const _isArray = Array.isArray;
    const _keys = Object.keys;

    /**
     * Tests for a plain object
     *
     * @param aObject   the object to test
     */
    function _isPlainObject(aObject: any): boolean {
        return aObject && !aObject.prototype && (typeof aObject === 'object');
    }

    const KEY_WEIGHTS: {[key: string]: number} = {
        'name': 1,
        'description': 2,
        'id': 3,
        'classification': 4
    };

    function _compareNumber(aLeft: number, aRight: number): number {
        return (aLeft < aRight) ? -1 : (aLeft > aRight) ? +1 : 0;
    }

    function _getKey(aName: string): number {
        return KEY_WEIGHTS[aName] || Number.MAX_SAFE_INTEGER;
    }

    function _compareName(aLeft: string, aRight: string): number {
        // first by key
        let c = _compareNumber(_getKey(aLeft), _getKey(aRight));
        if (c === 0) {
            c = aLeft.localeCompare(aRight);
        }
        // ok
        return c;
    }

    function _canonicalize(aData: any): any {
        // handle
        if (_isArray(aData)) {
            const copy: any[] = [];
            aData.forEach(v => copy.push(_canonicalize(v)));
            return copy;
        }
        if (_isPlainObject(aData)) {
            // sort the keys
            const copy: any = {};
            _keys(aData).sort(_compareName).forEach(k => copy[k] = _canonicalize(aData[k]));
            return copy;
        }
        // nothing to do
        return aData;
    }

    export {
        _canonicalize as canonicalizeJSON
    };