/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright 2003-2005 Colin Percival
 * 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 <sys/types.h>

#include <bzlib.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/mman.h>

#ifndef O_BINARY
#define O_BINARY 0
#endif

#include "divsufsort64.h"
#define saidx_t saidx64_t
#define divsufsort divsufsort64

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

static off_t matchlen(u_char *old,off_t oldsize,u_char *new,off_t newsize)
{
        off_t i;

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

        return i;
}

static off_t search(off_t *I,u_char *old,off_t oldsize,
                u_char *new,off_t newsize,off_t st,off_t en,off_t *pos)
{
        off_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 void offtout(off_t x,u_char *buf)
{
        off_t y;

        if(x<0) y=-x; else y=x;

                buf[0]=y%256;y-=buf[0];
        y=y/256;buf[1]=y%256;y-=buf[1];
        y=y/256;buf[2]=y%256;y-=buf[2];
        y=y/256;buf[3]=y%256;y-=buf[3];
        y=y/256;buf[4]=y%256;y-=buf[4];
        y=y/256;buf[5]=y%256;y-=buf[5];
        y=y/256;buf[6]=y%256;y-=buf[6];
        y=y/256;buf[7]=y%256;

        if(x<0) buf[7]|=0x80;
}

static void
usage(void)
{

        fprintf(stderr, "usage: bsdiff oldfile newfile patchfile\n");
        exit(1);
}

int main(int argc,char *argv[])
{
        int fd;
        u_char *old,*new;
        off_t oldsize,newsize,xnewsize;
        saidx_t *I;
        off_t scan,pos,len;
        off_t lastscan,lastpos,lastoffset;
        off_t oldscore,scsc;
        off_t s,Sf,lenf,Sb,lenb;
        off_t overlap,Ss,lens;
        off_t i;
        off_t dblen,eblen;
        u_char *db,*eb;
        u_char buf[8];
        u_char header[32];
        FILE * pf;
        BZFILE * pfbz2;
        int bz2err;

        if (argc != 4)
                usage();

        /* 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))
                err(1, "%s", argv[1]);

        if (oldsize > SSIZE_MAX ||
            (uintmax_t)oldsize >= SIZE_T_MAX / sizeof(off_t) ||
            oldsize == OFF_MAX) {
                errno = EFBIG;
                err(1, "%s", argv[1]);
        }

        old = mmap(NULL, oldsize+1, PROT_READ, MAP_SHARED, fd, 0);
        if (old == MAP_FAILED || close(fd) == -1)
                err(1, "%s", argv[1]);

        if(((I=malloc((oldsize+1)*sizeof(saidx_t)))==NULL)) err(1,NULL);

        if(divsufsort(old, I, oldsize)) err(1, "divsufsort");

        /* 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))
                err(1, "%s", argv[2]);

        if (newsize > SSIZE_MAX || (uintmax_t)newsize >= SIZE_T_MAX ||
            newsize == OFF_MAX) {
                errno = EFBIG;
                err(1, "%s", argv[2]);
        }

        new = mmap(NULL, newsize+1, PROT_READ, MAP_SHARED, fd, 0);
        if (new == MAP_FAILED || close(fd) == -1)
                err(1, "%s", argv[2]);

        if(((db=malloc(newsize+1))==NULL) ||
                ((eb=malloc(newsize+1))==NULL)) err(1,NULL);
        dblen=0;
        eblen=0;

        /* Create the patch file */
        if ((pf = fopen(argv[3], "wb")) == NULL)
                err(1, "%s", argv[3]);

        /* Header is
                0       8        "BSDIFF40"
                8       8       length of bzip2ed ctrl block
                16      8       length of bzip2ed diff block
                24      8       length of new file */
        /* File is
                0       32      Header
                32      ??      Bzip2ed ctrl block
                ??      ??      Bzip2ed diff block
                ??      ??      Bzip2ed extra block */
        memcpy(header,"BSDIFF40",8);
        offtout(0, header + 8);
        offtout(0, header + 16);
        offtout(newsize, header + 24);
        if (fwrite(header, 32, 1, pf) != 1)
                err(1, "fwrite(%s)", argv[3]);

        /* Compute the differences, writing ctrl as we go */
        if ((pfbz2 = BZ2_bzWriteOpen(&bz2err, pf, 9, 0, 0)) == NULL)
                errx(1, "BZ2_bzWriteOpen, bz2err = %d", bz2err);
        scan=0;len=0;pos=0;
        lastscan=0;lastpos=0;lastoffset=0;
        while(scan<newsize) {
                oldscore=0;

                for(scsc=scan+=len;scan<newsize;scan++) {
                        len=search(I,old,oldsize,new+scan,newsize-scan,
                                        0,oldsize-1,&pos);

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

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

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

                if((len!=oldscore) || (scan==newsize)) {
                        s=0;Sf=0;lenf=0;
                        for(i=0;(lastscan+i<scan)&&(lastpos+i<oldsize);) {
                                if(old[lastpos+i]==new[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]==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(new[lastscan+lenf-overlap+i]==
                                           old[lastpos+lenf-overlap+i]) s++;
                                        if(new[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]=new[lastscan+i]-old[lastpos+i];
                        for(i=0;i<(scan-lenb)-(lastscan+lenf);i++)
                                eb[eblen+i]=new[lastscan+lenf+i];

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

                        offtout(lenf,buf);
                        BZ2_bzWrite(&bz2err, pfbz2, buf, 8);
                        if (bz2err != BZ_OK)
                                errx(1, "BZ2_bzWrite, bz2err = %d", bz2err);

                        offtout((scan-lenb)-(lastscan+lenf),buf);
                        BZ2_bzWrite(&bz2err, pfbz2, buf, 8);
                        if (bz2err != BZ_OK)
                                errx(1, "BZ2_bzWrite, bz2err = %d", bz2err);

                        offtout((pos-lenb)-(lastpos+lenf),buf);
                        BZ2_bzWrite(&bz2err, pfbz2, buf, 8);
                        if (bz2err != BZ_OK)
                                errx(1, "BZ2_bzWrite, bz2err = %d", bz2err);

                        lastscan=scan-lenb;
                        lastpos=pos-lenb;
                        lastoffset=pos-scan;
                }
        }
        BZ2_bzWriteClose(&bz2err, pfbz2, 0, NULL, NULL);
        if (bz2err != BZ_OK)
                errx(1, "BZ2_bzWriteClose, bz2err = %d", bz2err);

        /* Compute size of compressed ctrl data */
        if ((len = ftello(pf)) == -1)
                err(1, "ftello");
        offtout(len-32, header + 8);

        /* Write compressed diff data */
        if ((pfbz2 = BZ2_bzWriteOpen(&bz2err, pf, 9, 0, 0)) == NULL)
                errx(1, "BZ2_bzWriteOpen, bz2err = %d", bz2err);
        BZ2_bzWrite(&bz2err, pfbz2, db, dblen);
        if (bz2err != BZ_OK)
                errx(1, "BZ2_bzWrite, bz2err = %d", bz2err);
        BZ2_bzWriteClose(&bz2err, pfbz2, 0, NULL, NULL);
        if (bz2err != BZ_OK)
                errx(1, "BZ2_bzWriteClose, bz2err = %d", bz2err);

        /* Compute size of compressed diff data */
        if ((xnewsize = ftello(pf)) == -1)
                err(1, "ftello");
        offtout(xnewsize - len, header + 16);

        /* Write compressed extra data */
        if ((pfbz2 = BZ2_bzWriteOpen(&bz2err, pf, 9, 0, 0)) == NULL)
                errx(1, "BZ2_bzWriteOpen, bz2err = %d", bz2err);
        BZ2_bzWrite(&bz2err, pfbz2, eb, eblen);
        if (bz2err != BZ_OK)
                errx(1, "BZ2_bzWrite, bz2err = %d", bz2err);
        BZ2_bzWriteClose(&bz2err, pfbz2, 0, NULL, NULL);
        if (bz2err != BZ_OK)
                errx(1, "BZ2_bzWriteClose, bz2err = %d", bz2err);

        /* Seek to the beginning, write the header, and close the file */
        if (fseeko(pf, 0, SEEK_SET))
                err(1, "fseeko");
        if (fwrite(header, 32, 1, pf) != 1)
                err(1, "fwrite(%s)", argv[3]);
        if (fclose(pf))
                err(1, "fclose");

        /* Free the memory we used */
        free(db);
        free(eb);
        free(I);
        munmap(old, oldsize+1);
        munmap(new, newsize+1);

        return 0;
}