class Baggage

final class Baggage implements BaggageInterface {
    private static ?self $emptyBaggage = null;
    
    /** @inheritDoc */
    public static function fromContext(ContextInterface $context) : BaggageInterface {
        return $context->get(ContextKeys::baggage()) ?? self::getEmpty();
    }
    
    /** @inheritDoc */
    public static function getBuilder() : BaggageBuilderInterface {
        return new BaggageBuilder();
    }
    
    /** @inheritDoc */
    public static function getCurrent() : BaggageInterface {
        return self::fromContext(Context::getCurrent());
    }
    
    /** @inheritDoc */
    public static function getEmpty() : BaggageInterface {
        if (null === self::$emptyBaggage) {
            self::$emptyBaggage = new self();
        }
        return self::$emptyBaggage;
    }
    
    /** @param array<string, Entry> $entries */
    public function __construct(array $entries = []) {
    }
    
    /** @inheritDoc */
    public function activate() : ScopeInterface {
        return Context::getCurrent()->withContextValue($this)
            ->activate();
    }
    
    /** @inheritDoc */
    public function getEntry(string $key) : ?Entry {
        return $this->entries[$key] ?? null;
    }
    
    /** @inheritDoc */
    public function getValue(string $key) {
        if (($entry = $this->getEntry($key)) !== null) {
            return $entry->getValue();
        }
        return null;
    }
    
    /** @inheritDoc */
    public function getAll() : iterable {
        foreach ($this->entries as $key => $entry) {
            (yield $key => $entry);
        }
    }
    
    /** @inheritDoc */
    public function isEmpty() : bool {
        return $this->entries === [];
    }
    
    /** @inheritDoc */
    public function toBuilder() : BaggageBuilderInterface {
        return new BaggageBuilder($this->entries);
    }
    
    /** @inheritDoc */
    public function storeInContext(ContextInterface $context) : ContextInterface {
        return $context->with(ContextKeys::baggage(), $this);
    }

}