Introduce CSSLayoutSetLogger to pass the print result to C# side

Summary:
- CSSLayoutSetLogger
  - Problem: Unity or other logging system can't use printf output
  - Solution: Add CSSLogger to pass CSSNodePrint result to UnityEngine.Debug.Log or other logging system via CSSLogger function for debugging purpose

Reviewed By: emilsjolander

Differential Revision: D4027044

fbshipit-source-id: 90e2e449260888770f71fa7ea790ca9764d91c44

csharp/Facebook.CSSLayout/CSSAssert.cs

@@ -16,14 +16,16 @@ namespace Facebook.CSSLayout
         public delegate void FailFunc(string message);
 
         private static bool _assertInitialized;
+        private static FailFunc _failFunc;
 
         public static void Initialize()
         {
             if (!_assertInitialized)
             {
-                Native.CSSAssertSetFailFunc((message) => {
+                _failFunc = (message) => {
                     throw new InvalidOperationException(message);
-                });
+                };
+                Native.CSSAssertSetFailFunc(_failFunc);
                 _assertInitialized = true;
             }
         }

csharp/Facebook.CSSLayout/CSSLogger.cs

@@ -0,0 +1,38 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+using System;
+
+namespace Facebook.CSSLayout
+{
+    internal static class CSSLogger
+    {
+        public delegate void Func(string message);
+
+        private static bool _initialized;
+        private static Func _managedLogger = null;
+
+        public static Func Logger = null;
+
+        public static void Initialize()
+        {
+            if (!_initialized)
+            {
+                _managedLogger = (message) => {
+                    if (Logger != null)
+                    {
+                        Logger(message);
+                    }
+                };
+                Native.CSSInteropSetLogger(_managedLogger);
+                _initialized = true;
+            }
+        }
+    }
+}

csharp/Facebook.CSSLayout/CSSNode.cs

@@ -11,6 +11,7 @@ using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.Runtime.InteropServices;
+using System.Text;
 
 namespace Facebook.CSSLayout
 {
@@ -110,9 +111,9 @@ namespace Facebook.CSSLayout
             }
 
             CSSAssert.Initialize();
+            CSSLogger.Initialize();
             _cssNode = Native.CSSNodeNew();
             _children = new List<CSSNode>(4);
-            Native.CSSNodeSetPrintFunc(_cssNode, PrintInternal);
         }
 
         public void Free()
@@ -704,9 +705,14 @@ namespace Facebook.CSSLayout
             return new CSSSize { width = measureResult.Width, height = measureResult.Height };
         }
 
-        private void PrintInternal(IntPtr context)
+        public string Print(CSSPrintOptions options = CSSPrintOptions.Layout|CSSPrintOptions.Style|CSSPrintOptions.Children)
         {
-            System.Diagnostics.Debug.WriteLine(ToString());
+            AssertNativeInstance();
+            StringBuilder sb = new StringBuilder();
+            CSSLogger.Logger = (message) => {sb.Append(message);};
+            Native.CSSNodePrint(_cssNode, options);
+            CSSLogger.Logger = null;
+            return sb.ToString();
         }
 
         public IEnumerator<CSSNode> GetEnumerator()

csharp/Facebook.CSSLayout/CSSPrintFunc.cs

@@ -1,15 +0,0 @@
-/**
- * Copyright (c) 2014-present, Facebook, Inc.
- * All rights reserved.
- *
- * This source code is licensed under the BSD-style license found in the
- * LICENSE file in the root directory of this source tree. An additional grant
- * of patent rights can be found in the PATENTS file in the same directory.
- */
-
-using System;
-
-namespace Facebook.CSSLayout
-{
-    public delegate void CSSPrintFunc(IntPtr context);
-}

csharp/Facebook.CSSLayout/Native.cs

@@ -20,6 +20,9 @@ namespace Facebook.CSSLayout
         private const string DllName = "CSSLayout";
 #endif
 
+        [DllImport(DllName)]
+        public static extern void CSSInteropSetLogger(CSSLogger.Func func);
+
         [DllImport(DllName)]
         public static extern void CSSAssertSetFailFunc(CSSAssert.FailFunc func);
 
@@ -81,12 +84,6 @@ namespace Facebook.CSSLayout
         [DllImport(DllName)]
         public static extern CSSMeasureFunc CSSNodeGetMeasureFunc(IntPtr node);
 
-        [DllImport(DllName)]
-        public static extern void CSSNodeSetPrintFunc(IntPtr node, CSSPrintFunc printFunc);
-
-        [DllImport(DllName)]
-        public static extern CSSPrintFunc CSSNodeGePrintFunc(IntPtr node);
-
         [DllImport(DllName)]
         public static extern void CSSNodeSetIsTextnode(IntPtr node, [MarshalAs(UnmanagedType.I1)] bool isTextNode);