// Another way is to use const serializables = Symbol();
const serializables = new WeakMap<object, string[]>();

type Context =
    | ClassAccessorDecoratorContext
    | ClassGetterDecoratorContext
    | ClassFieldDecoratorContext
    ;

function serialize(_target: any, context: Context): void {
    if (context.static || context.private) {
        throw new Error("Can only serialize public instance members.")
    }
    if (typeof context.name !== "string") {
        throw new Error("Can only serialize string properties.");
    }

    // if Symbol used: const propNames = (context.metadata[serializables] as string[] | undefined) ??= [];

    let propNames = serializables.get(context.metadata || {});
    if (propNames === undefined) {
        serializables.set(context.metadata || {}, propNames = []);
    }
    propNames.push(context.name);
}
function jsonify(instance: object): string {
    
    // @ts-ignore 
    const metadata = instance.constructor[Symbol.metadata];

    // if Symbol used: const propNames = metadata?.[serializables] as string[] | undefined;
    const propNames = metadata && serializables.get(metadata);
    if (!propNames) {
        throw new Error("No members marked with @serialize.");
    }
    const pairStrings = propNames.map((key: string) => {
        const strKey = JSON.stringify(key);
        const strValue = JSON.stringify((instance as any)[key]);
        return `${strKey}: ${strValue}`;
    });
    return `{ ${pairStrings.join(", ")} }`;
}


class Person {
    firstName: string;
    lastName: string;

    @serialize
    age: number

    @serialize
    get fullName() {
        return `${this.firstName} ${this.lastName}`;
    }
    toJSON() {
        return jsonify(this)
    }
    constructor(firstName: string, lastName: string, age: number) {
        this.firstName = firstName
        this.lastName = lastName
        this.age = age
    }
}

const person = new Person('Alice', 'Sofia', 4)

console.log(person.toJSON())