class ClassDiscovery

abstract class ClassDiscovery {
    
    /**
     * A list of strategies to find classes.
     *
     * @var DiscoveryStrategy[]
     */
    private static $strategies = [
        Strategy\GeneratedDiscoveryStrategy::class,
        Strategy\CommonClassesStrategy::class,
        Strategy\CommonPsr17ClassesStrategy::class,
        Strategy\PuliBetaStrategy::class,
    ];
    private static $deprecatedStrategies = [
        Strategy\PuliBetaStrategy::class => true,
    ];
    
    /**
     * Discovery cache to make the second time we use discovery faster.
     *
     * @var array
     */
    private static $cache = [];
    
    /**
     * Finds a class.
     *
     * @param string $type
     *
     * @return string|\Closure
     *
     * @throws DiscoveryFailedException
     */
    protected static function findOneByType($type) {
        // Look in the cache
        if (null !== ($class = self::getFromCache($type))) {
            return $class;
        }
        static $skipStrategy;
        $skipStrategy ?? ($skipStrategy = self::safeClassExists(Strategy\GeneratedDiscoveryStrategy::class) ? false : Strategy\GeneratedDiscoveryStrategy::class);
        $exceptions = [];
        foreach (self::$strategies as $strategy) {
            if ($skipStrategy === $strategy) {
                continue;
            }
            try {
                $candidates = $strategy::getCandidates($type);
            } catch (StrategyUnavailableException $e) {
                if (!isset(self::$deprecatedStrategies[$strategy])) {
                    $exceptions[] = $e;
                }
                continue;
            }
            foreach ($candidates as $candidate) {
                if (isset($candidate['condition'])) {
                    if (!self::evaluateCondition($candidate['condition'])) {
                        continue;
                    }
                }
                // save the result for later use
                self::storeInCache($type, $candidate);
                return $candidate['class'];
            }
            $exceptions[] = new NoCandidateFoundException($strategy, $candidates);
        }
        throw DiscoveryFailedException::create($exceptions);
    }
    
    /**
     * Get a value from cache.
     *
     * @param string $type
     *
     * @return string|null
     */
    private static function getFromCache($type) {
        if (!isset(self::$cache[$type])) {
            return;
        }
        $candidate = self::$cache[$type];
        if (isset($candidate['condition'])) {
            if (!self::evaluateCondition($candidate['condition'])) {
                return;
            }
        }
        return $candidate['class'];
    }
    
    /**
     * Store a value in cache.
     *
     * @param string $type
     * @param string $class
     */
    private static function storeInCache($type, $class) {
        self::$cache[$type] = $class;
    }
    
    /**
     * Set new strategies and clear the cache.
     *
     * @param string[] $strategies list of fully qualified class names that implement DiscoveryStrategy
     */
    public static function setStrategies(array $strategies) {
        self::$strategies = $strategies;
        self::clearCache();
    }
    
    /**
     * Returns the currently configured discovery strategies as fully qualified class names.
     *
     * @return string[]
     */
    public static function getStrategies() : iterable {
        return self::$strategies;
    }
    
    /**
     * Append a strategy at the end of the strategy queue.
     *
     * @param string $strategy Fully qualified class name of a DiscoveryStrategy
     */
    public static function appendStrategy($strategy) {
        self::$strategies[] = $strategy;
        self::clearCache();
    }
    
    /**
     * Prepend a strategy at the beginning of the strategy queue.
     *
     * @param string $strategy Fully qualified class name to a DiscoveryStrategy
     */
    public static function prependStrategy($strategy) {
        array_unshift(self::$strategies, $strategy);
        self::clearCache();
    }
    public static function clearCache() {
        self::$cache = [];
    }
    
    /**
     * Evaluates conditions to boolean.
     *
     * @return bool
     */
    protected static function evaluateCondition($condition) {
        if (is_string($condition)) {
            // Should be extended for functions, extensions???
            return self::safeClassExists($condition);
        }
        if (is_callable($condition)) {
            return (bool) $condition();
        }
        if (is_bool($condition)) {
            return $condition;
        }
        if (is_array($condition)) {
            foreach ($condition as $c) {
                if (false === static::evaluateCondition($c)) {
                    // Immediately stop execution if the condition is false
                    return false;
                }
            }
            return true;
        }
        return false;
    }
    
    /**
     * Get an instance of the $class.
     *
     * @param string|\Closure $class a FQCN of a class or a closure that instantiate the class
     *
     * @return object
     *
     * @throws ClassInstantiationFailedException
     */
    protected static function instantiateClass($class) {
        try {
            if (is_string($class)) {
                return new $class();
            }
            if (is_callable($class)) {
                return $class();
            }
        } catch (\Exception $e) {
            throw new ClassInstantiationFailedException('Unexpected exception when instantiating class.', 0, $e);
        }
        throw new ClassInstantiationFailedException('Could not instantiate class because parameter is neither a callable nor a string');
    }
    
    /**
     * We need a "safe" version of PHP's "class_exists" because Magento has a bug
     * (or they call it a "feature"). Magento is throwing an exception if you do class_exists()
     * on a class that ends with "Factory" and if that file does not exits.
     *
     * This function catches all potential exceptions and makes sure to always return a boolean.
     *
     * @param string $class
     *
     * @return bool
     */
    public static function safeClassExists($class) {
        try {
            return class_exists($class) || interface_exists($class);
        } catch (\Exception $e) {
            return false;
        }
    }

}