/*

 * Copyright © 2007,2008,2009,2010  Red Hat, Inc.

 * 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.

 *

 * Red Hat Author(s): Behdad Esfahbod

 * Google Author(s): Behdad Esfahbod

 */

#ifndef HB_OT_LAYOUT_GSUBGPOS_PRIVATE_HH

#define HB_OT_LAYOUT_GSUBGPOS_PRIVATE_HH

#include "hb-buffer-private.hh"

#include "hb-ot-layout-gdef-table.hh"

#include "hb-set-private.hh"

namespace OT {

#ifndef HB_DEBUG_CLOSURE

#define HB_DEBUG_CLOSURE (HB_DEBUG+0)

#endif

#define TRACE_CLOSURE(this) \

	hb_auto_trace_t<HB_DEBUG_CLOSURE, hb_void_t> trace \

	(&c->debug_depth, c->get_name (), this, HB_FUNC, \

	 "");

struct hb_closure_context_t :

       hb_dispatch_context_t<hb_closure_context_t, hb_void_t, HB_DEBUG_CLOSURE>

{

  inline const char *get_name (void) { return "CLOSURE"; }

  typedef return_t (*recurse_func_t) (hb_closure_context_t *c, unsigned int lookup_index);

  template <typename T>

  inline return_t dispatch (const T &obj) { obj.closure (this); return HB_VOID; }

  static return_t default_return_value (void) { return HB_VOID; }

  bool stop_sublookup_iteration (return_t r HB_UNUSED) const { return false; }

  return_t recurse (unsigned int lookup_index)

  {

    if (unlikely (nesting_level_left == 0 || !recurse_func))

      return default_return_value ();

    nesting_level_left--;

    recurse_func (this, lookup_index);

    nesting_level_left++;

    return HB_VOID;

  }

  hb_face_t *face;

  hb_set_t *glyphs;

  recurse_func_t recurse_func;

  unsigned int nesting_level_left;

  unsigned int debug_depth;

  hb_closure_context_t (hb_face_t *face_,

			hb_set_t *glyphs_,

		        unsigned int nesting_level_left_ = HB_MAX_NESTING_LEVEL) :

			  face (face_),

			  glyphs (glyphs_),

			  recurse_func (NULL),

			  nesting_level_left (nesting_level_left_),

			  debug_depth (0) {}

  void set_recurse_func (recurse_func_t func) { recurse_func = func; }

};

#ifndef HB_DEBUG_WOULD_APPLY

#define HB_DEBUG_WOULD_APPLY (HB_DEBUG+0)

#endif

#define TRACE_WOULD_APPLY(this) \

	hb_auto_trace_t<HB_DEBUG_WOULD_APPLY, bool> trace \

	(&c->debug_depth, c->get_name (), this, HB_FUNC, \

	 "%d glyphs", c->len);

struct hb_would_apply_context_t :

       hb_dispatch_context_t<hb_would_apply_context_t, bool, HB_DEBUG_WOULD_APPLY>

{

  inline const char *get_name (void) { return "WOULD_APPLY"; }

  template <typename T>

  inline return_t dispatch (const T &obj) { return obj.would_apply (this); }

  static return_t default_return_value (void) { return false; }

  bool stop_sublookup_iteration (return_t r) const { return r; }

  hb_face_t *face;

  const hb_codepoint_t *glyphs;

  unsigned int len;

  bool zero_context;

  unsigned int debug_depth;

  hb_would_apply_context_t (hb_face_t *face_,

			    const hb_codepoint_t *glyphs_,

			    unsigned int len_,

			    bool zero_context_) :

			      face (face_),

			      glyphs (glyphs_),

			      len (len_),

			      zero_context (zero_context_),

			      debug_depth (0) {}

};

#ifndef HB_DEBUG_COLLECT_GLYPHS

#define HB_DEBUG_COLLECT_GLYPHS (HB_DEBUG+0)

#endif

#define TRACE_COLLECT_GLYPHS(this) \

	hb_auto_trace_t<HB_DEBUG_COLLECT_GLYPHS, hb_void_t> trace \

	(&c->debug_depth, c->get_name (), this, HB_FUNC, \

	 "");

struct hb_collect_glyphs_context_t :

       hb_dispatch_context_t<hb_collect_glyphs_context_t, hb_void_t, HB_DEBUG_COLLECT_GLYPHS>

{

  inline const char *get_name (void) { return "COLLECT_GLYPHS"; }

  typedef return_t (*recurse_func_t) (hb_collect_glyphs_context_t *c, unsigned int lookup_index);

  template <typename T>

  inline return_t dispatch (const T &obj) { obj.collect_glyphs (this); return HB_VOID; }

  static return_t default_return_value (void) { return HB_VOID; }

  bool stop_sublookup_iteration (return_t r HB_UNUSED) const { return false; }

  return_t recurse (unsigned int lookup_index)

  {

    if (unlikely (nesting_level_left == 0 || !recurse_func))

      return default_return_value ();

    /* Note that GPOS sets recurse_func to NULL already, so it doesn't get

     * past the previous check.  For GSUB, we only want to collect the output

     * glyphs in the recursion.  If output is not requested, we can go home now.

     *

     * Note further, that the above is not exactly correct.  A recursed lookup

     * is allowed to match input that is not matched in the context, but that's

     * not how most fonts are built.  It's possible to relax that and recurse

     * with all sets here if it proves to be an issue.

     */

    if (output == hb_set_get_empty ())

      return HB_VOID;

    /* Return if new lookup was recursed to before. */

    if (recursed_lookups.has (lookup_index))

      return HB_VOID;

    hb_set_t *old_before = before;

    hb_set_t *old_input  = input;

    hb_set_t *old_after  = after;

    before = input = after = hb_set_get_empty ();

    nesting_level_left--;

    recurse_func (this, lookup_index);

    nesting_level_left++;

    before = old_before;

    input  = old_input;

    after  = old_after;

    recursed_lookups.add (lookup_index);

    return HB_VOID;

  }

  hb_face_t *face;

  hb_set_t *before;

  hb_set_t *input;

  hb_set_t *after;

  hb_set_t *output;

  recurse_func_t recurse_func;

  hb_set_t recursed_lookups;

  unsigned int nesting_level_left;

  unsigned int debug_depth;

  hb_collect_glyphs_context_t (hb_face_t *face_,

			       hb_set_t  *glyphs_before, /* OUT. May be NULL */

			       hb_set_t  *glyphs_input,  /* OUT. May be NULL */

			       hb_set_t  *glyphs_after,  /* OUT. May be NULL */

			       hb_set_t  *glyphs_output, /* OUT. May be NULL */

			       unsigned int nesting_level_left_ = HB_MAX_NESTING_LEVEL) :

			      face (face_),

			      before (glyphs_before ? glyphs_before : hb_set_get_empty ()),

			      input  (glyphs_input  ? glyphs_input  : hb_set_get_empty ()),

			      after  (glyphs_after  ? glyphs_after  : hb_set_get_empty ()),

			      output (glyphs_output ? glyphs_output : hb_set_get_empty ()),

			      recurse_func (NULL),

			      recursed_lookups (),

			      nesting_level_left (nesting_level_left_),

			      debug_depth (0)

  {

    recursed_lookups.init ();

  }

  ~hb_collect_glyphs_context_t (void)

  {

    recursed_lookups.fini ();

  }

  void set_recurse_func (recurse_func_t func) { recurse_func = func; }

};

#ifndef HB_DEBUG_GET_COVERAGE

#define HB_DEBUG_GET_COVERAGE (HB_DEBUG+0)

#endif

/* XXX Can we remove this? */

template <typename set_t>

struct hb_add_coverage_context_t :

       hb_dispatch_context_t<hb_add_coverage_context_t<set_t>, const Coverage &, HB_DEBUG_GET_COVERAGE>

{

  inline const char *get_name (void) { return "GET_COVERAGE"; }

  typedef const Coverage &return_t;

  template <typename T>

  inline return_t dispatch (const T &obj) { return obj.get_coverage (); }

  static return_t default_return_value (void) { return Null(Coverage); }

  bool stop_sublookup_iteration (return_t r) const

  {

    r.add_coverage (set);

    return false;

  }

  hb_add_coverage_context_t (set_t *set_) :

			    set (set_),

			    debug_depth (0) {}

  set_t *set;

  unsigned int debug_depth;

};

#ifndef HB_DEBUG_APPLY

#define HB_DEBUG_APPLY (HB_DEBUG+0)

#endif

#define TRACE_APPLY(this) \

	hb_auto_trace_t<HB_DEBUG_APPLY, bool> trace \

	(&c->debug_depth, c->get_name (), this, HB_FUNC, \

	 "idx %d gid %u lookup %d", \

	 c->buffer->idx, c->buffer->cur().codepoint, (int) c->lookup_index);

struct hb_apply_context_t :

       hb_dispatch_context_t<hb_apply_context_t, bool, HB_DEBUG_APPLY>

{

  struct matcher_t

  {

    inline matcher_t (void) :

	     lookup_props (0),

	     ignore_zwnj (false),

	     ignore_zwj (false),

	     mask (-1),

#define arg1(arg) (arg) /* Remove the macro to see why it's needed! */

	     syllable arg1(0),

#undef arg1

	     match_func (NULL),

	     match_data (NULL) {};

    typedef bool (*match_func_t) (hb_codepoint_t glyph_id, const USHORT &value, const void *data);

    inline void set_ignore_zwnj (bool ignore_zwnj_) { ignore_zwnj = ignore_zwnj_; }

    inline void set_ignore_zwj (bool ignore_zwj_) { ignore_zwj = ignore_zwj_; }

    inline void set_lookup_props (unsigned int lookup_props_) { lookup_props = lookup_props_; }

    inline void set_mask (hb_mask_t mask_) { mask = mask_; }

    inline void set_syllable (uint8_t syllable_)  { syllable = syllable_; }

    inline void set_match_func (match_func_t match_func_,

				const void *match_data_)

    { match_func = match_func_; match_data = match_data_; }

    enum may_match_t {

      MATCH_NO,

      MATCH_YES,

      MATCH_MAYBE

    };

    inline may_match_t may_match (const hb_glyph_info_t &info,

				  const USHORT          *glyph_data) const

    {

      if (!(info.mask & mask) ||

	  (syllable && syllable != info.syllable ()))

	return MATCH_NO;

      if (match_func)

        return match_func (info.codepoint, *glyph_data, match_data) ? MATCH_YES : MATCH_NO;

      return MATCH_MAYBE;

    }

    enum may_skip_t {

      SKIP_NO,

      SKIP_YES,

      SKIP_MAYBE

    };

    inline may_skip_t

    may_skip (const hb_apply_context_t *c,

	      const hb_glyph_info_t    &info) const

    {

      if (!c->check_glyph_property (&info, lookup_props))

	return SKIP_YES;

      if (unlikely (_hb_glyph_info_is_default_ignorable_and_not_hidden (&info) &&

		    (ignore_zwnj || !_hb_glyph_info_is_zwnj (&info)) &&

		    (ignore_zwj || !_hb_glyph_info_is_zwj (&info))))

	return SKIP_MAYBE;

      return SKIP_NO;

    }

    protected:

    unsigned int lookup_props;

    bool ignore_zwnj;

    bool ignore_zwj;

    hb_mask_t mask;

    uint8_t syllable;

    match_func_t match_func;

    const void *match_data;

  };

  struct skipping_iterator_t

  {

    inline void init (hb_apply_context_t *c_, bool context_match = false)

    {

      c = c_;

      match_glyph_data = NULL;

      matcher.set_match_func (NULL, NULL);

      matcher.set_lookup_props (c->lookup_props);

      /* Ignore ZWNJ if we are matching GSUB context, or matching GPOS. */

      matcher.set_ignore_zwnj (c->table_index == 1 || (context_match && c->auto_zwnj));

      /* Ignore ZWJ if we are matching GSUB context, or matching GPOS, or if asked to. */

      matcher.set_ignore_zwj  (c->table_index == 1 || (context_match || c->auto_zwj));

      matcher.set_mask (context_match ? -1 : c->lookup_mask);

    }

    inline void set_lookup_props (unsigned int lookup_props)

    {

      matcher.set_lookup_props (lookup_props);

    }

    inline void set_match_func (matcher_t::match_func_t match_func_,

				const void *match_data_,

				const USHORT glyph_data[])

    {

      matcher.set_match_func (match_func_, match_data_);

      match_glyph_data = glyph_data;

    }

    inline void reset (unsigned int start_index_,

		       unsigned int num_items_)

    {

      idx = start_index_;

      num_items = num_items_;

      end = c->buffer->len;

      matcher.set_syllable (start_index_ == c->buffer->idx ? c->buffer->cur().syllable () : 0);

    }

    inline void reject (void) { num_items++; match_glyph_data--; }

    inline bool next (void)

    {

      assert (num_items > 0);

      while (idx + num_items < end)

      {

	idx++;

	const hb_glyph_info_t &info = c->buffer->info[idx];

	matcher_t::may_skip_t skip = matcher.may_skip (c, info);

	if (unlikely (skip == matcher_t::SKIP_YES))

	  continue;

	matcher_t::may_match_t match = matcher.may_match (info, match_glyph_data);

	if (match == matcher_t::MATCH_YES ||

	    (match == matcher_t::MATCH_MAYBE &&

	     skip == matcher_t::SKIP_NO))

	{

	  num_items--;

	  match_glyph_data++;

	  return true;

	}

	if (skip == matcher_t::SKIP_NO)

	  return false;

      }

      return false;

    }

    inline bool prev (void)

    {

      assert (num_items > 0);

      while (idx >= num_items)

      {

	idx--;

	const hb_glyph_info_t &info = c->buffer->out_info[idx];

	matcher_t::may_skip_t skip = matcher.may_skip (c, info);

	if (unlikely (skip == matcher_t::SKIP_YES))

	  continue;

	matcher_t::may_match_t match = matcher.may_match (info, match_glyph_data);

	if (match == matcher_t::MATCH_YES ||

	    (match == matcher_t::MATCH_MAYBE &&

	     skip == matcher_t::SKIP_NO))

	{

	  num_items--;

	  match_glyph_data++;

	  return true;

	}

	if (skip == matcher_t::SKIP_NO)

	  return false;

      }

      return false;

    }

    unsigned int idx;

    protected:

    hb_apply_context_t *c;

    matcher_t matcher;

    const USHORT *match_glyph_data;

    unsigned int num_items;

    unsigned int end;

  };

  inline const char *get_name (void) { return "APPLY"; }

  typedef return_t (*recurse_func_t) (hb_apply_context_t *c, unsigned int lookup_index);

  template <typename T>

  inline return_t dispatch (const T &obj) { return obj.apply (this); }

  static return_t default_return_value (void) { return false; }

  bool stop_sublookup_iteration (return_t r) const { return r; }

  return_t recurse (unsigned int lookup_index)

  {

    if (unlikely (nesting_level_left == 0 || !recurse_func))

      return default_return_value ();

    nesting_level_left--;

    bool ret = recurse_func (this, lookup_index);

    nesting_level_left++;

    return ret;

  }

  skipping_iterator_t iter_input, iter_context;

  hb_font_t *font;

  hb_face_t *face;

  hb_buffer_t *buffer;

  recurse_func_t recurse_func;

  const GDEF &gde;;

  const VariationStore &var_store;

  hb_direction_t direction;

  hb_mask_t lookup_mask;

  unsigned int table_index; /* GSUB/GPOS */

  unsigned int lookup_index;

  unsigned int lookup_props;

  unsigned int nesting_level_left;

  unsigned int debug_depth;

  bool auto_zwnj;

  bool auto_zwj;

  bool has_glyph_classes;

  hb_apply_context_t (unsigned int table_index_,

		      hb_font_t *font_,

		      hb_buffer_t *buffer_) :

			iter_input (), iter_context (),

			font (font_), face (font->face), buffer (buffer_),

			recurse_func (NULL),

			gdef (*hb_ot_layout_from_face (face)->gdef),

			var_store (gdef.get_var_store ()),

			direction (buffer_->props.direction),

			lookup_mask (1),

			table_index (table_index_),

			lookup_index ((unsigned int) -1),

			lookup_props (0),

			nesting_level_left (HB_MAX_NESTING_LEVEL),

			debug_depth (0),

			auto_zwnj (true),

			auto_zwj (true),

			has_glyph_classes (gdef.has_glyph_classes ()) {}

  inline void set_lookup_mask (hb_mask_t mask) { lookup_mask = mask; }

  inline void set_auto_zwj (bool auto_zwj_) { auto_zwj = auto_zwj_; }

  inline void set_auto_zwnj (bool auto_zwnj_) { auto_zwnj = auto_zwnj_; }

  inline void set_recurse_func (recurse_func_t func) { recurse_func = func; }

  inline void set_lookup_index (unsigned int lookup_index_) { lookup_index = lookup_index_; }

  inline void set_lookup_props (unsigned int lookup_props_)

  {

    lookup_props = lookup_props_;

    iter_input.init (this, false);

    iter_context.init (this, true);

  }

  inline bool

  match_properties_mark (hb_codepoint_t  glyph,

			 unsigned int    glyph_props,

			 unsigned int    match_props) const

  {

    /* If using mark filtering sets, the high short of

     * match_props has the set index.

     */

    if (match_props & LookupFlag::UseMarkFilteringSet)

      return gdef.mark_set_covers (match_props >> 16, glyph);

    /* The second byte of match_props has the meaning

     * "ignore marks of attachment type different than

     * the attachment type specified."

     */

    if (match_props & LookupFlag::MarkAttachmentType)

      return (match_props & LookupFlag::MarkAttachmentType) == (glyph_props & LookupFlag::MarkAttachmentType);

    return true;

  }

  inline bool

  check_glyph_property (const hb_glyph_info_t *info,

			unsigned int  match_props) const

  {

    hb_codepoint_t glyph = info->codepoint;

    unsigned int glyph_props = _hb_glyph_info_get_glyph_props (info);

    /* Not covered, if, for example, glyph class is ligature and

     * match_props includes LookupFlags::IgnoreLigatures

     */

    if (glyph_props & match_props & LookupFlag::IgnoreFlags)

      return false;

    if (unlikely (glyph_props & HB_OT_LAYOUT_GLYPH_PROPS_MARK))

      return match_properties_mark (glyph, glyph_props, match_props);

    return true;

  }

  inline void _set_glyph_props (hb_codepoint_t glyph_index,

			  unsigned int class_guess = 0,

			  bool ligature = false,

			  bool component = false) const

  {

    unsigned int add_in = _hb_glyph_info_get_glyph_props (&buffer->cur()) &

			  HB_OT_LAYOUT_GLYPH_PROPS_PRESERVE;

    add_in |= HB_OT_LAYOUT_GLYPH_PROPS_SUBSTITUTED;

    if (ligature)

    {

      add_in |= HB_OT_LAYOUT_GLYPH_PROPS_LIGATED;

      /* In the only place that the MULTIPLIED bit is used, Uniscribe

       * seems to only care about the "last" transformation between

       * Ligature and Multiple substitions.  Ie. if you ligate, expand,

       * and ligate again, it forgives the multiplication and acts as

       * if only ligation happened.  As such, clear MULTIPLIED bit.

       */

      add_in &= ~HB_OT_LAYOUT_GLYPH_PROPS_MULTIPLIED;

    }

    if (component)

      add_in |= HB_OT_LAYOUT_GLYPH_PROPS_MULTIPLIED;

    if (likely (has_glyph_classes))

      _hb_glyph_info_set_glyph_props (&buffer->cur(), add_in | gdef.get_glyph_props (glyph_index));

    else if (class_guess)

      _hb_glyph_info_set_glyph_props (&buffer->cur(), add_in | class_guess);

  }

  inline void replace_glyph (hb_codepoint_t glyph_index) const

  {

    _set_glyph_props (glyph_index);

    buffer->replace_glyph (glyph_index);

  }

  inline void replace_glyph_inplace (hb_codepoint_t glyph_index) const

  {

    _set_glyph_props (glyph_index);

    buffer->cur().codepoint = glyph_index;

  }

  inline void replace_glyph_with_ligature (hb_codepoint_t glyph_index,

					   unsigned int class_guess) const

  {

    _set_glyph_props (glyph_index, class_guess, true);

    buffer->replace_glyph (glyph_index);

  }

  inline void output_glyph_for_component (hb_codepoint_t glyph_index,

					  unsigned int class_guess) const

  {

    _set_glyph_props (glyph_index, class_guess, false, true);

    buffer->output_glyph (glyph_index);

  }

};

typedef bool (*intersects_func_t) (hb_set_t *glyphs, const USHORT &value, const void *data);

typedef void (*collect_glyphs_func_t) (hb_set_t *glyphs, const USHORT &value, const void *data);

typedef bool (*match_func_t) (hb_codepoint_t glyph_id, const USHORT &value, const void *data);

struct ContextClosureFuncs

{

  intersects_func_t intersects;

};

struct ContextCollectGlyphsFuncs

{

  collect_glyphs_func_t collect;

};

struct ContextApplyFuncs

{

  match_func_t match;

};

static inline bool intersects_glyph (hb_set_t *glyphs, const USHORT &value, const void *data HB_UNUSED)

{

  return glyphs->has (value);

}

static inline bool intersects_class (hb_set_t *glyphs, const USHORT &value, const void *data)

{

  const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);

  return class_def.intersects_class (glyphs, value);

}

static inline bool intersects_coverage (hb_set_t *glyphs, const USHORT &value, const void *data)

{

  const OffsetTo<Coverage> &coverage = (const OffsetTo<Coverage>&)value;

  return (data+coverage).intersects (glyphs);

}

static inline bool intersects_array (hb_closure_context_t *c,

				     unsigned int count,

				     const USHORT values[],

				     intersects_func_t intersects_func,

				     const void *intersects_data)

{

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

    if (likely (!intersects_func (c->glyphs, values[i], intersects_data)))

      return false;

  return true;

}

static inline void collect_glyph (hb_set_t *glyphs, const USHORT &value, const void *data HB_UNUSED)

{

  glyphs->add (value);

}

static inline void collect_class (hb_set_t *glyphs, const USHORT &value, const void *data)

{

  const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);

  class_def.add_class (glyphs, value);

}

static inline void collect_coverage (hb_set_t *glyphs, const USHORT &value, const void *data)

{

  const OffsetTo<Coverage> &coverage = (const OffsetTo<Coverage>&)value;

  (data+coverage).add_coverage (glyphs);

}

static inline void collect_array (hb_collect_glyphs_context_t *c HB_UNUSED,

				  hb_set_t *glyphs,

				  unsigned int count,

				  const USHORT values[],

				  collect_glyphs_func_t collect_func,

				  const void *collect_data)

{

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

    collect_func (glyphs, values[i], collect_data);

}

static inline bool match_glyph (hb_codepoint_t glyph_id, const USHORT &value, const void *data HB_UNUSED)

{

  return glyph_id == value;

}

static inline bool match_class (hb_codepoint_t glyph_id, const USHORT &value, const void *data)

{

  const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);

  return class_def.get_class (glyph_id) == value;

}

static inline bool match_coverage (hb_codepoint_t glyph_id, const USHORT &value, const void *data)

{

  const OffsetTo<Coverage> &coverage = (const OffsetTo<Coverage>&)value;

  return (data+coverage).get_coverage (glyph_id) != NOT_COVERED;

}

static inline bool would_match_input (hb_would_apply_context_t *c,

				      unsigned int count, /* Including the first glyph (not matched) */

				      const USHORT input[], /* Array of input values--start with second glyph */

				      match_func_t match_func,

				      const void *match_data)

{

  if (count != c->len)

    return false;

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

    if (likely (!match_func (c->glyphs[i], input[i - 1], match_data)))

      return false;

  return true;

}

static inline bool match_input (hb_apply_context_t *c,

				unsigned int count, /* Including the first glyph (not matched) */

				const USHORT input[], /* Array of input values--start with second glyph */

				match_func_t match_func,

				const void *match_data,

				unsigned int *end_offset,

				unsigned int match_positions[HB_MAX_CONTEXT_LENGTH],

				bool *p_is_mark_ligature = NULL,

				unsigned int *p_total_component_count = NULL)

{

  TRACE_APPLY (NULL);

  if (unlikely (count > HB_MAX_CONTEXT_LENGTH)) return_trace (false);

  hb_buffer_t *buffer = c->buffer;

  hb_apply_context_t::skipping_iterator_t &skippy_iter = c->iter_input;

  skippy_iter.reset (buffer->idx, count - 1);

  skippy_iter.set_match_func (match_func, match_data, input);

  /*

   * This is perhaps the trickiest part of OpenType...  Remarks:

   *

   * - If all components of the ligature were marks, we call this a mark ligature.

   *

   * - If there is no GDEF, and the ligature is NOT a mark ligature, we categorize

   *   it as a ligature glyph.

   *

   * - Ligatures cannot be formed across glyphs attached to different components

   *   of previous ligatures.  Eg. the sequence is LAM,SHADDA,LAM,FATHA,HEH, and

   *   LAM,LAM,HEH form a ligature, leaving SHADDA,FATHA next to eachother.

   *   However, it would be wrong to ligate that SHADDA,FATHA sequence.o

   *   There is an exception to this: If a ligature tries ligating with marks that

   *   belong to it itself, go ahead, assuming that the font designer knows what

   *   they are doing (otherwise it can break Indic stuff when a matra wants to

   *   ligate with a conjunct...)

   */

  bool is_mark_ligature = _hb_glyph_info_is_mark (&buffer->cur());

  unsigned int total_component_count = 0;

  total_component_count += _hb_glyph_info_get_lig_num_comps (&buffer->cur());

  unsigned int first_lig_id = _hb_glyph_info_get_lig_id (&buffer->cur());

  unsigned int first_lig_comp = _hb_glyph_info_get_lig_comp (&buffer->cur());

  match_positions[0] = buffer->idx;

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

  {

    if (!skippy_iter.next ()) return_trace (false);

    match_positions[i] = skippy_iter.idx;

    unsigned int this_lig_id = _hb_glyph_info_get_lig_id (&buffer->info[skippy_iter.idx]);

    unsigned int this_lig_comp = _hb_glyph_info_get_lig_comp (&buffer->info[skippy_iter.idx]);

    if (first_lig_id && first_lig_comp) {

      /* If first component was attached to a previous ligature component,

       * all subsequent components should be attached to the same ligature

       * component, otherwise we shouldn't ligate them. */

      if (first_lig_id != this_lig_id || first_lig_comp != this_lig_comp)

	return_trace (false);

    } else {

      /* If first component was NOT attached to a previous ligature component,

       * all subsequent components should also NOT be attached to any ligature

       * component, unless they are attached to the first component itself! */

      if (this_lig_id && this_lig_comp && (this_lig_id != first_lig_id))

	return_trace (false);

    }

    is_mark_ligature = is_mark_ligature && _hb_glyph_info_is_mark (&buffer->info[skippy_iter.idx]);

    total_component_count += _hb_glyph_info_get_lig_num_comps (&buffer->info[skippy_iter.idx]);

  }

  *end_offset = skippy_iter.idx - buffer->idx + 1;

  if (p_is_mark_ligature)

    *p_is_mark_ligature = is_mark_ligature;

  if (p_total_component_count)

    *p_total_component_count = total_component_count;

  return_trace (true);

}

static inline bool ligate_input (hb_apply_context_t *c,

				 unsigned int count, /* Including the first glyph */

				 unsigned int match_positions[HB_MAX_CONTEXT_LENGTH], /* Including the first glyph */

				 unsigned int match_length,

				 hb_codepoint_t lig_glyph,

				 bool is_mark_ligature,

				 unsigned int total_component_count)

{

  TRACE_APPLY (NULL);

  hb_buffer_t *buffer = c->buffer;

  buffer->merge_clusters (buffer->idx, buffer->idx + match_length);

  /*

   * - If it *is* a mark ligature, we don't allocate a new ligature id, and leave

   *   the ligature to keep its old ligature id.  This will allow it to attach to

   *   a base ligature in GPOS.  Eg. if the sequence is: LAM,LAM,SHADDA,FATHA,HEH,

   *   and LAM,LAM,HEH for a ligature, they will leave SHADDA and FATHA wit a

   *   ligature id and component value of 2.  Then if SHADDA,FATHA form a ligature

   *   later, we don't want them to lose their ligature id/component, otherwise

   *   GPOS will fail to correctly position the mark ligature on top of the

   *   LAM,LAM,HEH ligature.  See:

   *     https://bugzilla.gnome.org/show_bug.cgi?id=676343

   *

   * - If a ligature is formed of components that some of which are also ligatures

   *   themselves, and those ligature components had marks attached to *their*

   *   components, we have to attach the marks to the new ligature component

   *   positions!  Now *that*'s tricky!  And these marks may be following the

   *   last component of the whole sequence, so we should loop forward looking

   *   for them and update them.

   *

   *   Eg. the sequence is LAM,LAM,SHADDA,FATHA,HEH, and the font first forms a

   *   'calt' ligature of LAM,HEH, leaving the SHADDA and FATHA with a ligature

   *   id and component == 1.  Now, during 'liga', the LAM and the LAM-HEH ligature

   *   form a LAM-LAM-HEH ligature.  We need to reassign the SHADDA and FATHA to

   *   the new ligature with a component value of 2.

   *

   *   This in fact happened to a font...  See:

   *   https://bugzilla.gnome.org/show_bug.cgi?id=437633

   */

  unsigned int klass = is_mark_ligature ? 0 : HB_OT_LAYOUT_GLYPH_PROPS_LIGATURE;

  unsigned int lig_id = is_mark_ligature ? 0 : _hb_allocate_lig_id (buffer);

  unsigned int last_lig_id = _hb_glyph_info_get_lig_id (&buffer->cur());

  unsigned int last_num_components = _hb_glyph_info_get_lig_num_comps (&buffer->cur());

  unsigned int components_so_far = last_num_components;

  if (!is_mark_ligature)

  {

    _hb_glyph_info_set_lig_props_for_ligature (&buffer->cur(), lig_id, total_component_count);

    if (_hb_glyph_info_get_general_category (&buffer->cur()) == HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK)

    {

      _hb_glyph_info_set_general_category (&buffer->cur(), HB_UNICODE_GENERAL_CATEGORY_OTHER_LETTER);

    }

  }

  c->replace_glyph_with_ligature (lig_glyph, klass);

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

  {

    while (buffer->idx < match_positions[i] && !buffer->in_error)

    {

      if (!is_mark_ligature) {

        unsigned int this_comp = _hb_glyph_info_get_lig_comp (&buffer->cur());

	if (this_comp == 0)

	  this_comp = last_num_components;

	unsigned int new_lig_comp = components_so_far - last_num_components +

				    MIN (this_comp, last_num_components);

	  _hb_glyph_info_set_lig_props_for_mark (&buffer->cur(), lig_id, new_lig_comp);

      }

      buffer->next_glyph ();

    }

    last_lig_id = _hb_glyph_info_get_lig_id (&buffer->cur());

    last_num_components = _hb_glyph_info_get_lig_num_comps (&buffer->cur());

    components_so_far += last_num_components;

    /* Skip the base glyph */

    buffer->idx++;

  }

  if (!is_mark_ligature && last_lig_id) {

    /* Re-adjust components for any marks following. */

    for (unsigned int i = buffer->idx; i < buffer->len; i++) {

      if (last_lig_id == _hb_glyph_info_get_lig_id (&buffer->info[i])) {

        unsigned int this_comp = _hb_glyph_info_get_lig_comp (&buffer->info[i]);

	if (!this_comp)

	  break;

	unsigned int new_lig_comp = components_so_far - last_num_components +