Add UUIDResolver

The UUIDResolver adds a route at `/by-uuid/:uuid` that enables
applications to request information about a given UUID.

The UUID must be a Random UUID (version 4, see RFC 4122).

If an invalid UUID is given, the controller will return 422 Unprocessable Entity.

If a valid UUID is given:

- 404 indicates that the UUID is not assigned to anything known to the system.
- 302 indicates that the UUID was assigned to a record, and the User-Agent
  will be redirected to that record's Location as indicated in the response header.
- 200 indicates that the UUID was assigned to more than one record (which is unlikely)
  and will list those records.

1 files changed, 55 insertions, 0 deletions

diff --git a/app/lib/uuid_resolver.rb b/app/lib/uuid_resolver.rb
new file mode 100644
index 0000000..acca494
--- /dev/null
+++ b/app/lib/uuid_resolver.rb
@@ -0,0 +1,55 @@
+class UUIDResolver
+  # Note the static '4' in the third group: that's the UUID version.
+  UUID_V4_REGEX = %r[\A[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[0-9a-f]{4}-[0-9a-f]{12}\z]
+
+  attr_reader :records, :count, :record, :uuid
+
+  def initialize(uuid)
+    @uuid   = validate!(uuid)
+    @records, @count = resolve!
+
+  end
+
+  def record
+    case @count
+    when 0
+      nil
+    else
+      records.first
+    end
+  end
+
+  private
+
+  # List models that have UUIDs
+  def public_record_types
+    [
+      ::Agent,
+      ::Map,
+      ::Resource,
+      ::Taxonomy
+    ].freeze
+  end
+
+  # Find records with this UUID
+  def resolve!
+    records = []
+
+    public_record_types.each do |model|
+      records << model.find_by(uuid: @uuid)
+    end
+
+    [records.compact, records.compact.size]
+  end
+
+  # Ensure the passed UUID is correct
+  def validate!(uuid)
+    validate_uuid_v4(uuid) || raise(ArgumentError.new("You must pass a valid random UUID (https://tools.ietf.org/html/rfc4122)"))
+  end
+
+  # Validate a UUID version 4 (random)
+  def validate_uuid_v4(uuid)
+    uuid = uuid.to_s.downcase
+    uuid.match?(UUID_V4_REGEX) ? uuid : false
+  end
+end