/* link_ref -- reference to a link */
struct link_ref {
  struct Blob id;     /* must be the first field as in footnote struct */
  struct Blob link;
  struct Blob title;
};

/* A footnote's data.
** id, text, and upc fields must be in that particular order.
*/
struct footnote {
  struct Blob id;      /* must be the first field as in link_ref struct  */
  struct Blob text;    /* footnote's content that is rendered at the end */
  struct Blob upc;     /* user-provided classes  .ASCII-alnum.or-hypen:  */
  int bRndred;         /* indicates if `text` holds a rendered content   */

  int defno;  /* serial number of definition, set during the first pass  */

  upc_offset = upc_size = 0;
  if( data[i]!='\n' && data[i]!='\r' ){
    size_t j;
    upc_size = is_footnote_classlist(data+i, end-i, 1);
    upc_offset = i; /* prevent further checks for a classlist */
    i += upc_size;
    j = i;
    while( i<end && data[i]!='\n' && data[i]!='\r' ){ i++; };
    if( i!=j )blob_append(&fn.text, data+j, i-j);
    if( i<end ){
      blob_append_char(&fn.text, data[i]);
      i++;
      if( i<end && data[i]=='\n' && data[i-1]=='\r' ){
        blob_append_char(&fn.text, data[i]);
        i++;
      }
    }
  }else{
    i++;
    if( i<end && data[i]=='\n' && data[i-1]=='\r' ) i++;
  }
  if( i<end ){

    /* compute the indentation from the 2nd line  */
    size_t indent = i;
    const char *spaces = data+i;
    while( indent<end && data[indent]==' ' ){ indent++; }
    if( indent>=end ) goto footnote_finish;
    indent -= i;

    if( indent<2 ) goto footnote_finish;

    /* process the 2nd and the following lines */
    while( i+indent<end && memcmp(data+i,spaces,indent)==0 ){
      size_t j;
      i += indent;
      if( !upc_offset ){
        /* a classlist must be provided no later than at the 2nd line */
        upc_offset = i + sizeof_blank_prefix(data+i, end-i, 1);
        upc_size = is_footnote_classlist(data+upc_offset, end-upc_offset, 1);
        if( upc_size ){
          i = upc_offset + upc_size;
        }
      }
      j = i;
      while( i<end && data[i]!='\n' && data[i]!='\r' ){ i++; }
      if( i!=j ) blob_append(&fn.text, data+j, i-j);
      if( i>=end ) break;
      blob_append_char(&fn.text, data[i]);
      i++;
      if( i<end && data[i]=='\n' && data[i-1]=='\r' ){
        blob_append_char(&fn.text, data[i]);
        i++;
      }

    int nDups = 0;
    fn = CAST_AS_FOOTNOTES( allNotes );
    qsort(fn, rndr.notes.nLbled, sizeof(struct footnote), cmp_footnote_id);

    /* concatenate footnotes with equal labels */
    for(i=0; i<rndr.notes.nLbled ;){
      struct footnote *x = fn + i;
      size_t j = i+1, k = blob_size(&x->text) + 64 + blob_size(&x->upc);
      while(j<rndr.notes.nLbled && !blob_compare(&x->id, &fn[j].id)){
        k += blob_size(&fn[j].text) + 10 + blob_size(&fn[j].upc);
        j++;
        nDups++;
      }
      if( i+1<j ){
        Blob list = empty_blob;
        blob_reserve(&list, k);
        /* must match _joined_footnote_indicator in html_footnote_item() */
        blob_append_string(&list, "<ul class='fn-joined'>\n");
        for(k=i; k<j; k++){
          struct footnote *y = fn + k;
          blob_append_string(&list, "<li>");
          if( blob_size(&y->upc) ){
            blob_append(&list, blob_buffer(&y->upc), blob_size(&y->upc));
            blob_reset(&y->upc);
          }
          blob_append(&list, blob_buffer(&y->text), blob_size(&y->text));
          blob_append_string(&list, "</li>\n");

          /* free memory buffer */
          blob_reset(&y->text);
          if( k!=i ) blob_reset(&y->id);
        }

    }
    release_work_buffer(&rndr,tmp);

    /* footnotes rendering */
    if( rndr.make.footnote_item && rndr.make.footnotes ){
      Blob *all_items = new_work_buffer(&rndr);
      int j = -1;

      /* Assert that the in-memory layout of id, text and upc within
      ** footnote struct matches the expectations of html_footnote_item()
      ** If it doesn't then a compiler has done something very weird.
      */
      const struct footnote *dummy = 0;
      assert( &(dummy->id)  == &(dummy->text) - 1 );
      assert( &(dummy->upc) == &(dummy->text) + 1 );

      for(i=0; i<COUNT_FOOTNOTES(notes); i++){
        const struct footnote* x = CAST_AS_FOOTNOTES(notes) + i;
        if( !x->iMark ) break;
        assert( x->nUsed );
        rndr.make.footnote_item(all_items, &x->text, x->iMark,
                 x->bRndred ? x->nUsed : 0, rndr.make.opaque);
        j = i;

      }
      if( rndr.notes.misref.nUsed ){
        rndr.make.footnote_item(all_items, 0, -1,
                    rndr.notes.misref.nUsed, rndr.make.opaque);
        g.ftntsIssues[0] += rndr.notes.misref.nUsed;
      }
      while( ++j < COUNT_FOOTNOTES(notes) ){
        const struct footnote* x = CAST_AS_FOOTNOTES(notes) + j;
        assert( !x->iMark );
        assert( !x->nUsed );

        assert( !x->bRndred );
        rndr.make.footnote_item(all_items,&x->text,0,0,rndr.make.opaque);
        g.ftntsIssues[1]++;
      }
      rndr.make.footnotes(ob, all_items, rndr.make.opaque);
      release_work_buffer(&rndr, all_items);
    }
    release_work_buffer(&rndr, notes);

/* Render a single item of the footnotes list.
 * Each backref gets a unique id to enable dynamic styling. */
static void html_footnote_item(
  struct Blob *ob, const struct Blob *text, int iMark, int nUsed, void *opaque
){
  const struct MarkdownToHtml* ctx = (struct MarkdownToHtml*)opaque;
  const char * const unique = ctx->unique.c;
  /* make.footnote_item() invocations should pass args accordingly */
  const struct Blob *upc = text+1;
  assert( nUsed >= 0 );
  /* expect BUGs if the following yields compiler warnings */

  if( iMark < 0 ){                     /* misreferences */
    assert( iMark == -1 );
    assert( nUsed );
    BLOB_APPEND_LITERAL(ob,"<li class='fn-misreference'>"
                              "<sup class='fn-backrefs'>");
    if( nUsed == 1 ){
      blob_appendf(ob,"<a id='misreference%s-a' href='", unique);
      BLOB_APPEND_URI(ob, ctx);
      blob_appendf(ob,"#misref%s-a'>^</a>", unique);
    }else{
      int i;
      blob_append_char(ob, '^');
      for(i=0; i<nUsed && i<26; i++){
        const int c = i + (unsigned)'a';
        blob_appendf(ob," <a id='misreference%s-%c' href='", unique,c);
        BLOB_APPEND_URI(ob, ctx);
        blob_appendf(ob,"#misref%s-%c'>%c</a>", unique,c, c);
      }
      if( i < nUsed ) BLOB_APPEND_LITERAL(ob," &hellip;");
    }
    BLOB_APPEND_LITERAL(ob,"</sup>\n<span>Misreference</span>");

  }else if( iMark > 0 ){  /* regular, joined and overnested footnotes */
    char pos[24];
    int bJoin = 0;


    #define _joined_footnote_indicator "<ul class='fn-joined'>"
    #define _jfi_sz (sizeof(_joined_footnote_indicator)-1)
    assert( text );
    assert( blob_size(text) );
    memset(pos,0,24);
    sprintf(pos, "%s-%i", unique, iMark);

        blob_appendf(ob," <a id='footnote%s-%s' href='", pos, l.c);
        BLOB_APPEND_URI(ob, ctx);
        blob_appendf(ob,"#noteref%s-%s'>%s</a>", pos,l.c, l.c);
      }
      if( i < nUsed ) BLOB_APPEND_LITERAL(ob," &hellip;");
    }
    BLOB_APPEND_LITERAL(ob,"</sup>\n");

    if( bJoin ){
      BLOB_APPEND_LITERAL(ob,"<sup class='fn-joined'></sup><ul>");
      blob_append(ob,blob_buffer(text)+_jfi_sz,blob_size(text)-_jfi_sz);
    }else if( nUsed ){
      append_footnote_upc(ob, upc, 1);
      BLOB_APPEND_BLOB(ob, text);
    }else{
      BLOB_APPEND_LITERAL(ob,"<i></i>\n"
          "<pre><code class='language-markdown'>");
      if( blob_size(upc) ){
        BLOB_APPEND_BLOB(ob, upc);
      }
      html_escape(ob, blob_buffer(text), blob_size(text));
      BLOB_APPEND_LITERAL(ob,"</code></pre>");
    }
    #undef _joined_footnote_indicator
    #undef _jfi_sz

  }else{             /* a footnote was defined but wasn't referenced */
    /* make.footnote_item() invocations should pass args accordingly */
    const struct Blob * id = text-1;
    assert( !nUsed );
    assert( text );
    assert( blob_size(text) );
    assert( blob_size(id) );
    BLOB_APPEND_LITERAL(ob,"<li class='fn-unreferenced'>\n[^&nbsp;<code>");
    html_escape(ob, blob_buffer(id), blob_size(id));
    BLOB_APPEND_LITERAL(ob, "</code>&nbsp;]<i></i>\n"
        "<pre><code class='language-markdown'>");
    if( blob_size(upc) ){
      BLOB_APPEND_BLOB(ob, upc);
    }
    html_escape(ob, blob_buffer(text), blob_size(text));
    BLOB_APPEND_LITERAL(ob,"</code></pre>");
  }
  BLOB_APPEND_LITERAL(ob, "\n</li>\n");
}
static void html_footnotes(
  struct Blob *ob, const struct Blob *items, void *opaque

  span.notescope.fn-upc-example sup.noteref::after {
    content: " ⛄";
  }
  sup.noteref.fn-upc-example:hover::after,
  span.notescope.fn-upc-example sup.noteref:hover::after {
    content: " 👻";
  }
  li.fn-upc-l span.fn-upc  {
    font-size: 60%;
    color: orange;
  }
  li.fn-upc-l span.fn-upc span.fn-upcDot {
    display: none;
  }
</style>

It is possible to provide a list of classes for a particular footnote and
all its references. This is achieved by prepending a footnote's text with
a special token that starts with dot and ends with colon.
(^
   .alpha-Numeric123.EXAMPLE:

If a footnote consists just of a valid userclass token then this token
is not interpreted as such, instead it is emitted as plain text.
(^  
   .bare.classlist.inside.inline.footnote:  
)[^bare1]
[^bare2]

[^duplicate]: .with.UPC.token:   
   When duplicates are joined their UPC tokens are treated as plain-text.
   Blank characters between token and main text must be preserved.

<html>
  Click
  <a href="?a=B&quote='&nonASCII=😂&script=<script>alert('Broken!');</script>">
  here</a> and
  <a href='?a=B&quote="&nonASCII=😂&script=<script>alert("Broken!");</script>'>
  here</a>
  to test escaping of REQUEST_URI in the generated footnote markers.
</html>

A depth of nesting must be limited.
(^
 .L.1: A long chain of nested inline footnotes...
 (^
  .L.2: is a rather unusual thing...
  (^
   .L.3: and requires extra CPU cycles for processing.
   (^
    .L.4: Theoretically speaking O(n<sup>2</sup>).
    (^
     .L.5: Thus it is worth dismissing those footnotes...
     (^
      .L.6: that are nested deeper than on a certain level.
      (^
       .L.7: A particular value for that limit...
       (^
        is hard-coded in src/markdown.c ...
        (^
         in function `markdown()` ...
         (^
          in variable named `maxDepth`.
          (^

[^bare1]:  .at.the.1st.line.of.labeled.footnote.definition:
     

[^bare2]:  
           .at.the.2nd.line.of.labeled.footnote.definition:
           
[^stray with UPC]: .UPC-token:
    A token of user-provided classes must be rendered within strays.
    Aslo: this and the previous line may not have extra indentation.

[^nostyle]:
  .unused.classes:
  In that case text of the footnote just looks like as if
  no special processing occured.


[^ <script>alert("You have been pwned!");</script> ]: Labels are escaped

[^ <textarea>"Last words here...' ]:
  <textarea>Content is also escaped</textarea>