#include <stdio.h>

int main(int argc,char*argv[])
{
char pn[100],p[100],sp[100],*prog=argv[0];FILE*fp;
int comp(char*,char*),sost(FILE*,char*,char*,char*);
if(argc==2&&comp("--help",argv[1]))
	{printf("%s: usage: %s pathname pattern new_pattern\n",prog,prog);exit(0);}
else if(argc==4)
	{strcpy(pn,argv[1]);
	 strcpy(p,argv[2]);
	 strcpy(sp,argv[3]);}
else if(argc==1)
	{printf("digitare : pathname    pattern    nuovo_pattern    : ");
	scanf("%s%s%s",pn,p,sp);for(;(getchar())!='\n';);}
else	{printf("%s: error: type %s --help for more information\n",p,p);exit(1);}
if(!(fp=fopen(pn,"r+")))
	{fprintf(stderr,"%s: file \"%s\" doesn't exist .\n",prog,pn);exit(1);}
else	printf("%s: %d sostituzioni effettuate .\n",prog,sost(fp,p,sp,pn));
printf("\n\n\n");
system("cat ciao");
}

int comp(char*a,char*b)
{
for(;*a!='\0';)
	if(*a++!=*b++)
		return 0;
return 1;
}

int sost(FILE*fp,char*p,char*sp,char*pn)
{
char c;int fcomp(FILE*,char*),count=0;
void write(FILE*,char*,int,int*,char*);
for(;(c=getc(fp))!=EOF;)
	if(c==*p&&fcomp(fp,p))
		write(fp,sp,strlen(p),&count,pn);
fclose(fp);
if(fp=fopen(".~tmp","r+"))
	{fclose(fp);
	 system("rm .~tmp");}
return count;
}

int fcomp(FILE*fp,char*p)
{
int l=strlen(p),i=0;char tmp[100],*t=tmp;
for(fseek(fp,-1,SEEK_CUR);i<l;++i)
	*t++=getc(fp);
*t='\0';
fseek(fp,-l+1,SEEK_CUR);
return comp(tmp,p);
}

void write(FILE*fp,char*sp,int p,int*count,char*pn)
{
FILE*dest,*tmp;
int sps=strlen(sp),i,t,pp,ppp,copia(FILE*,char*);char c;
++*count;
fseek(fp,-1,SEEK_CUR);
if(sps==p)
	fwrite(sp,sps,1,fp);
else if(sps<p)
	{fwrite(sp,sps,1,fp);
	 fseek(fp,p-sps,SEEK_CUR);
	 for(t=0;(c=getc(fp))!=EOF;++t);
	 fseek(fp,-1,SEEK_CUR);
	 putc('\0',fp);
	 fseek(fp,-t,SEEK_CUR);
	 for(;(c=getc(fp))!='\0';)
	 	{fseek(fp,sps-p-1,SEEK_CUR);
	 	 putc(c,fp);
	 	 if(fseek(fp,p-sps,SEEK_CUR))
	 	 	break;}
	 fseek(fp,-1-(p-sps),SEEK_CUR);
	 putc('\0',fp);
	 fseek(fp,-3-t,SEEK_END);
	 if(!copia(fp,pn))
		 fprintf(stderr,"impossibile creare files temporanei");}
else if(sps>p)
	{fseek(fp,p-1,SEEK_CUR);
	 for(t=-2;(c=getc(fp))!=EOF;++t);
	 for(i=sps-p,pp=t,ppp=i;i>0;--i,t=pp)
	 	for(fseek(fp,-1,SEEK_END);t>-1;--t)
	 		 {c=getc(fp);
	 		  putc(c,fp);
	 		  fseek(fp,-3,SEEK_CUR);}
	 fseek(fp,-1-pp-ppp-p,SEEK_END);
	 fwrite(sp,sps,1,fp);}
}

int copia(FILE*fp,char*pn)
{
FILE*tmp;
int t=0;
char c;
if(!(tmp=fopen(".~tmp","w+")))
	return 0;
for(;!fseek(fp,-1,SEEK_CUR);++t);
for(;(c=getc(fp))!='\0';putc(c,tmp));putc('\0',tmp);
fclose(fp);
fp=fopen(pn,"w+");
for(fseek(tmp,0,SEEK_SET);(c=getc(tmp))!=EOF;putc(c,fp));putc('\0',fp);
fclose(tmp);
fseek(fp,t,SEEK_SET);
return 1;
}
// gestisco errori in scrittura su file e ferror