/*-
 * Copyright (c) 2003-2007 Tim Kientzle
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR(S) ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/*-
 * This is a new directory-walking system that addresses a number
 * of problems I've had with fts(3).  In particular, it has no
 * pathname-length limits (other than the size of 'int'), handles
 * deep logical traversals, uses considerably less memory, and has
 * an opaque interface (easier to modify in the future).
 *
 * Internally, it keeps a single list of "tree_entry" items that
 * represent filesystem objects that require further attention.
 * Non-directories are not kept in memory: they are pulled from
 * readdir(), returned to the client, then freed as soon as possible.
 * Any directory entry to be traversed gets pushed onto the stack.
 *
 * There is surprisingly little information that needs to be kept for
 * each item on the stack.  Just the name, depth (represented here as the
 * string length of the parent directory's pathname), and some markers
 * indicating how to get back to the parent (via chdir("..") for a
 * regular dir or via fchdir(2) for a symlink).
 */
#include "tree_config.h"
__FBSDID("$FreeBSD$");

#ifdef HAVE_SYS_STAT_H
#include <sys/stat.h>
#endif
#ifdef HAVE_DIRENT_H
#include <dirent.h>
#endif
#ifdef HAVE_ERRNO_H
#include <errno.h>
#endif
#ifdef HAVE_FCNTL_H
#include <fcntl.h>
#endif
#ifdef HAVE_STDLIB_H
#include <stdlib.h>
#endif
#ifdef HAVE_STRING_H
#include <string.h>
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

#include "tree.h"

/*
 * TODO:
 *    1) Loop checking.
 *    3) Arbitrary logical traversals by closing/reopening intermediate fds.
 */

struct tree_entry {
    struct tree_entry *next;
    struct tree_entry *parent;
    char *name;
    size_t dirname_length;
    dev_t dev;
    ino_t ino;
    int fd;
    int flags;
};

/* Definitions for tree_entry.flags bitmap. */
#define isDir 1 /* This entry is a regular directory. */
#define isDirLink 2 /* This entry is a symbolic link to a directory. */
#define needsPreVisit 4 /* This entry needs to be previsited. */
#define needsPostVisit 8 /* This entry needs to be postvisited. */

/*
 * Local data for this package.
 */
struct tree {
    struct tree_entry   *stack;
    struct tree_entry   *current;
    DIR *d;
    int  initialDirFd;
    int  flags;
    int  visit_type;
    int  tree_errno; /* Error code from last failed operation. */

    char    *buff;
    const char  *basename;
    size_t   buff_length;
    size_t   path_length;
    size_t   dirname_length;

    int  depth;
    int  openCount;
    int  maxOpenCount;

    struct stat lst;
    struct stat st;
};

/* Definitions for tree.flags bitmap. */
#define needsReturn 8  /* Marks first entry as not having been returned yet. */
#define hasStat 16  /* The st entry is set. */
#define hasLstat 32 /* The lst entry is set. */


#ifdef HAVE_DIRENT_D_NAMLEN
/* BSD extension; avoids need for a strlen() call. */
#define D_NAMELEN(dp)   (dp)->d_namlen
#else
#define D_NAMELEN(dp)   (strlen((dp)->d_name))
#endif

#if 0
#include <stdio.h>
void
tree_dump(struct tree *t, FILE *out)
{
    struct tree_entry *te;

    fprintf(out, "\tdepth: %d\n", t->depth);
    fprintf(out, "\tbuff: %s\n", t->buff);
    fprintf(out, "\tpwd: "); fflush(stdout); system("pwd");
    fprintf(out, "\taccess: %s\n", t->basename);
    fprintf(out, "\tstack:\n");
    for (te = t->stack; te != NULL; te = te->next) {
        fprintf(out, "\t\tte->name: %s%s%s\n", te->name,
            te->flags & needsPreVisit ? "" : " *",
            t->current == te ? " (current)" : "");
    }
}
#endif

/*
 * Add a directory path to the current stack.
 */
static void
tree_push(struct tree *t, const char *path)
{
    struct tree_entry *te;

    te = malloc(sizeof(*te));
    memset(te, 0, sizeof(*te));
    te->next = t->stack;
    t->stack = te;
    te->fd = -1;
    te->name = strdup(path);
    te->flags = needsPreVisit | needsPostVisit;
    te->dirname_length = t->dirname_length;
}

/*
 * Append a name to the current path.
 */
static void
tree_append(struct tree *t, const char *name, size_t name_length)
{
    char *p;

    if (t->buff != NULL)
        t->buff[t->dirname_length] = '\0';
    /* Strip trailing '/' from name, unless entire name is "/". */
    while (name_length > 1 && name[name_length - 1] == '/')
        name_length--;

    /* Resize pathname buffer as needed. */
    while (name_length + 1 + t->dirname_length >= t->buff_length) {
        t->buff_length *= 2;
        if (t->buff_length < 1024)
            t->buff_length = 1024;
        t->buff = realloc(t->buff, t->buff_length);
    }
    p = t->buff + t->dirname_length;
    t->path_length = t->dirname_length + name_length;
    /* Add a separating '/' if it's needed. */
    if (t->dirname_length > 0 && p[-1] != '/') {
        *p++ = '/';
        t->path_length ++;
    }
    strncpy(p, name, name_length);
    p[name_length] = '\0';
    t->basename = p;
}

/*
 * Open a directory tree for traversal.
 */
struct tree *
tree_open(const char *path)
{
    struct tree *t;

    t = malloc(sizeof(*t));
    memset(t, 0, sizeof(*t));
    tree_append(t, path, strlen(path));
    t->initialDirFd = open(".", O_RDONLY);
    /*
     * During most of the traversal, items are set up and then
     * returned immediately from tree_next().  That doesn't work
     * for the very first entry, so we set a flag for this special
     * case.
     */
    t->flags = needsReturn;
    return (t);
}

/*
 * We've finished a directory; ascend back to the parent.
 */
static void
tree_ascend(struct tree *t)
{
    struct tree_entry *te;

    te = t->stack;
    t->depth--;
    if (te->flags & isDirLink) {
        fchdir(te->fd);
        close(te->fd);
        t->openCount--;
    } else {
        chdir("..");
    }
}

/*
 * Pop the working stack.
 */
static void
tree_pop(struct tree *t)
{
    struct tree_entry *te;

    t->buff[t->dirname_length] = '\0';
    if (t->stack == t->current && t->current != NULL)
        t->current = t->current->parent;
    te = t->stack;
    t->stack = te->next;
    t->dirname_length = te->dirname_length;
    t->basename = t->buff + t->dirname_length;
    /* Special case: starting dir doesn't skip leading '/'. */
    if (t->dirname_length > 0)
        t->basename++;
    free(te->name);
    free(te);
}

/*
 * Get the next item in the tree traversal.
 */
int
tree_next(struct tree *t)
{
    struct dirent *de = NULL;

    /* Handle the startup case by returning the initial entry. */
    if (t->flags & needsReturn) {
        t->flags &= ~needsReturn;
        return (t->visit_type = TREE_REGULAR);
    }

    while (t->stack != NULL) {
        /* If there's an open dir, get the next entry from there. */
        while (t->d != NULL) {
            de = readdir(t->d);
            if (de == NULL) {
                closedir(t->d);
                t->d = NULL;
            } else if (de->d_name[0] == '.'
                && de->d_name[1] == '\0') {
                /* Skip '.' */
            } else if (de->d_name[0] == '.'
                && de->d_name[1] == '.'
                && de->d_name[2] == '\0') {
                /* Skip '..' */
            } else {
                /*
                 * Append the path to the current path
                 * and return it.
                 */
                tree_append(t, de->d_name, D_NAMELEN(de));
                t->flags &= ~hasLstat;
                t->flags &= ~hasStat;
                return (t->visit_type = TREE_REGULAR);
            }
        }

        /* If the current dir needs to be visited, set it up. */
        if (t->stack->flags & needsPreVisit) {
            t->current = t->stack;
            tree_append(t, t->stack->name, strlen(t->stack->name));
            t->stack->flags &= ~needsPreVisit;
            /* If it is a link, set up fd for the ascent. */
            if (t->stack->flags & isDirLink) {
                t->stack->fd = open(".", O_RDONLY);
                t->openCount++;
                if (t->openCount > t->maxOpenCount)
                    t->maxOpenCount = t->openCount;
            }
            t->dirname_length = t->path_length;
            if (chdir(t->stack->name) != 0) {
                /* chdir() failed; return error */
                tree_pop(t);
                t->tree_errno = errno;
                return (t->visit_type = TREE_ERROR_DIR);
            }
            t->depth++;
            t->d = opendir(".");
            if (t->d == NULL) {
                tree_ascend(t); /* Undo "chdir" */
                tree_pop(t);
                t->tree_errno = errno;
                return (t->visit_type = TREE_ERROR_DIR);
            }
            t->flags &= ~hasLstat;
            t->flags &= ~hasStat;
            t->basename = ".";
            return (t->visit_type = TREE_POSTDESCENT);
        }

        /* We've done everything necessary for the top stack entry. */
        if (t->stack->flags & needsPostVisit) {
            tree_ascend(t);
            tree_pop(t);
            t->flags &= ~hasLstat;
            t->flags &= ~hasStat;
            return (t->visit_type = TREE_POSTASCENT);
        }
    }
    return (t->visit_type = 0);
}

/*
 * Return error code.
 */
int
tree_errno(struct tree *t)
{
    return (t->tree_errno);
}

/*
 * Called by the client to mark the directory just returned from
 * tree_next() as needing to be visited.
 */
void
tree_descend(struct tree *t)
{
    if (t->visit_type != TREE_REGULAR)
        return;

    if (tree_current_is_physical_dir(t)) {
        tree_push(t, t->basename);
        t->stack->flags |= isDir;
    } else if (tree_current_is_dir(t)) {
        tree_push(t, t->basename);
        t->stack->flags |= isDirLink;
    }
}

/*
 * Get the stat() data for the entry just returned from tree_next().
 */
const struct stat *
tree_current_stat(struct tree *t)
{
    if (!(t->flags & hasStat)) {
        if (stat(t->basename, &t->st) != 0)
            return NULL;
        t->flags |= hasStat;
    }
    return (&t->st);
}

/*
 * Get the lstat() data for the entry just returned from tree_next().
 */
const struct stat *
tree_current_lstat(struct tree *t)
{
    if (!(t->flags & hasLstat)) {
        if (lstat(t->basename, &t->lst) != 0)
            return NULL;
        t->flags |= hasLstat;
    }
    return (&t->lst);
}

/*
 * Test whether current entry is a dir or link to a dir.
 */
int
tree_current_is_dir(struct tree *t)
{
    const struct stat *st;

    /*
     * If we already have lstat() info, then try some
     * cheap tests to determine if this is a dir.
     */
    if (t->flags & hasLstat) {
        /* If lstat() says it's a dir, it must be a dir. */
        if (S_ISDIR(tree_current_lstat(t)->st_mode))
            return 1;
        /* Not a dir; might be a link to a dir. */
        /* If it's not a link, then it's not a link to a dir. */
        if (!S_ISLNK(tree_current_lstat(t)->st_mode))
            return 0;
        /*
         * It's a link, but we don't know what it's a link to,
         * so we'll have to use stat().
         */
    }

    st = tree_current_stat(t);
    /* If we can't stat it, it's not a dir. */
    if (st == NULL)
        return 0;
    /* Use the definitive test.  Hopefully this is cached. */
    return (S_ISDIR(st->st_mode));
}

/*
 * Test whether current entry is a physical directory.  Usually, we
 * already have at least one of stat() or lstat() in memory, so we
 * use tricks to try to avoid an extra trip to the disk.
 */
int
tree_current_is_physical_dir(struct tree *t)
{
    const struct stat *st;

    /*
     * If stat() says it isn't a dir, then it's not a dir.
     * If stat() data is cached, this check is free, so do it first.
     */
    if ((t->flags & hasStat)
        && (!S_ISDIR(tree_current_stat(t)->st_mode)))
        return 0;

    /*
     * Either stat() said it was a dir (in which case, we have
     * to determine whether it's really a link to a dir) or
     * stat() info wasn't available.  So we use lstat(), which
     * hopefully is already cached.
     */

    st = tree_current_lstat(t);
    /* If we can't stat it, it's not a dir. */
    if (st == NULL)
        return 0;
    /* Use the definitive test.  Hopefully this is cached. */
    return (S_ISDIR(st->st_mode));
}

/*
 * Test whether current entry is a symbolic link.
 */
int
tree_current_is_physical_link(struct tree *t)
{
    const struct stat *st = tree_current_lstat(t);
    if (st == NULL)
        return 0;
    return (S_ISLNK(st->st_mode));
}

/*
 * Return the access path for the entry just returned from tree_next().
 */
const char *
tree_current_access_path(struct tree *t)
{
    return (t->basename);
}

/*
 * Return the full path for the entry just returned from tree_next().
 */
const char *
tree_current_path(struct tree *t)
{
    return (t->buff);
}

/*
 * Return the length of the path for the entry just returned from tree_next().
 */
size_t
tree_current_pathlen(struct tree *t)
{
    return (t->path_length);
}

/*
 * Return the nesting depth of the entry just returned from tree_next().
 */
int
tree_current_depth(struct tree *t)
{
    return (t->depth);
}

/*
 * Terminate the traversal and release any resources.
 */
void
tree_close(struct tree *t)
{
    /* Release anything remaining in the stack. */
    while (t->stack != NULL)
        tree_pop(t);
    if (t->buff)
        free(t->buff);
    /* chdir() back to where we started. */
    if (t->initialDirFd >= 0) {
        fchdir(t->initialDirFd);
        close(t->initialDirFd);
        t->initialDirFd = -1;
    }
    free(t);
}
