Спринт 12. Строим JSON. Задание 1.

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json.h
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#pragma once

#include <iostream>
#include <map>
#include <string>
#include <variant>
#include <vector>

namespace json {

class Node;
using Dict = std::map<std::string, Node>;
using Array = std::vector<Node>;

class ParsingError : public std::runtime_error {
public:
    using runtime_error::runtime_error;
};

class Node final : private std::variant<std::nullptr_t, Array, Dict, bool, int, double, std::string> {
public:
    using variant::variant;
    using Value = variant;

    bool IsInt() const {
        return std::holds_alternative<int>(*this);
    }

    int AsInt() const {
        using namespace std::literals;
        if (!IsInt()) {
            throw std::logic_error("Not an int"s);
        }
        return std::get<int>(*this);
    }

    bool IsPureDouble() const {
        return std::holds_alternative<double>(*this);
    }

    bool IsDouble() const {
        return IsInt() || IsPureDouble();
    }

    double AsDouble() const {
        using namespace std::literals;

        if (!IsDouble()) {
            throw std::logic_error("Not a double"s);
        }
        return IsPureDouble() ? std::get<double>(*this) : AsInt();
    }

    bool IsBool() const {
        return std::holds_alternative<bool>(*this);
    }

    bool AsBool() const {
        using namespace std::literals;

        if (!IsBool()) {
            throw std::logic_error("Not a bool"s);
        }

        return std::get<bool>(*this);
    }

    bool IsNull() const {
        return std::holds_alternative<std::nullptr_t>(*this);
    }

    bool IsArray() const {
        return std::holds_alternative<Array>(*this);
    }

    const Array& AsArray() const {
        using namespace std::literals;

        if (!IsArray()) {
            throw std::logic_error("Not an array"s);
        }

        return std::get<Array>(*this);
    }

    bool IsString() const {
        return std::holds_alternative<std::string>(*this);
    }

    const std::string& AsString() const {
        using namespace std::literals;

        if (!IsString()) {
            throw std::logic_error("Not a string"s);
        }

        return std::get<std::string>(*this);
    }

    bool IsDict() const {
        return std::holds_alternative<Dict>(*this);
    }

    const Dict& AsDict() const {
        using namespace std::literals;

        if (!IsDict()) {
            throw std::logic_error("Not a dict"s);
        }

        return std::get<Dict>(*this);
    }

    bool operator==(const Node& rhs) const {
        return GetValue() == rhs.GetValue();
    }

    const Value& GetValue() const {
        return *this;
    }
};

inline bool operator!=(const Node& lhs, const Node& rhs) {
    return !(lhs == rhs);
}

class Document {
public:
    explicit Document(Node root)
        : root_(std::move(root)) {
    }

    const Node& GetRoot() const {
        return root_;
    }

private:
    Node root_;
};

inline bool operator==(const Document& lhs, const Document& rhs) {
    return lhs.GetRoot() == rhs.GetRoot();
}

inline bool operator!=(const Document& lhs, const Document& rhs) {
    return !(lhs == rhs);
}

Document Load(std::istream& input);

void Print(const Document& doc, std::ostream& output);

}//end namespace json
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json.cpp
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#include "json.h"

#include <iterator>

namespace json {

namespace {
using namespace std::literals;

Node LoadNode(std::istream& input);
Node LoadString(std::istream& input);

std::string LoadLiteral(std::istream& input) {
    std::string s;

    while (std::isalpha(input.peek())) {
        s.push_back(static_cast<char>(input.get()));
    }
    return s;
}

Node LoadArray(std::istream& input) {
    std::vector<Node> result;

    for (char c; input >> c && c != ']';) {

        if (c != ',') {
            input.putback(c);
        }
        result.push_back(LoadNode(input));
    }

    if (!input) {
        throw ParsingError("Array parsing error"s);
    }

    return Node(std::move(result));
}

Node LoadDict(std::istream& input) {
    Dict dict;

    for (char c; input >> c && c != '}';) {

        if (c == '"') {
            std::string key = LoadString(input).AsString();

            if (input >> c && c == ':') {

                if (dict.find(key) != dict.end()) {
                    throw ParsingError("Duplicate key '"s + key + "' have been found");
                }

                dict.emplace(std::move(key), LoadNode(input));

            } else {

                throw ParsingError(": is expected but '"s + c + "' has been found"s);
            }

        } else if (c != ',') {
            throw ParsingError(R"(',' is expected but ')"s + c + "' has been found"s);
        }
    }

    if (!input) {
        throw ParsingError("Dictionary parsing error"s);
    }

    return Node(std::move(dict));
}

Node LoadString(std::istream& input) {
    auto it = std::istreambuf_iterator<char>(input);
    auto end = std::istreambuf_iterator<char>();
    std::string s;

    while (true) {

        if (it == end) {
            throw ParsingError("String parsing error");
        }

        const char ch = *it;
        if (ch == '"') {
            ++it;
            break;

        } else if (ch == '\\') {
            ++it;

            if (it == end) {
                throw ParsingError("String parsing error");
            }

            const char escaped_char = *(it);
            switch (escaped_char) {
                case 'n':
                    s.push_back('\n');
                    break;
                case 't':
                    s.push_back('\t');
                    break;
                case 'r':
                    s.push_back('\r');
                    break;
                case '"':
                    s.push_back('"');
                    break;
                case '\\':
                    s.push_back('\\');
                    break;
                default:
                    throw ParsingError("Unrecognized escape sequence \\"s + escaped_char);

            }

        } else if (ch == '\n' || ch == '\r') {
            throw ParsingError("Unexpected end of line"s);

        } else {
            s.push_back(ch);

        }

        ++it;
    }

    return Node(std::move(s));
}

Node LoadBool(std::istream& input) {
    const auto s = LoadLiteral(input);

    if (s == "true"sv) {
        return Node{true};

    } else if (s == "false"sv) {
        return Node{false};

    } else {
        throw ParsingError("Failed to parse '"s + s + "' as bool"s);
    }
}

Node LoadNull(std::istream& input) {
    if (auto literal = LoadLiteral(input); literal == "null"sv) {
        return Node{nullptr};

    } else {
        throw ParsingError("Failed to parse '"s + literal + "' as null"s);
    }
}

Node LoadNumber(std::istream& input) {
    std::string parsed_num;

    auto read_char = [&parsed_num, &input] {
        parsed_num += static_cast<char>(input.get());

        if (!input) {
            throw ParsingError("Failed to read number from stream"s);
        }
    };

    auto read_digits = [&input, read_char] {
        if (!std::isdigit(input.peek())) {
            throw ParsingError("A digit is expected"s);
        }

        while (std::isdigit(input.peek())) {
            read_char();
        }

    };

    if (input.peek() == '-') {
        read_char();

    }

    if (input.peek() == '0') {
        read_char();

    } else {
        read_digits();

    }

    bool is_int = true;
    if (input.peek() == '.') {
        read_char();
        read_digits();
        is_int = false;

    }

    if (int ch = input.peek(); ch == 'e' || ch == 'E') {
        read_char();

        if (ch = input.peek(); ch == '+' || ch == '-') {
            read_char();
        }

        read_digits();
        is_int = false;
    }

    try {

        if (is_int) {

            try {
                return std::stoi(parsed_num);
            } catch (...) {

            }
        }

        return std::stod(parsed_num);

    } catch (...) {
        throw ParsingError("Failed to convert "s + parsed_num + " to number"s);
    }

}

Node LoadNode(std::istream& input) {
    char c;

    if (!(input >> c)) {
        throw ParsingError("Unexpected EOF"s);
    }

    switch (c) {
        case '[':
            return LoadArray(input);
        case '{':
            return LoadDict(input);
        case '"':
            return LoadString(input);
        case 't':
            [[fallthrough]];
        case 'f':
            input.putback(c);
            return LoadBool(input);
        case 'n':
            input.putback(c);
            return LoadNull(input);
        default:
            input.putback(c);
            return LoadNumber(input);
    }
}

struct PrintContext {
    std::ostream& out;
    int indent_step = 4;
    int indent = 0;

    void PrintIndent() const {
        for (int i = 0; i < indent; ++i) {
            out.put(' ');
        }
    }

    PrintContext Indented() const {
        return {out,
                indent_step,
                indent_step + indent};
    }
};

void PrintNode(const Node& value, const PrintContext& ctx);

template <typename Value>
void PrintValue(const Value& value, const PrintContext& ctx) {
    ctx.out << value;
}

void PrintString(const std::string& value, std::ostream& out) {
    out.put('"');

    for (const char c : value) {
        switch (c) {
            case '\r':
                out << "\\r"sv;
                break;
            case '\n':
                out << "\\n"sv;
                break;
            case '"':
                [[fallthrough]];
            case '\\':
                out.put('\\');
                [[fallthrough]];
            default:
                out.put(c);
                break;
        }
    }

    out.put('"');
}

template <>
void PrintValue<std::string>(const std::string& value, const PrintContext& ctx) {
    PrintString(value, ctx.out);
}

template <>
void PrintValue<std::nullptr_t>(const std::nullptr_t&, const PrintContext& ctx) {
    ctx.out << "null"sv;
}

template <>
void PrintValue<bool>(const bool& value, const PrintContext& ctx) {
    ctx.out << (value ? "true"sv : "false"sv);
}

template <>
void PrintValue<Array>(const Array& nodes, const PrintContext& ctx) {
    std::ostream& out = ctx.out;
    out << "[\n"sv;
    bool first = true;

    auto inner_ctx = ctx.Indented();
    for (const Node& node : nodes) {
        if (first) {
            first = false;

        } else {
            out << ",\n"sv;

        }

        inner_ctx.PrintIndent();
        PrintNode(node, inner_ctx);
    }

    out.put('\n');
    ctx.PrintIndent();
    out.put(']');
}

template <>
void PrintValue<Dict>(const Dict& nodes, const PrintContext& ctx) {
    std::ostream& out = ctx.out;
    out << "{\n"sv;
    bool first = true;

    auto inner_ctx = ctx.Indented();
    for (const auto& [key, node] : nodes) {

        if (first) {
            first = false;
        } else {
            out << ",\n"sv;
        }

        inner_ctx.PrintIndent();
        PrintString(key, ctx.out);
        out << ": "sv;
        PrintNode(node, inner_ctx);
    }

    out.put('\n');
    ctx.PrintIndent();
    out.put('}');
}

void PrintNode(const Node& node, const PrintContext& ctx) {
    std::visit(
        [&ctx](const auto& value) {PrintValue(value, ctx);},node.GetValue());
}

}//end namespace

Document Load(std::istream& input) {
    return Document{LoadNode(input)};
}

void Print(const Document& doc, std::ostream& output) {
    PrintNode(doc.GetRoot(), PrintContext{output});
}

}//end namespace json
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json_builder.h
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#pragma once

#include "json.h"
#include <stack>
#include <string>
#include <memory>

namespace json {

class Builder {
public:

    Node make_node(Node::Value value_);
    void add_node(Node node);

    Builder& Key(std::string key_);
    Builder& Value(Node::Value value_);

    Builder& StartDict();
    Builder& EndDict();

    Builder& StartArray();
    Builder& EndArray();

    Node Build();

private:
    Node root_;
    std::vector<std::unique_ptr<Node>>nodes_stack_;

};

}//end namespace json
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json_builder.cpp
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#include "json_builder.h"

namespace json {

Node Builder::make_node(Node::Value value_) {
    Node node;

    if (std::holds_alternative<bool>(value_)) {
        bool bol = std::get<bool>(value_);
        node = Node(bol);

    } else if (std::holds_alternative<int>(value_)) {
        int intt = std::get<int>(value_);
        node = Node(intt);

    } else if (std::holds_alternative<double>(value_)) {
        double doble = std::get<double>(value_);
        node = Node(doble);

    } else if (std::holds_alternative<std::string>(value_)) {
        std::string str = std::get<std::string>(value_);
        node = Node(std::move(str));

    } else if (std::holds_alternative<Array>(value_)) {
        Array arr = std::get<Array>(value_);
        node = Node(std::move(arr));

    } else if (std::holds_alternative<Dict>(value_)) {
        Dict dictionary = std::get<Dict>(value_);
        node = Node(std::move(dictionary));

    } else {
        node = Node();
    }

    return node;
}

void Builder::add_node(Node node) {

    if (nodes_stack_.empty()) {

        if (!root_.IsNull()) {
            throw std::logic_error("root has been added");
        }

        root_ = node;
        return;

    } else {

        if (!nodes_stack_.back()->IsArray()
            && !nodes_stack_.back()->IsString()) {

            throw std::logic_error("unable to create node");
        }

        if (nodes_stack_.back()->IsArray()) {
            Array arr = nodes_stack_.back()->AsArray();
            arr.emplace_back(node);

            nodes_stack_.pop_back();
            auto arr_ptr = std::make_unique<Node>(arr);
            nodes_stack_.emplace_back(std::move(arr_ptr));

            return;
        }

        if (nodes_stack_.back()->IsString()) {
            std::string str = nodes_stack_.back()->AsString();
            nodes_stack_.pop_back();

            if (nodes_stack_.back()->IsDict()) {
                Dict dictionary = nodes_stack_.back()->AsDict();
                dictionary.emplace(std::move(str), node);

                nodes_stack_.pop_back();
                auto dictionary_ptr = std::make_unique<Node>(dictionary);
                nodes_stack_.emplace_back(std::move(dictionary_ptr));
            }

            return;
        }
    }
}

Builder& Builder::Key(std::string key_) {

    if (nodes_stack_.empty()) {
        throw std::logic_error("unable to create key");
    }

    auto key_ptr = std::make_unique<Node>(key_);

    if (nodes_stack_.back()->IsDict()) {
        nodes_stack_.emplace_back(std::move(key_ptr));
    }

    return *this;
}

Builder& Builder::Value(Node::Value value_){
    add_node(make_node(value_));
    return *this;
}

Builder& Builder::StartDict() {
    nodes_stack_.emplace_back(std::move(std::make_unique<Node>(Dict())));
    return *this;
}

Builder& Builder::EndDict() {

    if (nodes_stack_.empty()) {
        throw std::logic_error("unable to close as without opening");
    }

    Node node = *nodes_stack_.back();

    if (!node.IsDict()) {
        throw std::logic_error("object isn't dictionary");
    }

    nodes_stack_.pop_back();
    add_node(node);

    return *this;
}

Builder& Builder::StartArray() {
    nodes_stack_.emplace_back(std::move(std::make_unique<Node>(Array())));
    return *this;
}

Builder& Builder::EndArray() {

    if (nodes_stack_.empty()) {
        throw std::logic_error("unable to close without opening");
    }

    Node node = *nodes_stack_.back();

    if (!node.IsArray()) {
        throw std::logic_error("object isn't array");
    }

    nodes_stack_.pop_back();
    add_node(node);

    return *this;
}

Node Builder::Build() {

    if (root_.IsNull()) {
        throw std::logic_error("empty json");
    }

    if (!nodes_stack_.empty()) {
        throw std::logic_error("invalid json");
    }

    return root_;
}

}//end namespace json
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main.cpp
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#include "json_builder.h"

#include <iostream>

using namespace std;

int main() {

    json::Print(
        json::Document{
            json::Builder{}
            .StartDict()
                .Key("key1"s).Value(123)
                .Key("key2"s).Value("value2"s)
                .Key("key3"s).StartArray()
                    .Value(456)
                    .StartDict().EndDict()
                    .StartDict()
                        .Key(""s)
                        .Value(nullptr)
                    .EndDict()
                    .Value(""s)
                .EndArray()
            .EndDict()
            .Build()
        },
        cout
    );
    cout << endl;

    json::Print(
        json::Document{
            json::Builder{}
            .Value("just a string"s)
            .Build()
        },
        cout
    );
    cout << endl;

}