/* 
 * Copyright (c) 1998 Michael Smith.
 * Copyright (c) 2000 Maxim Sobolev
 * 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 AND CONTRIBUTORS ``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 OR CONTRIBUTORS 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.
 */

#ifndef REGRESSION
#include "stand.h"
#else
#include <stdlib.h>
#include <sys/errno.h>
#include <sys/fcntl.h>
#include <sys/types.h>
#include <sys/unistd.h>

struct open_file {
    int                 f_flags;        /* see F_* below */
    void                *f_fsdata;      /* file system specific data */
};
#define F_READ          0x0001  /* file opened for reading */
#define EOFFSET (ELAST+8)       /* relative seek not supported */
static inline u_int min(u_int a, u_int b) { return(a < b ? a : b); }
#define panic(x, y) abort()
#endif

#include <sys/stat.h>
#include <string.h>
#include <bzlib.h>

#define BZ_BUFSIZE 2048 /* XXX larger? */

struct bz_file
{
    int                 bzf_rawfd;
    bz_stream           bzf_bzstream;
    char                bzf_buf[BZ_BUFSIZE];
    int                 bzf_endseen;
};

static int      bzf_fill(struct bz_file *z);
static int      bzf_open(const char *path, struct open_file *f);
static int      bzf_close(struct open_file *f);
static int      bzf_read(struct open_file *f, void *buf, size_t size, size_t *resid);
static off_t    bzf_seek(struct open_file *f, off_t offset, int where);
static int      bzf_stat(struct open_file *f, struct stat *sb);

#ifndef REGRESSION
struct fs_ops bzipfs_fsops = {
        .fs_name = "bzip",
        .fs_flags = 0,
        .fo_open = bzf_open,
        .fo_close = bzf_close,
        .fo_read = bzf_read,
        .fo_write = null_write,
        .fo_seek = bzf_seek,
        .fo_stat = bzf_stat,
        .fo_readdir = null_readdir,
};
#endif

static int
bzf_fill(struct bz_file *bzf)
{
    int         result;
    int         req;
    
    req = BZ_BUFSIZE - bzf->bzf_bzstream.avail_in;
    result = 0;
    
    /* If we need more */
    if (req > 0) {
        /* move old data to bottom of buffer */
        if (req < BZ_BUFSIZE)
            bcopy(bzf->bzf_buf + req, bzf->bzf_buf, BZ_BUFSIZE - req);
        
        /* read to fill buffer and update availibility data */
        result = read(bzf->bzf_rawfd, bzf->bzf_buf + bzf->bzf_bzstream.avail_in, req);
        bzf->bzf_bzstream.next_in = bzf->bzf_buf;
        if (result >= 0)
            bzf->bzf_bzstream.avail_in += result;
    }
    return(result);
}

/*
 * Adapted from get_byte/check_header in libz
 *
 * Returns 0 if the header is OK, nonzero if not.
 */
static int
get_byte(struct bz_file *bzf)
{
    if ((bzf->bzf_bzstream.avail_in == 0) && (bzf_fill(bzf) == -1))
        return(-1);
    bzf->bzf_bzstream.avail_in--;
    return(*(bzf->bzf_bzstream.next_in)++);
}

static int bz_magic[3] = {'B', 'Z', 'h'}; /* bzip2 magic header */

static int
check_header(struct bz_file *bzf)
{
    unsigned int len;
    int          c;

    /* Check the bzip2 magic header */
    for (len = 0; len < 3; len++) {
        c = get_byte(bzf);
        if (c != bz_magic[len]) {
            return(1);
        }
    }
    /* Check that the block size is valid */
    c = get_byte(bzf);
    if (c < '1' || c > '9')
        return(1);

    /* Put back bytes that we've took from the input stream */
    bzf->bzf_bzstream.next_in -= 4;
    bzf->bzf_bzstream.avail_in += 4;

    return(0);
}
        
static int
bzf_open(const char *fname, struct open_file *f)
{
    static char         *bzfname;
    int                 rawfd;
    struct bz_file      *bzf;
    char                *cp;
    int                 error;
    struct stat         sb;

    /* Have to be in "just read it" mode */
    if (f->f_flags != F_READ)
        return(EPERM);

    /* If the name already ends in .gz or .bz2, ignore it */
    if ((cp = strrchr(fname, '.')) && (!strcmp(cp, ".gz")
            || !strcmp(cp, ".bz2") || !strcmp(cp, ".split")))
        return(ENOENT);

    /* Construct new name */
    bzfname = malloc(strlen(fname) + 5);
    if (bzfname == NULL)
        return(ENOMEM);
    sprintf(bzfname, "%s.bz2", fname);

    /* Try to open the compressed datafile */
    rawfd = open(bzfname, O_RDONLY);
    free(bzfname);
    if (rawfd == -1)
        return(ENOENT);

    if (fstat(rawfd, &sb) < 0) {
        printf("bzf_open: stat failed\n");
        close(rawfd);
        return(ENOENT);
    }
    if (!S_ISREG(sb.st_mode)) {
        printf("bzf_open: not a file\n");
        close(rawfd);
        return(EISDIR);                 /* best guess */
    }

    /* Allocate a bz_file structure, populate it */
    bzf = malloc(sizeof(struct bz_file));
    if (bzf == NULL)
        return(ENOMEM);
    bzero(bzf, sizeof(struct bz_file));
    bzf->bzf_rawfd = rawfd;

    /* Verify that the file is bzipped */
    if (check_header(bzf)) {
        close(bzf->bzf_rawfd);
        free(bzf);
        return(EFTYPE);
    }

    /* Initialise the inflation engine */
    if ((error = BZ2_bzDecompressInit(&(bzf->bzf_bzstream), 0, 1)) != BZ_OK) {
        printf("bzf_open: BZ2_bzDecompressInit returned %d\n", error);
        close(bzf->bzf_rawfd);
        free(bzf);
        return(EIO);
    }

    /* Looks OK, we'll take it */
    f->f_fsdata = bzf;
    return(0);
}

static int
bzf_close(struct open_file *f)
{
    struct bz_file      *bzf = (struct bz_file *)f->f_fsdata;
    
    BZ2_bzDecompressEnd(&(bzf->bzf_bzstream));
    close(bzf->bzf_rawfd);
    free(bzf);
    return(0);
}
 
static int 
bzf_read(struct open_file *f, void *buf, size_t size, size_t *resid)
{
    struct bz_file      *bzf = (struct bz_file *)f->f_fsdata;
    int                 error;

    bzf->bzf_bzstream.next_out = buf;                   /* where and how much */
    bzf->bzf_bzstream.avail_out = size;

    while (bzf->bzf_bzstream.avail_out && bzf->bzf_endseen == 0) {
        if ((bzf->bzf_bzstream.avail_in == 0) && (bzf_fill(bzf) == -1)) {
            printf("bzf_read: fill error\n");
            return(EIO);
        }
        if (bzf->bzf_bzstream.avail_in == 0) {          /* oops, unexpected EOF */
            printf("bzf_read: unexpected EOF\n");
            if (bzf->bzf_bzstream.avail_out == size)
                return(EIO);
            break;
        }

        error = BZ2_bzDecompress(&bzf->bzf_bzstream);   /* decompression pass */
        if (error == BZ_STREAM_END) {                   /* EOF, all done */
            bzf->bzf_endseen = 1;
            break;
        }
        if (error != BZ_OK) {                           /* argh, decompression error */
            printf("bzf_read: BZ2_bzDecompress returned %d\n", error);
            return(EIO);
        }
    }
    if (resid != NULL)
        *resid = bzf->bzf_bzstream.avail_out;
    return(0);
}

static int
bzf_rewind(struct open_file *f)
{
    struct bz_file      *bzf = (struct bz_file *)f->f_fsdata;
    struct bz_file      *bzf_tmp;

    /*
     * Since bzip2 does not have an equivalent inflateReset function a crude
     * one needs to be provided.  The functions all called in such a way that
     * at any time an error occurs a roll back can be done (effectively making
     * this rewind 'atomic', either the reset occurs successfully or not at all,
     * with no 'undefined' state happening).
     */

    /* Allocate a bz_file structure, populate it */
    bzf_tmp = malloc(sizeof(struct bz_file));
    if (bzf_tmp == NULL)
        return(-1);
    bzero(bzf_tmp, sizeof(struct bz_file));
    bzf_tmp->bzf_rawfd = bzf->bzf_rawfd;

    /* Initialise the inflation engine */
    if (BZ2_bzDecompressInit(&(bzf_tmp->bzf_bzstream), 0, 1) != BZ_OK) {
        free(bzf_tmp);
        return(-1);
    }

    /* Seek back to the beginning of the file */
    if (lseek(bzf->bzf_rawfd, 0, SEEK_SET) == -1) {
        BZ2_bzDecompressEnd(&(bzf_tmp->bzf_bzstream));
        free(bzf_tmp);
        return(-1);
    }

    /* Free old bz_file data */
    BZ2_bzDecompressEnd(&(bzf->bzf_bzstream));
    free(bzf);

    /* Use the new bz_file data */
    f->f_fsdata = bzf_tmp;

    return(0);
}

static off_t
bzf_seek(struct open_file *f, off_t offset, int where)
{
    struct bz_file      *bzf = (struct bz_file *)f->f_fsdata;
    off_t               target;
    char                discard[16];
    
    switch (where) {
    case SEEK_SET:
        target = offset;
        break;
    case SEEK_CUR:
        target = offset + bzf->bzf_bzstream.total_out_lo32;
        break;
    default:
        errno = EINVAL;
        return(-1);
    }

    /* Can we get there from here? */
    if (target < bzf->bzf_bzstream.total_out_lo32 && bzf_rewind(f) != 0) {
        errno = EOFFSET;
        return -1;
    }

    /* if bzf_rewind was called then bzf has changed */
    bzf = (struct bz_file *)f->f_fsdata;

    /* skip forwards if required */
    while (target > bzf->bzf_bzstream.total_out_lo32) {
        errno = bzf_read(f, discard, min(sizeof(discard),
            target - bzf->bzf_bzstream.total_out_lo32), NULL);
        if (errno)
            return(-1);
        /* Break out of loop if end of file has been reached. */
        if (bzf->bzf_endseen)
            break;
    }
    /* This is where we are (be honest if we overshot) */
    return(bzf->bzf_bzstream.total_out_lo32);
}

static int
bzf_stat(struct open_file *f, struct stat *sb)
{
    struct bz_file      *bzf = (struct bz_file *)f->f_fsdata;
    int                 result;

    /* stat as normal, but indicate that size is unknown */
    if ((result = fstat(bzf->bzf_rawfd, sb)) == 0)
        sb->st_size = -1;
    return(result);
}

void
bz_internal_error(int errorcode)
{
    panic("bzipfs: critical error %d in bzip2 library occurred", errorcode);
}

#ifdef REGRESSION
/* Small test case, open and decompress test.bz2 */
int main(void)
{
    struct open_file f;
    char buf[1024];
    size_t resid;
    int err;

    memset(&f, '\0', sizeof(f));
    f.f_flags = F_READ;
    err = bzf_open("test", &f);
    if (err != 0)
        exit(1);
    do {
        err = bzf_read(&f, buf, sizeof(buf), &resid);
    } while (err == 0 && resid != sizeof(buf));

    if (err != 0)
        exit(2);
    exit(0);
}
#endif