/*
* getcwdʵ��˼·������֮ǰ����ʵѵ��дһ���Լ���ls
* ��ʱ������c�⺯���е�opendir,readdir��closedir����
* ���Ծ�ȥc���������������������Ӧ�Ľṹ����˹���
* ���⣬�ٽ����ϵͳ���ú���read,fstat,stat��chdir
* ��������������ʵ�������ͱȽϼ���
*/

#define __LIBRARY__
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <fcntl.h>

#include <linux/kernel.h>
#include <linux/sched.h>
#include <asm/segment.h>
#include <sys/stat.h>

#define BUF_MAX  128
#define	DIRBUF  8192
#define NAME_MAX  14

struct dirent {                            /* Ŀ¼��ṹ�� */
	long           d_ino;                  /* i�ڵ� */
	off_t          d_off;                  /* � */
	unsigned short d_reclen;               /* �ļ������� */
	char           d_name[NAME_MAX + 1];   /* �ļ��� */
};

typedef struct
{
	int	dd_fd;			/* �ļ������� */
	int	dd_loc;			/* ����ƫ�� */
	int	dd_size;		/* ��Ч���ݴ�С */
	char* dd_buf;		/* -> directory block */
}	DIR;			    /* Ŀ¼�� */

struct direct {
	ino_t d_ino;
	char d_name[NAME_MAX];
};

static struct dirent result;

/* ����Ҫ�õ����ں�ϵͳ���ú��� */
_syscall3(int, read, int, fildes, char*, buf, off_t, count)         /* open�����ļ����������ļ� */
_syscall2(int, fstat, int, fildes, struct stat*, stat_buf)          /* fstat�����ļ���������ȡ�ļ�״̬��Ϣ������statָ��Ľṹ�� */
_syscall2(int, stat, const char*, filename, struct stat*, stat_buf) /* stat�����ļ�����ȡ�ļ�״̬��Ϣ������statָ��Ľṹ�� */
_syscall1(int, chdir, const char*, filename)                        /* chdir�л���filename����Ŀ¼ */

/* ������������������c���е�ʵ�� */
struct dirent* readdir(DIR* dir)              /* ���ز���dirĿ¼�����¸�Ŀ¼����� */
{                                             /* ��ȡ��Ŀ¼��Ϣ�����ptrָ���Ŀ¼�ṹ���У�ֻ��i�ڵ��Ŀ¼�� */
	struct direct* ptr;                       /* ��ȡ��ǰĿ¼��ͬʱ��ȡ���¸�Ŀ¼����Ϣ�������result�� */
											  /* ����ĩβ���������NULL */
	if (!dir) {
		errno = EBADF;
		return NULL;
	}
	if (!dir->dd_buf)
		if (!(dir->dd_buf = malloc(DIRBUF)))
			return NULL;
		else
			dir->dd_size = dir->dd_loc = 0;
	while (1) {
		if (dir->dd_size <= dir->dd_loc) {
			dir->dd_loc = 0;
			dir->dd_size = read(dir->dd_fd, dir->dd_buf, DIRBUF);
		}
		if (dir->dd_size <= 0)
			return NULL;
		ptr = (struct direct*)(dir->dd_loc + dir->dd_buf);
		dir->dd_loc += sizeof(*ptr);
		if (!ptr->d_ino)
			continue;
		result.d_ino = ptr->d_ino;
		strncpy(result.d_name, ptr->d_name, NAME_MAX);
		result.d_name[NAME_MAX] = 0;
		result.d_reclen = strlen(result.d_name);
		return &result;
	}
}

int closedir(DIR* dir)        /* �رղ���dir��ָ���Ŀ¼�� */
{
	int fd;

	if (!dir) {
		errno = EBADF;
		return -1;
	}
	fd = dir->dd_fd;
	free(dir->dd_buf);
	free(dir);
	return close(fd);
}

DIR* opendir(const char* dirname)         /* �򿪲���dirnameָ����Ŀ¼��������DIR��̬��Ŀ¼����ʧ�ܷ���NULL */
{
	int fd;
	struct stat stat_buf;
	DIR* ptr;

	if ((fd = open(dirname, O_RDONLY)) < 0)  /* ִ��ϵͳ����read����ȡ�ļ������� */
		return NULL;
	if (fstat(fd, &stat_buf) < 0 ||          /* ִ��ϵͳ����fstat��ͨ���ļ���������ȡ�ļ�״̬��Ϣ�����뻺����stat_buf */
		!S_ISDIR(stat_buf.st_mode) ||
		!(ptr = malloc(sizeof(*ptr)))) {
		close(fd);
		return NULL;
	}
	memset(ptr, 0, sizeof(*ptr));
	ptr->dd_fd = fd;
	return ptr;
}

/* ʵ��getcwd */
char* sys_getcwd(char* buf, size_t size) {
	char through_name[BUF_MAX], cwd[BUF_MAX];
	DIR* pre_fstream;
	struct dirent* through_stream;
	struct stat current_direct_state, through_state, pre_direct_state;
	dev_t current_direct_dev;
	ino_t current_direct_inum;

	while (1) {
		if (stat(".", &current_direct_state == 0)) {            /* ��ȡ��ǰĿ¼���ļ�״̬��Ϣ */
			current_direct_dev = current_direct_state.st_dev;
			current_direct_inum = current_direct_state.st_ino;
		}

		pre_fstream = opendir("..");                            /* ��ȡ��ǰĿ¼�ĸ�Ŀ¼���ļ��� */
		stat("..", &pre_direct_state);                          /* ��ȡ��ǰĿ¼�ĸ�Ŀ¼���ļ���Ϣ */
		if (pre_direct_state.st_dev == current_direct_dev && pre_direct_state.st_ino == current_direct_inum)
			break;                                              /* �����Ŀ¼�͵�ǰĿ¼��ͬ��˵���Ѿ����˸�Ŀ¼����ʱ�˳�ѭ�� */

		while ((through_stream = readdir(pre_fstream)) != NULL) {           /* ������Ŀ¼�µ�Ŀ¼�����ƥ�� */
			memcpy(through_name, through_stream->d_name, BUF_MAX);          /* �������Ŀ¼������֣�����ʹ��stat������ȡ��״̬��Ϣ */
			stat(through_name, &through_state);                             /* �������Ŀ¼���״̬��Ϣ������ƥ�� */

			if (current_direct_dev == through_state.st_dev && current_direct_inum == through_state.st_ino) {
				memset(cwd, 0, sizeof(cwd));                    /* ƥ�䵽�˵�ǰĿ¼����������׷�ӵ�cwd�� */
				strcat(cwd, "/");
				strcat(cwd, through_stream->d_name);
				strcat(cwd, buf);                               /* buf��¼������һ��ѭ����cwd������׷�Ӹ���ǰѭ����cwd */
				strncpy(buf, cwd, BUF_MAX);                     /* ��cwd������buf */
				break;
			}
		}
		closedir(pre_fstream);
		chdir("..");											/* �ı䵱ǰĿ¼Ϊ�丸Ŀ¼ */
	}
	return buf;
}