use Benchmark qw/cmpthese/;
use Test::More;
use experimental 'signatures'; # for daxim

my $string ="test\nI want length of this line\n test";
my $position = 12; # Note this postion can be any position in any line. 
                   # currently considering it inside 2nd line

if ($ENV{BENCHMARK}) {
    cmpthese(-$ENV{BENCHMARK}, {
         cur_strlen => sub { cur_strlen($string, $position) },
            rlindex => sub { rlindex($string, $position) },
             op => sub { op($string, $position) },
              daxim => sub { daxim($string, $position) },
    });
}

my @tests = (
    [ "\nString\n", 2, 6, 'Surrounded' ],
    [ "String\n",   2, 6, 'No first \n' ],
    [ "\nString",   2, 6, 'No last \n' ],
    [ "String",     2, 6, 'No \n' ],
    [ "",           0, 0, 'Blank' ],
);

if ($ENV{TEST}) {
    for (@tests) {
        ($string, $position, my $expected, my $desc) = @$_;
        is cur_strlen($string, $position), $expected, "cur_strlen: $desc";
        is    rlindex($string, $position), $expected, "rlindex: $desc";
        is         op($string, $position), $expected, "op: $desc";
        is      daxim($string, $position), $expected, "daxim: $desc";
    }
    done_testing;
}

use Inline C => q@
int cur_strlen(char * str, int pos) {
    int rindex = 0;
    int lindex = 0;

    for (rindex = pos; str[rindex] != '\n' && str[rindex]; rindex++);
    for (lindex = pos; lindex && str[lindex] != '\n'; lindex--);
    if (lindex == 0 && str[lindex] != '\n')
        lindex--;

    return(rindex - lindex - 1);
}
@;

sub rlindex {
    my ($str, $pos) = @_;
    my $right = index $str, "\n", $pos;
    my $left = rindex $str, "\n", $pos;
    $right = length $str if $right == -1;

    $right - $left - 1;
}

sub daxim($s, $p, $n = "\n") {
    no warnings 'uninitialized';
    my ($prev, $next);
    while ($s =~ /$n/g) {
        $prev = $next;
        $next = pos $s;
        last if $next > $p;
    }
    return $next - $prev;
}

sub tybalt89 {
    my ($string, $position) = @_;
    pos($string) = $position;
    $string =~ /.*\G.*\n?/;
    my $length_of_line = length $&;
}

sub op {
    my ($str, $pos) = @_;
    die "str is not defined" unless defined $str;
    die "pos is not defined" unless defined $pos;
    my @newlines; # for storing \n positions 
    push @newlines, 0;
    while ($str =~/\n/g) {
        push @newlines, pos($str);
    }
    my $itr = scalar @newlines - 1;
    while ($newlines[$itr] > $pos) {
        $itr--;
    }
    my $length_of_line = $newlines[$itr + 1] - $newlines[$itr];
}