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@@ -0,0 +1,105 @@
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+//
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+// json_polymorphic_binder.hpp
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+// json
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+//
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+// Created by Sam Jaffe on 11/15/18.
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+// Copyright © 2018 Sam Jaffe. All rights reserved.
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+//
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+
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+#pragma once
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+
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+namespace json { namespace binder {
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+ template <typename PtrBase, typename Derived>
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+ class polymorphic_pointer_binder : public binder_impl<PtrBase> {
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+ public:
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+ polymorphic_pointer_binder(binder<Derived> impl) : m_impl(impl) {}
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+ virtual binder_impl<PtrBase>* clone() const { return new polymorphic_pointer_binder(*this); }
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+
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+ virtual void parse(PtrBase & v, char const*& data, parser::options opts) const {
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+ if (!strncmp(data, "null", 4)) v = nullptr;
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+ else m_impl.parse(reinterpret_cast<Derived &>(*(v = PtrBase(new Derived))), data, opts);
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+ }
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+
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+ void write(PtrBase const & v, std::ostream & os) const {
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+ if (v) m_impl.write(reinterpret_cast<Derived const &>(*v), os);
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+ else os << "null";
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+ }
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+ private:
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+ binder<Derived> m_impl;
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+ };
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+
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+ template <typename Ptr>
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+ class polymorphic_binder : public binder_impl<Ptr> {
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+ private:
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+ using Base = typename std::remove_reference<decltype(*std::declval<Ptr>())>::type;
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+ static_assert(std::is_polymorphic<Base>::value, "Must use a polymorphic type");
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+ public:
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+ polymorphic_binder() = default;
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+ virtual binder_impl<Ptr>* clone() const override { return new polymorphic_binder(*this); }
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+
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+ template <typename Derived>
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+ polymorphic_binder& operator()(std::string const&k, binder_impl<Derived> const&v) {
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+ mapping.emplace(k, polymorphic_pointer_binder<Ptr, Derived>(v));
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+ reverse_lookup.emplace(k, [](Base const * p) { return dynamic_cast<Derived const *>(p); });
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+ return *this;
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+ }
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+
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+ virtual void parse(Ptr & object, char const*& data, parser::options opts) const override {
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+ const char ch = json::helper::get_next_element(data);
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+ if (ch == '{') {
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+ parse_object(object, ++data, opts);
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+ } else {
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+ throw json::malformed_json_exception(std::string("Expected an object type for binding to ") + typeid(Base).name());
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+ }
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+ }
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+ virtual void write(Ptr const & val, std::ostream & data) const override {
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+ data << '{';
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+ using pair_t = typename decltype(reverse_lookup)::value_type;
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+ Base const * p = std::addressof(*val);
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+ auto it = std::find_if(reverse_lookup.begin(), reverse_lookup.end(),
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+ [p](pair_t const & pair) { return pair.second(p); });
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+ if (it == reverse_lookup.end()) {
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+ throw std::domain_error("Unknown JSON binding object");
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+ }
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+ data << "\"@id\":\"" << it->first << "\",";
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+ data << "\"@value\":";
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+ mapping.find(it->first)->second.write(val, data);
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+ data << '}';
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+ }
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+
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+ void parse_object(Ptr & object, char const*& data, parser::options opts) const {
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+ std::string key;
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+ fetch_expected_key("@id", data);
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+ if (json::helper::get_next_element(++data) != '"') {
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+ throw json::malformed_json_exception(std::string("Expected polymorphic id starting with '\"', got '") + *data + "' instead");
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+ }
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+ json::helper::parse_string(key, data);
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+ auto it = mapping.find(key);
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+ if (it == mapping.end()) {
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+ throw json::malformed_json_exception(std::string("Unknown polymorphic type-id: '") + key + "'");
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+ }
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+ fetch_expected_key("@value", ++data);
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+ it->second.parse(object, ++data, opts);
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+ if (!*data) throw json::unterminated_json_exception("Reached end of parse string without finding object end");
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+ else if (*data != '}') throw json::malformed_json_exception(std::string("Unexpected non-terminated object '") + *data + "'");
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+ else ++data;
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+ }
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+
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+ void fetch_expected_key(std::string const & expected, char const*& data) const {
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+ std::string key;
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+ if (json::helper::get_next_element(data) != '"') {
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+ throw json::malformed_json_exception(std::string("Expected object key starting with '\"', got '") + *data + "' instead");
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+ }
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+ json::helper::parse_string(key, data);
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+ if (key != expected) {
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+ throw json::malformed_json_exception(std::string("Expecting '") + expected + "' polymorphic token, got '" + key + "' instead");
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+ }
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+ if (json::helper::get_next_element(data) != ':') {
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+ throw json::malformed_json_exception(std::string("Expected key:value pair delimited by ':', got '") + *data + "' instead");
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+ }
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+ }
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+ private:
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+ std::map<std::string, std::function<bool(Base const*)>> reverse_lookup;
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+ std::map<std::string, binder<Ptr>> mapping;
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+ };
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+} }
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Sam Jaffe