/**
 * mds — A micro-display server
 * Copyright © 2014, 2015, 2016, 2017  Mattias Andrée (m@maandree.se)
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
#include "paths.h"

#include <libmdsserver/macros.h>

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



/**
 * Get the current working directory
 * 
 * @return  The current working directory
 */
char *
curpath(void)
{
	static size_t cwd_size = 4096;
	char *cwd = NULL;
	char *old = NULL;
	int saved_errno;

	/* glibc offers ways to do this in just one function call,
	 * but we will not assume that glibc is used here. */
	for (;;) {
		fail_if (xxrealloc(old, cwd, cwd_size + 1, char));
		if (getcwd(cwd, cwd_size))
			break;
		else
			fail_if (errno != ERANGE);
		cwd_size <<= 1;
	}

	return cwd;
fail:
	saved_errno = errno;
	free(old);
	free(cwd);
	errno = saved_errno;
	return NULL;
}


/**
 * Get the absolute path of a file
 * 
 * @param   path  The filename of the file
 * @return        The file's absolute path, `NULL` on error
 */
char *
abspath(const char *path)
{
	char *cwd = NULL;
	char *buf = NULL;
	int saved_errno, slash = 1;
	size_t size, p;

	if (*path == '/') {
		fail_if (xstrdup(buf, path));
		return buf;
	}

	fail_if (!(cwd = curpath()));
	size = (p = strlen(cwd)) + strlen(path) + 2;
	fail_if (xmalloc(buf, size + 1, char));
	memcpy(buf, cwd, (p + 1) * sizeof(char));
	if (buf[p - 1] != '/')
		buf[p++] = '/';

	while (*path) {
		if (slash && path[0] == '/') {
			path += 1;
		} else if (slash && path[0] == '.' && path[1] == '/') {
			path += 2;
		} else if (slash && path[0] == '.' && path[1] == '.' && path[2] == '/') {
			path += 3;
			p--;
			while (p && buf[--p] != '/');
			p++;
		} else {
			buf[p++] = *path;
			slash = *path++ == '/';
		}
	}

	buf[p] = '\0';

	free(cwd);
	return buf;
fail:
	saved_errno = errno;
	free(cwd);
	errno = saved_errno;
	return NULL;
}


/**
 * Get a relative path of a file
 * 
 * @param   path  The filename of the file
 * @param   base  The pathname of the base directory,
 *                `NULL` for the current working directroy
 * @return        The file's relative path, `NULL` on error
 */
char *
relpath(const char *path, const char *base)
{
	char *abs = abspath(path);
	char *absbase = NULL;
	char *buf = NULL;
	char *old = NULL;
	int saved_errno;
	size_t p, slash = 1, back = 0; 

	fail_if (!abs);
	absbase = base ? abspath(base) : curpath();
	fail_if (!absbase);

	if (absbase[strlen(absbase) - 1] != '/')
		/* Both `abspath` and `curpath` (and `relpath`) allocates one extra slot. */
		absbase[strlen(absbase) + 1] = '\0', absbase[strlen(absbase)] = '/';

	for (p = 1; abs[p] && absbase[p] && abs[p] == absbase[p]; p++)
		if (abs[p] == '/')
			slash = p + 1;

	for (p = slash; absbase[p]; p++)
		if (absbase[p] == '/')
			back++;

	fail_if (xmalloc(buf, back * 3 + strlen(abs + slash) + 2, char));

	for (p = 0; back--;)
		buf[p++] = '.', buf[p++] = '.', buf[p++] = '/';
	memcpy(buf + p, abs + slash, (strlen(abs + slash) + 1) * sizeof(char));

	free(abs);
	free(absbase);
	return buf;
fail:
	saved_errno = errno;
	free(abs);
	free(absbase);
	free(old);
	errno = saved_errno;
	return NULL;
}