use strict;
use warnings;

use Test::More;
use POSIX;

my @TESTS
    = (
       [(0, 0)  => undef],
       [(0, 1)  => undef],
       [(1, 0)  => undef],
       [(1, 1)  => 'AB'],
       [(2, 1)  => 'ABA'],
       [(3, 1)  => { map {$_=>1} qw(ABAA AABA)}],
       [(4, 1)  => { map {$_=>1} qw(ABAAA AABAA AAABA)}],
       [(1, 2)  => { map {$_=>1} qw(ABB BBA BAB)}],
       [(2, 2)  => 'ABBA'],
       [(7, 6)  => 'ABABABABABABA'],
       [(3, 3)  => { map {$_=>1} qw(ABBABA ABABBA)}],
       [(4, 14) => { map {$_=>1} qw(
                                    ABBBBABBBBBABBBBBA
                                    ABBBBBABBBBABBBBBA
                                    ABBBBBABBBBBABBBBA
                                    )}],
       );
plan tests => scalar @TESTS;

for my $test (@TESTS) {

    my $skewer;
    my ($n_a, $n_b, $expected) = @$test;

    eval {
        $skewer = interleave( $n_a, $n_b );
    };
    if ($@) {
        ok(
           !defined( $expected ),
           "($n_a, $n_b) => undef"
           );
        next;
    }
    if (ref $expected) {
        ok(
           exists $expected->{ $skewer },
           "($n_a, $n_b) => $skewer"
           );
    }
    else {
        ok(
           $expected eq $skewer,
           "($n_a, $n_b) => $skewer"
           );
    }
}
exit( 0 );

##-------------------------------------------------------------------+
sub interleave {
    my ($n_a, $n_b) = @_;

    if ($n_a < 1 or $n_b < 1) {
        die "Bad args to interleave: ($n_a, $n_b)";
    }
    if ($n_a == 1) {
        return 'A' . 'B' x $n_b;
    }
    my $min_b = floor( $n_b / ($n_a - 1) );
    my $leftover_b = $n_b - $min_b * ($n_a - 1);
    ##warn "($n_a, $n_b) => min_b:$min_b, lefto:$leftover_b";

    my $skewer = 'A';
    for (1..$leftover_b) {
        $skewer .= 'B' x ($min_b + 1);
        $skewer .= 'A';
    }
    for ($leftover_b + 1 .. $n_a - 1) {
        $skewer .= 'B' x $min_b;
        $skewer .= 'A';
    }
    ##warn "returning ($n_a, $n_b) => $skewer";

    return $skewer;
}