--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lib/IMPL/Debug.pm	Sun Aug 20 00:20:41 2017 +0300
@@ -0,0 +1,66 @@
+package IMPL::Debug;
+use strict;
+use warnings;
+
+our $ENABLE = 0;
+our %ENABLE;
+
+my %subscriptions;
+my @subscriptions;
+
+sub stub { }
+
+sub import {
+    my ( $self, @args ) = @_;
+
+    my $caller = caller;
+    no strict 'refs';
+
+    my $enabled = exists $ENABLE{$caller} ? $ENABLE{$caller} : $ENABLE;
+
+    *{"${caller}::dbg_log"} = $enabled
+      ? sub {
+        $self->log( $caller, @_ );
+      }
+      : \&stub;
+
+    *{"${caller}::dbg_error"} = $enabled
+      ? sub {
+        $self->log( $caller, @_ );
+      }
+      : \&stub;
+
+    *{"${caller}::dbg_warn"} = $enabled
+      ? sub {
+        $self->log( $caller, @_ );
+      }
+      : \&stub;
+}
+
+sub log {
+    my $self    = shift;
+    my $channel = shift;
+    $_->(@_) foreach @{ $subscriptions{$channel} || [] };
+    $_->(@_) foreach @subscriptions;
+}
+
+sub subscribe {
+    my ( $self, $channel, $callback ) = @_;
+
+    if ( @_ == 2 ) {
+        $callback = $channel;
+        $channel  = undef;
+    }
+
+    die IMPL::InvalidArgumentException->new('callback')
+      unless ref $callback eq 'CODE';
+
+    if ($channel) {
+        push @{ $subscriptions{$channel} }, $callback;
+    }
+    else {
+        push @subscriptions, $callback;
+    }
+}
+
+1;