README

Rule Engine lets you express business logic in plain PHP arrays and evaluate it with ease. Pick the API that matches the shape of your data:

FlatRuleAPI – send a linear array in Reverse Polish Notation for fast stack-based evaluation.
NestedRuleApi – describe rules as nested associative arrays that read like infix notation.
StringRuleApi – parse and evaluate human readable infix expressions.

Both APIs accept arrays decoded from JSON and can work with callables inside the evaluation context, giving you a flexible way to run rules or trigger simple actions.

How it works

The library implements the Rule Archetype Pattern from the book "Enterprise Patterns and MDA: Building Better Software with Archetype Patterns and UML" by Jim Arlow and Ila Neustadt. Rules are composed of propositions, operators and optional actions. Depending on whether you use FlatRuleAPI or NestedRuleApi, the rule is converted to a uniform internal structure that the engine evaluates against the provided context.

Requirements

PHP 8.4 or higher
Composer

Installation

To install the library, use Composer:

composer require jakubciszak/rule-engine

Usage

Notation

This implementation use Reverse Polish Notation (RPN).
RPN is a mathematical notation in which operators follow their operands. This notation eliminates the need for parentheses that are used in standard infix notation, making the evaluation of expressions simpler and more efficient.

For example, the expression
(2 + 3) * 5
in standard notation would be written as
2 3 + 5 * in RPN.

In this notation, you first add 2 and 3 to get 5, and then multiply by 5 to get 25.

The Rule Engine uses RPN to simplify the process of building conditions, making it more intuitive to construct complex logical expressions.

Creating Rules

You can create rules using the provided methods for different operators:

use JakubCiszak\RuleEngine\Rule;
use JakubCiszak\RuleEngine\Operator;

$rule = (new Rule())
    ->variable('expectedAge', 22)
    ->variable('age')
    ->greaterThan()
    ->evaluate($context);

Evaluating Rules

To evaluate a rule, you need to provide a RuleContext:

use JakubCiszak\RuleEngine\RuleContext;

$context = new RuleContext();
$result = $rule->evaluate($context);

FlatRuleAPI context

Rules can also be defined using JSON in RPN order. The example below presents two rules:

{
  "rules": [
    {
      "name": "rule1",
      "elements": [
        {"type": "variable", "name": "a"},
        {"type": "variable", "name": "b"},
        {"type": "operator", "name": "EQUAL_TO"}
      ]
    },
    {
      "name": "rule2",
      "elements": [
        {"type": "variable", "name": "amount"},
        {"type": "variable", "name": "max"},
        {"type": "operator", "name": "GREATER_THAN"}
      ]
    }
  ]
}

This JSON can be decoded and passed to the FlatRuleAPI context to get the evaluation result in the same structure.

$rulesJson = '{"rules": [...]}';
$contextJson = '{"a":1,"b":2}';
$resultJson = FlatRuleAPI::evaluate(
    json_decode($rulesJson, true, 512, JSON_THROW_ON_ERROR),
    json_decode($contextJson, true, 512, JSON_THROW_ON_ERROR)
);

NestedRuleApi format

NestedRuleApi accepts rules defined using a JSON structure that resembles infix notation. Operators are written as keys and their arguments are provided in nested arrays.

use JakubCiszak\RuleEngine\Api\NestedRuleApi;

$rules = ['and' => [
    ['<' => [['var' => 'temp'], 110]],
    ['==' => [['var' => 'pie.filling'], 'apple']],
]];

$data = ['temp' => 100, 'pie' => ['filling' => 'apple']];

$result = NestedRuleApi::evaluate($rules, $data); // true

You can also pass a set of named rules for evaluation:

$ruleset = [
    'rule1' => ['==' => [['var' => 'a'], 1]],
    'rule2' => ['>' => [['var' => 'b'], 2]],
];

$data = ['a' => 1, 'b' => 3];

NestedRuleApi::evaluate($ruleset, $data); // true

StringRuleApi usage

StringRuleApi accepts conditions written as human readable infix expressions. Variables are denoted by a leading dot and resolved from the supplied data array.

use JakubCiszak\RuleEngine\Api\StringRuleApi;

$expr = '(.actualAge > 18 or .name is Adam) or (.citizenship is PL and .actualAge > 15)';
$data = ['actualAge' => 16, 'name' => 'John', 'citizenship' => 'PL'];

$result = StringRuleApi::evaluate($expr, $data); // true

Complex nested conditions are also supported:

$complex = '((.a > 1 and (.b < 3 or .c is 2)) or ((.d >= 5 and .e <= 10) and not (.f != 7))) and (.g is true or .h is false)';
$data = [
    'a' => 2,
    'b' => 2,
    'c' => 2,
    'd' => 5,
    'e' => 10,
    'f' => 7,
    'g' => true,
    'h' => true,
];

$result = StringRuleApi::evaluate($complex, $data); // true

StringRuleApi can evaluate a set of named expressions as a ruleset, returning a single boolean result:

$rules = [
    'adult' => '.actualAge > 18',
    'plCitizen' => '.citizenship is PL',
];
$data = ['actualAge' => 16, 'citizenship' => 'PL'];

$result = StringRuleApi::evaluate($rules, $data); // false

Boolean variables can be referenced directly without explicit comparison and negated using not:

$flags = '.g and not .h';
$data = ['g' => true, 'h' => false];

StringRuleApi::evaluate($flags, $data); // true

Rule actions

Each rule may include simple actions executed when the rule is evaluated. Actions are expressed as strings:

"var.count + 5"
"var.name = John"
"var.total + var.amount"

Supported operators are + (addition), - (subtraction), . (concatenation) and = (assignment). Values starting with var. reference variables from the evaluation context.

When using NestedRuleApi, specify actions under the actions key alongside the rule expression or within each rule of a ruleset.

FlatRuleAPI example

{
  "rules": [
    {
      "name": "rule1",
      "elements": [
        {"type": "variable", "name": "a"},
        {"type": "variable", "name": "b"},
        {"type": "operator", "name": "EQUAL_TO"}
      ],
      "actions": ["var.count + 1"]
    }
  ]
}

Evaluating the JSON above with { "a": 1, "b": 1, "count": 0 } updates count to 1 when the rule evaluates to true.

NestedRuleApi example

$ruleset = [
    'rule1' => [
        '==' => [['var' => 'a'], 1],
        'actions' => ['var.count + 1'],
    ],
    'rule2' => [
        '==' => [['var' => 'count'], 1],
    ],
];

$data = ['a' => 1, 'count' => 0];

NestedRuleApi::evaluate($ruleset, $data); // true

Development

Running Tests

To run the tests, use PHPUnit:

vendor/bin/phpunit

Contributing

Contributions are welcome! Please open an issue or submit a pull request.

License

This project is licensed under the MIT License.

Authors

Jakub Ciszak - j.ciszak@gmail.com

Additional Information

The project uses the munusphp/munus library for functional programming constructs.
The source code is located in the src/ directory.
Tests are located in the tests/ directory.

jakubciszak / rule-engine

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