/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/*
  bsdiff.c -- Binary patch generator.

  Copyright 2003 Colin Percival

  For the terms under which this work may be distributed, please see
  the adjoining file "LICENSE".

  ChangeLog:
  2005-05-05 - Use the modified header struct from bspatch.h; use 32-bit
               values throughout.
                 --Benjamin Smedberg <benjamin@smedbergs.us>
  2005-05-18 - Use the same CRC algorithm as bzip2, and leverage the CRC table
               provided by libbz2.
                 --Darin Fisher <darin@meer.net>
*/

#include "bspatch.h"

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <stdarg.h>
#ifdef _WIN32
#include <io.h>
#include <winsock2.h>
#else
#include <unistd.h>
#include <arpa/inet.h>
#define _O_BINARY 0
#endif

#undef MIN
#define MIN(x,y) (((x)<(y)) ? (x) : (y))

/*---------------------------------------------------------------------------*/

/* This variable lives in libbz2.  It's declared in bzlib_private.h, so we just
 * declare it here to avoid including that entire header file.
 */
extern "C"  unsigned int BZ2_crc32Table[256];

static unsigned int
crc32(const unsigned char *buf, unsigned int len)
{
    unsigned int crc = 0xffffffffL;

    const unsigned char *end = buf + len;
    for (; buf != end; ++buf)
        crc = (crc << 8) ^ BZ2_crc32Table[(crc >> 24) ^ *buf];

    crc = ~crc;
    return crc;
}

/*---------------------------------------------------------------------------*/

static void
reporterr(int e, const char *fmt, ...)
{
    if (fmt) {
        va_list args;
        va_start(args, fmt);
        vfprintf(stderr, fmt, args);
        va_end(args);
    }

    exit(e);
}

static void
split(int32_t *I,int32_t *V,int32_t start,int32_t len,int32_t h)
{
    int32_t i,j,k,x,tmp,jj,kk;

    if(len<16) {
        for(k=start;k<start+len;k+=j) {
            j=1;x=V[I[k]+h];
            for(i=1;k+i<start+len;i++) {
                if(V[I[k+i]+h]<x) {
                    x=V[I[k+i]+h];
                    j=0;
                };
                if(V[I[k+i]+h]==x) {
                    tmp=I[k+j];I[k+j]=I[k+i];I[k+i]=tmp;
                    j++;
                };
            };
            for(i=0;i<j;i++) V[I[k+i]]=k+j-1;
            if(j==1) I[k]=-1;
        };
        return;
    };

    x=V[I[start+len/2]+h];
    jj=0;kk=0;
    for(i=start;i<start+len;i++) {
        if(V[I[i]+h]<x) jj++;
        if(V[I[i]+h]==x) kk++;
    };
    jj+=start;kk+=jj;

    i=start;j=0;k=0;
    while(i<jj) {
        if(V[I[i]+h]<x) {
            i++;
        } else if(V[I[i]+h]==x) {
            tmp=I[i];I[i]=I[jj+j];I[jj+j]=tmp;
            j++;
        } else {
            tmp=I[i];I[i]=I[kk+k];I[kk+k]=tmp;
            k++;
        };
    };

    while(jj+j<kk) {
        if(V[I[jj+j]+h]==x) {
            j++;
        } else {
            tmp=I[jj+j];I[jj+j]=I[kk+k];I[kk+k]=tmp;
            k++;
        };
    };

    if(jj>start) split(I,V,start,jj-start,h);

    for(i=0;i<kk-jj;i++) V[I[jj+i]]=kk-1;
    if(jj==kk-1) I[jj]=-1;

    if(start+len>kk) split(I,V,kk,start+len-kk,h);
}

static void
qsufsort(int32_t *I,int32_t *V,unsigned char *old,int32_t oldsize)
{
    int32_t buckets[256];
    int32_t i,h,len;

    for(i=0;i<256;i++) buckets[i]=0;
    for(i=0;i<oldsize;i++) buckets[old[i]]++;
    for(i=1;i<256;i++) buckets[i]+=buckets[i-1];
    for(i=255;i>0;i--) buckets[i]=buckets[i-1];
    buckets[0]=0;

    for(i=0;i<oldsize;i++) I[++buckets[old[i]]]=i;
    I[0]=oldsize;
    for(i=0;i<oldsize;i++) V[i]=buckets[old[i]];
    V[oldsize]=0;
    for(i=1;i<256;i++) if(buckets[i]==buckets[i-1]+1) I[buckets[i]]=-1;
    I[0]=-1;

    for(h=1;I[0]!=-(oldsize+1);h+=h) {
        len=0;
        for(i=0;i<oldsize+1;) {
            if(I[i]<0) {
                len-=I[i];
                i-=I[i];
            } else {
                if(len) I[i-len]=-len;
                len=V[I[i]]+1-i;
                split(I,V,i,len,h);
                i+=len;
                len=0;
            };
        };
        if(len) I[i-len]=-len;
    };

    for(i=0;i<oldsize+1;i++) I[V[i]]=i;
}

static int32_t
matchlen(unsigned char *old,int32_t oldsize,unsigned char *newbuf,int32_t newsize)
{
    int32_t i;

    for(i=0;(i<oldsize)&&(i<newsize);i++)
        if(old[i]!=newbuf[i]) break;

    return i;
}

static int32_t
search(int32_t *I,unsigned char *old,int32_t oldsize,
       unsigned char *newbuf,int32_t newsize,int32_t st,int32_t en,int32_t *pos)
{
    int32_t x,y;

    if(en-st<2) {
        x=matchlen(old+I[st],oldsize-I[st],newbuf,newsize);
        y=matchlen(old+I[en],oldsize-I[en],newbuf,newsize);

        if(x>y) {
            *pos=I[st];
            return x;
        } else {
            *pos=I[en];
            return y;
        }
    };

    x=st+(en-st)/2;
    if(memcmp(old+I[x],newbuf,MIN(oldsize-I[x],newsize))<0) {
        return search(I,old,oldsize,newbuf,newsize,x,en,pos);
    } else {
        return search(I,old,oldsize,newbuf,newsize,st,x,pos);
    };
}

int main(int argc,char *argv[])
{
    int fd;
    unsigned char *old = nullptr,*newbuf = nullptr;
    int32_t oldsize = 0, newsize = 0;
    int32_t *I = nullptr,*V = nullptr;

    int32_t scan,pos = 0,len;
    int32_t lastscan,lastpos,lastoffset;
    int32_t oldscore,scsc;

    int32_t s,Sf,lenf,Sb,lenb;
    int32_t overlap,Ss,lens;
    int32_t i;

    int32_t dblen,eblen;
    unsigned char *db,*eb = nullptr;

    unsigned int scrc;

    MBSPatchHeader header = {
        {'M','B','D','I','F','F','1','0'},
        0, 0, 0, 0, 0, 0
    };

    uint32_t numtriples;

    if(argc!=4)
        reporterr(1,"usage: %s <oldfile> <newfile> <patchfile>\n",argv[0]);

    /* Allocate oldsize+1 bytes instead of oldsize bytes to ensure
        that we never try to malloc(0) and get a NULL pointer */
    if(((fd=open(argv[1],O_RDONLY|_O_BINARY,0))<0) ||
        ((oldsize=lseek(fd,0,SEEK_END))==-1) ||
        ((old=(unsigned char*) malloc(oldsize+1))==NULL) ||
        (lseek(fd,0,SEEK_SET)!=0) ||
        (read(fd,old,oldsize)!=oldsize) ||
        (close(fd)==-1))
        reporterr(1,"%s\n",argv[1]);

    scrc = crc32(old, oldsize);

    if(((I=(int32_t*) malloc((oldsize+1)*sizeof(int32_t)))==NULL) ||
        ((V=(int32_t*) malloc((oldsize+1)*sizeof(int32_t)))==NULL))
        reporterr(1,NULL);

    qsufsort(I,V,old,oldsize);

    free(V);

    /* Allocate newsize+1 bytes instead of newsize bytes to ensure
        that we never try to malloc(0) and get a NULL pointer */
    if(((fd=open(argv[2],O_RDONLY|_O_BINARY,0))<0) ||
        ((newsize=lseek(fd,0,SEEK_END))==-1) ||
        ((newbuf=(unsigned char*) malloc(newsize+1))==NULL) ||
        (lseek(fd,0,SEEK_SET)!=0) ||
        (read(fd,newbuf,newsize)!=newsize) ||
        (close(fd)==-1)) reporterr(1,"%s\n",argv[2]);

    if(((db=(unsigned char*) malloc(newsize+1))==NULL) ||
        ((eb=(unsigned char*) malloc(newsize+1))==NULL))
        reporterr(1,NULL);

    dblen=0;
    eblen=0;

    if((fd=open(argv[3],O_CREAT|O_TRUNC|O_WRONLY|_O_BINARY,0666))<0)
        reporterr(1,"%s\n",argv[3]);

    /* start writing here */

    /* We don't know the lengths yet, so we will write the header again
         at the end */

    if(write(fd,&header,sizeof(MBSPatchHeader))!=sizeof(MBSPatchHeader))
        reporterr(1,"%s\n",argv[3]);

    scan=0;len=0;
    lastscan=0;lastpos=0;lastoffset=0;
    numtriples = 0;
    while(scan<newsize) {
        oldscore=0;

        for(scsc=scan+=len;scan<newsize;scan++) {
            len=search(I,old,oldsize,newbuf+scan,newsize-scan,
                    0,oldsize,&pos);

            for(;scsc<scan+len;scsc++)
            if((scsc+lastoffset<oldsize) &&
                (old[scsc+lastoffset] == newbuf[scsc]))
                oldscore++;

            if(((len==oldscore) && (len!=0)) ||
                (len>oldscore+8)) break;

            if((scan+lastoffset<oldsize) &&
                (old[scan+lastoffset] == newbuf[scan]))
                oldscore--;
        };

        if((len!=oldscore) || (scan==newsize)) {
            MBSPatchTriple triple;

            s=0;Sf=0;lenf=0;
            for(i=0;(lastscan+i<scan)&&(lastpos+i<oldsize);) {
                if(old[lastpos+i]==newbuf[lastscan+i]) s++;
                i++;
                if(s*2-i>Sf*2-lenf) { Sf=s; lenf=i; };
            };

            lenb=0;
            if(scan<newsize) {
                s=0;Sb=0;
                for(i=1;(scan>=lastscan+i)&&(pos>=i);i++) {
                    if(old[pos-i]==newbuf[scan-i]) s++;
                    if(s*2-i>Sb*2-lenb) { Sb=s; lenb=i; };
                };
            };

            if(lastscan+lenf>scan-lenb) {
                overlap=(lastscan+lenf)-(scan-lenb);
                s=0;Ss=0;lens=0;
                for(i=0;i<overlap;i++) {
                    if(newbuf[lastscan+lenf-overlap+i]==
                       old[lastpos+lenf-overlap+i]) s++;
                    if(newbuf[scan-lenb+i]==
                       old[pos-lenb+i]) s--;
                    if(s>Ss) { Ss=s; lens=i+1; };
                };

                lenf+=lens-overlap;
                lenb-=lens;
            };

            for(i=0;i<lenf;i++)
                db[dblen+i]=newbuf[lastscan+i]-old[lastpos+i];
            for(i=0;i<(scan-lenb)-(lastscan+lenf);i++)
                eb[eblen+i]=newbuf[lastscan+lenf+i];

            dblen+=lenf;
            eblen+=(scan-lenb)-(lastscan+lenf);

            triple.x = htonl(lenf);
            triple.y = htonl((scan-lenb)-(lastscan+lenf));
            triple.z = htonl((pos-lenb)-(lastpos+lenf));
            if (write(fd,&triple,sizeof(triple)) != sizeof(triple))
                reporterr(1,NULL);

#ifdef DEBUG_bsmedberg
            printf("Writing a block:\n"
                   "    X: %u\n"
                   "    Y: %u\n"
                   "    Z: %i\n",
                   (uint32_t) lenf,
                   (uint32_t) ((scan-lenb)-(lastscan+lenf)),
                   (uint32_t) ((pos-lenb)-(lastpos+lenf)));
#endif

            ++numtriples;

            lastscan=scan-lenb;
            lastpos=pos-lenb;
            lastoffset=pos-scan;
        };
    };

    if(write(fd,db,dblen)!=dblen)
        reporterr(1,NULL);

    if(write(fd,eb,eblen)!=eblen)
        reporterr(1,NULL);

    header.slen    = htonl(oldsize);
    header.scrc32    = htonl(scrc);
    header.dlen    = htonl(newsize);
    header.cblen    = htonl(numtriples * sizeof(MBSPatchTriple));
    header.difflen    = htonl(dblen);
    header.extralen = htonl(eblen);

    if (lseek(fd,0,SEEK_SET) == -1 ||
        write(fd,&header,sizeof(header)) != sizeof(header) ||
        close(fd) == -1)
        reporterr(1,NULL);

    free(db);
    free(eb);
    free(I);
    free(old);
    free(newbuf);

    return 0;
}

/* vim:set shiftwidth=4 softtabstop=4 expandtab: */