map_parser.hpp

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#pragma once
 
/// @file userver/formats/json/parser/map_parser.hpp
/// @brief @copybrief formats::json::parser::MapParser
/// @ingroup userver_universal
 
#include <userver/formats/json/parser/typed_parser.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace formats::json::parser {
 
/// @brief SAX parser that fills maps from JSON objects.
template <typename Map, typename ValueParser>
class MapParser final : public TypedParser<Map>, public Subscriber<typename Map::mapped_type> {
public:
    using Value = typename Map::mapped_type;
 
    explicit MapParser(ValueParser& value_parser)
        : value_parser_(value_parser)
    {}
 
    void Reset() override { this->state_ = State::kStart; }
 
    void StartObject() override {
        switch (state_) {
            case State::kStart:
                this->state_ = State::kInside;
                break;
 
            case State::kInside:
                this->Throw("{");
        }
    }
 
    void Key(std::string_view key) override {
        if (state_ != State::kInside) {
            this->Throw("object");
        }
 
        key_ = key;
        this->value_parser_.Reset();
        this->value_parser_.Subscribe(*this);
        this->parser_state_->PushParser(this->value_parser_.GetParser());
    }
 
    void EndObject() override {
        if (state_ == State::kInside) {
            this->SetResult(std::move(result_));
            return;
        }
        // impossible?
        this->Throw("}");
    }
 
    std::string Expected() const override {
        switch (state_) {
            case State::kInside:
                return "string";
 
            case State::kStart:
                return "object";
        }
 
        UINVARIANT(false, "Unexpected parser state");
    }
 
private:
    void OnSend(Value&& value) override { this->result_.emplace(std::move(key_), std::move(value)); }
 
    std::string GetPathItem() const override { return key_; }
 
    enum class State {
        kStart,
        kInside,
    };
    State state_{State::kStart};
    std::string key_;
    Map result_;
    ValueParser& value_parser_;
};
 
}  // namespace formats::json::parser
 
USERVER_NAMESPACE_END