class size {
    _value;

    constructor(value) {
        this.value = value;
    }

    set value(content) {
        if (typeof(content) !== "number") {
            throw "Size must be numeric.";
        }

        this._value = content;
    }

    get value() {
        return this._value;
    }

    get _unit() {
        throw "This getter is abstract.";
    }

    get as_css() {
        return this._value.toString() + this._unit;
    }
}

class percent extends size {
    get _unit() {
        return "%";
    }
}

class pixel extends size {
    get _unit() {
        return "px";
    }
}

class emunit extends size {
    get _unit() {
        return "em";
    }
}

class width_percent extends size {
    get _unit() {
        return "wv";
    }
}

class height_percent extends size {
    get _unit() {
        return "hv";
    }
}

class auto extends size {
    get _unit() {
        return "";
    }

    constructor() {
        super(0);
    }

    set _value(content) {
        throw "Auto have no value.";
    }

    get _value() {
        throw "Auto have no value.";
    }

    get as_css() {
        return "auto";
    }
}

export { size, percent, pixel, emunit, width_percent, height_percent, auto };