sots-engine/tests/game_sim/mini_json.h

// Tiny dependency-free JSON reader for the real-save smoke test. Not for production use:
// no error recovery, accepts a superset of JSON, numbers parsed as double.
#pragma once

#include <cctype>
#include <cstdlib>
#include <map>
#include <memory>
#include <string>
#include <vector>

namespace minijson {

struct Value {
    enum Kind { Null, Bool, Number, String, Array, Object } kind = Null;
    bool b = false;
    double num = 0;
    std::string str;
    std::vector<Value> arr;
    std::map<std::string, Value> obj;

    const Value* get(const std::string& key) const {
        if (kind != Object) return nullptr;
        auto it = obj.find(key);
        return it == obj.end() ? nullptr : &it->second;
    }
    double number(double dflt = 0) const { return kind == Number ? num : (kind == Bool ? (b ? 1 : 0) : dflt); }
    bool boolean(bool dflt = false) const { return kind == Bool ? b : (kind == Number ? num != 0 : dflt); }
    const std::string& string() const { return str; }
    bool isArray() const { return kind == Array; }
    bool isObject() const { return kind == Object; }
};

class Parser {
  public:
    explicit Parser(const std::string& s) : s_(s) {}

    bool parse(Value& out) {
        skip();
        if (!value(out)) return false;
        skip();
        return pos_ == s_.size();
    }

  private:
    const std::string& s_;
    std::size_t pos_ = 0;

    void skip() { while (pos_ < s_.size() && std::isspace(static_cast<unsigned char>(s_[pos_]))) ++pos_; }
    bool eat(char c) { if (pos_ < s_.size() && s_[pos_] == c) { ++pos_; return true; } return false; }

    bool value(Value& v) {
        if (pos_ >= s_.size()) return false;
        const char c = s_[pos_];
        if (c == '{') return object(v);
        if (c == '[') return array(v);
        if (c == '"') { v.kind = Value::String; return stringLit(v.str); }
        if (s_.compare(pos_, 4, "true") == 0) { pos_ += 4; v.kind = Value::Bool; v.b = true; return true; }
        if (s_.compare(pos_, 5, "false") == 0) { pos_ += 5; v.kind = Value::Bool; v.b = false; return true; }
        if (s_.compare(pos_, 4, "null") == 0) { pos_ += 4; v.kind = Value::Null; return true; }
        if (s_.compare(pos_, 3, "NaN") == 0) { pos_ += 3; v.kind = Value::Number; v.num = 0; return true; }
        if (s_.compare(pos_, 8, "Infinity") == 0) { pos_ += 8; v.kind = Value::Number; v.num = 0; return true; }
        if (s_.compare(pos_, 9, "-Infinity") == 0) { pos_ += 9; v.kind = Value::Number; v.num = 0; return true; }
        return number(v);
    }

    bool number(Value& v) {
        const char* begin = s_.c_str() + pos_;
        char* end = nullptr;
        const double d = std::strtod(begin, &end);
        if (end == begin) return false;
        pos_ += static_cast<std::size_t>(end - begin);
        v.kind = Value::Number;
        v.num = d;
        return true;
    }

    bool stringLit(std::string& out) {
        if (!eat('"')) return false;
        out.clear();
        while (pos_ < s_.size()) {
            const char c = s_[pos_++];
            if (c == '"') return true;
            if (c != '\\') { out.push_back(c); continue; }
            if (pos_ >= s_.size()) return false;
            const char e = s_[pos_++];
            switch (e) {
                case 'n': out.push_back('\n'); break;
                case 't': out.push_back('\t'); break;
                case 'r': out.push_back('\r'); break;
                case 'b': out.push_back('\b'); break;
                case 'f': out.push_back('\f'); break;
                case 'u': {
                    if (pos_ + 4 > s_.size()) return false;
                    const unsigned long cp = std::strtoul(s_.substr(pos_, 4).c_str(), nullptr, 16);
                    pos_ += 4;
                    if (cp < 0x80) out.push_back(static_cast<char>(cp));
                    else if (cp < 0x800) { out.push_back(static_cast<char>(0xC0 | (cp >> 6))); out.push_back(static_cast<char>(0x80 | (cp & 0x3F))); }
                    else { out.push_back(static_cast<char>(0xE0 | (cp >> 12))); out.push_back(static_cast<char>(0x80 | ((cp >> 6) & 0x3F))); out.push_back(static_cast<char>(0x80 | (cp & 0x3F))); }
                    break;
                }
                default: out.push_back(e); break;
            }
        }
        return false;
    }

    bool array(Value& v) {
        if (!eat('[')) return false;
        v.kind = Value::Array;
        skip();
        if (eat(']')) return true;
        for (;;) {
            Value item;
            skip();
            if (!value(item)) return false;
            v.arr.push_back(std::move(item));
            skip();
            if (eat(',')) continue;
            return eat(']');
        }
    }

    bool object(Value& v) {
        if (!eat('{')) return false;
        v.kind = Value::Object;
        skip();
        if (eat('}')) return true;
        for (;;) {
            skip();
            std::string key;
            if (!stringLit(key)) return false;
            skip();
            if (!eat(':')) return false;
            skip();
            Value item;
            if (!value(item)) return false;
            v.obj[key] = std::move(item);
            skip();
            if (eat(',')) continue;
            return eat('}');
        }
    }
};

}  // namespace minijson