Hoa is a modular, extensible and structured set of PHP libraries. Moreover, Hoa aims at being a bridge between industrial and research worlds.

Hoa\Ruler

This library allows to manipulate a rule engine. Rules can be written by using a dedicated language, very close to SQL. Therefore, they can be written by a user and saved in a database.

Such rules are useful, for example, for commercial solutions that need to manipulate promotion or special offer rules written by a user. To quote Wikipedia:

A business rules engine is a software system that executes one or more business rules in a runtime production environment. The rules might come from legal regulation (“An employee can be fired for any reason or no reason but not for an illegal reason”), company policy (“All customers that spend more than $100 at one time will receive a 10% discount”), or other sources. A business rule system enables these company policies and other operational decisions to be defined, tested, executed and maintained separately from application code.

Installation

With Composer, to include this library into your dependencies, you need to require hoa/ruler:

{
    "require": {
        "hoa/ruler": "~1.0"
    }
}

Please, read the website to get more informations about how to install.

Quick usage

As a quick overview, we propose to see a very simple example that manipulates a simple rule with a simple context. After, we will add a new operator in the rule. And finally, we will see how to save a rule in a database.

Three steps

So first, we create a context with two variables: group and points, and we then assert a rule. A context holds values to concretize a rule. A value can also be the result of a callable. Thus:

$ruler = new Hoa\Ruler\Ruler();

// 1. Write a rule.
$rule  = 'group in ["customer", "guest"] and points > 30';

// 2. Create a context.
$context           = new Hoa\Ruler\Context();
$context['group']  = 'customer';
$context['points'] = function () {
    return 42;
};

// 3. Assert!
var_dump(
    $ruler->assert($rule, $context)
);

/**
 * Will output:
 *     bool(true)
 */

In the next example, we have a User object and a context that is populated dynamically (when the user variable is concretized, two new variables, group and points are created). Moreover, we will create a new operator/function called logged. There is no difference between an operator and a function except that an operator has two operands (so arguments).

Adding operators and functions

For now, we have the following operators/functions by default: and, or, xor, not, = (is as an alias), !=, >, >=, <, <=, in and sum. We can add our own by different way. The simplest and volatile one is given in the following example. Thus:

// The User object.
class User
{
    const DISCONNECTED = 0;
    const CONNECTED    = 1;

    public $group      = 'customer';
    public $points     = 42;
    protected $_status = 1;

    public function getStatus()
    {
        return $this->_status;
    }
}

$ruler = new Hoa\Ruler\Ruler();

// New rule.
$rule  = 'logged(user) and group in ["customer", "guest"] and points > 30';

// New context.
$context         = new Hoa\Ruler\Context();
$context['user'] = function () use ($context) {
    $user              = new User();
    $context['group']  = $user->group;
    $context['points'] = $user->points;

    return $user;
};

// We add the logged() operator.
$ruler->getDefaultAsserter()->setOperator('logged', function (User $user) {
    return $user::CONNECTED === $user->getStatus();
});

// Finally, we assert the rule.
var_dump(
    $ruler->assert($rule, $context)
);

/**
 * Will output:
 *     bool(true)
 */

Also, if a variable in the context is an array, we can access to its values from a rule with the same syntax as PHP. For example, if the a variable is an array, we can write a[0] to access to the value associated to the 0 key. It works as an hashmap (PHP array implementation), so we can have strings & co. as keys. In the same way, if a variable is an object, we can call a method on it. For example, if the a variable is an array where the value associated to the first key is an object with a foo method, we can write: a[0].foo(b) where b is another variable in the context. Also, we can access to the public attributes of an object. Obviously, we can mixe array and object accesses. Please, take a look at the grammar (hoa://Library/Ruler/Grammar.pp) to see all the possible constructions.

Saving a rule

Now, we have two options to save the rule, for example, in a database. Either we save the rule as a string directly, or we will save the serialization of the rule which will avoid further interpretations. In the next example, we see how to serialize and unserialize a rule by using the Hoa\Ruler\Ruler::interpret static method:

$database->save(
    serialize(
        Hoa\Ruler\Ruler::interpret(
            'logged(user) and group in ["customer", "guest"] and points > 30'
        )
    )
);

And for next executions:

$rule = unserialize($database->read());
var_dump(
    $ruler->assert($rule, $context)
);

When a rule is interpreted, its object model is created. We serialize and unserialize this model. To see the PHP code needed to create such a model, we can print the model itself (as an example). Thus:

echo Hoa\Ruler\Ruler::interpret(
    'logged(user) and group in ["customer", "guest"] and points > 30'
);

/**
 * Will output:
 *     $model = new \Hoa\Ruler\Model();
 *     $model->expression =
 *         $model->and(
 *             $model->func(
 *                 'logged',
 *                 $model->variable('user')
 *             ),
 *             $model->and(
 *                 $model->in(
 *                     $model->variable('group'),
 *                     [
 *                         'customer',
 *                         'guest'
 *                     ]
 *                 ),
 *                 $model->{'>'}(
 *                     $model->variable('points'),
 *                     30
 *                 )
 *             )
 *         );
 */

Have fun!

Documentation

Different documentations can be found on the website: http://hoa-project.net/.

License

Hoa is under the New BSD License (BSD-3-Clause). Please, see LICENSE.