Add Graph+Debug API (#106)

Sources/OpenGraphShims/Graph+Debug.swift

@@ -0,0 +1,41 @@
+//
+//  Graph+Debug.swift
+//  OpenGraphShims
+
+// FIXME: Update name in OpenGraph
+public typealias Graph = OGGraph
+public typealias Subgraph = OGSubgraph
+
+#if canImport(Darwin)
+
+import Foundation
+
+@_spi(Debug)
+extension Graph {
+    public var dict: [String: Any]? {
+        let options = ["format": "graph/dict"] as NSDictionary
+        guard let description = Graph.description(nil, options: options) else {
+            return nil
+        }
+        guard let dictionary = description.takeUnretainedValue() as? NSDictionary else {
+            return nil
+        }
+        return dictionary as? [String: Any]
+    }
+
+    // style:
+    // - bold: empty input/output edge
+    // - dashed: indirect or has no value
+    // color:
+    // - red: is_changed
+    public var dot: String? {
+        let options = ["format": "graph/dot"] as NSDictionary
+        guard let description = Graph.description(self, options: options)
+        else {
+            return nil
+        }
+        return description.takeUnretainedValue() as? String
+    }
+}
+
+#endif