NPathComplexity

Emitted when a method has too many possible execution paths. NPath is the product of all decision outcomes, growing exponentially with each condition.

<?php
public function validate(array $data): bool
{
    if (isset($data['name'])) {           // 2 paths
        if (strlen($data['name']) > 0) {   // 2 paths
            if (isset($data['email'])) {   // 2 paths
                if (filter_var($data['email'], FILTER_VALIDATE_EMAIL)) {  // 2 paths
                    if (isset($data['age'])) {  // 2 paths
                        if ($data['age'] >= 18) {  // 2 paths
                            return true;
                        }
                    }
                }
            }
        }
    }
    return false;
    // NPath = 2 × 2 × 2 × 2 × 2 × 2 = 64 paths
}

Why this is bad

Exponential test cases: Need to test all possible paths
Deep nesting: Hard to follow the logic
Hidden conditions: Easy to miss failure cases
Maintenance nightmare: Each new condition doubles the paths

How to fix

Use early returns (guard clauses) to flatten the structure:

<?php
public function validate(array $data): bool
{
    if (!isset($data['name'])) {
        return false;
    }
    if (strlen($data['name']) === 0) {
        return false;
    }
    if (!isset($data['email'])) {
        return false;
    }
    if (!filter_var($data['email'], FILTER_VALIDATE_EMAIL)) {
        return false;
    }
    if (!isset($data['age'])) {
        return false;
    }
    if ($data['age'] < 18) {
        return false;
    }

    return true;
    // NPath = 7 paths (linear, not exponential)
}

Threshold

Level	NPath Value
🍝 Piccolo	≤50
🍝🍝 Medio	51-200
🍝🍝🍝 Grande	201-500
🍝🍝🍝🍝 Mamma Mia!	501+