/*
 * Author: Adrian Keet
 * Last modified: October 21, 2012
 *
 * This code is in the public domain. Go ahead and use it for whatever you
 * want. I don't care. :)
 */

#include <stdio.h>
#include <malloc.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>

int usage()
{
    fprintf(stderr, "Usage: oggextract <filename> [<filename> ...]");
    return 255;
}

int findpattern(unsigned char *data, int datalen, int start)
{
    int i;

    for (i = start; i < datalen - 4; i++)
        if (*(int *)(data + i) == 0x5367674f) /* "OggS" */
            return i;
    return -1;
}

int ogg_ispage(unsigned char *data)
{
    /* capture pattern */
    if (*(int *)data != 0x5367674f) /* "OggS" */
        return 0;

    /* stream structure version */
    if (data[4] != 0x00)
        return 0;

    /* header type flag */
    if ((data[5] & ~7) != 0x00)
        return 0;

    /* I think we can reasonably assume it is a real page now */
    return 1;
}

unsigned int ogg_getlength(unsigned char *data)
{
    unsigned char nsegs;
    unsigned char *segs;
    int i;
    int length;

    nsegs = data[26];
    segs = data + 27;
    length = 27 + nsegs;

    for (i = 0; i < nsegs; i++)
        length += segs[i];
    return length;
}

int ogg_isinitial(unsigned char *data)
{
    return data[5] & 2;
}

int ogg_isfinal(unsigned char *data)
{
    return data[5] & 4;
}

int extract(char *filename)
{
    int fd;
    struct stat statdata;
    int filesize;
    unsigned char *filedata, *oggdata;

    int pos = 0;

    int pagelen;
    int outfd = -1;
    char *outfilename;

    int numfiles = 0;

    printf("Extracting %s...\n", filename);
    if (stat(filename, &statdata) < 0)
    {
        perror("stat");
        return 1;
    }
    if (statdata.st_mode & S_IFDIR)
    {
        fprintf(stderr, "error: Is a directory\n", filename);
        return 1;
    }
    filesize = statdata.st_size;

    /* FIXME: prone to race conditions */

    fd = open(filename, O_RDONLY);
    if (fd < 0)
    {
        perror("open");
        return 1;
    }

    filedata = mmap(0, filesize, PROT_READ, MAP_PRIVATE, fd, 0);

    outfilename = malloc(strlen(filename) + 16);

    while (1)
    {
        pos = findpattern(filedata, filesize, pos);
        if (pos < 0)
            break;

        oggdata = filedata + pos;
        if (ogg_ispage(oggdata))
        {
            pagelen = ogg_getlength(oggdata);

            if (outfd < 0 && ogg_isinitial(oggdata))
            {
                sprintf(outfilename, "%s_%08x.ogg", filename, pos);
                outfd = creat(outfilename, -1);
                numfiles++;
            }
            if (outfd >= 0)
            {
                write(outfd, oggdata, pagelen);
                if (ogg_isfinal(oggdata))
                {
                    close(outfd);
                    outfd = -1;
                }
            }
        }

        pos += pagelen;
    }

    if (outfd != -1 && ogg_isfinal(oggdata))
        close(outfd);
    free(outfilename);
    munmap(filedata, filesize);
    close(fd);

    printf("%d file(s) written.\n", numfiles);

    return 0;
}

int main(int argc, char **argv)
{
    int i;
    int failures;

    if (argc < 2)
        return usage();

    failures = 0;
    for (i = 1; i < argc; i++)
        failures += extract(argv[i]);
    if (failures > 0)
        fprintf(stderr, "Errors processing %d file(s).\n", failures);
}