#include <ctype.h>
#include <err.h>
#include <stddef.h>

#include "parse.h"

#define ADVANCE(s, n) do { \
	size_t i_; \
	for (i_ = 0; i_ < (n); i_++) { \
		if (!*(++(s))) \
			goto end; \
	} \
} while (0)

typedef enum { 
	DATA = 1, 
	TAG_OPEN, 
	TAG_CLOSE, 
	ATTR_NAME, 
	ATTR_VALUE, 
	DOCTYPE, 
	COMMENT 
} parse_mode;

extern void on_open(const char *tag, size_t n);
extern void on_open_end(void);
extern void on_close(const char *tag, size_t n);
extern void on_text(const char *text, size_t n);
extern void on_attr(const char *name, size_t nname, 
	const char *val, size_t nval);

void parse(const char *s)
{
	int blank;
	parse_mode mode;
	size_t n, attr_name_len;
	const char *p, *attr_name;

	if (!s)
		return;

	mode = DATA;
	
	while (*s) {
		switch (mode) {
		case DATA:
			p = s;
			n = 0;
			blank = 1;
			while (*s) {
				if (*s == '<') {
					if (isalpha((unsigned char)s[1])) {
						mode = TAG_OPEN;
						ADVANCE(s, 1);
						break;
					} else if (s[1] == '/') {
						mode = TAG_CLOSE;
						ADVANCE(s, 2);
						break;
					} else if (s[1] == '!') {
						if (s[2] == '-' && s[3] == '-') {
							mode = COMMENT;
							ADVANCE(s, 3);
						} else {
							mode = DOCTYPE;
							ADVANCE(s, 2);
						}
						break;
					}
				}

				if (!isspace((unsigned char)*s))
					blank = 0;
				
				n++;
				ADVANCE(s, 1);
			}

			if (n > 0 && !blank)
				on_text(p, n);

			break;
		case TAG_OPEN:
			p = s;
			n = 0;
			while (*s) {
				if (*s == '>') {
					if (n > 0 && s[-1] == '/')
						n--;

					if (n > 0)
						on_open(p, n);
					on_open_end();

					ADVANCE(s, 1);
					mode = DATA;
					break;
				}

				if (*s == ' ') {
					if (n > 0)
						on_open(p, n);

					while (*s == ' ')
						ADVANCE(s, 1);

					if (isalpha((unsigned char)*s))
						mode = ATTR_NAME;
					else if (*s == '>') {
						on_open_end();
						ADVANCE(s, 1);
						mode = DATA;
					} else if (*s == '/' && s[1] == '>') {
						on_open_end();
						ADVANCE(s, 2);
						mode = DATA;
					} else
						errx(1, "Invalid character in open tag: %c", *s);

					break;
				}

				n++;
				ADVANCE(s, 1);
			}
			break;
		case TAG_CLOSE:
			p = s;
			n = 0;
			while (*s) {
				if (*s == '>') {
					on_close(p, n);
					mode = DATA;
					ADVANCE(s, 1);
					break;
				}

				n++;
				ADVANCE(s, 1);
			}
			break;
		case ATTR_NAME:
			p = s;
			n = 0;
			while (*s) {
				if (*s == '=') {
					attr_name = p;
					attr_name_len = n;
					ADVANCE(s, 1);
					if (*s == '"' || *s == '\'')
						ADVANCE(s, 1);
					mode = ATTR_VALUE;
					break;
				}

				if (*s == '>') {  // <input disabled>
					on_attr(p, n, NULL, 0);
					on_open_end();
					ADVANCE(s, 1);
					mode = DATA;
					break;
				}

				n++;
				ADVANCE(s, 1);
			}
			break;
		case ATTR_VALUE:
			p = s;
			n = 0;
			while (*s) {
				if (*s == '"' || *s == '\'' || *s == '>') {
					on_attr(attr_name, attr_name_len, p, n);
					mode = *s == '>' ? DATA : TAG_OPEN;
					ADVANCE(s, 1);
					break;
				}

				n++;
				ADVANCE(s, 1);
			}
			break;
		case DOCTYPE:
			while (*s) {
				if (*s == '>') {
					mode = DATA;
					ADVANCE(s, 1);
					break;
				}
				ADVANCE(s, 1);
			}
			break;
		case COMMENT:
			n = 0;
			while (*s) {
				if (*s == '>' && n >= 2 && s[-1] == '-' && s[-2] == '-') {
					mode = DATA;
					ADVANCE(s, 1);
					break;
				}

				n++;
				ADVANCE(s, 1);
			}
			break;
		default:
			break;
		}
	}

end:
	return;
}