#! /usr/bin/perl -w

use strict;
use Benchmark;
use File::ReadBackwards;
use File::Tail;

use constant VERIFY => 0;
my $count = shift or die "Benchmark count not specified, try 1000 (iters) or -10 (CPU secs).\n";
my $limit = shift or die "Number of lines not specified, try 100.\n";
my $file  = shift or die "No filename specified on command-line.\n";
my @result;

sub f_rb_obj {
	my $lim = $limit;
	my $bw = File::ReadBackwards->new( $file ) or die "can't read $file: $!\n" ;

	my $line;
	my @lines;
	while( defined( my $line = $bw->readline ) ) {
    	push @lines, $line;
		last if --$lim <= 0;
	}
	reverse @lines;
}

sub f_rb_tie {
	my $lim = $limit;
	tie *BW, 'File::ReadBackwards', $file or die "can't read $file: $!\n" ;

	my @lines;
	while( <BW> ) {
    	push @lines, $_;
		last if --$lim <= 0;
	}
	reverse @lines;
}

sub f_rb_obj_u {
	my $lim = $limit;
	my $bw = File::ReadBackwards->new( $file ) or die "can't read $file: $!\n" ;

	my $line;
	my @lines;
	while( defined( my $line = $bw->readline ) ) {
    	unshift @lines, $line;
		last if --$lim <= 0;
	}
	@lines;
}

sub f_rb_tie_u {
	my $lim = $limit;
	tie *BW, 'File::ReadBackwards', $file or die "can't read $file: $!\n" ;

	my @lines;
	while( <BW> ) {
    	unshift @lines, $_;
		last if --$lim <= 0;
	}
	@lines;
}

sub grinder {
	my $lim = $limit;

	my @alpha;
	my @beta;
	my $current = \@alpha;

	open( IN, $file ) or die "Cannot open $file for input: $!\n";
	while( <IN> ) {
		push @$current, $_;
		if( scalar @$current > $limit ) {
			if( $current == \@alpha ) {
				@beta = ();
				$current = \@beta;
			}
			else {
				@alpha = ();
				$current = \@alpha;
			}
		}	
	}
	close IN;

	return @{$current == \@alpha ? \@beta : \@alpha}[-($limit - scalar @$current)..-1],
		@$current;
}

sub lastn {
	my $lines = $limit;
    my $fh;
    if (! open($fh, $file) ) {
        print "Can't open $file: $!";
        return;
    }
    binmode($fh);
    sysseek($fh, 0, 2);  # Seek to end
    my $nlcount=0;
    while($nlcount<$lines) {
        last unless sysseek($fh, -1, 1);
        sysread($fh, $_, 1, 0) || die;
        $nlcount++ if ( $_ eq "\n");
        last if $nlcount==$lines;
        last unless (sysseek($fh, -1, 1));
    }
    seek($fh, sysseek($fh, 0, 1), 0) || warn;
    my @lines = <$fh>;
	close $fh;
	@lines;
}

sub lastn_getc {
	my $lines = $limit;
    my $fh;
    if (! open($fh, $file) ) {
        print "Can't open $file: $!";
        return;

    }
    binmode($fh);
    seek($fh, 0, 2);  # Seek to end
    my $nlcount=0;
    while($nlcount<$lines) {
        last unless seek($fh, -1, 1);
        $_=getc($fh);
        die unless defined $_;
        $nlcount++ if ( $_ eq "\n");
        last if $nlcount==$lines;
        last unless (seek($fh, -1, 1));
    }
    my @lines = <$fh>;
	close $fh;
	@lines;
}

sub file_tail {
	my $fh = File::Tail->new(name=>$file,tail=>$limit);
	if( !defined $fh ) {
		die "Could not create File::Tail object on $file: $!\n";
	}
	$fh->nowait(1);
	my @lines;
	local $" = "";
	while( defined( my $line = $fh->read() )) {
		last unless $line;
		push @lines, $line;
	}
	# $fh->close;
	@lines;
}

if( VERIFY ) {
	local $" = "";
	for my $test( qw/f_rb_obj f_rb_tie grinder lastn lastn_getc file_tail/ ) {
		warn "$test\n", eval( "$test()" ), "\n";
	}
	exit;
}

timethese( $count, {
	'f_rb_obj'   => \&f_rb_obj, 
	'f_rb_tie'   => \&f_rb_tie, 
	'f_rb_obj_u' => \&f_rb_obj_u, 
	'f_rb_tie_u' => \&f_rb_tie_u, 
	'grinder'    => \&grinder, 
	'file_tail'  => \&file_tail, 
	'lastn'      => \&lastn, 
	'lastn_getc' => \&lastn_getc, 
});
__END__