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kennyth01 merged 1 commit into from
Mar 1, 2026
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feat: Add support for fact-to-fact comparison #2

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126 changes: 126 additions & 0 deletions FACT_TO_FACT_FEATURE.md
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# Fact-to-Fact Comparison Feature

## Overview
Added support for fact-to-fact comparison in the PHP Rules Engine, allowing rules to compare two dynamic facts at runtime instead of comparing a fact to a static value.

## Changes Made

### 1. Updated `src/Rule.php`

#### Modified `evaluateCondition()` method (lines 198-222)
Added logic to resolve fact references in the `value` field:

```php
// Resolve value if it's another fact (fact-to-fact comparison)
if (is_array($value) && isset($value['fact'])) {
$value = $facts->get($value['fact'], $value['path'] ?? null);
}
```

This checks if the value is structured as a fact reference (an array with a `fact` key), and if so, retrieves that fact's value dynamically before performing the comparison.

#### Modified `interpretCondition()` method (lines 265-303)
Added logic to display fact-to-fact comparisons in human-readable format:

```php
// Handle fact-to-fact comparison display
if (is_array($value) && isset($value['fact'])) {
$valueFact = $value['fact'];
$valuePath = $value['path'] ?? null;
$valueDisplay = $valueFact;
if ($valuePath) {
$valuePathParts = explode('.', ltrim($valuePath, '$.'));
$valueDisplay = end($valuePathParts);
}
return "$factDisplay $operatorText $valueDisplay";
}
```

### 2. Updated `README.md`
- Added "Fact-to-Fact Comparison" to the Features list
- Added comprehensive documentation with examples:
- Speed Limit Check example
- Age Verification with nested paths example

### 3. Added `tests/EngineTest.php::testFactToFactComparison()`
Created comprehensive test coverage with three test cases:
- Basic fact-to-fact comparison (distance vs limit)
- Fact-to-fact comparison with failure scenario
- Nested fact comparison with paths (user.age vs requirements.minimumAge)

### 4. Created `examples/fact-to-fact-comparison.php`
Added a complete working example file demonstrating:
- Speed limit checking
- Age verification with nested paths
- Credit limit checking with multiple fact comparisons

## Usage Examples

### Basic Example
```php
$ruleConfig = [
"name" => "test.factToFact",
"conditions" => [
"all" => [
[
"fact" => "distance",
"operator" => "lessThanInclusive",
"value" => ["fact" => "limit"] // Reference another fact
]
]
],
"event" => ["type" => "passed", "params" => []],
"failureEvent" => ["type" => "failed", "params" => []]
];

$engine->addRule(new Rule($ruleConfig));
$engine->setTargetRule('test.factToFact');

$engine->addFact('distance', 40);
$engine->addFact('limit', 50);

$result = $engine->evaluate();
// Result: passed (40 <= 50)
```

### Nested Facts Example
```php
$ruleConfig = [
"conditions" => [
"all" => [
[
"fact" => "user",
"path" => "$.age",
"operator" => "greaterThanInclusive",
"value" => [
"fact" => "requirements",
"path" => "$.minimumAge"
]
]
]
]
];

$engine->addFact('user', ['age' => 25]);
$engine->addFact('requirements', ['minimumAge' => 18]);
// Compares: user.age (25) >= requirements.minimumAge (18)
```

## Benefits
1. **Dynamic Thresholds**: Comparison values can change based on context without modifying rule definitions
2. **Runtime Flexibility**: Different scenarios can use different limits/thresholds
3. **Real-world Use Cases**:
- Compare `currentSpeed` to `speedLimit` (where limit changes by zone)
- Compare `userAge` to `minimumAge` (where minimum might vary by country)
- Compare `accountBalance` to `creditLimit` (personalized per user)

## Testing
All tests pass successfully:
```bash
./vendor/bin/phpunit tests/EngineTest.php

OK (8 tests, 32 assertions)
```

## Backward Compatibility
This feature is fully backward compatible. Existing rules that use static values continue to work as before. The fact-to-fact comparison is only activated when the `value` is an array with a `fact` key.
59 changes: 59 additions & 0 deletions README.md
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Expand Up @@ -8,6 +8,7 @@ This library, inspired by the `json-rules-engine`, ([link](https://github.com/Ca

## Features
- **JSON-Configurable Rules**: Easily define rules and conditions in JSON format.
- **Fact-to-Fact Comparison**: Compare two dynamic facts at runtime instead of comparing to static values.
- **Rule Dependencies**: Reference other rules as conditions to create complex evaluations.
- **Logical Operators**: Supports `all` (AND), `any` (OR), and `not` operators, allowing for nested conditions.
- **Custom Events and Failure Messages**: Attach custom messages for success or failure, making evaluations easy to interpret.
Expand Down Expand Up @@ -114,6 +115,64 @@ print_r($result);
## Advanced Examples
For other examples, refer to the `tests` directory

### Fact-to-Fact Comparison
The engine supports comparing two facts dynamically at runtime. This allows for flexible rule evaluation where comparison values can change based on context.

**Example: Speed Limit Check**
```php
$engine = new Engine();

$ruleConfig = [
"name" => "speed.check",
"conditions" => [
"all" => [
[
"fact" => "currentSpeed",
"operator" => "lessThanInclusive",
"value" => ["fact" => "speedLimit"] // Compare to another fact
]
]
],
"event" => ["type" => "withinLimit", "params" => ["message" => "Speed is within limit"]],
"failureEvent" => ["type" => "speeding", "params" => ["message" => "Exceeding speed limit"]]
];

$engine->addRule(new Rule($ruleConfig));
$engine->setTargetRule('speed.check');

// Add both facts dynamically
$engine->addFact('currentSpeed', 55);
$engine->addFact('speedLimit', 60);

$result = $engine->evaluate();
// Result: withinLimit - Speed is within limit
```

**Example: Nested Fact Comparison**
```php
$ruleConfig = [
"name" => "age.verification",
"conditions" => [
"all" => [
[
"fact" => "user",
"path" => "$.age",
"operator" => "greaterThanInclusive",
"value" => [
"fact" => "requirements",
"path" => "$.minimumAge"
]
]
]
],
"event" => ["type" => "ageVerified", "params" => []],
"failureEvent" => ["type" => "ageFailed", "params" => []]
];

$engine->addFact('user', ['age' => 25]);
$engine->addFact('requirements', ['minimumAge' => 18]);
```

## Run the test
```bash
./vendor/bin/phpunit tests
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169 changes: 169 additions & 0 deletions examples/fact-to-fact-comparison.php
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<?php

require_once __DIR__ . '/../vendor/autoload.php';

use Kennyth01\PhpRulesEngine\Engine;
use Kennyth01\PhpRulesEngine\Rule;

echo "=== Fact-to-Fact Comparison Examples ===\n\n";

// Example 1: Speed Limit Check
echo "Example 1: Speed Limit Check\n";
echo "-----------------------------\n";

$engine1 = new Engine();

$speedRule = [
"name" => "speed.check",
"conditions" => [
"all" => [
[
"fact" => "currentSpeed",
"operator" => "lessThanInclusive",
"value" => ["fact" => "speedLimit"]
]
]
],
"event" => [
"type" => "withinLimit",
"params" => ["message" => "Speed is within limit"]
],
"failureEvent" => [
"type" => "speeding",
"params" => ["message" => "Exceeding speed limit"]
]
];

$engine1->addRule(new Rule($speedRule));
$engine1->setTargetRule('speed.check');
$engine1->showInterpretation(true);

// Scenario A: Within speed limit
$engine1->addFact('currentSpeed', 55);
$engine1->addFact('speedLimit', 60);
$result1 = $engine1->evaluate();

echo "Scenario A: currentSpeed = 55, speedLimit = 60\n";
echo "Result: " . $result1[0]['type'] . "\n";
echo "Message: " . $result1[0]['params']['message'] . "\n";
echo "Interpretation: " . $result1[0]['interpretation'] . "\n\n";

// Scenario B: Exceeding speed limit
$engine1b = new Engine();
$engine1b->addRule(new Rule($speedRule));
$engine1b->setTargetRule('speed.check');
$engine1b->showInterpretation(true);
$engine1b->addFact('currentSpeed', 75);
$engine1b->addFact('speedLimit', 60);
$result1b = $engine1b->evaluate();

echo "Scenario B: currentSpeed = 75, speedLimit = 60\n";
echo "Result: " . $result1b[0]['type'] . "\n";
echo "Message: " . $result1b[0]['params']['message'] . "\n\n";

// Example 2: Age Verification with Nested Paths
echo "\nExample 2: Age Verification (Nested Paths)\n";
echo "-------------------------------------------\n";

$engine2 = new Engine();

$ageRule = [
"name" => "age.verification",
"conditions" => [
"all" => [
[
"fact" => "user",
"path" => "$.age",
"operator" => "greaterThanInclusive",
"value" => [
"fact" => "requirements",
"path" => "$.minimumAge"
]
]
]
],
"event" => [
"type" => "ageVerified",
"params" => ["message" => "User meets age requirement"]
],
"failureEvent" => [
"type" => "ageFailed",
"params" => ["message" => "User does not meet age requirement"]
]
];

$engine2->addRule(new Rule($ageRule));
$engine2->setTargetRule('age.verification');
$engine2->showInterpretation(true);

// Scenario A: User meets age requirement
$engine2->addFact('user', ['age' => 25, 'name' => 'John']);
$engine2->addFact('requirements', ['minimumAge' => 18, 'country' => 'US']);
$result2 = $engine2->evaluate();

echo "Scenario A: user.age = 25, requirements.minimumAge = 18\n";
echo "Result: " . $result2[0]['type'] . "\n";
echo "Message: " . $result2[0]['params']['message'] . "\n";
echo "Interpretation: " . $result2[0]['interpretation'] . "\n\n";

// Scenario B: User does not meet age requirement
$engine2b = new Engine();
$engine2b->addRule(new Rule($ageRule));
$engine2b->setTargetRule('age.verification');
$engine2b->showInterpretation(true);
$engine2b->addFact('user', ['age' => 16, 'name' => 'Jane']);
$engine2b->addFact('requirements', ['minimumAge' => 18, 'country' => 'US']);
$result2b = $engine2b->evaluate();

echo "Scenario B: user.age = 16, requirements.minimumAge = 18\n";
echo "Result: " . $result2b[0]['type'] . "\n";
echo "Message: " . $result2b[0]['params']['message'] . "\n\n";

// Example 3: Credit Limit Check
echo "\nExample 3: Credit Limit Check\n";
echo "------------------------------\n";

$engine3 = new Engine();

$creditRule = [
"name" => "credit.limit.check",
"conditions" => [
"all" => [
[
"fact" => "requestedAmount",
"operator" => "lessThanInclusive",
"value" => ["fact" => "creditLimit"]
],
[
"fact" => "currentBalance",
"operator" => "lessThan",
"value" => ["fact" => "creditLimit"]
]
]
],
"event" => [
"type" => "approved",
"params" => ["message" => "Transaction approved"]
],
"failureEvent" => [
"type" => "declined",
"params" => ["message" => "Transaction declined"]
]
];

$engine3->addRule(new Rule($creditRule));
$engine3->setTargetRule('credit.limit.check');
$engine3->showInterpretation(true);

// Scenario: Transaction within limits
$engine3->addFact('requestedAmount', 500);
$engine3->addFact('currentBalance', 3000);
$engine3->addFact('creditLimit', 5000);
$result3 = $engine3->evaluate();

echo "Scenario: requestedAmount = 500, currentBalance = 3000, creditLimit = 5000\n";
echo "Result: " . $result3[0]['type'] . "\n";
echo "Message: " . $result3[0]['params']['message'] . "\n";
echo "Interpretation: " . $result3[0]['interpretation'] . "\n\n";

echo "=== All Examples Completed ===\n";
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