stewed frog

use LWP;
use JSON;
#use URI::Escape;
use Modern::Perl;
use Data::Dumper;
my $UA = LWP::UserAgent->new;
$UA->env_proxy;
my $LONGEST = { path => [] };
my %ECHONEST_UNKNOWN;
my %PATHS_EXPLORED;

main: {
    explore(@ARGV);
    say "The longest path seen was $LONGEST->{path}[0]{name} to $LONGEST->{path}[-1]{name} with length " . @{ $LONGEST->{path}};
}

sub explore {
    my ( $start, $end ) = @_;
    my @artists = get_similar($end,30);
    say "Got " . ( scalar @artists ) . " artists like $end from last.fm";
    my %frogs;
    for $a (@artists) {
        $ECHONEST_UNKNOWN{$a} and next;
        my $frog= get_frog( $start, $a ) or next;
        $frogs{"$start->$a"} = $frog;
    }
    if( keys %frogs == 0 ) {
        warn "$start leads nowhere (no paths lead to the top 15 similar artists)\n";
    }
    else {
        for (reverse sort { scalar @{ $a->{path} } <=> scalar @{ $b->{path} }} values %frogs ) {
            if( not $LONGEST or @{ $_->{path} } >= ( @{ $LONGEST->{path} } - 1) ) {
                # interestingly long enough.  Investigate the reverse
                say "Path from $_->{path}[0]{name} to $_->{path}[-1]{name} has length " . @{ $_->{path} };
                @{ $_->{path} } >  @{ $LONGEST->{path} } and $LONGEST = $_;
                explore( $_->{path}[-1]{name}, $_->{path}[0]{name} );
            }
        }
    }
}

sub get_similar {
    my ($name,$how_many) = @_;
    my @like;
    my @artists;
    my $page = 0;
    while( @artists < $how_many ) {
        $page++;
        push @artists,
          ( $UA->get("http://www.last.fm/music/$name/+similar?page=$page")->content =~
              m{class="remove-bottom-margin">([^<]+)}g );
    }
    s/&amp;/&/g for @artists; # not seeing any other html entities
    return @artists[0..($how_many-1)];
}

sub get_frog {
    my ( $start, $end ) = @_;
    # $referer = "http://static.echonest.com/frog/?src=$start&dest=$end"
    $end =  URI::Escape::uri_escape($end);
    $start = URI::Escape::uri_escape($start);
    $PATHS_EXPLORED{"$start->$end"}++ > 2 and return;
    $PATHS_EXPLORED{"$end->$start"}++ > 2 and return;
    my $url = "http://labs.echonest.com/ArtistGraphServer/find_path?start=$start&end=$end";
    my $content = $UA->get($url)->content;
    my $frog = eval { from_json( $content ) };
    $@ and die "$!\n$url\n$content\n";
    if( $frog->{status} =~ /cant find/ ) {
        warn qq{echonest doesn't know about "$a" yet.\n};
        $ECHONEST_UNKNOWN{$a}++;
        return
    }
    return $frog;
}