/*-
 * Copyright 2003-2005 Colin Percival
 * Copyright 2012 Matthew Endsley
 * All rights reserved
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted providing 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 ``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 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.
 */

#include "bsdiff.h"

#include <limits.h>
#include <string.h>

#ifndef MIN
#define MIN(x,y) (((x)<(y)) ? (x) : (y))
#endif

static void split(int64_t *I,int64_t *V,int64_t start,int64_t len,int64_t h)
{
	int64_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(int64_t *I,int64_t *V,const uint8_t *old,int64_t oldsize)
{
	int64_t buckets[256];
	int64_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 int64_t matchlen(const uint8_t *old,int64_t oldsize,const uint8_t *new,int64_t newsize)
{
	int64_t i;

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

	return i;
}

static int64_t search(const int64_t *I,const uint8_t *old,int64_t oldsize,
		const uint8_t *new,int64_t newsize,int64_t st,int64_t en,int64_t *pos)
{
	int64_t x,y;

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

static int64_t writedata(struct bsdiff_stream* stream, const void* buffer, int64_t length)
{
	int64_t result = 0;

	while (length > 0)
	{
		const int smallsize = (int)MIN(length, INT_MAX);
		const int writeresult = stream->write(stream, buffer, smallsize);
		if (writeresult == -1)
		{
			return -1;
		}

		result += writeresult;
		length -= smallsize;
		buffer = (uint8_t*)buffer + smallsize;
	}

	return result;
}

struct bsdiff_request
{
	const uint8_t* old;
	int64_t oldsize;
	const uint8_t* new;
	int64_t newsize;
	struct bsdiff_stream* stream;
	int64_t *I;
	uint8_t *buffer;
};

static int bsdiff_internal(const struct bsdiff_request req)
{
	int64_t *I,*V;
	int64_t scan,pos,len;
	int64_t lastscan,lastpos,lastoffset;
	int64_t oldscore,scsc;
	int64_t s,Sf,lenf,Sb,lenb;
	int64_t overlap,Ss,lens;
	int64_t i;
	uint8_t *buffer;
	uint8_t buf[8 * 3];

	if((V=req.stream->malloc((req.oldsize+1)*sizeof(int64_t)))==NULL) return -1;
	I = req.I;

	qsufsort(I,V,req.old,req.oldsize);
	req.stream->free(V);

	buffer = req.buffer;

	/* Compute the differences, writing ctrl as we go */
	scan=0;len=0;pos=0;
	lastscan=0;lastpos=0;lastoffset=0;
	while(scan<req.newsize) {
		oldscore=0;

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

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

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

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

		if((len!=oldscore) || (scan==req.newsize)) {
			s=0;Sf=0;lenf=0;
			for(i=0;(lastscan+i<scan)&&(lastpos+i<req.oldsize);) {
				if(req.old[lastpos+i]==req.new[lastscan+i]) s++;
				i++;
				if(s*2-i>Sf*2-lenf) { Sf=s; lenf=i; };
			};

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

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

			offtout(lenf,buf);
			offtout((scan-lenb)-(lastscan+lenf),buf+8);
			offtout((pos-lenb)-(lastpos+lenf),buf+16);

			/* Write control data */
			if (writedata(req.stream, buf, sizeof(buf)))
				return -1;

			/* Write diff data */
			for(i=0;i<lenf;i++)
				buffer[i]=req.new[lastscan+i]-req.old[lastpos+i];
			if (writedata(req.stream, buffer, lenf))
				return -1;

			/* Write extra data */
			for(i=0;i<(scan-lenb)-(lastscan+lenf);i++)
				buffer[i]=req.new[lastscan+lenf+i];
			if (writedata(req.stream, buffer, (scan-lenb)-(lastscan+lenf)))
				return -1;

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

	return 0;
}

TOOLKIT_API int bsdiff(const uint8_t* old, int64_t oldsize, const uint8_t* newone, int64_t newsize, struct bsdiff_stream* diffstream)
{
	int result;
	struct bsdiff_request req;

	if((req.I= diffstream->malloc((oldsize+1)*sizeof(int64_t)))==NULL)
		return -1;

	if((req.buffer= diffstream->malloc(newsize+1))==NULL)
	{
		diffstream->free(req.I);
		return -1;
	}

	req.old = old;
	req.oldsize = oldsize;
	req.new = newone;
	req.newsize = newsize;
	req.stream = diffstream;

	result = bsdiff_internal(req);

	diffstream->free(req.buffer);
	diffstream->free(req.I);

	return result;
}