/*

 * 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-private.hh"

#include "hb-ot-shape-complex-private.hh"

#include "hb-ot-shape-private.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 decomposition,

 *     well, use the decomposition (preferring the canonical decomposition, but

 *     falling back to the compatibility decomposition if necessary).  The

 *     compatibility decomposition is really nice to have, for characters like

 *     ellipsis, or various-sized space characters.

 *

 *   - 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.

 *

 *   - We try compatibility decomposition if decomposing through canonical

 *     decomposition alone failed to find a sequence that the font supports.

 *     We don't try compatibility decomposition recursively during the canonical

 *     decomposition phase.  This has minimal impact.  There are only a handful

 *     of Greek letter that have canonical decompositions that include characters

 *     with compatibility decomposition.  Those can be found using this command:

 *

 *     egrep  "`echo -n ';('; grep ';<' UnicodeData.txt | cut -d';' -f1 | tr '\n' '|'; echo ') '`" UnicodeData.txt

 */

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 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 c->unicode->compose (a, b, ab);

}

static inline void

set_glyph (hb_glyph_info_t &info, hb_font_t *font)

{

  font->get_glyph (info.codepoint, 0, &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);

  _hb_glyph_info_set_unicode_props (&buffer->prev(), buffer->unicode);

}

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, b, a_glyph, b_glyph;

  hb_buffer_t * const buffer = c->buffer;

  hb_font_t * const font = c->font;

  if (!c->decompose (c, ab, &a, &b) ||

      (b && !font->get_glyph (b, 0, &b_glyph)))

    return 0;

  bool has_a = font->get_glyph (a, 0, &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;

}

/* Returns 0 if didn't decompose, number of resulting characters otherwise. */

static inline unsigned int

decompose_compatibility (const hb_ot_shape_normalize_context_t *c, hb_codepoint_t u)

{

  unsigned int len, i;

  hb_codepoint_t decomposed[HB_UNICODE_MAX_DECOMPOSITION_LEN];

  hb_codepoint_t glyphs[HB_UNICODE_MAX_DECOMPOSITION_LEN];

  len = c->buffer->unicode->decompose_compatibility (u, decomposed);

  if (!len)

    return 0;

  for (i = 0; i < len; i++)

    if (!c->font->get_glyph (decomposed[i], 0, &glyphs[i]))

      return 0;

  for (i = 0; i < len; i++)

    output_char (c->buffer, decomposed[i], glyphs[i]);

  return len;

}

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;

  /* Kind of a cute waterfall here... */

  if (shortest && c->font->get_glyph (u, 0, &glyph))

    next_char (buffer, glyph);

  else if (decompose (c, shortest, u))

    skip_char (buffer);

  else if (!shortest && c->font->get_glyph (u, 0, &glyph))

    next_char (buffer, glyph);

  else if (decompose_compatibility (c, u))

    skip_char (buffer);

  else

    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)

{

  /* 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;) {

    if (unlikely (buffer->unicode->is_variation_selector (buffer->cur(+1).codepoint))) {

      /* The next two lines are some ugly lines... But work. */

      if (font->get_glyph (buffer->cur().codepoint, buffer->cur(+1).codepoint, &buffer->cur().glyph_index()))

      {

        buffer->replace_glyphs (2, 1, &buffer->cur().codepoint);

      }

      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; 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)

    decompose_current_character (c, short_circuit);

}

static inline void

decompose_cluster (const hb_ot_shape_normalize_context_t *c, unsigned int end, bool might_short_circuit, bool always_short_circuit)

{

  if (likely (c->buffer->idx + 1 == end))

    decompose_current_character (c, might_short_circuit);

  else

    decompose_multi_char_cluster (c, end, always_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;

  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 */

  buffer->clear_output ();

  count = buffer->len;

  for (buffer->idx = 0; buffer->idx < count;)

  {

    unsigned int end;

    for (end = buffer->idx + 1; end < count; end++)

      if (likely (!HB_UNICODE_GENERAL_CATEGORY_IS_MARK (_hb_glyph_info_get_general_category (&buffer->info[end]))))

        break;

    decompose_cluster (&c, end, might_short_circuit, always_short_circuit);

  }

  buffer->swap_buffers ();

  /* Second round, reorder (inplace) */

  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 > 10) {

      i = end;

      continue;

    }

    buffer->sort (i, end, compare_combining_class);

    i = end;

  }

  if (mode == HB_OT_SHAPE_NORMALIZATION_MODE_NONE ||

      mode == HB_OT_SHAPE_NORMALIZATION_MODE_DECOMPOSED)

    return;

  /* Third round, recompose */

  /* 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)

  {

    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 there's anything between the starter and this char, they should have CCC

         * smaller than this character's. */

        (starter == buffer->out_len - 1 ||

         _hb_glyph_info_get_modified_combining_class (&buffer->prev()) < _hb_glyph_info_get_modified_combining_class (&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_glyph (composed, 0, &glyph))

    {

      /* Composes. */

      buffer->next_glyph (); /* Copy to out-buffer. */

      if (unlikely (buffer->in_error))

        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->unicode);

      continue;

    }

    /* Blocked, or doesn't compose. */

    buffer->next_glyph ();

    if (_hb_glyph_info_get_modified_combining_class (&buffer->prev()) == 0)

      starter = buffer->out_len - 1;

  }

  buffer->swap_buffers ();

}