use strict;
use warnings;

use Tk;

my $mw = MainWindow->new ;

my $canvas ;
my $text ;
my $text_var    = 'Canvas example' ;
my $text_len    = length( $text_var ) ;
my $cur_pos     = $text_len ;
my $width       = 200 ;
my $height      = 100 ;

    $mw->title( 'Canvas Example' ) ;

    $canvas = $mw->Canvas(
                            -background     => 'white',
                            -width          => $width,
                            -height         => $height,
                            -scrollregion   => [ 0, 0, 500, 500 ],
                        ) ;

    $canvas->CanvasFocus() ;

    $text = $canvas->createText(
                    100,
                    90, 
                    -text           => $text_var,
                    -tags           => 'title',
                ) ;

    $canvas->focus( $text ) ;
    $canvas->icursor( $text, $cur_pos ) ;

    $canvas->bind( 'title', '<KeyRelease>' => \&updater ) ;

    my $exit = $mw->Button(
                        -text       => 'Exit',
                        -command    => [$mw => 'destroy'],
                    ) ;

    $canvas->pack;
    $exit->pack;

#########
MainLoop;
#########

    #function to manipulate text in the field or to move cursor around
sub updater {

    my ( $k ) = @_ ;
    my $e     = $k->XEvent ; #get event object
    my $k_val = $e->N ;  #get decimal equivalent
    my $k_str = $e->K ;  #get ascii equivalent

    #print "updater $k_val\n" ;

        #should move the cursor to left in text
    if( $k_str eq 'Left' ) {

        $cur_pos = $cur_pos > 0 ? $cur_pos - 1 : 0 ;

    }
    elsif( $k_str eq 'Right' ) {

        $cur_pos = $cur_pos < length( $text_var ) ? $cur_pos + 1 : length( $text_var ) ;

    }
    else{

            #append new char to the text
        $text_var .= $k_str ;
        $text_len = length( $text_var ) ;
        $cur_pos++ ;

            #show updated text
        $canvas->itemconfigure(
                        -text           => $text_var,
                        -tags           => 'title',
                    ) ;

    }

    $canvas->icursor( $text, $cur_pos ) ;

}