/*
 * Copyright (c) 2021 Omar Polo <op@omarpolo.com>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

/*
 * This is mostly copied from gmid' iri.c, with minor changes.  Bugs
 * fixed here should be ported to gmid and vice-versa.
 */

#include <config.h>
#include <url.h>

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

struct shallow_url {
	char			*scheme;
	char			*host;
	char			*port;
	uint16_t		 port_no;
	char			*path;
	char			*query;
	char			*fragment;
};

struct parser {
	char			 buf[GEMINI_URL_LEN+1];
	char			*iri;
	struct shallow_url	*parsed;
	const char		*err;
};

static inline int
unreserved(int p)
{
	return isalnum(p)
		|| p == '-'
		|| p == '.'
		|| p == '_'
		|| p == '~';
}

static inline int
sub_delimiters(int p)
{
	return p == '!'
		|| p == '$'
		|| p == '&'
		|| p == '\''
		|| p == '('
		|| p == ')'
		|| p == '*'
		|| p == '+'
		|| p == ','
		|| p == ';'
		|| p == '=';
}

static int
valid_pct_enc_string(char *s)
{
	if (*s != '%')
		return 1;

	if (!isxdigit(s[1]) || !isxdigit(s[2]))
		return 0;

	if (s[1] == '0' && s[2] == '0')
		return 0;

	return 1;
}

static int
valid_pct_encoded(struct parser *p)
{
	if (p->iri[0] != '%')
		return 0;

	if (!valid_pct_enc_string(p->iri)) {
		p->err = "illegal percent-encoding";
		return 0;
	}

	p->iri += 2;
	return 1;
}

static void
pct_decode(char *s)
{
	sscanf(s+1, "%2hhx", s);
	memmove(s+1, s+3, strlen(s+3)+1);
}

static int
parse_pct_encoded(struct parser *p)
{
	if (p->iri[0] != '%')
		return 0;

	if (!valid_pct_enc_string(p->iri)) {
		p->err = "illegal percent-encoding";
		return 0;
	}

	pct_decode(p->iri);
	if (*p->iri == '\0') {
		p->err = "illegal percent-encoding";
		return 0;
	}

	return 1;
}

/* ALPHA *( ALPHA / DIGIT / "+" / "-" / "." ) "://" */
static int
parse_scheme(struct parser *p)
{
	p->parsed->scheme = p->iri;

	if (!isalpha(*p->iri)) {
		p->err = "illegal character in scheme";
		return 0;
	}

	do {
		/* normalize the scheme (i.e. lowercase it)
		 *
		 * XXX: since we cannot have good things, tolower
		 * behaviour depends on the LC_CTYPE locale.  The good
		 * news is that we're sure p->iri points to something
		 * that's in the ASCII range, so tolower can't
		 * mis-behave on some systems due to the locale. */
		*p->iri = tolower(*p->iri);
		p->iri++;
	} while (isalnum(*p->iri)
	    || *p->iri == '+'
	    || *p->iri == '-'
	    || *p->iri == '.');

	if (*p->iri != ':') {
		p->err = "illegal character in scheme";
		return 0;
	}

	*p->iri = '\0';
	if (p->iri[1] != '/' || p->iri[2] != '/') {
		p->err = "invalid marker after scheme";
		return 0;
	}

	p->iri += 3;
	return 1;
}

/* *DIGIT */
static int
parse_port(struct parser *p)
{
	uint32_t i = 0;

	p->parsed->port = p->iri;

	for (; isdigit(*p->iri); p->iri++) {
		i = i * 10 + *p->iri - '0';
		if (i > UINT16_MAX) {
			p->err = "port number too large";
			return 0;
		}
	}

	if (*p->iri != '/' && *p->iri != '\0') {
		p->err = "illegal character in port number";
		return 0;
	}

	p->parsed->port_no = i;

	if (*p->iri != '\0') {
		*p->iri = '\0';
		p->iri++;
	}

	return 1;
}

/* TODO: add support for ip-literal and ipv4addr ? */
/* *( unreserved / sub-delims / pct-encoded ) */
static int
parse_authority(struct parser *p)
{
	p->parsed->host = p->iri;

	while (unreserved(*p->iri)
	    || sub_delimiters(*p->iri)
	    || parse_pct_encoded(p)) {
		/* normalize the host name. */
		if (*p->iri < 0x7F)
			*p->iri = tolower(*p->iri);
		p->iri++;
	}

	if (p->err != NULL)
		return 0;

	if (*p->iri == ':') {
		*p->iri = '\0';
		p->iri++;
		return parse_port(p);
	} else
		p->parsed->port_no = 1965;

	if (*p->iri == '/') {
		*p->iri = '\0';
		p->iri++;
		return 1;
	}

	if (*p->iri == '\0')
		return 1;

	p->err = "illegal character in authority section";
	return 0;
}

/* Routine for path_clean.  Elide the pointed .. with the preceding
 * element.  Return 0 if it's not possible.  incr is the length of
 * the increment, 3 for ../ and 2 for .. */
static int
path_elide_dotdot(char *path, char *i, int incr)
{
	char *j;

	if (i == path)
		return 0;
	for (j = i-2; j != path && *j != '/'; j--)
                /* noop */ ;
	if (*j == '/')
		j++;
	i += incr;
	memmove(j, i, strlen(i)+1);
	return 1;
}

/*
 * Use an algorithm similar to the one implemented in go' path.Clean:
 *
 * 1. Replace multiple slashes with a single slash
 * 2. Eliminate each . path name element
 * 3. Eliminate each inner .. along with the non-.. element that precedes it
 * 4. Eliminate trailing .. if possible or error (go would only discard)
 *
 * Unlike path.Clean, this function return the empty string if the
 * original path is equivalent to "/".
 */
static int
path_clean(char *path)
{
	char *i;

	/* 1. replace multiple slashes with a single one */
	for (i = path; *i; ++i) {
		if (*i == '/' && *(i+1) == '/') {
			memmove(i, i+1, strlen(i)); /* move also the \0 */
			i--;
		}
	}

	/* 2. eliminate each . path name element */
	for (i = path; *i; ++i) {
		if ((i == path || *i == '/') &&
		    *i != '.' && i[1] == '.' && i[2] == '/') {
			/* move also the \0 */
			memmove(i, i+2, strlen(i)-1);
			i--;
		}
	}
	if (!strcmp(path, ".") || !strcmp(path, "/.")) {
		*path = '\0';
		return 1;
	}

	/* 3. eliminate each inner .. along with the preceding non-.. */
	for (i = strstr(path, "../"); i != NULL; i = strstr(path, ".."))
		if (!path_elide_dotdot(path, i, 3))
			return 0;

	/* 4. eliminate trailing ..*/
	if ((i = strstr(path, "..")) != NULL)
		if (!path_elide_dotdot(path, i, 2))
			return 0;

	return 1;
}

static int
parse_query(struct parser *p)
{
	p->parsed->query = p->iri;
	if (*p->iri == '\0')
		return 1;

	while (unreserved(*p->iri)
	    || sub_delimiters(*p->iri)
	    || *p->iri == '/'
	    || *p->iri == '?'
	    || *p->iri == ':'
	    || *p->iri == '@'
	    || valid_pct_encoded(p))
		p->iri++;

	if (p->err != NULL)
		return 0;

	if (*p->iri != '\0' && *p->iri != '#') {
		p->err = "illegal character in query";
		return 0;
	}

	if (*p->iri != '\0') {
		*p->iri = '\0';
		p->iri++;
	}

	return 1;
}

/* don't even bother */
static int
parse_fragment(struct parser *p)
{
	p->parsed->fragment = p->iri;
	return 1;
}

/* XXX: is it too broad? */
/* *(pchar / "/") */
static int
parse_path(struct parser *p)
{
	char c;

	/* trim initial slashes */
	while (*p->iri == '/')
		p->iri++;

	p->parsed->path = p->iri;
	if (*p->iri == '\0') {
		p->parsed->query = p->parsed->fragment = p->iri;
		return 1;
	}

	while (unreserved(*p->iri)
	    || sub_delimiters(*p->iri)
	    || *p->iri == '/'
	    || parse_pct_encoded(p))
		p->iri++;

	if (p->err != NULL)
		return 0;

	if (*p->iri != '\0' && *p->iri != '?' && *p->iri != '#') {
		p->err = "illegal character in path";
		return 0;
	}

	if (*p->iri != '\0') {
		c = *p->iri;
		*p->iri = '\0';
		p->iri++;

		if (c == '#') {
			if (!parse_fragment(p))
				return 0;
		} else
			if (!parse_query(p) || !parse_fragment(p))
				return 0;
	}

	if (!path_clean(p->parsed->path)) {
		p->err = "illegal path";
		return 0;
	}

	return 1;
}

int
url_parse(const char *data, struct url *url, const char **err)
{
	struct shallow_url	u;
	struct parser		p;

	memset(url, 0, sizeof(*url));
	memset(&p, 0, sizeof(p));
	memset(&u, 0, sizeof(u));

	strlcpy(p.buf, data, sizeof(p.buf));
	p.iri = p.buf;
	p.parsed = &u;

	if (!parse_scheme(&p) || !parse_authority(&p) || !parse_path(&p)) {
		*err = p.err;
		return 0;
	}

	if (u.scheme != NULL)
		strlcpy(url->scheme, u.scheme, sizeof(url->scheme));
	if (u.host != NULL)
		strlcpy(url->host, u.host, sizeof(url->host));
	if (u.port != NULL)
		strlcpy(url->port, u.port, sizeof(url->port));
	if (u.path != NULL)
		strlcpy(url->path, u.path, sizeof(url->path));
	if (u.query != NULL)
		strlcpy(url->query, u.query, sizeof(url->query));
	if (u.fragment != NULL)
		strlcpy(url->fragment, u.fragment, sizeof(url->fragment));

	return 1;
}