text: // Copyright (c) 2015 Sandstorm Development Group, Inc. and contributors
  // Licensed under the MIT License:
  //
  // Permission is hereby granted, free of charge, to any person obtaining a copy
  // of this software and associated documentation files (the "Software"), to deal
  // in the Software without restriction, including without limitation the rights
  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  // copies of the Software, and to permit persons to whom the Software is
  // furnished to do so, subject to the following conditions:
  //
  // The above copyright notice and this permission notice shall be included in
  // all copies or substantial portions of the Software.
  //
  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  // THE SOFTWARE.
  
  #pragma once
  
  #include <capnp/schema.h>
  #include <capnp/dynamic.h>
  #include <capnp/compat/json.capnp.h>
  
  namespace capnp {
  
  class JsonCodec {
    // Flexible class for encoding Cap'n Proto types as JSON, and decoding JSON back to Cap'n Proto.
    //
    // Typical usage:
    //
    //     JsonCodec json;
    //
    //     // encode
    //     kj::String encoded = json.encode(someStructReader);
    //
    //     // decode
    //     json.decode(encoded, someStructBuilder);
    //
    // Advanced users can do fancy things like override the way certain types or fields are
    // represented in JSON by registering handlers. See the unit test for an example.
    //
    // Notes:
    // - When encoding, all primitive fields are always encoded, even if default-valued. Pointer
    //   fields are only encoded if they are non-null.
    // - 64-bit integers are encoded as strings, since JSON "numbers" are double-precision floating
    //   points which cannot store a 64-bit integer without losing data.
    // - NaNs and infinite floating point numbers are not allowed by the JSON spec, and so are encoded
    //   as null. This matches the behavior of `JSON.stringify` in at least Firefox and Chrome.
    // - Data is encoded as an array of numbers in the range [0,255]. You probably want to register
    //   a handler that does something better, like maybe base64 encoding, but there are a zillion
    //   different ways people do this.
    // - Encoding/decoding capabilities and AnyPointers requires registering a Handler, since there's
    //   no obvious default behavior.
    // - When decoding, unrecognized field names are ignored. Note: This means that JSON is NOT a
    //   good format for receiving input from a human. Consider `capnp eval` or the SchemaParser
    //   library for human input.
  
  public:
    JsonCodec();
    ~JsonCodec() noexcept(false);
  
    // ---------------------------------------------------------------------------
    // standard API
  
    void setPrettyPrint(bool enabled);
    // Enable to insert newlines, indentation, and other extra spacing into the output. The default
    // is to use minimal whitespace.
  
    void setMaxNestingDepth(size_t maxNestingDepth);
    // Set maximum nesting depth when decoding JSON to prevent highly nested input from overflowing
    // the call stack. The default is 64.
  
    void setHasMode(HasMode mode);
    // Normally, primitive field values are always included even if they are equal to the default
    // value (HasMode::NON_NULL -- only null pointers are omitted). You can use
    // setHasMode(HasMode::NON_DEFAULT) to specify that default-valued primitive fields should be
    // omitted as well.
  
    template <typename T>
    kj::String encode(T&& value) const;
    // Encode any Cap'n Proto value to JSON, including primitives and
    // Dynamic{Enum,Struct,List,Capability}, but not DynamicValue (see below).
  
    kj::String encode(DynamicValue::Reader value, Type type) const;
    // Encode a DynamicValue to JSON. `type` is needed because `DynamicValue` itself does
    // not distinguish between e.g. int32 and int64, which in JSON are handled differently. Most
    // of the time, though, you can use the single-argument templated version of `encode()` instead.
  
    void decode(kj::ArrayPtr<const char> input, DynamicStruct::Builder output) const;
    // Decode JSON text directly into a struct builder. This only works for structs since lists
    // need to be allocated with the correct size in advance.
    //
    // (Remember that any Cap'n Proto struct reader type can be implicitly cast to
    // DynamicStruct::Reader.)
  
    template <typename T>
    Orphan<T> decode(kj::ArrayPtr<const char> input, Orphanage orphanage) const;
    // Decode JSON text to any Cap'n Proto object (pointer value), allocated using the given
    // orphanage. T must be specified explicitly and cannot be dynamic, e.g.:
    //
    //     Orphan<MyType> orphan = json.decode<MyType>(text, orphanage);
  
    template <typename T>
    ReaderFor<T> decode(kj::ArrayPtr<const char> input) const;
    // Decode JSON text into a primitive or capability value. T must be specified explicitly and
    // cannot be dynamic, e.g.:
    //
    //     uint32_t n = json.decode<uint32_t>(text);
  
    Orphan<DynamicValue> decode(kj::ArrayPtr<const char> input, Type type, Orphanage orphanage) const;
    Orphan<DynamicList> decode(
        kj::ArrayPtr<const char> input, ListSchema type, Orphanage orphanage) const;
    Orphan<DynamicStruct> decode(
        kj::ArrayPtr<const char> input, StructSchema type, Orphanage orphanage) const;
    DynamicCapability::Client decode(kj::ArrayPtr<const char> input, InterfaceSchema type) const;
    DynamicEnum decode(kj::ArrayPtr<const char> input, EnumSchema type) const;
    // Decode to a dynamic value, specifying the type schema.
  
    // ---------------------------------------------------------------------------
    // layered API
    //
    // You can separate text <-> JsonValue from JsonValue <-> T. These are particularly useful
    // for calling from Handler implementations.
  
    kj::String encodeRaw(JsonValue::Reader value) const;
    void decodeRaw(kj::ArrayPtr<const char> input, JsonValue::Builder output) const;
    // Translate JsonValue <-> text.
  
    template <typename T>
    void encode(T&& value, JsonValue::Builder output) const;
    void encode(DynamicValue::Reader input, Type type, JsonValue::Builder output) const;
    void decode(JsonValue::Reader input, DynamicStruct::Builder output) const;
    template <typename T>
    Orphan<T> decode(JsonValue::Reader input, Orphanage orphanage) const;
    template <typename T>
    ReaderFor<T> decode(JsonValue::Reader input) const;
  
    Orphan<DynamicValue> decode(JsonValue::Reader input, Type type, Orphanage orphanage) const;
    Orphan<DynamicList> decode(JsonValue::Reader input, ListSchema type, Orphanage orphanage) const;
    Orphan<DynamicStruct> decode(
        JsonValue::Reader input, StructSchema type, Orphanage orphanage) const;
    DynamicCapability::Client decode(JsonValue::Reader input, InterfaceSchema type) const;
    DynamicEnum decode(JsonValue::Reader input, EnumSchema type) const;
  
    // ---------------------------------------------------------------------------
    // specializing particular types
  
    template <typename T, Style s = style<T>()>
    class Handler;
    // Implement this interface to specify a special encoding for a particular type or field.
    //
    // The templates are a bit ugly, but subclasses of this type essentially implement two methods,
    // one to encode values of this type and one to decode values of this type. `encode()` is simple:
    //
    //   void encode(const JsonCodec& codec, ReaderFor<T> input, JsonValue::Builder output) const;
    //
    // `decode()` is a bit trickier. When T is a struct (including DynamicStruct), it is:
    //
    //   void decode(const JsonCodec& codec, JsonValue::Reader input, BuilderFor<T> output) const;
    //
    // However, when T is a primitive, decode() is:
    //
    //   T decode(const JsonCodec& codec, JsonValue::Reader input) const;
    //
    // Or when T is any non-struct object (list, blob), decode() is:
    //
    //   Orphan<T> decode(const JsonCodec& codec, JsonValue::Reader input, Orphanage orphanage) const;
    //
    // Or when T is an interface:
    //
    //   T::Client decode(const JsonCodec& codec, JsonValue::Reader input) const;
    //
    // Additionally, when T is a struct you can *optionally* also implement the orphan-returning form
    // of decode(), but it will only be called when the struct would be allocated as an individual
    // object, not as part of a list. This allows you to return "nullptr" in these cases to say that
    // the pointer value should be null. This does not apply to list elements because struct list
    // elements cannot ever be null (since Cap'n Proto encodes struct lists as a flat list rather
    // than list-of-pointers).
  
    template <typename T>
    void addTypeHandler(Handler<T>& handler);
    void addTypeHandler(Type type, Handler<DynamicValue>& handler);
    void addTypeHandler(EnumSchema type, Handler<DynamicEnum>& handler);
    void addTypeHandler(StructSchema type, Handler<DynamicStruct>& handler);
    void addTypeHandler(ListSchema type, Handler<DynamicList>& handler);
    void addTypeHandler(InterfaceSchema type, Handler<DynamicCapability>& handler);
    // Arrange that whenever the type T appears in the message, your handler will be used to
    // encode/decode it.
    //
    // Note that if you register a handler for a capability type, it will also apply to subtypes.
    // Thus Handler<Capability> handles all capabilities.
  
    template <typename T>
    void addFieldHandler(StructSchema::Field field, Handler<T>& handler);
    // Matches only the specific field. T can be a dynamic type. T must match the field's type.
  
    // ---------------------------------------------------------------------------
    // Hack to support string literal parameters
  
    template <size_t size, typename... Params>
    auto decode(const char (&input)[size], Params&&... params) const
        -> decltype(decode(kj::arrayPtr(input, size), kj::fwd<Params>(params)...)) {
      return decode(kj::arrayPtr(input, size - 1), kj::fwd<Params>(params)...);
    }
    template <size_t size, typename... Params>
    auto decodeRaw(const char (&input)[size], Params&&... params) const
        -> decltype(decodeRaw(kj::arrayPtr(input, size), kj::fwd<Params>(params)...)) {
      return decodeRaw(kj::arrayPtr(input, size - 1), kj::fwd<Params>(params)...);
    }
  
  private:
    class HandlerBase;
    struct Impl;
  
    kj::Own<Impl> impl;
  
    void encodeField(StructSchema::Field field, DynamicValue::Reader input,
                     JsonValue::Builder output) const;
    void decodeArray(List<JsonValue>::Reader input, DynamicList::Builder output) const;
    void decodeObject(List<JsonValue::Field>::Reader input, DynamicStruct::Builder output) const;
    void addTypeHandlerImpl(Type type, HandlerBase& handler);
    void addFieldHandlerImpl(StructSchema::Field field, Type type, HandlerBase& handler);
  };
  
  // =======================================================================================
  // inline implementation details
  
  template <bool isDynamic>
  struct EncodeImpl;
  
  template <typename T>
  kj::String JsonCodec::encode(T&& value) const {
    Type type = Type::from(value);
    typedef FromAny<kj::Decay<T>> Base;
    return encode(DynamicValue::Reader(ReaderFor<Base>(kj::fwd<T>(value))), type);
  }
  
  template <typename T>
  inline Orphan<T> JsonCodec::decode(kj::ArrayPtr<const char> input, Orphanage orphanage) const {
    return decode(input, Type::from<T>(), orphanage).template releaseAs<T>();
  }
  
  template <typename T>
  inline ReaderFor<T> JsonCodec::decode(kj::ArrayPtr<const char> input) const {
    static_assert(style<T>() == Style::PRIMITIVE || style<T>() == Style::CAPABILITY,
                  "must specify an orphanage to decode an object type");
    return decode(input, Type::from<T>(), Orphanage()).getReader().template as<T>();
  }
  
  inline Orphan<DynamicList> JsonCodec::decode(
      kj::ArrayPtr<const char> input, ListSchema type, Orphanage orphanage) const {
    return decode(input, Type(type), orphanage).releaseAs<DynamicList>();
  }
  inline Orphan<DynamicStruct> JsonCodec::decode(
      kj::ArrayPtr<const char> input, StructSchema type, Orphanage orphanage) const {
    return decode(input, Type(type), orphanage).releaseAs<DynamicStruct>();
  }
  inline DynamicCapability::Client JsonCodec::decode(
      kj::ArrayPtr<const char> input, InterfaceSchema type) const {
    return decode(input, Type(type), Orphanage()).getReader().as<DynamicCapability>();
  }
  inline DynamicEnum JsonCodec::decode(kj::ArrayPtr<const char> input, EnumSchema type) const {
    return decode(input, Type(type), Orphanage()).getReader().as<DynamicEnum>();
  }
  
  // -----------------------------------------------------------------------------
  
  template <typename T>
  void JsonCodec::encode(T&& value, JsonValue::Builder output) const {
    typedef FromAny<kj::Decay<T>> Base;
    encode(DynamicValue::Reader(ReaderFor<Base>(kj::fwd<T>(value))), Type::from<Base>(), output);
  }
  
  template <typename T>
  inline Orphan<T> JsonCodec::decode(JsonValue::Reader input, Orphanage orphanage) const {
    return decode(input, Type::from<T>(), orphanage).template releaseAs<T>();
  }
  
  template <typename T>
  inline ReaderFor<T> JsonCodec::decode(JsonValue::Reader input) const {
    static_assert(style<T>() == Style::PRIMITIVE || style<T>() == Style::CAPABILITY,
                  "must specify an orphanage to decode an object type");
    return decode(input, Type::from<T>(), Orphanage()).getReader().template as<T>();
  }
  
  inline Orphan<DynamicList> JsonCodec::decode(
      JsonValue::Reader input, ListSchema type, Orphanage orphanage) const {
    return decode(input, Type(type), orphanage).releaseAs<DynamicList>();
  }
  inline Orphan<DynamicStruct> JsonCodec::decode(
      JsonValue::Reader input, StructSchema type, Orphanage orphanage) const {
    return decode(input, Type(type), orphanage).releaseAs<DynamicStruct>();
  }
  inline DynamicCapability::Client JsonCodec::decode(
      JsonValue::Reader input, InterfaceSchema type) const {
    return decode(input, Type(type), Orphanage()).getReader().as<DynamicCapability>();
  }
  inline DynamicEnum JsonCodec::decode(JsonValue::Reader input, EnumSchema type) const {
    return decode(input, Type(type), Orphanage()).getReader().as<DynamicEnum>();
  }
  
  // -----------------------------------------------------------------------------
  
  class JsonCodec::HandlerBase {
    // Internal helper; ignore.
  public:
    virtual void encodeBase(const JsonCodec& codec, DynamicValue::Reader input,
                            JsonValue::Builder output) const = 0;
    virtual Orphan<DynamicValue> decodeBase(const JsonCodec& codec, JsonValue::Reader input,
                                            Type type, Orphanage orphanage) const;
    virtual void decodeStructBase(const JsonCodec& codec, JsonValue::Reader input,
                                  DynamicStruct::Builder output) const;
  };
  
  template <typename T>
  class JsonCodec::Handler<T, Style::POINTER>: private JsonCodec::HandlerBase {
  public:
    virtual void encode(const JsonCodec& codec, ReaderFor<T> input,
                        JsonValue::Builder output) const = 0;
    virtual Orphan<T> decode(const JsonCodec& codec, JsonValue::Reader input,
                             Orphanage orphanage) const = 0;
  
  private:
    void encodeBase(const JsonCodec& codec, DynamicValue::Reader input,
                    JsonValue::Builder output) const override final {
      encode(codec, input.as<T>(), output);
    }
    Orphan<DynamicValue> decodeBase(const JsonCodec& codec, JsonValue::Reader input,
                                    Type type, Orphanage orphanage) const override final {
      return decode(codec, input, orphanage);
    }
    friend class JsonCodec;
  };
  
  template <typename T>
  class JsonCodec::Handler<T, Style::STRUCT>: private JsonCodec::HandlerBase {
  public:
    virtual void encode(const JsonCodec& codec, ReaderFor<T> input,
                        JsonValue::Builder output) const = 0;
    virtual void decode(const JsonCodec& codec, JsonValue::Reader input,
                        BuilderFor<T> output) const = 0;
    virtual Orphan<T> decode(const JsonCodec& codec, JsonValue::Reader input,
                             Orphanage orphanage) const {
      // If subclass does not override, fall back to regular version.
      auto result = orphanage.newOrphan<T>();
      decode(codec, input, result.get());
      return result;
    }
  
  private:
    void encodeBase(const JsonCodec& codec, DynamicValue::Reader input,
                    JsonValue::Builder output) const override final {
      encode(codec, input.as<T>(), output);
    }
    Orphan<DynamicValue> decodeBase(const JsonCodec& codec, JsonValue::Reader input,
                                    Type type, Orphanage orphanage) const override final {
      return decode(codec, input, orphanage);
    }
    void decodeStructBase(const JsonCodec& codec, JsonValue::Reader input,
                          DynamicStruct::Builder output) const override final {
      decode(codec, input, output.as<T>());
    }
    friend class JsonCodec;
  };
  
  template <>
  class JsonCodec::Handler<DynamicStruct>: private JsonCodec::HandlerBase {
    // Almost identical to Style::STRUCT except that we pass the struct type to decode().
  
  public:
    virtual void encode(const JsonCodec& codec, DynamicStruct::Reader input,
                        JsonValue::Builder output) const = 0;
    virtual void decode(const JsonCodec& codec, JsonValue::Reader input,
                        DynamicStruct::Builder output) const = 0;
    virtual Orphan<DynamicStruct> decode(const JsonCodec& codec, JsonValue::Reader input,
                                         StructSchema type, Orphanage orphanage) const {
      // If subclass does not override, fall back to regular version.
      auto result = orphanage.newOrphan(type);
      decode(codec, input, result.get());
      return result;
    }
  
  private:
    void encodeBase(const JsonCodec& codec, DynamicValue::Reader input,
                    JsonValue::Builder output) const override final {
      encode(codec, input.as<DynamicStruct>(), output);
    }
    Orphan<DynamicValue> decodeBase(const JsonCodec& codec, JsonValue::Reader input,
                                    Type type, Orphanage orphanage) const override final {
      return decode(codec, input, type.asStruct(), orphanage);
    }
    void decodeStructBase(const JsonCodec& codec, JsonValue::Reader input,
                          DynamicStruct::Builder output) const override final {
      decode(codec, input, output.as<DynamicStruct>());
    }
    friend class JsonCodec;
  };
  
  template <typename T>
  class JsonCodec::Handler<T, Style::PRIMITIVE>: private JsonCodec::HandlerBase {
  public:
    virtual void encode(const JsonCodec& codec, T input, JsonValue::Builder output) const = 0;
    virtual T decode(const JsonCodec& codec, JsonValue::Reader input) const = 0;
  
  private:
    void encodeBase(const JsonCodec& codec, DynamicValue::Reader input,
                    JsonValue::Builder output) const override final {
      encode(codec, input.as<T>(), output);
    }
    Orphan<DynamicValue> decodeBase(const JsonCodec& codec, JsonValue::Reader input,
                                    Type type, Orphanage orphanage) const override final {
      return decode(codec, input);
    }
    friend class JsonCodec;
  };
  
  template <typename T>
  class JsonCodec::Handler<T, Style::CAPABILITY>: private JsonCodec::HandlerBase {
  public:
    virtual void encode(const JsonCodec& codec, typename T::Client input,
                        JsonValue::Builder output) const = 0;
    virtual typename T::Client decode(const JsonCodec& codec, JsonValue::Reader input) const = 0;
  
  private:
    void encodeBase(const JsonCodec& codec, DynamicValue::Reader input,
                    JsonValue::Builder output) const override final {
      encode(codec, input.as<T>(), output);
    }
    Orphan<DynamicValue> decodeBase(const JsonCodec& codec, JsonValue::Reader input,
                                    Type type, Orphanage orphanage) const override final {
      return orphanage.newOrphanCopy(decode(codec, input));
    }
    friend class JsonCodec;
  };
  
  template <typename T>
  inline void JsonCodec::addTypeHandler(Handler<T>& handler) {
    addTypeHandlerImpl(Type::from<T>(), handler);
  }
  inline void JsonCodec::addTypeHandler(Type type, Handler<DynamicValue>& handler) {
    addTypeHandlerImpl(type, handler);
  }
  inline void JsonCodec::addTypeHandler(EnumSchema type, Handler<DynamicEnum>& handler) {
    addTypeHandlerImpl(type, handler);
  }
  inline void JsonCodec::addTypeHandler(StructSchema type, Handler<DynamicStruct>& handler) {
    addTypeHandlerImpl(type, handler);
  }
  inline void JsonCodec::addTypeHandler(ListSchema type, Handler<DynamicList>& handler) {
    addTypeHandlerImpl(type, handler);
  }
  inline void JsonCodec::addTypeHandler(InterfaceSchema type, Handler<DynamicCapability>& handler) {
    addTypeHandlerImpl(type, handler);
  }
  
  template <typename T>
  inline void JsonCodec::addFieldHandler(StructSchema::Field field, Handler<T>& handler) {
    addFieldHandlerImpl(field, Type::from<T>(), handler);
  }
  
  template <> void JsonCodec::addTypeHandler(Handler<DynamicValue>& handler)
      KJ_UNAVAILABLE("JSON handlers for type sets (e.g. all structs, all lists) not implemented; "
                     "try specifying a specific type schema as the first parameter");
  template <> void JsonCodec::addTypeHandler(Handler<DynamicEnum>& handler)
      KJ_UNAVAILABLE("JSON handlers for type sets (e.g. all structs, all lists) not implemented; "
                     "try specifying a specific type schema as the first parameter");
  template <> void JsonCodec::addTypeHandler(Handler<DynamicStruct>& handler)
      KJ_UNAVAILABLE("JSON handlers for type sets (e.g. all structs, all lists) not implemented; "
                     "try specifying a specific type schema as the first parameter");
  template <> void JsonCodec::addTypeHandler(Handler<DynamicList>& handler)
      KJ_UNAVAILABLE("JSON handlers for type sets (e.g. all structs, all lists) not implemented; "
                     "try specifying a specific type schema as the first parameter");
  template <> void JsonCodec::addTypeHandler(Handler<DynamicCapability>& handler)
      KJ_UNAVAILABLE("JSON handlers for type sets (e.g. all structs, all lists) not implemented; "
                     "try specifying a specific type schema as the first parameter");
  // TODO(someday): Implement support for registering handlers that cover thinsg like "all structs"
  //   or "all lists". Currently you can only target a specific struct or list type.
  
  } // namespace capnp
  