/**
 * Constants
 */

const STRING = 'string';
const NUMBER = 'number';
const FUNCTION = 'function';
const OBJECT = 'object';

export class Metadata {

    /**
     * Constructor and Instance Methods
     */

    constructor(data) {
        // Define the main "_data" private property as an immutable property.
        // IMPORTANT: This property can only be set during instance construction.
        Object.defineProperty(this, '_data', {
            configurable: false,
            enumerable: false,
            writable: false,
            value: data
        });
    }

    getData() {
        return this._data;
    }

    getDataProperty(propertyName) {
        let propertyValue;
        const _data = this._data;
        if (_data instanceof Object || typeof _data === OBJECT && _data !== null) {
            propertyValue = _data[propertyName];
        }
        return propertyValue;
    }

    /**
     * Static Methods
     */

    static isValidUID(uid) {
        return typeof uid === STRING && uid.length > 0;
    }

    static isValidIndex(index) {
        return typeof index === NUMBER && index >= 0 && (index | 0) === index;
    }

    static isValidCallback(callback) {
        return typeof callback === FUNCTION;
    }

}