implement Tail; include "sys.m";sys: Sys; include "draw.m"; include "bufio.m";bufmod : Bufio;Iobuf : import bufmod; include "string.m";	str : String; count, anycount, follow : int;file : ref sys->FD;bout : ref Iobuf;BSize : con 8*1024; BEG, END, CHARS, LINES , FWD, REV : con iota; origin := END;units := LINES;dir := FWD;  Tail: module{	init:	fn(nil: ref Draw->Context, argv: list of string);};  init(nil: ref Draw->Context, argv: list of string){	sys = load Sys Sys->PATH;	str = load String String->PATH;	bufmod = load Bufio Bufio->PATH;	seekable : int;	bout = bufmod->fopen(sys->fildes(1),bufmod->OWRITE);	argv=parse(tl argv);	if(dir==REV && (units==CHARS || follow || origin==BEG))		fail("incompatible options");	if(!anycount){		if (dir==REV)			count= 16r7fffffff;		else			count = 10;	}	if(origin==BEG && units==LINES && count>0)		count--;	if(len argv > 1)		usage();	if(argv == nil || hd argv == "-") {		file = sys->fildes(0);		seekable = 0;	}	else {		if((file=sys->open(hd argv,sys->OREAD)) == nil )			fatal(hd argv);		(nil, stat) := sys->fstat(file);		seekable = sys->seek(file,big 0,sys->SEEKSTART) == big 0 && stat.length > big 0;	} 	if(!seekable && origin==END)		keep();	else if(!seekable && origin==BEG)		skip();	else if(units==CHARS && origin==END){		tseek(big -count, Sys->SEEKEND);		copy();	}	else if(units==CHARS && origin==BEG){		tseek(big count, Sys->SEEKSTART);		copy();	}	else if(units==LINES && origin==END)		reverse();	else if(units==LINES && origin==BEG)		skip();	if(follow){		if(seekable){			d : sys->Dir;			d.length=big -1;			for(;;){				d=trunc(d.length);				copy();				sys->sleep(5000);			}		}else{			for(;;){				copy();				sys->sleep(5000);			}		}	}	exit;}  trunc(length : big) : sys->Dir{	(nil,d):=sys->fstat(file);	if(d.length < length)		d.length = tseek(big 0, sys->SEEKSTART);	return d;}  skip()	# read past head of the file to find tail {	n : int;	buf := array[BSize] of byte;	if(units == CHARS) {		for( ; count>0; count -=n) {			if (count<BSize) 				n=count;			else				n=BSize;			n = tread(buf, n);			if(n == 0)				return;		}	} else { # units == LINES		i:=0;		n=0;		while(count > 0) {			n = tread(buf, BSize);			if(n == 0)				return;			for(i=0; i<n && count>0; i++)				if(buf[i]==byte '\n')					count--;		}		twrite(buf[i:n]);	}	copy();}  copy(){	buf := array[BSize] of byte;	while((n := tread(buf, BSize)) > 0){		twrite(buf[0:n]);	}	bout.flush();	}  keep()	# read whole file, keeping the tail {	# complexity=length(file)*length(tail).  could be linear	j, k : int;	length:=0;	buf : array of byte;	tbuf : array of byte;	bufsize := 0;	for(n:=1; n;) {		if(length+BSize > bufsize ) {			bufsize += 2*BSize;			tbuf = array[bufsize+1] of byte;			tbuf[0:]=buf[0:];			buf = tbuf;		}		for( ; n && length<bufsize; length+=n)			n = tread(buf[length:], bufsize-length);		if(count >= length)			continue;		if(units == CHARS)			j = length - count;		else{ # units == LINES 			if (int buf[length-1]=='\n')				j =  length-1;			else				j=length;			for(k=0; j>0; j--)				if(int buf[j-1] == '\n')					if(++k >= count)						break;		}		length-=j;		buf[0:]=buf[j:j+length];	}	if(dir == REV) {		if(length>0 && buf[length-1]!= byte '\n')			buf[length++] = byte '\n';		for(j=length-1 ; j>0; j--)			if(buf[j-1] == byte '\n') {				twrite(buf[j:length]);				if(--count <= 0)					return;				length = j;			}	}	if(count > 0 && length > 0)		twrite(buf[0:length]);	bout.flush();} reverse()	# count backward and print tail of file {	length := 0;	n := 0;	buf : array of byte;	pos := tseek(big 0, sys->SEEKEND);	bufsize := 0;	for(first:=1; pos>big 0 && count>0; first=0) {		if (pos>big BSize)			n = BSize;		else			n = int pos;		pos -= big n;		if(length+2*n > bufsize) {			bufsize += BSize*((length+2*n-bufsize+BSize-1)/BSize);			tbuf := array[bufsize+1] of byte;			tbuf[0:] = buf;			buf = tbuf;		}		length += n;		abuf := array[length] of byte;		abuf[0:] = buf[0:length];		buf[n:] = abuf;		tseek(pos, sys->SEEKSTART);		if(tread(buf, n) != n)			fatal("length error");		if(first && buf[length-1]!= byte '\n')			buf[length++] = byte '\n';		for(n=length-1 ; n>0 && count>0; n--)			if(buf[n-1] == byte '\n') {				count--;				if(dir == REV){					twrite(buf[n:length]);					bout.flush();				}				length = n;			}	}	if(dir == FWD) {		if (n==0)			tseek(big 0 , sys->SEEKSTART);		else			tseek(pos+big n+big 1, sys->SEEKSTART);					copy();	} else if(count > 0)		twrite(buf[0:length]);	bout.flush();}  tseek(o : big, p: int) : big{	o = sys->seek(file, o, p);	if(o == big -1)		fatal("");	return o;}  tread(buf: array of byte, n: int): int{	r := sys->read(file, buf, n);	if(r == -1)		fatal("");	return r;}  twrite(buf:array of byte){	str1:= string buf;	if(bout.puts(str1)!=len str1)		fatal("");}  		fatal(s : string){	sys->fprint(sys->fildes(2), "tail: %s: %r\n", s);	exit;} fail(s : string){	sys->fprint(sys->fildes(2), "tail: %s\n", s);	exit;}  usage(){	sys->fprint(sys->fildes(2), "usage: tail [-n N] [-c N] [-f] [-r] [+-N[bc][fr]] [file]\n");	exit;}  getnumber(s: string) : int{	i:=0;	if (len s == 0) return 0;	if(s[i]=='-' || s[i]=='+') {		if (len s == 1)			return 0;		i++;	}	if(!(s[i]>='0' && s[i]<='9'))		return 0;	if(s[0] == '+')		origin = BEG;	if(anycount++)		fail("excess option");	if (s[0]=='-')		s=s[1:];	(count,nil) = str->toint(s,10);	if(count < 0){	# protect int args (read, fwrite) 		fail("too big");	}	return 1;}	parse(args : list of string) : list of string {	for(; args!=nil ; args = tl args ) {		hdarg := hd args;		if(getnumber(hdarg))			suffix(hdarg);		else if(len hdarg > 1 && hdarg[0] == '-')			case (hdarg[1]) {			 'c' or 'n'=>				if (hdarg[1]=='c')					units = CHARS;				if(len hdarg>2 && getnumber(hdarg[2:]))					;				else if(tl args != nil && getnumber(hd tl args)) {					args = tl args;				} else					usage();			 'r' =>				dir = REV;			 'f' =>				follow++;			 '-' =>				args = tl args;			}		else			break;	}	return args;}  suffix(s : string){	i:=0;	while(i < len s && str->in(s[i],"0123456789+-"))		i++;	if (i==len s)		return;	if (s[i]=='b')		if((count*=1024) < 0)			fail("too big");	if (s[i]=='c' || s[i]=='b')		units = CHARS;	if (s[i]=='l' || s[i]=='c' || s[i]=='b')		i++;	if (i<len s){		case s[i] {		 'r'=>			dir = REV;			return;		 'f'=>			follow++;			return;		}	}	i++;	if (i<len s)		usage();}