/* vim:set ts=8 sw=8 sts=8 noet: */
/*
  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 XP_WIN
#include <io.h>
#include <winsock2.h>
#define open _open
#define close _close
#define read _read
#define lseek _lseek
#define write _write
#else
#include <unistd.h>
#include <arpa/inet.h>
#define _O_BINARY 0
#endif

#include "crctable.h"

#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 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,*newbuf;
	int32_t oldsize,newsize;
	int32_t *I,*V;

	int32_t scan,pos,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;

	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+10)) 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*3-i*2>Sf*3-lenf*2) { 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*3-i*2>Sb*3-lenb*2) { 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;
}