1 files changed, 103 insertions, 0 deletions
diff --git a/include/jsoncons_ext/mergepatch/mergepatch.hpp b/include/jsoncons_ext/mergepatch/mergepatch.hpp
new file mode 100644
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+++ b/include/jsoncons_ext/mergepatch/mergepatch.hpp
@@ -0,0 +1,103 @@
+// Copyright 2017 Daniel Parker
+// Distributed under the Boost license, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+// See https://github.com/danielaparker/jsoncons for latest version
+
+#ifndef JSONCONS_JSONMERGEPATCH_JSONMERGEPATCH_HPP
+#define JSONCONS_JSONMERGEPATCH_JSONMERGEPATCH_HPP
+
+#include <string>
+#include <vector> 
+#include <memory>
+#include <algorithm> // std::min
+#include <utility> // std::move
+#include <jsoncons/json.hpp>
+
+namespace jsoncons { 
+namespace mergepatch {
+
+    template <class Json>
+    Json from_diff(const Json& source, const Json& target)
+    {
+        if (!source.is_object() || !target.is_object())
+        {
+            return target;
+        }
+        Json result(json_object_arg);
+
+        for (const auto& member : source.object_range())
+        {
+            auto it = target.find(member.key());
+            if (it != target.object_range().end())
+            {
+                if (member.value() != it->value())
+                {
+                    result.try_emplace(member.key(), from_diff(member.value(), it->value()));
+                }
+            }
+            else
+            {
+                result.try_emplace(member.key(), Json::null());
+            }
+        }
+
+        for (const auto& member : target.object_range())
+        {
+            auto it = source.find(member.key());
+            if (it == source.object_range().end())
+            {
+                result.try_emplace(member.key(), member.value());
+            }
+        }
+
+        return result;
+    }
+
+    namespace detail {
+        template <class Json>
+        Json apply_merge_patch_(Json& target, const Json& patch)
+        {
+            if (patch.is_object())
+            {
+                if (!target.is_object())
+                {
+                    target = Json(json_object_arg);
+                }
+                for (auto& member : patch.object_range())
+                {
+                    auto it = target.find(member.key());
+                    if (it != target.object_range().end())
+                    {
+                        Json item = it->value();
+                        target.erase(it);
+                        if (!member.value().is_null())
+                        {
+                            target.try_emplace(member.key(), apply_merge_patch_(item, member.value()));
+                        }
+                    }
+                    else if (!member.value().is_null())
+                    {
+                        Json item(json_object_arg);
+                        target.try_emplace(member.key(), apply_merge_patch_(item, member.value()));
+                    }
+                }
+                return target;
+            }
+            else
+            {
+                return patch;
+            }
+        }
+    } // namespace detail
+
+    template <class Json>
+    void apply_merge_patch(Json& target, const Json& patch)
+    {
+        target = detail::apply_merge_patch_(target, patch);
+    }
+
+} // namespace mergepatch
+} // namespace jsoncons
+
+#endif