1 files changed, 95 insertions, 0 deletions
diff --git a/app/graphql/resolvers/design_management/version/design_at_version_resolver.rb b/app/graphql/resolvers/design_management/version/design_at_version_resolver.rb
new file mode 100644
index 00000000000..03f7908780c
--- /dev/null
+++ b/app/graphql/resolvers/design_management/version/design_at_version_resolver.rb
@@ -0,0 +1,95 @@
+# frozen_string_literal: true
+
+module Resolvers
+  module DesignManagement
+    module Version
+      # Resolver for a DesignAtVersion object given an implicit version context
+      class DesignAtVersionResolver < BaseResolver
+        include Gitlab::Graphql::Authorize::AuthorizeResource
+
+        type Types::DesignManagement::DesignAtVersionType, null: true
+
+        authorize :read_design
+
+        argument :id, GraphQL::ID_TYPE,
+                 required: false,
+                 as: :design_at_version_id,
+                 description: 'The ID of the DesignAtVersion'
+        argument :design_id, GraphQL::ID_TYPE,
+                 required: false,
+                 description: 'The ID of a specific design'
+        argument :filename, GraphQL::STRING_TYPE,
+                 required: false,
+                 description: 'The filename of a specific design'
+
+        def self.single
+          self
+        end
+
+        def resolve(design_id: nil, filename: nil, design_at_version_id: nil)
+          validate_arguments(design_id, filename, design_at_version_id)
+
+          return unless Ability.allowed?(current_user, :read_design, issue)
+          return specific_design_at_version(design_at_version_id) if design_at_version_id
+
+          find(design_id, filename).map { |d| make(d) }.first
+        end
+
+        private
+
+        def validate_arguments(design_id, filename, design_at_version_id)
+          args = { filename: filename, id: design_at_version_id, design_id: design_id }
+          passed = args.compact.keys
+
+          return if passed.size == 1
+
+          msg = "Exactly one of #{args.keys.join(', ')} expected, got #{passed}"
+
+          raise Gitlab::Graphql::Errors::ArgumentError, msg
+        end
+
+        def specific_design_at_version(id)
+          dav = GitlabSchema.object_from_id(id, expected_type: ::DesignManagement::DesignAtVersion)
+          return unless consistent?(dav)
+
+          dav
+        end
+
+        # Test that the DAV found by ID actually belongs on this version, and
+        # that it is visible at this version.
+        def consistent?(dav)
+          return false unless dav.present?
+
+          dav.design.issue_id == issue.id &&
+            dav.version.id == version.id &&
+            dav.design.visible_in?(version)
+        end
+
+        def find(id, filename)
+          ids = [parse_design_id(id).model_id] if id
+          filenames = [filename] if filename
+
+          ::DesignManagement::DesignsFinder
+            .new(issue, current_user, ids: ids, filenames: filenames, visible_at_version: version)
+            .execute
+        end
+
+        def parse_design_id(id)
+          GitlabSchema.parse_gid(id, expected_type: ::DesignManagement::Design)
+        end
+
+        def issue
+          version.issue
+        end
+
+        def version
+          object
+        end
+
+        def make(design)
+          ::DesignManagement::DesignAtVersion.new(design: design, version: version)
+        end
+      end
+    end
+  end
+end