README

A flexible PHP library for managing feature flags with multiple storage backends.

Installation

You can install the library via Composer:

composer require digital-gravy/feature-flag

Features

• Simple on/off feature flag management
• Multiple storage backends:
  • JSON file
  • PHP Constants
  • Array-based storage
• Type-safe implementation
• Extensible storage interface
• Exception handling for invalid flags

Usage

Basic Usage

use DigitalGravy\FeatureFlag\FeatureFlagStore;
use DigitalGravy\FeatureFlag\Storage\KeyedArray;

// Create a feature flag store with array storage
$flags = new KeyedArray([
    'dark_mode' => 'on',
    'beta_feature' => 'off'
]);

$store = new FeatureFlagStore($flags->get_flags());

// Check if a feature is enabled
if ($store->is_on('dark_mode')) {
    // Dark mode is enabled
}

JSON File Storage

use DigitalGravy\FeatureFlag\Storage\JsonFile;

$flags = new JsonFile('/path/to/flags.json');
$store = new FeatureFlagStore($flags->get_flags());

Example flags.json:

{
  "dark_mode": "on",
  "beta_feature": "off"
}

PHP Constants Storage

use DigitalGravy\FeatureFlag\Storage\PHPConstant;

define('DARK_MODE', true);
define('BETA_FEATURE', 'off');

$flags = new PHPConstant(['DARK_MODE', 'BETA_FEATURE']);
$store = new FeatureFlagStore($flags->get_flags());

Multiple Sources

The FeatureFlagStore constructor accepts an array of flags from different storage backends. When multiple sources are provided, the flags are merged together, and the last source overrides the previous ones.

$store = new FeatureFlagStore(
    $jsonFlags->get_flags(),
    $constantFlags->get_flags(),
    $arrayFlags->get_flags()
);

Flag Rules

• Flag keys must contain only alphanumeric characters, underscores, and dashes
• Flag values must be either 'on' or 'off'
• Flag keys are case-insensitive and stored in lowercase

Custom Storage Backend

You can implement your own storage backend by implementing the FlagStorageInterface:

use DigitalGravy\FeatureFlag\Storage\FlagStorageInterface;

class CustomStorage implements FlagStorageInterface {
    public function get_flags(): array {
        // Return array of FeatureFlag objects
    }
}

Error Handling

The library includes several exception types:

• Invalid_Flag_Key: Thrown when a flag key contains invalid characters
• Invalid_Flag_Value: Thrown when a flag value is not 'on' or 'off'
• Flag_Key_Not_Found: Thrown when attempting to check a non-existent flag
• Not_A_Flag: Thrown when invalid flag types are provided
• FileNotFoundException: Thrown when the JSON file does not exist
• FileNotReadableException: Thrown when the JSON file exists but is not readable

License

GPLv3 - see LICENSE file for details