/**
 * Class HashTable
 *
 * @param {object} obj
 */
let HashTable = function( obj ) {
    let length = 0;
    this._items = ( function( obj ) {
        let items = {};
        for ( let p in obj ) {
                items[p] = obj[p];
                length++;
        }
        return items;
    }( obj ) );

    /**
     * Associates the specified value to the specified key
     *
     * @param {string} key The key to which associate the value
     * @param {string} value The value to associate to the key
     *
     * @return {(undefined|object)} Undefined is object didn't exists before this call
     */
    this.set = function( key, value ) {
        let previous = undefined;

        if ( this.has( key ) ) {
            previous = this._items[key];
        } else {
            length++;
        }

        this._items[key] = value;

        return previous;
    };

    /**
     * Returns the value associated to the specified key
     *
     * @param {string} key The key from which retrieve the value
     *
     * @return {(undefined|string)} Undefined or associated value
     */
    this.get = function( key ) {
        return this._items.hasOwnProperty( key ) ? this._items[key] : undefined;
    };

    /**
     * Returns whether the hashtable contains the specified key
     *
     * @param {string} key The key to check
     *
     * @return {boolean}
     */
    this.has = function( key ) {
        return this._items.hasOwnProperty( key );
    };

    /**
     * Removes the specified key with its value
     *
     * @param {string} key The key to remove
     *
     * @return {(undefined|string)} Undefined if key doesn't exist and
     * string (previous value) - value of deleted item
     */
    this.remove = function( key ) {
        if ( this.has( key ) ) {
            let previous = this._items[key];
            length--;
            delete this._items[key];
            return previous;
        } else {
            return undefined;
        }
    };

    /**
     * Returns an array with all the registered keys
     *
     * @return {array}
     */
    this.getKeys = function() {
        let keys = [];

        for ( let i in this._items ) {
            if ( this.has( i ) ) {
                keys.push( i );
            }
        }

        return keys;
    };

    /**
     * Returns an array with all the registered values
     *
     * @return {array}
     */
    this.getValues = function() {
        let values = [];

        for ( let i in this._items ) {
            if ( this.has( i ) ) {
                values.push( this._items[i] );
            }
        }

        return values;
    };

    /**
     * Iterates all entries in the specified iterator callback
     * @param {function} callback A method with 2 parameters: key, value
     */
    this.each = function( callback ) {
        for ( let i in this._items ) {
            if ( this.has( i ) ) {
                callback( i, this._items[i] );
            }
        }
    };

    /**
     * Deletes all the key-value pairs on the hashmap
     */
    this.clear = function() {
        this._items = {};
        length = 0;
    };

    /**
     * Gets the count of the entries in the hashtable
     */
    Object.defineProperty( this, 'length', {
        get: function() {
            return length;
        },
    });

    /**
     * Gets an array of all keys in the hashtable
     */
    Object.defineProperty(this, 'keys', {
        get: function() {
            return this.getKeys();
        },
    });

    /**
     * Gets an array of all values in the hashtable
     */
    Object.defineProperty(this, 'values', {
        get: function() {
            return this.getValues();
        },
    });
};

let hashtable = new HashTable({'one': 1, 'two': 2, 'three': 3, 'cuatro': 4});

console.log( 'Original length: ' + hashtable.length ); // Original length: 4
console.log( 'Value of key "one": ' + hashtable.get( 'one' ) ); // Value of key "one": 1
console.log( 'Has key "foo"? ' + hashtable.has( 'foo' )); // Has key "foo"? false
console.log( 'Previous value of key "foo": ' + hashtable.set( 'foo', 'bar' ) ); // Previous value of key "foo": undefined
console.log( 'Length after set: ' + hashtable.length ); // Length after set: 5
console.log( 'Value of key "foo": ' + hashtable.get( 'foo' ) ); // Value of key "foo": bar
console.log( 'Value of key "cuatro": ' + hashtable.get( 'cuatro' )); // Value of key "cuatro": 4
console.log( 'Get keys by using property: ' + hashtable.keys ); // Get keys by using property: one,two,three,cuatro,foo
hashtable.clear();
console.log( 'Length after clear: ' + hashtable.length ); // Length after clear: 0