

  NUM_STATE_MACHINE_COLS  = 6,

  JOINING_TYPE_T = 7,

  JOINING_TYPE_X = 8  /* means: use general-category to choose between U or T. */

};

#include "hb-ot-shaper-arabic-table.hh"

static unsigned int get_joining_type (hb_codepoint_t u, hb_unicode_general_category_t gen_cat)

{

  unsigned int j_type = joining_type(u);

  if (likely (j_type != JOINING_TYPE_X))

    return j_type;

  return (FLAG_UNSAFE(gen_cat) &

    (FLAG(HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK) |

     FLAG(HB_UNICODE_GENERAL_CATEGORY_ENCLOSING_MARK) |

     FLAG(HB_UNICODE_GENERAL_CATEGORY_FORMAT))

   ) ?  JOINING_TYPE_T : JOINING_TYPE_U;

}

#define FEATURE_IS_SYRIAC(tag) hb_in_range<unsigned char> ((unsigned char) (tag), '2', '3')

static const hb_tag_t arabic_features[] =

{

  HB_TAG('i','s','o','l'),

  HB_TAG('f','i','n','a'),

  HB_TAG('f','i','n','2'),

  HB_TAG('f','i','n','3'),

  HB_TAG('m','e','d','i'),

  HB_TAG('m','e','d','2'),

  HB_TAG('i','n','i','t'),

  HB_TAG_NONE

};

/* Same order as the feature array */

enum arabic_action_t {

  ISOL,

  FINA,

  FIN2,

  FIN3,

  MEDI,

  MED2,

  INIT,

  NONE,

  ARABIC_NUM_FEATURES = NONE,

  /* We abuse the same byte for other things... */

  STCH_FIXED,

  STCH_REPEATING,

};

static const struct arabic_state_table_entry {

  uint8_t prev_action;

  uint8_t curr_action;

  uint16_t next_state;

} arabic_state_table[][NUM_STATE_MACHINE_COLS] =

{

  /*   jt_U,          jt_L,          jt_R,          jt_D,          jg_ALAPH,      jg_DALATH_RISH */

  /* State 0: prev was U, not willing to join. */

  { {NONE,NONE,0}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,6}, },

  /* State 1: prev was R or ISOL/ALAPH, not willing to join. */

  { {NONE,NONE,0}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,2}, {NONE,FIN2,5}, {NONE,ISOL,6}, },

  /* State 2: prev was D/L in ISOL form, willing to join. */

  { {NONE,NONE,0}, {NONE,ISOL,2}, {INIT,FINA,1}, {INIT,FINA,3}, {INIT,FINA,4}, {INIT,FINA,6}, },

  /* State 3: prev was D in FINA form, willing to join. */

  { {NONE,NONE,0}, {NONE,ISOL,2}, {MEDI,FINA,1}, {MEDI,FINA,3}, {MEDI,FINA,4}, {MEDI,FINA,6}, },

  /* State 4: prev was FINA ALAPH, not willing to join. */

  { {NONE,NONE,0}, {NONE,ISOL,2}, {MED2,ISOL,1}, {MED2,ISOL,2}, {MED2,FIN2,5}, {MED2,ISOL,6}, },

  /* State 5: prev was FIN2/FIN3 ALAPH, not willing to join. */

  { {NONE,NONE,0}, {NONE,ISOL,2}, {ISOL,ISOL,1}, {ISOL,ISOL,2}, {ISOL,FIN2,5}, {ISOL,ISOL,6}, },

  /* State 6: prev was DALATH/RISH, not willing to join. */

  { {NONE,NONE,0}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,2}, {NONE,FIN3,5}, {NONE,ISOL,6}, }

};

static bool

arabic_fallback_shape (const hb_ot_shape_plan_t *plan,

           hb_font_t *font,

           hb_buffer_t *buffer);

static bool

record_stch (const hb_ot_shape_plan_t *plan,

       hb_font_t *font,

       hb_buffer_t *buffer);

static bool

deallocate_buffer_var (const hb_ot_shape_plan_t *plan,

           hb_font_t *font,

           hb_buffer_t *buffer)

{

  HB_BUFFER_DEALLOCATE_VAR (buffer, arabic_shaping_action);

  return false;

}

static void

collect_features_arabic (hb_ot_shape_planner_t *plan)

{

  hb_ot_map_builder_t *map = &plan->map;

  /* We apply features according to the Arabic spec, with pauses

   * in between most.

   *

   * The pause between init/medi/... and rlig is required.  See eg:

   * https://bugzilla.mozilla.org/show_bug.cgi?id=644184

   *

   * The pauses between init/medi/... themselves are not necessarily

   * needed as only one of those features is applied to any character.

   * The only difference it makes is when fonts have contextual

   * substitutions.  We now follow the order of the spec, which makes

   * for better experience if that's what Uniscribe is doing.

   *

   * At least for Arabic, looks like Uniscribe has a pause between

   * rlig and calt.  Otherwise the IranNastaliq's ALLAH ligature won't

   * work.  However, testing shows that rlig and calt are applied

   * together for Mongolian in Uniscribe.  As such, we only add a

   * pause for Arabic, not other scripts.

   */

  map->enable_feature (HB_TAG('s','t','c','h'));

  map->add_gsub_pause (record_stch);

  map->enable_feature (HB_TAG('c','c','m','p'), F_MANUAL_ZWJ);

  map->enable_feature (HB_TAG('l','o','c','l'), F_MANUAL_ZWJ);

  map->add_gsub_pause (nullptr);

  for (unsigned int i = 0; i < ARABIC_NUM_FEATURES; i++)

  {

    bool has_fallback = plan->props.script == HB_SCRIPT_ARABIC && !FEATURE_IS_SYRIAC (arabic_features[i]);

    map->add_feature (arabic_features[i], F_MANUAL_ZWJ | (has_fallback ? F_HAS_FALLBACK : F_NONE));

    map->add_gsub_pause (nullptr);

  }

   map->add_gsub_pause (deallocate_buffer_var);

  /* Normally, Unicode says a ZWNJ means "don't ligate".  In Arabic script

   * however, it says a ZWJ should also mean "don't ligate".  So we run

   * the main ligating features as MANUAL_ZWJ. */

  map->enable_feature (HB_TAG('r','l','i','g'), F_MANUAL_ZWJ | F_HAS_FALLBACK);

  if (plan->props.script == HB_SCRIPT_ARABIC)

    map->add_gsub_pause (arabic_fallback_shape);

   map->enable_feature (HB_TAG('c','a','l','t'), F_MANUAL_ZWJ);

   /* https://github.com/harfbuzz/harfbuzz/issues/1573 */

   if (!map->has_feature (HB_TAG('r','c','l','t')))

     map->add_gsub_pause (nullptr);

   map->enable_feature (HB_TAG('l','i','g','a'), F_MANUAL_ZWJ);

   map->enable_feature (HB_TAG('c','l','i','g'), F_MANUAL_ZWJ);

  /* The spec includes 'cswh'.  Earlier versions of Windows

   * used to enable this by default, but testing suggests

   * that Windows 8 and later do not enable it by default,

   * and spec now says 'Off by default'.

   * We disabled this in ae23c24c32.

   * Note that IranNastaliq uses this feature extensively

   * to fixup broken glyph sequences.  Oh well...

   * Test case: U+0643,U+0640,U+0631. */

  //map->enable_feature (HB_TAG('c','s','w','h'), F_MANUAL_ZWJ);

  map->enable_feature (HB_TAG('m','s','e','t'), F_MANUAL_ZWJ);

}

#include "hb-ot-shaper-arabic-fallback.hh"

struct arabic_shape_plan_t

{

  /* The "+ 1" in the next array is to accommodate for the "NONE" command,

   * which is not an OpenType feature, but this simplifies the code by not

   * having to do a "if (... < NONE) ..." and just rely on the fact that

   * mask_array[NONE] == 0. */

  hb_mask_t mask_array[ARABIC_NUM_FEATURES + 1];

  mutable hb_atomic_t<arabic_fallback_plan_t *> fallback_plan;

  unsigned int do_fallback : 1;

  unsigned int has_stch : 1;

};

void *

data_create_arabic (const hb_ot_shape_plan_t *plan)

{

  arabic_shape_plan_t *arabic_plan = (arabic_shape_plan_t *) hb_calloc (1, sizeof (arabic_shape_plan_t));

  if (unlikely (!arabic_plan))

    return nullptr;

  arabic_plan->do_fallback = plan->props.script == HB_SCRIPT_ARABIC;

  arabic_plan->has_stch = !!plan->map.get_1_mask (HB_TAG ('s','t','c','h'));

  for (unsigned int i = 0; i < ARABIC_NUM_FEATURES; i++) {

    arabic_plan->mask_array[i] = plan->map.get_1_mask (arabic_features[i]);

    arabic_plan->do_fallback = arabic_plan->do_fallback &&

             (FEATURE_IS_SYRIAC (arabic_features[i]) ||

        plan->map.needs_fallback (arabic_features[i]));

  }

  return arabic_plan;

}

void

data_destroy_arabic (void *data)

{

  arabic_shape_plan_t *arabic_plan = (arabic_shape_plan_t *) data;

  arabic_fallback_plan_destroy (arabic_plan->fallback_plan);

  hb_free (data);

}

static void

arabic_joining (hb_buffer_t *buffer)

{

  unsigned int count = buffer->len;

  hb_glyph_info_t *info = buffer->info;

  unsigned int prev = UINT_MAX, state = 0;

  /* Check pre-context */

  for (unsigned int i = 0; i < buffer->context_len[0]; i++)

  {

    unsigned int this_type = get_joining_type (buffer->context[0][i], buffer->unicode->general_category (buffer->context[0][i]));

    if (unlikely (this_type == JOINING_TYPE_T))

      continue;

    const arabic_state_table_entry *entry = &arabic_state_table[state][this_type];

    state = entry->next_state;

    break;

  }

  for (unsigned int i = 0; i < count; i++)

  {

    unsigned int this_type = get_joining_type (info[i].codepoint, _hb_glyph_info_get_general_category (&info[i]));

    if (unlikely (this_type == JOINING_TYPE_T)) {

      info[i].arabic_shaping_action() = NONE;

      continue;

    }

    const arabic_state_table_entry *entry = &arabic_state_table[state][this_type];

    if (entry->prev_action != NONE && prev != UINT_MAX)

    {

      info[prev].arabic_shaping_action() = entry->prev_action;

      buffer->safe_to_insert_tatweel (prev, i + 1);

    }

    else

    {

      if (prev == UINT_MAX)

      {

        if (this_type >= JOINING_TYPE_R)

    buffer->unsafe_to_concat_from_outbuffer (0, i + 1);

      }

      else

      {

  if (this_type >= JOINING_TYPE_R ||

      (2 <= state && state <= 5) /* States that have a possible prev_action. */)

    buffer->unsafe_to_concat (prev, i + 1);

      }

    }

    info[i].arabic_shaping_action() = entry->curr_action;

    prev = i;

    state = entry->next_state;

  }

  for (unsigned int i = 0; i < buffer->context_len[1]; i++)

  {

    unsigned int this_type = get_joining_type (buffer->context[1][i], buffer->unicode->general_category (buffer->context[1][i]));

    if (unlikely (this_type == JOINING_TYPE_T))

      continue;

    const arabic_state_table_entry *entry = &arabic_state_table[state][this_type];

    if (entry->prev_action != NONE && prev != UINT_MAX)

    {

      info[prev].arabic_shaping_action() = entry->prev_action;

      buffer->safe_to_insert_tatweel (prev, buffer->len);

    }

    else if (2 <= state && state <= 5) /* States that have a possible prev_action. */

    {

      buffer->unsafe_to_concat (prev, buffer->len);

    }

    break;

  }

}

static void

mongolian_variation_selectors (hb_buffer_t *buffer)

{

  /* Copy arabic_shaping_action() from base to Mongolian variation selectors. */

  unsigned int count = buffer->len;

  hb_glyph_info_t *info = buffer->info;

  for (unsigned int i = 1; i < count; i++)

    if (unlikely (hb_in_ranges<hb_codepoint_t> (info[i].codepoint, 0x180Bu, 0x180Du, 0x180Fu, 0x180Fu)))

      info[i].arabic_shaping_action() = info[i - 1].arabic_shaping_action();

}

void

setup_masks_arabic_plan (const arabic_shape_plan_t *arabic_plan,

       hb_buffer_t               *buffer,

       hb_script_t                script)

{

  HB_BUFFER_ALLOCATE_VAR (buffer, arabic_shaping_action);

  arabic_joining (buffer);

  if (script == HB_SCRIPT_MONGOLIAN)

    mongolian_variation_selectors (buffer);

  unsigned int count = buffer->len;

  hb_glyph_info_t *info = buffer->info;

  for (unsigned int i = 0; i < count; i++)

    info[i].mask |= arabic_plan->mask_array[info[i].arabic_shaping_action()];

}

static void

setup_masks_arabic (const hb_ot_shape_plan_t *plan,

        hb_buffer_t              *buffer,

        hb_font_t                *font HB_UNUSED)

{

  const arabic_shape_plan_t *arabic_plan = (const arabic_shape_plan_t *) plan->data;

  setup_masks_arabic_plan (arabic_plan, buffer, plan->props.script);

}

static bool

arabic_fallback_shape (const hb_ot_shape_plan_t *plan,

           hb_font_t *font,

           hb_buffer_t *buffer)

{

#ifdef HB_NO_OT_SHAPER_ARABIC_FALLBACK

  return false;

#endif

  const arabic_shape_plan_t *arabic_plan = (const arabic_shape_plan_t *) plan->data;

  if (!arabic_plan->do_fallback)

    return false;

retry:

  arabic_fallback_plan_t *fallback_plan = arabic_plan->fallback_plan;

  if (unlikely (!fallback_plan))

  {

    /* This sucks.  We need a font to build the fallback plan... */

    fallback_plan = arabic_fallback_plan_create (plan, font);

    if (unlikely (!arabic_plan->fallback_plan.cmpexch (nullptr, fallback_plan)))

    {

      arabic_fallback_plan_destroy (fallback_plan);

      goto retry;

    }

  }

  arabic_fallback_plan_shape (fallback_plan, font, buffer);

  return true;

}

/*

 * Stretch feature: "stch".

 * See example here:

 * https://docs.microsoft.com/en-us/typography/script-development/syriac

 * We implement this in a generic way, such that the Arabic subtending

 * marks can use it as well.

 */

static bool

record_stch (const hb_ot_shape_plan_t *plan,

       hb_font_t *font HB_UNUSED,

       hb_buffer_t *buffer)

{

  const arabic_shape_plan_t *arabic_plan = (const arabic_shape_plan_t *) plan->data;

  if (!arabic_plan->has_stch)

    return false;

  /* 'stch' feature was just applied.  Look for anything that multiplied,

   * and record it for stch treatment later.  Note that rtlm, frac, etc

   * are applied before stch, but we assume that they didn't result in

   * anything multiplying into 5 pieces, so it's safe-ish... */

  unsigned int count = buffer->len;

  hb_glyph_info_t *info = buffer->info;

  for (unsigned int i = 0; i < count; i++)

    if (unlikely (_hb_glyph_info_multiplied (&info[i])))

    {

      unsigned int comp = _hb_glyph_info_get_lig_comp (&info[i]);

      info[i].arabic_shaping_action() = comp % 2 ? STCH_REPEATING : STCH_FIXED;

      buffer->scratch_flags |= HB_BUFFER_SCRATCH_FLAG_ARABIC_HAS_STCH;

    }

  return false;

}

static void

apply_stch (const hb_ot_shape_plan_t *plan HB_UNUSED,

      hb_buffer_t              *buffer,

      hb_font_t                *font)

{

  if (likely (!(buffer->scratch_flags & HB_BUFFER_SCRATCH_FLAG_ARABIC_HAS_STCH)))

    return;

  bool rtl = buffer->props.direction == HB_DIRECTION_RTL;

  if (!rtl)

    buffer->reverse ();

  /* We do a two pass implementation:

   * First pass calculates the exact number of extra glyphs we need,

   * We then enlarge buffer to have that much room,

   * Second pass applies the stretch, copying things to the end of buffer.

   */

  int sign = font->x_scale < 0 ? -1 : +1;

  unsigned int extra_glyphs_needed = 0; // Set during MEASURE, used during CUT

  enum { MEASURE, CUT } /* step_t */;

  for (unsigned int step = MEASURE; step <= CUT; step = step + 1)

  {

    unsigned int count = buffer->len;

    hb_glyph_info_t *info = buffer->info;

    hb_glyph_position_t *pos = buffer->pos;

    unsigned int new_len = count + extra_glyphs_needed; // write head during CUT

    unsigned int j = new_len;

    for (unsigned int i = count; i; i--)

    {

      if (!hb_in_range<uint8_t> (info[i - 1].arabic_shaping_action(), STCH_FIXED, STCH_REPEATING))

      {

  if (step == CUT)

  {

    --j;

    info[j] = info[i - 1];

    pos[j] = pos[i - 1];

  }

  continue;

      }

      /* Yay, justification! */

      hb_position_t w_total = 0; // Total to be filled

      hb_position_t w_fixed = 0; // Sum of fixed tiles

      hb_position_t w_repeating = 0; // Sum of repeating tiles

      int n_fixed = 0;

      int n_repeating = 0;

      unsigned int end = i;

      while (i &&

       hb_in_range<uint8_t> (info[i - 1].arabic_shaping_action(), STCH_FIXED, STCH_REPEATING))

      {

  i--;

  hb_position_t width = font->get_glyph_h_advance (info[i].codepoint);

  if (info[i].arabic_shaping_action() == STCH_FIXED)

  {

    w_fixed += width;

    n_fixed++;

  }

  else

  {

    w_repeating += width;

    n_repeating++;

  }

      }

      unsigned int start = i;

      unsigned int context = i;

      while (context &&

       !hb_in_range<uint8_t> (info[context - 1].arabic_shaping_action(), STCH_FIXED, STCH_REPEATING) &&

       (_hb_glyph_info_is_default_ignorable (&info[context - 1]) ||

        HB_ARABIC_GENERAL_CATEGORY_IS_WORD (_hb_glyph_info_get_general_category (&info[context - 1]))))

      {

  context--;

  w_total += pos[context].x_advance;

      }

      i++; // Don't touch i again.

      DEBUG_MSG (ARABIC, nullptr, "%s stretch at (%u,%u,%u)",

     step == MEASURE ? "measuring" : "cutting", context, start, end);

      DEBUG_MSG (ARABIC, nullptr, "rest of word:    count=%u width %" PRId32, start - context, w_total);

      DEBUG_MSG (ARABIC, nullptr, "fixed tiles:     count=%d width=%" PRId32, n_fixed, w_fixed);

      DEBUG_MSG (ARABIC, nullptr, "repeating tiles: count=%d width=%" PRId32, n_repeating, w_repeating);

      /* Number of additional times to repeat each repeating tile. */

      int n_copies = 0;

      hb_position_t w_remaining = w_total - w_fixed;

      if (sign * w_remaining > sign * w_repeating && sign * w_repeating > 0)

  n_copies = (sign * w_remaining) / (sign * w_repeating) - 1;

      /* See if we can improve the fit by adding an extra repeat and squeezing them together a bit. */

      hb_position_t extra_repeat_overlap = 0;

      hb_position_t shortfall = sign * w_remaining - sign * w_repeating * (n_copies + 1);

      if (shortfall > 0 && n_repeating > 0)

      {

  ++n_copies;

  hb_position_t excess = (n_copies + 1) * sign * w_repeating - sign * w_remaining;

  if (excess > 0)

  {

    extra_repeat_overlap = excess / (n_copies * n_repeating);

    w_remaining = 0;

  }

      }

      if (step == MEASURE)

      {

  extra_glyphs_needed += n_copies * n_repeating;

  DEBUG_MSG (ARABIC, nullptr, "will add extra %d copies of repeating tiles", n_copies);

      }

      else

      {

  buffer->unsafe_to_break (context, end);

  hb_position_t x_offset = w_remaining / 2;

  for (unsigned int k = end; k > start; k--)

  {

    hb_position_t width = font->get_glyph_h_advance (info[k - 1].codepoint);

    unsigned int repeat = 1;

    if (info[k - 1].arabic_shaping_action() == STCH_REPEATING)

      repeat += n_copies;

    DEBUG_MSG (ARABIC, nullptr, "appending %u copies of glyph %" PRIu32 "; j=%u",

         repeat, info[k - 1].codepoint, j);

    pos[k - 1].x_advance = 0;

    for (unsigned int n = 0; n < repeat; n++)

    {

      if (rtl)

      {

        x_offset -= width;

        if (n > 0)

    x_offset += extra_repeat_overlap;

      }

      pos[k - 1].x_offset = x_offset;

      /* Append copy. */

      --j;

      info[j] = info[k - 1];

      pos[j] = pos[k - 1];

      if (!rtl)

      {

        x_offset += width;

        if (n > 0)

    x_offset -= extra_repeat_overlap;

      }

    }

  }

      }

    }

    if (step == MEASURE)

    {

      if (unlikely (!buffer->ensure (count + extra_glyphs_needed)))

  break;

    }

    else

    {

      assert (j == 0);

      buffer->len = new_len;

    }

  }

  if (!rtl)

    buffer->reverse ();

}

static void

postprocess_glyphs_arabic (const hb_ot_shape_plan_t *plan,

         hb_buffer_t              *buffer,

         hb_font_t                *font)

{

  apply_stch (plan, buffer, font);

}

/* https://www.unicode.org/reports/tr53/ */

static hb_codepoint_t

modifier_combining_marks[] =

{

  0x0654u, /* ARABIC HAMZA ABOVE */

  0x0655u, /* ARABIC HAMZA BELOW */

  0x0658u, /* ARABIC MARK NOON GHUNNA */

  0x06DCu, /* ARABIC SMALL HIGH SEEN */

  0x06E3u, /* ARABIC SMALL LOW SEEN */

  0x06E7u, /* ARABIC SMALL HIGH YEH */

  0x06E8u, /* ARABIC SMALL HIGH NOON */

  0x08CAu, /* ARABIC SMALL HIGH FARSI YEH */

  0x08CBu, /* ARABIC SMALL HIGH YEH BARREE WITH TWO DOTS BELOW */

  0x08CDu, /* ARABIC SMALL HIGH ZAH */

  0x08CEu, /* ARABIC LARGE ROUND DOT ABOVE */

  0x08CFu, /* ARABIC LARGE ROUND DOT BELOW */

  0x08D3u, /* ARABIC SMALL LOW WAW */

  0x08F3u, /* ARABIC SMALL HIGH WAW */

};

static inline bool

info_is_mcm (const hb_glyph_info_t &info)

{

  hb_codepoint_t u = info.codepoint;

  for (unsigned int i = 0; i < ARRAY_LENGTH (modifier_combining_marks); i++)

    if (u == modifier_combining_marks[i])

      return true;

  return false;

}

static void

reorder_marks_arabic (const hb_ot_shape_plan_t *plan HB_UNUSED,

          hb_buffer_t              *buffer,

          unsigned int              start,

          unsigned int              end)

{

  hb_glyph_info_t *info = buffer->info;

  DEBUG_MSG (ARABIC, buffer, "Reordering marks from %u to %u", start, end);

  unsigned int i = start;

  for (unsigned int cc = 220; cc <= 230; cc += 10)

  {

    DEBUG_MSG (ARABIC, buffer, "Looking for %u's starting at %u", cc, i);

    while (i < end && info_cc(info[i]) < cc)

      i++;

    DEBUG_MSG (ARABIC, buffer, "Looking for %u's stopped at %u", cc, i);

    if (i == end)

      break;

    if (info_cc(info[i]) > cc)

      continue;

    unsigned int j = i;

    while (j < end && info_cc(info[j]) == cc && info_is_mcm (info[j]))

      j++;

    if (i == j)

      continue;

    DEBUG_MSG (ARABIC, buffer, "Found %u's from %u to %u", cc, i, j);

    /* Shift it! */

    DEBUG_MSG (ARABIC, buffer, "Shifting %u's: %u %u", cc, i, j);

    hb_glyph_info_t temp[HB_OT_SHAPE_MAX_COMBINING_MARKS];

    assert (j - i <= ARRAY_LENGTH (temp));

    buffer->merge_clusters (start, j);

    memmove (temp, &info[i], (j - i) * sizeof (hb_glyph_info_t));

    memmove (&info[start + j - i], &info[start], (i - start) * sizeof (hb_glyph_info_t));

    memmove (&info[start], temp, (j - i) * sizeof (hb_glyph_info_t));

    /* Renumber CC such that the reordered sequence is still sorted.

     * 22 and 26 are chosen because they are smaller than all Arabic categories,

     * and are folded back to 220/230 respectively during fallback mark positioning.

     *

     * We do this because the CGJ-handling logic in the normalizer relies on

     * mark sequences having an increasing order even after this reordering.

     * https://github.com/harfbuzz/harfbuzz/issues/554

     * This, however, does break some obscure sequences, where the normalizer

     * might compose a sequence that it should not.  For example, in the seequence

     * ALEF, HAMZAH, MADDAH, we should NOT try to compose ALEF+MADDAH, but with this

     * renumbering, we will.

     */

    unsigned int new_start = start + j - i;

    unsigned int new_cc = cc == 220 ? HB_MODIFIED_COMBINING_CLASS_CCC22 : HB_MODIFIED_COMBINING_CLASS_CCC26;

    while (start < new_start)

    {

      _hb_glyph_info_set_modified_combining_class (&info[start], new_cc);

      start++;

    }

    i = j;

  }

}

const hb_ot_shaper_t _hb_ot_shaper_arabic =

{

  collect_features_arabic,

  nullptr, /* override_features */

  data_create_arabic,

  data_destroy_arabic,

  nullptr, /* preprocess_text */

  postprocess_glyphs_arabic,

  nullptr, /* decompose */

  nullptr, /* compose */

  setup_masks_arabic,

  reorder_marks_arabic,

  HB_TAG_NONE, /* gpos_tag */

  HB_OT_SHAPE_NORMALIZATION_MODE_DEFAULT,

  HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_LATE,

  true, /* fallback_position */

};

#endif