path: root/src/inlines.c

#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <ctype.h>

#include "config.h"
#include "node.h"
#include "parser.h"
#include "references.h"
#include "cmark.h"
#include "houdini.h"
#include "utf8.h"
#include "scanners.h"
#include "inlines.h"


// Macros for creating various kinds of simple.
#define make_str(s) make_literal(CMARK_NODE_TEXT, s)
#define make_code(s) make_literal(CMARK_NODE_INLINE_CODE, s)
#define make_raw_html(s) make_literal(CMARK_NODE_INLINE_HTML, s)
#define make_linebreak() make_simple(CMARK_NODE_LINEBREAK)
#define make_softbreak() make_simple(CMARK_NODE_SOFTBREAK)
#define make_emph() make_simple(CMARK_NODE_EMPH)
#define make_strong() make_simple(CMARK_NODE_STRONG)

typedef struct delimiter {
    struct delimiter *previous;
    struct delimiter *next;
    cmark_node *inl_text;
    unsigned char delim_char;
    int position;
    bool can_open;
    bool can_close;
} delimiter;

typedef struct {
    chunk input;
    int pos;
    cmark_reference_map *refmap;
    delimiter *last_delim;
} subject;

static delimiter*
S_insert_emph(subject *subj, delimiter *opener, delimiter *closer);

static int parse_inline(subject* subj, cmark_node * parent);

static void subject_from_buf(subject *e, strbuf *buffer,
                 cmark_reference_map *refmap);
static int subject_find_special_char(subject *subj);

static unsigned char *cmark_clean_autolink(chunk *url, int is_email)
{
    strbuf buf = GH_BUF_INIT;

    chunk_trim(url);

    if (url->len == 0)
        return NULL;

    if (is_email)
        strbuf_puts(&buf, "mailto:");

    houdini_unescape_html_f(&buf, url->data, url->len);
    return strbuf_detach(&buf);
}

static inline cmark_node *make_link(cmark_node *label, unsigned char *url, unsigned char *title)
{
    cmark_node* e = (cmark_node *)calloc(1, sizeof(*e));
    if(e != NULL) {
        e->type = CMARK_NODE_LINK;
        e->first_child   = label;
                e->last_child    = label;
        e->as.link.url   = url;
        e->as.link.title = title;
        e->next = NULL;
                label->parent = e;
    }
    return e;
}

static inline cmark_node* make_autolink(cmark_node* label, cmark_chunk url, int is_email)
{
    return make_link(label, cmark_clean_autolink(&url, is_email), NULL);
}

// Create an inline with a literal string value.
static inline cmark_node* make_literal(cmark_node_type t, cmark_chunk s)
{
    cmark_node * e = (cmark_node *)calloc(1, sizeof(*e));
    if(e != NULL) {
        e->type = t;
        e->as.literal = s;
        e->next = NULL;
                e->prev = NULL;
                e->parent = NULL;
                e->first_child = NULL;
                e->last_child = NULL;
                // These fields aren't used for inlines:
                e->start_line = 0;
                e->start_column = 0;
                e->end_line = 0;
    }
    return e;
}

// Create an inline with no value.
static inline cmark_node* make_simple(cmark_node_type t)
{
    cmark_node* e = (cmark_node *)calloc(1, sizeof(*e));
    if(e != NULL) {
        e->type = t;
        e->next = NULL;
                e->prev = NULL;
                e->parent = NULL;
                e->first_child = NULL;
                e->last_child = NULL;
                // These fields aren't used for inlines:
                e->start_line = 0;
                e->start_column = 0;
                e->end_line = 0;
    }
    return e;
}

static unsigned char *bufdup(const unsigned char *buf)
{
    unsigned char *new_buf = NULL;

    if (buf) {
        int len = strlen((char *)buf);
        new_buf = (unsigned char *)calloc(len + 1, sizeof(*new_buf));
        if(new_buf != NULL) {
            memcpy(new_buf, buf, len + 1);
        }
    }

    return new_buf;
}

static void subject_from_buf(subject *e, strbuf *buffer,
                 cmark_reference_map *refmap)
{
    e->input.data = buffer->ptr;
    e->input.len = buffer->size;
    e->input.alloc = 0;
    e->pos = 0;
    e->refmap = refmap;
    e->last_delim = NULL;

    chunk_rtrim(&e->input);
}

static inline int isbacktick(int c)
{
    return (c == '`');
}

static inline unsigned char peek_char(subject *subj)
{
    return (subj->pos < subj->input.len) ? subj->input.data[subj->pos] : 0;
}

static inline unsigned char peek_at(subject *subj, int pos)
{
    return subj->input.data[pos];
}

// Return true if there are more characters in the subject.
static inline int is_eof(subject* subj)
{
    return (subj->pos >= subj->input.len);
}

// Advance the subject.  Doesn't check for eof.
#define advance(subj) (subj)->pos += 1

// Take characters while a predicate holds, and return a string.
static inline chunk take_while(subject* subj, int (*f)(int))
{
    unsigned char c;
    int startpos = subj->pos;
    int len = 0;

    while ((c = peek_char(subj)) && (*f)(c)) {
        advance(subj);
        len++;
    }

    return chunk_dup(&subj->input, startpos, len);
}

// Try to process a backtick code span that began with a
// span of ticks of length openticklength length (already
// parsed).  Return 0 if you don't find matching closing
// backticks, otherwise return the position in the subject
// after the closing backticks.
static int scan_to_closing_backticks(subject* subj, int openticklength)
{
    // read non backticks
    unsigned char c;
    while ((c = peek_char(subj)) && c != '`') {
        advance(subj);
    }
    if (is_eof(subj)) {
        return 0;  // did not find closing ticks, return 0
    }
    int numticks = 0;
    while (peek_char(subj) == '`') {
        advance(subj);
        numticks++;
    }
    if (numticks != openticklength){
        return(scan_to_closing_backticks(subj, openticklength));
    }
    return (subj->pos);
}

// Parse backtick code section or raw backticks, return an inline.
// Assumes that the subject has a backtick at the current position.
static cmark_node* handle_backticks(subject *subj)
{
    chunk openticks = take_while(subj, isbacktick);
    int startpos = subj->pos;
    int endpos = scan_to_closing_backticks(subj, openticks.len);

    if (endpos == 0) { // not found
        subj->pos = startpos; // rewind
        return make_str(openticks);
    } else {
        strbuf buf = GH_BUF_INIT;

        strbuf_set(&buf, subj->input.data + startpos, endpos - startpos - openticks.len);
        strbuf_trim(&buf);
        strbuf_normalize_whitespace(&buf);

        return make_code(chunk_buf_detach(&buf));
    }
}

// Scan ***, **, or * and return number scanned, or 0.
// Advances position.
static int scan_delims(subject* subj, unsigned char c, bool * can_open, bool * can_close)
{
    int numdelims = 0;
    unsigned char char_before, char_after;

    char_before = subj->pos == 0 ? '\n' : peek_at(subj, subj->pos - 1);
    while (peek_char(subj) == c) {
        numdelims++;
        advance(subj);
    }
    char_after = peek_char(subj);
    *can_open = numdelims > 0 && !isspace(char_after);
    *can_close = numdelims > 0 && !isspace(char_before);
    if (c == '_') {
        *can_open = *can_open && !isalnum(char_before);
        *can_close = *can_close && !isalnum(char_after);
    }
    return numdelims;
}

/*
static void print_delimiters(subject *subj)
{
    delimiter *delim;
    delim = subj->last_delim;
    while (delim != NULL) {
        printf("Item at %p: %d %d %d next(%p) prev(%p)\n",
               delim, delim->delim_char,
               delim->can_open, delim->can_close,
               delim->next, delim->previous);
        delim = delim->previous;
    }
}
*/

static void remove_delimiter(subject *subj, delimiter *delim)
{
    if (delim == NULL) return;
    if (delim->next == NULL) {
        // end of list:
        assert(delim == subj->last_delim);
        subj->last_delim = delim->previous;
    } else {
        delim->next->previous = delim->previous;
    }
    if (delim->previous != NULL) {
        delim->previous->next = delim->next;
    }
    free(delim);
}

static void push_delimiter(subject *subj, unsigned char c, bool can_open,
               bool can_close, cmark_node *inl_text)
{
    delimiter *delim =
        (delimiter*)malloc(sizeof(delimiter));
    if (delim == NULL) {
        return;
    }
    delim->delim_char = c;
    delim->can_open = can_open;
    delim->can_close = can_close;
    delim->inl_text = inl_text;
    delim->previous = subj->last_delim;
    delim->next = NULL;
    if (delim->previous != NULL) {
        delim->previous->next = delim;
    }
    delim->position = subj->pos;
    subj->last_delim = delim;
}

// Parse strong/emph or a fallback.
// Assumes the subject has '_' or '*' at the current position.
static cmark_node* handle_strong_emph(subject* subj, unsigned char c)
{
    int numdelims;
    cmark_node * inl_text;
    bool can_open, can_close;

    numdelims = scan_delims(subj, c, &can_open, &can_close);

    inl_text = make_str(chunk_dup(&subj->input, subj->pos - numdelims, numdelims));

    if (can_open || can_close) {
        push_delimiter(subj, c, can_open, can_close, inl_text);
    }

    return inl_text;
}

static void process_emphasis(subject *subj, delimiter *start_delim)
{
    delimiter *closer = subj->last_delim;
    delimiter *opener;

    // move back to first relevant delim.
    while (closer != NULL && closer->previous != start_delim) {
        closer = closer->previous;
    }

    // now move forward, looking for closers, and handling each
    while (closer != NULL) {
        if (closer->can_close &&
            (closer->delim_char == '*' || closer->delim_char == '_')) {
            // Now look backwards for first matching opener:
            opener = closer->previous;
            while (opener != NULL && opener != start_delim) {
                if (opener->delim_char == closer->delim_char &&
                    opener->can_open) {
                    break;
                }
                opener = opener->previous;
            }
            if (opener != NULL && opener != start_delim) {
                closer = S_insert_emph(subj, opener, closer);
            } else {
                closer = closer->next;
            }
        } else {
            closer = closer->next;
        }
    }
    // free all delimiters in list until start_delim:
    while (subj->last_delim != start_delim) {
        remove_delimiter(subj, subj->last_delim);
    }
}

static delimiter*
S_insert_emph(subject *subj, delimiter *opener, delimiter *closer)
{
    delimiter *delim, *tmp_delim;
    int use_delims;
    cmark_node *opener_inl = opener->inl_text;
    cmark_node *closer_inl = closer->inl_text;
    int opener_num_chars = opener_inl->as.literal.len;
    int closer_num_chars = closer_inl->as.literal.len;
    cmark_node *tmp, *emph, *first_child, *last_child;

    // calculate the actual number of characters used from this closer
    if (closer_num_chars < 3 || opener_num_chars < 3) {
        use_delims = closer_num_chars <= opener_num_chars ?
            closer_num_chars : opener_num_chars;
    } else { // closer and opener both have >= 3 characters
        use_delims = closer_num_chars % 2 == 0 ? 2 : 1;
    }

    // remove used characters from associated inlines.
    opener_num_chars -= use_delims;
    closer_num_chars -= use_delims;
    opener_inl->as.literal.len = opener_num_chars;
    closer_inl->as.literal.len = closer_num_chars;

    // free delimiters between opener and closer
    delim = closer->previous;
    while (delim != NULL && delim != opener) {
        tmp_delim = delim->previous;
        remove_delimiter(subj, delim);
        delim = tmp_delim;
    }

    first_child = opener_inl->next;
    last_child  = closer_inl->prev;

    // if opener has 0 characters, remove it and its associated inline
    if (opener_num_chars == 0) {
        // replace empty opener inline with emph
        chunk_free(&(opener_inl->as.literal));
        emph = opener_inl;
        emph->type = use_delims == 1 ? NODE_EMPH : NODE_STRONG;
        // remove opener from list
        remove_delimiter(subj, opener);
    }
    else {
        // create new emph or strong, and splice it in to our inlines
        // between the opener and closer
        emph = use_delims == 1 ? make_emph() : make_strong();
        emph->parent = opener_inl->parent;
        emph->prev = opener_inl;
        opener_inl->next = emph;
    }

    // push children below emph
    emph->next = closer_inl;
    closer_inl->prev = emph;
    emph->first_child = first_child;
    emph->last_child  = last_child;

    // fix children pointers
    first_child->prev = NULL;
    last_child->next  = NULL;
    for (tmp = first_child; tmp != NULL; tmp = tmp->next) {
        tmp->parent = emph;
    }

    // if closer has 0 characters, remove it and its associated inline
    if (closer_num_chars == 0) {
        // remove empty closer inline
        cmark_node_free(closer_inl);
        // remove closer from list
        tmp_delim = closer->next;
        remove_delimiter(subj, closer);
        closer = tmp_delim;
    }

    return closer;
}

// Parse backslash-escape or just a backslash, returning an inline.
static cmark_node* handle_backslash(subject *subj)
{
    advance(subj);
    unsigned char nextchar = peek_char(subj);
    if (ispunct(nextchar)) {  // only ascii symbols and newline can be escaped
        advance(subj);
        return make_str(chunk_dup(&subj->input, subj->pos - 1, 1));
    } else if (nextchar == '\n') {
        advance(subj);
        return make_linebreak();
    } else {
        return make_str(chunk_literal("\\"));
    }
}

// Parse an entity or a regular "&" string.
// Assumes the subject has an '&' character at the current position.
static cmark_node* handle_entity(subject* subj)
{
    strbuf ent = GH_BUF_INIT;
    size_t len;

    advance(subj);

    len = houdini_unescape_ent(&ent,
                   subj->input.data + subj->pos,
                   subj->input.len - subj->pos
                   );

    if (len == 0)
        return make_str(chunk_literal("&"));

    subj->pos += len;
    return make_str(chunk_buf_detach(&ent));
}

// Like make_str, but parses entities.
// Returns an inline sequence consisting of str and entity elements.
static cmark_node *make_str_with_entities(chunk *content)
{
    strbuf unescaped = GH_BUF_INIT;

    if (houdini_unescape_html(&unescaped, content->data, (size_t)content->len)) {
        return make_str(chunk_buf_detach(&unescaped));
    } else {
        return make_str(*content);
    }
}

// Clean a URL: remove surrounding whitespace and surrounding <>,
// and remove \ that escape punctuation.
unsigned char *cmark_clean_url(chunk *url)
{
    strbuf buf = GH_BUF_INIT;

    chunk_trim(url);

    if (url->len == 0)
        return NULL;

    if (url->data[0] == '<' && url->data[url->len - 1] == '>') {
        houdini_unescape_html_f(&buf, url->data + 1, url->len - 2);
    } else {
        houdini_unescape_html_f(&buf, url->data, url->len);
    }

    strbuf_unescape(&buf);
    return strbuf_detach(&buf);
}

unsigned char *cmark_clean_title(chunk *title)
{
       strbuf buf = GH_BUF_INIT;
       unsigned char first, last;

       if (title->len == 0)
               return NULL;

       first = title->data[0];
       last = title->data[title->len - 1];

       // remove surrounding quotes if any:
       if ((first == '\'' && last == '\'') ||
           (first == '(' && last == ')') ||
           (first == '"' && last == '"')) {
               houdini_unescape_html_f(&buf, title->data + 1, title->len - 2);
       } else {
               houdini_unescape_html_f(&buf, title->data, title->len);
       }

       strbuf_unescape(&buf);
       return strbuf_detach(&buf);
}

// Parse an autolink or HTML tag.
// Assumes the subject has a '<' character at the current position.
static cmark_node* handle_pointy_brace(subject* subj)
{
    int matchlen = 0;
    chunk contents;

    advance(subj);  // advance past first <

    // first try to match a URL autolink
    matchlen = scan_autolink_uri(&subj->input, subj->pos);
    if (matchlen > 0) {
        contents = chunk_dup(&subj->input, subj->pos, matchlen - 1);
        subj->pos += matchlen;

        return make_autolink(
                     make_str_with_entities(&contents),
                     contents, 0
                     );
    }

    // next try to match an email autolink
    matchlen = scan_autolink_email(&subj->input, subj->pos);
    if (matchlen > 0) {
        contents = chunk_dup(&subj->input, subj->pos, matchlen - 1);
        subj->pos += matchlen;

        return make_autolink(
                     make_str_with_entities(&contents),
                     contents, 1
                     );
    }

    // finally, try to match an html tag
    matchlen = scan_html_tag(&subj->input, subj->pos);
    if (matchlen > 0) {
        contents = chunk_dup(&subj->input, subj->pos - 1, matchlen + 1);
        subj->pos += matchlen;
        return make_raw_html(contents);
    }

    // if nothing matches, just return the opening <:
    return make_str(chunk_literal("<"));
}

// Parse a link label.  Returns 1 if successful.
// Note:  unescaped brackets are not allowed in labels.
// The label begins with `[` and ends with the first `]` character
// encountered.  Backticks in labels do not start code spans.
static int link_label(subject* subj, chunk *raw_label)
{
    int startpos = subj->pos;
    int length = 0;
    unsigned char c;

    // advance past [
    if (peek_char(subj) == '[') {
        advance(subj);
    } else {
        return 0;
    }

    while ((c = peek_char(subj)) && c != '[' && c != ']') {
        if (c == '\\') {
            advance(subj);
            length++;
            if (ispunct(peek_char(subj))) {
                advance(subj);
                length++;
            }
        } else {
            advance(subj);
            length++;
        }
        if (length > MAX_LINK_LABEL_LENGTH) {
            goto noMatch;
        }
    }

    if (c == ']') { // match found
        *raw_label = chunk_dup(&subj->input, startpos + 1, subj->pos - (startpos + 1));
        advance(subj);  // advance past ]
        return 1;
    }

 noMatch:
    subj->pos = startpos; // rewind
    return 0;

}

// Return a link, an image, or a literal close bracket.
static cmark_node* handle_close_bracket(subject* subj, cmark_node *parent)
{
    int initial_pos;
    int starturl, endurl, starttitle, endtitle, endall;
    int n;
    int sps;
    cmark_reference *ref;
    bool is_image = false;
    chunk urlchunk, titlechunk;
    unsigned char *url, *title;
    delimiter *opener;
    delimiter *tmp_delim;
    cmark_node *link_text;
    cmark_node *inl;
    chunk raw_label;
    int found_label;

    advance(subj);  // advance past ]
    initial_pos = subj->pos;

    // look through list of delimiters for a [ or !
    opener = subj->last_delim;
    while (opener) {
        if (opener->delim_char == '[' || opener->delim_char == '!') {
            break;
        }
        opener = opener->previous;
    }

    if (opener == NULL) {
        return make_str(chunk_literal("]"));
    }

    // If we got here, we matched a potential link/image text.
    is_image = opener->delim_char == '!';
    link_text = opener->inl_text->next;

    // Now we check to see if it's a link/image.

    // First, look for an inline link.
    if (peek_char(subj) == '(' &&
        ((sps = scan_spacechars(&subj->input, subj->pos + 1)) > -1) &&
        ((n = scan_link_url(&subj->input, subj->pos + 1 + sps)) > -1)) {

        // try to parse an explicit link:
        starturl = subj->pos + 1 + sps; // after (
        endurl = starturl + n;
        starttitle = endurl + scan_spacechars(&subj->input, endurl);

        // ensure there are spaces btw url and title
        endtitle = (starttitle == endurl) ? starttitle :
            starttitle + scan_link_title(&subj->input, starttitle);

        endall = endtitle + scan_spacechars(&subj->input, endtitle);

        if (peek_at(subj, endall) == ')') {
            subj->pos = endall + 1;

            urlchunk = chunk_dup(&subj->input, starturl, endurl - starturl);
            titlechunk = chunk_dup(&subj->input, starttitle, endtitle - starttitle);
            url = cmark_clean_url(&urlchunk);
            title = cmark_clean_title(&titlechunk);
            chunk_free(&urlchunk);
            chunk_free(&titlechunk);
            goto match;

        } else {
            goto noMatch;
        }
    }

    // Next, look for a following [link label] that matches in refmap.
    // skip spaces
    subj->pos = subj->pos + scan_spacechars(&subj->input, subj->pos);
    raw_label = chunk_literal("");
    found_label = link_label(subj, &raw_label);
    if (!found_label || raw_label.len == 0) {
        chunk_free(&raw_label);
        raw_label = chunk_dup(&subj->input, opener->position,
                      initial_pos - opener->position - 1);
    }

    if (!found_label) {
        // If we have a shortcut reference link, back up
        // to before the spacse we skipped.
        subj->pos = initial_pos;
    }

    ref = cmark_reference_lookup(subj->refmap, &raw_label);
    chunk_free(&raw_label);

    if (ref != NULL) { // found
        url = bufdup(ref->url);
        title = bufdup(ref->title);
        goto match;
    } else {
        goto noMatch;
    }

noMatch:
    // If we fall through to here, it means we didn't match a link:
    remove_delimiter(subj, opener);  // remove this opener from delimiter list
    subj->pos = initial_pos;
    return make_str(chunk_literal("]"));

match:
    inl = opener->inl_text;
    inl->type = is_image ? NODE_IMAGE : NODE_LINK;
    chunk_free(&inl->as.literal);
    inl->first_child = link_text;
    process_emphasis(subj, opener->previous);
    inl->as.link.url   = url;
    inl->as.link.title = title;
    inl->next = NULL;
    if (link_text) {
        cmark_node *tmp;
        link_text->prev = NULL;
        for (tmp = link_text; tmp->next != NULL; tmp = tmp->next) {
            tmp->parent = inl;
        }
        tmp->parent = inl;
        inl->last_child = tmp;
    }
    parent->last_child = inl;

    // process_emphasis will remove this delimiter and all later ones.
    // Now, if we have a link, we also want to remove earlier link
        // delimiters. (This code can be removed if we decide to allow links
    // inside links.)
    if (!is_image) {
        opener = subj->last_delim;
        while (opener != NULL) {
            tmp_delim = opener->previous;
            if (opener->delim_char == '[') {
                remove_delimiter(subj, opener);
            }
            opener = tmp_delim;
        }
    }

    return NULL;
}

// Parse a hard or soft linebreak, returning an inline.
// Assumes the subject has a newline at the current position.
static cmark_node* handle_newline(subject *subj)
{
    int nlpos = subj->pos;
    // skip over newline
    advance(subj);
    // skip spaces at beginning of line
    while (peek_char(subj) == ' ') {
        advance(subj);
    }
    if (nlpos > 1 &&
        peek_at(subj, nlpos - 1) == ' ' &&
        peek_at(subj, nlpos - 2) == ' ') {
        return make_linebreak();
    } else {
        return make_softbreak();
    }
}

static int subject_find_special_char(subject *subj)
{
    // "\n\\`&_*[]<!"
    static const int8_t SPECIAL_CHARS[256] = {
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 1,
        1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };

    int n = subj->pos + 1;

    while (n < subj->input.len) {
        if (SPECIAL_CHARS[subj->input.data[n]])
            return n;
        n++;
    }

    return subj->input.len;
}

// Parse an inline, advancing subject, and add it as a child of parent.
// Return 0 if no inline can be parsed, 1 otherwise.
static int parse_inline(subject* subj, cmark_node * parent)
{
    cmark_node* new_inl = NULL;
    chunk contents;
    unsigned char c;
    int endpos;
    c = peek_char(subj);
    if (c == 0) {
        return 0;
    }
    switch(c){
    case '\n':
        new_inl = handle_newline(subj);
        break;
    case '`':
        new_inl = handle_backticks(subj);
        break;
    case '\\':
        new_inl = handle_backslash(subj);
        break;
    case '&':
        new_inl = handle_entity(subj);
        break;
    case '<':
        new_inl = handle_pointy_brace(subj);
        break;
    case '*':
    case '_':
        new_inl = handle_strong_emph(subj, c);
        break;
    case '[':
        advance(subj);
        new_inl = make_str(chunk_literal("["));
        push_delimiter(subj, '[', true, false, new_inl);
        break;
    case ']':
        new_inl = handle_close_bracket(subj, parent);
        break;
    case '!':
        advance(subj);
        if (peek_char(subj) == '[') {
            advance(subj);
            new_inl = make_str(chunk_literal("!["));
            push_delimiter(subj, '!', false, true, new_inl);
        } else {
            new_inl = make_str(chunk_literal("!"));
        }
        break;
    default:
        endpos = subject_find_special_char(subj);
        contents = chunk_dup(&subj->input, subj->pos, endpos - subj->pos);
        subj->pos = endpos;

        // if we're at a newline, strip trailing spaces.
        if (peek_char(subj) == '\n') {
            chunk_rtrim(&contents);
        }

        new_inl = make_str(contents);
    }
    if (new_inl != NULL) {
        cmark_node_append_child(parent, new_inl);
    }

    return 1;
}

// Parse inlines from parent's string_content, adding as children of parent.
extern void cmark_parse_inlines(cmark_node* parent, cmark_reference_map *refmap)
{
    subject subj;
    subject_from_buf(&subj, &parent->string_content, refmap);

    while (!is_eof(&subj) && parse_inline(&subj, parent)) ;

    process_emphasis(&subj, NULL);
}

// Parse zero or more space characters, including at most one newline.
static void spnl(subject* subj)
{
    bool seen_newline = false;
    while (peek_char(subj) == ' ' ||
           (!seen_newline &&
        (seen_newline = peek_char(subj) == '\n'))) {
        advance(subj);
    }
}

// Parse reference.  Assumes string begins with '[' character.
// Modify refmap if a reference is encountered.
// Return 0 if no reference found, otherwise position of subject
// after reference is parsed.
int cmark_parse_reference_inline(strbuf *input, cmark_reference_map *refmap)
{
    subject subj;

    chunk lab;
    chunk url;
    chunk title;

    int matchlen = 0;
    int beforetitle;

    subject_from_buf(&subj, input, NULL);

    // parse label:
    if (!link_label(&subj, &lab))
        return 0;

    // colon:
    if (peek_char(&subj) == ':') {
        advance(&subj);
    } else {
        return 0;
    }

    // parse link url:
    spnl(&subj);
    matchlen = scan_link_url(&subj.input, subj.pos);
    if (matchlen) {
        url = chunk_dup(&subj.input, subj.pos, matchlen);
        subj.pos += matchlen;
    } else {
        return 0;
    }

    // parse optional link_title
    beforetitle = subj.pos;
    spnl(&subj);
    matchlen = scan_link_title(&subj.input, subj.pos);
    if (matchlen) {
        title = chunk_dup(&subj.input, subj.pos, matchlen);
        subj.pos += matchlen;
    } else {
        subj.pos = beforetitle;
        title = chunk_literal("");
    }
    // parse final spaces and newline:
    while (peek_char(&subj) == ' ') {
        advance(&subj);
    }
    if (peek_char(&subj) == '\n') {
        advance(&subj);
    } else if (peek_char(&subj) != 0) {
        return 0;
    }
    // insert reference into refmap
    cmark_reference_create(refmap, &lab, &url, &title);
    return subj.pos;
}