api/v0: implement similarity search for media

Use a very naive approach: define similarity as the number of shared
tags between two media pieces. It can be implemented in SQL and produces
decent results.

lib/Pooru/API/V0.pm

@@ -69,6 +69,8 @@ sub startup ($self)
 
 	$r->get("/media")->to("media#list")->name("list_media");
 	$r->get("/media/<media_id:num>")->to("media#show")->name("show_media");
+	$r->get("/media/similar/<media_id:num>")->to("media#similar")
+	    ->name("search_similar_media");
 
 	$r->get("/tag")->to("tags#show")->name("show_tag");
 	$r->get("/tags")->to("tags#list")->name("list_tags");

lib/Pooru/API/V0/Controller/Media.pm

@@ -119,4 +119,54 @@ sub show ($self)
 	});
 }
 
+# Executes
+# SELECT *, COUNT(tag_id) AS similarity_score FROM tagged_media_view
+# WHERE tag_id IN (
+#   SELECT tag_id FROM tagged_media_view WHERE media_id = m
+# ) AND media_id != m
+# GROUP BY media_id ORDER BY similarity_score
+sub similar ($self)
+{
+	my $media_id = $self->stash("media_id");
+	my $media = $self->schema->resultset("Media")
+	    ->single({id => $media_id});
+
+	return $self->render(
+		json => {error => "Media not found"},
+		status => 404,
+	) if !defined($media);
+
+	my %attrs = (
+		select => ["tag_id"],
+		rows => 100,
+	);
+	my $tags = $self->schema->resultset("MediaTag")
+	    ->search({media_id => $media_id}, \%attrs)->as_query;
+
+	my %search = (
+		media_id => {"!=", $media_id},
+		tag_id => {"-in", $tags},
+	);
+	%attrs = (
+		"+select" => [{count => "tag_id", -as => "similarity_score"}],
+		"+as" => ["similarity_score"],
+		group_by => "media_id",
+		order_by => {-desc => "similarity_score"},
+		rows => 6,
+	);
+	my @media = map +{
+		id => $_->media_id,
+		storage_id => $_->media_storage_id,
+		filename => $_->media_filename,
+		content_type => $_->media_content_type,
+		upload_datetime => $_->media_upload_datetime,
+		similarity_score => $_->get_column("similarity_score"),
+	}, $self->schema->resultset("TaggedMediaView")
+	    ->search(\%search, \%attrs)->all;
+
+	return $self->render(json => {
+		media => [@media],
+	});
+}
+
 1;