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

#include "markdown.h"

static char *
md_strdup(const char *s)
{
	char *out;
	size_t len;

	len = strlen(s);
	out = malloc(len + 1);
	if (out == NULL)
		return NULL;
	memcpy(out, s, len + 1);
	return out;
}

static void
markdown_inline(FILE *fp, const char *line,
    void (*esc_len)(FILE *, const char *, size_t))
{
	const char *code_end, *link_close, *link_end, *p, *url_start;
	size_t n;

	p = line;
	while (*p != '\0') {
		if (*p == '`') {
			code_end = strchr(p + 1, '`');
			if (code_end != NULL) {
				fputs("<code>", fp);
				esc_len(fp, p + 1,
				    (size_t)(code_end - (p + 1)));
				fputs("</code>", fp);
				p = code_end + 1;
				continue;
			}
		}
		if (*p == '[') {
			link_close = strchr(p + 1, ']');
			if (link_close != NULL && *(link_close + 1) == '(') {
				url_start = link_close + 2;
				link_end = strchr(url_start, ')');
				if (link_end != NULL) {
					fputs("<a href=\"", fp);
					esc_len(fp, url_start,
					    (size_t)(link_end - url_start));
					fputs("\">", fp);
					esc_len(fp, p + 1,
					    (size_t)(link_close - (p + 1)));
					fputs("</a>", fp);
					p = link_end + 1;
					continue;
				}
			}
		}
		n = strcspn(p, "`[");
		if (n == 0) {
			esc_len(fp, p, 1);
			p++;
		} else {
			esc_len(fp, p, n);
			p += n;
		}
	}
}

void
markdown_render(FILE *fp, const char *md,
    void (*esc_len)(FILE *, const char *, size_t))
{
	char *line;
	char *next;
	char *save;
	int in_code, in_list, in_p, level;

	save = md_strdup(md);
	if (save == NULL)
		return;
	in_code = 0;
	in_list = 0;
	in_p = 0;
	line = save;
	while (line != NULL) {
		next = strchr(line, '\n');
		if (next != NULL) {
			*next = '\0';
			next++;
		}
		while (*line == ' ' || *line == '\t')
			line++;
		if (strncmp(line, "```", 3) == 0) {
			if (in_p) {
				fputs("</p>\n", fp);
				in_p = 0;
			}
			if (in_list) {
				fputs("</ul>\n", fp);
				in_list = 0;
			}
			if (!in_code)
				fputs("<pre>", fp);
			else
				fputs("</pre>\n", fp);
			in_code = !in_code;
			line = next;
			continue;
		}
		if (in_code) {
			esc_len(fp, line, strlen(line));
			fputc('\n', fp);
			line = next;
			continue;
		}
		if (*line == '\0') {
			if (in_p) {
				fputs("</p>\n", fp);
				in_p = 0;
			}
			if (in_list) {
				fputs("</ul>\n", fp);
				in_list = 0;
			}
			line = next;
			continue;
		}
		if (*line == '#') {
			if (in_p) {
				fputs("</p>\n", fp);
				in_p = 0;
			}
			if (in_list) {
				fputs("</ul>\n", fp);
				in_list = 0;
			}
			level = 0;
			while (*line == '#' && level < 6) {
				level++;
				line++;
			}
			while (*line == ' ')
				line++;
			fprintf(fp, "<h%d>", level == 0 ? 1 : level);
			markdown_inline(fp, line, esc_len);
			fprintf(fp, "</h%d>\n", level == 0 ? 1 : level);
			line = next;
			continue;
		}
		if ((line[0] == '-' || line[0] == '*') && line[1] == ' ') {
			if (in_p) {
				fputs("</p>\n", fp);
				in_p = 0;
			}
			if (!in_list) {
				fputs("<ul>\n", fp);
				in_list = 1;
			}
			fputs("<li>", fp);
			markdown_inline(fp, line + 2, esc_len);
			fputs("</li>\n", fp);
			line = next;
			continue;
		}
		if (!in_p) {
			fputs("<p>", fp);
			in_p = 1;
		} else
			fputs("<br>\n", fp);
		markdown_inline(fp, line, esc_len);
		line = next;
	}
	if (in_code)
		fputs("</pre>\n", fp);
	if (in_p)
		fputs("</p>\n", fp);
	if (in_list)
		fputs("</ul>\n", fp);
	free(save);
}