/*
 * nihdoc.c -- Not Invented Here Doc
 *             -   -        -    ---
 *
 *              ~akarle, MIT License
 *
 * "because markdown isn't in base!"
 */
#include <stdio.h>
#ifndef __PLAN_9
#include <unistd.h>
#endif
#include <stdbool.h>

/* Global Constants and Enums */
char *FMT_STRS[] = {
	['_'] = "em",
	['*'] = "strong",
	['`'] = "code",
};

enum Block {
	NONE,
	HEADER,
	HEADER_PARSE,
	PARAGRAPH,
	CODE,
	LIST,
	LIST_PARSE,
};

enum Link {
	NOL,
	URL_PARSE,
	DESC_PARSE,
	OPT_URL,
};


/* Start Global State */
enum Block in = NONE;
enum Link in_link = NOL;
int hlvl = 0;
bool fmts[256] = {false}; /* indexed by _ * ` */
bool escape = false;
char lnkdes[2048] = {0};
int lnkidx = 0;
int indent = 0;
int previndent = 0;
int listdepth = 0;
int lastc = '0';
bool ol = false;
bool linestarted = false;
bool blockquote = false;


/* Helper functions */
void
putesc(int c)
{
	switch (c) {
	case '<':
		printf("&lt;");
		break;
	case '>':
		printf("&gt;");
		break;
	case '&':
		printf("&amp;");
		break;
	default:
		putchar(c);
	}
}

void
newlist(void)
{
	in = LIST;
	previndent = indent;
	printf("<%s>\n<li>\n", ol ? "ol" : "ul");
	listdepth++;
}

int
endlist(void)
{
	in = LIST;
	previndent = indent;
	printf("</li>\n</%s>\n", ol ? "ol" : "ul");
	return --listdepth;
}

/*
 * All inline types should start the paragraph if no other major type present.
 * This function does just that, IFF we aren't already in a major type.
 */
void
maybe_startp(void)
{
	if (in == NONE) {
		in = PARAGRAPH;
		printf("<p>\n");
	}
}

void
handle_lf(void)
{
	indent = 0;
	linestarted = false;

	/* single line types (one lf to close) */
	if (in == HEADER) {
		in = NONE;
		printf("</h%d>\n", hlvl);
	}

	/* multi-line types (two lf to close) */
	if (lastc == '\n' || (lastc == '>' && blockquote)) {
		switch (in) {
		case PARAGRAPH:
			printf("</p>\n");
			break;
		case CODE:
			printf("</code></pre>\n");
			break;
		case LIST:
			previndent = 0;
			while (endlist())
				;
			break;
		default:
			break; /* no op */
		}
		in = NONE;
		if (blockquote && lastc == '\n') {
			printf("</blockquote>\n");
			blockquote = false;
		}
	}
}

/* Returns whether inline styles should be allowed at this moment. */
bool
fmt_disabled(int c)
{
	/* `` blocks all but the next `, likewise CODE makes all disabled */
	if (in == CODE || in_link == URL_PARSE)
		return true;
	else
		return fmts['`'] && c != '`';
}

void
toggle_format(int c)
{
	if (!fmt_disabled(c)) {
		maybe_startp();
		printf("<%s%s>", fmts[c] ? "/" : "", FMT_STRS[c]);
		fmts[c] ^= true;
	} else
		putesc(c);
}


/*
 * The main state machine [1], abstracted into a function to allow
 * playback support for buffered types (i.e. link descriptions)
 *
 * [1]: home grown spaghetti code
 */
void
handlec(int c)
{
	/*
	 * Store link descriptions as we go, skipping the regular loop since
	 * we'll play them back later via recursion on handlec
	 */
	if (in_link == DESC_PARSE && c != ']') {
		lnkdes[lnkidx++] = c;
		return;
	}

	/* Any character other than a '(' terminates a link at ']' */
	if (in_link == OPT_URL && c != '(') {
		in_link = NOL;
		lnkdes[lnkidx] = '\0';
		printf("<a href=\"%s\">%s</a>", lnkdes, lnkdes);
	}

	/* Handle Escapes before any other bit of the main switch */
	if (escape) {
		maybe_startp();
		putesc(c);
		escape = false;
		return;
	}

	/* Store the indentation and return without printing */
	if (!linestarted && c == ' ') {
		indent++;
		return;
	}

	switch (c) {
	case '\\':
		escape = true;
		break;
	case '#':
		if (in == NONE) {
			in = HEADER_PARSE;
			hlvl = 1;
		} else if (in == HEADER_PARSE)
			hlvl++;
		else
			putesc(c);
		break;
	case ' ':
		if (in == HEADER_PARSE) {
			printf("<h%d>", hlvl);
			in = HEADER;
		} else if (in == LIST_PARSE) {
			if (!listdepth) {
				newlist();
			} else {
				if (previndent < indent) {
					newlist();
				} else if (previndent > indent) {
					endlist();
					printf("</li>\n<li>\n");
				} else {
					in = LIST;
					printf("</li>\n<li>\n");
				}
			}
		} else
			putesc(c);
		break;
	case '*':
	case '`':
	case '_':
		toggle_format(c);
		break;
	case '\t':
		if (in == NONE) {
			in = CODE;
			printf("<pre><code>");
		} else if (lastc != '\n')
			putesc(c);
		break;
	case '>':
		if (in == NONE) {
			in = PARAGRAPH;
			printf("%s", blockquote ? "<p>\n" : "<blockquote>\n<p>\n");
			blockquote = true;
		} else if (lastc != '\n')
			putesc(c);
		break;
	case '[':
		if (in_link == NOL && !fmt_disabled(c)) {
			maybe_startp();
			in_link = DESC_PARSE;
			lnkidx = 0;
		} else
			putesc(c);
		break;
	case ']':
		if (in_link == DESC_PARSE)
			in_link = OPT_URL;
		else
			putesc(c);
		break;
	case '(':
		if (in_link == OPT_URL) {
			in_link = URL_PARSE;
			printf("<a href=\"");
		} else
			putesc(c);
		break;
	case ')':
		if (in_link == URL_PARSE) {
			in_link = NOL;
			printf("\">");
			for (int i = 0; i < lnkidx; i++)
				handlec(lnkdes[i]);
			printf("</a>");
		} else
			putesc(c);
		break;
	case '1':
	case '2':
	case '3':
	case '4':
	case '5':
	case '6':
	case '7':
	case '8':
	case '9':
	case '.':
	case '-':
		if (in == NONE || !linestarted) {
			ol = c != '-';
			in = LIST_PARSE;
		} else if (in != LIST_PARSE)
			putesc(c);
		break;
	case '\n':
		handle_lf();
		if (in != NONE)
			putesc(c);
		break;
	default:
		maybe_startp();
		putesc(c);
		break;
	}
	lastc = c;
	linestarted = c != '\n';
}


/* nihdoc: a text -> HTML parser */
int
main(int argc, char *argv[])
{
	int c;

#ifdef __OpenBSD__
	pledge("stdio", "stdio");
#endif

	if (argc > 1) {
		fprintf(stderr, "error: %s takes no arguments\n", argv[0]);
		return 1;
	}

	while ((c = getchar()) != EOF)
		handlec(c);

	/* pretend there's a final LF to close any blocks */
	handle_lf();

	return 0;
}