feat: add subscription status APIs

[hyochan]

This PR implements standardized subscription management APIs as specified in the OpenIAP specification, providing a unified way to check subscription status across iOS and Android platforms with automatic detection of all active subscriptions and platform-specific details like iOS expiration dates and Android auto-renewal status.

OpenIAP Specification References

• getActiveSubscriptions
• hasActiveSubscriptions
• ActiveSubscription Type

Changes

New APIs

• Add getActiveSubscriptions() to retrieve detailed subscription information

  • Returns list of ActiveSubscription objects with platform-specific fields
  • Supports optional filtering by subscription IDs
  • Automatically detects all active subscriptions when no filter provided

• Add hasActiveSubscriptions() for simple boolean subscription checks

  • Returns true if user has any active subscriptions
  • Supports optional filtering by specific subscription IDs
  • Handles errors gracefully by returning false

Type System

• Add ActiveSubscription model with platform-specific fields:
  • iOS: expirationDateIOS, environmentIOS, daysUntilExpirationIOS
  • Android: autoRenewingAndroid
  • Cross-platform: productId, isActive, willExpireSoon (within 7 days)

Code Quality

• Rename IAPPlatform to IapPlatform following Dart naming conventions
• Fix type casting issues in extractPurchased and extractItems utilities
• Add proper iOS transaction state mapping in _convertToPurchase
• Replace getCurrentPlatform() calls with instance-based platform detection

Testing

• Add comprehensive unit tests for both iOS and Android platforms
• Test subscription filtering functionality
• Verify platform-specific field population

Usage Example

// Get all active subscriptions
final subscriptions = await FlutterInappPurchase.instance.getActiveSubscriptions();

// Check specific subscriptions
final hasMonthly = await FlutterInappPurchase.instance.hasActiveSubscriptions(
  subscriptionIds: ['monthly_subscription', 'yearly_subscription'],
);

// Access platform-specific information
for (final sub in subscriptions) {
  if (Platform.isIOS && sub.daysUntilExpirationIOS != null) {
    print('Expires in ${sub.daysUntilExpirationIOS} days');
  }
  if (Platform.isAndroid && sub.autoRenewingAndroid == true) {
    print('Auto-renewing subscription');
  }
}

Breaking Changes

None - these are new additions to the API surface.

Migration Notes

• Developers using custom subscription checking logic can migrate to these standardized APIs
• The deprecated checkSubscribed() method (removed in v6.0.0) can now be replaced with hasActiveSubscriptions()

Related

• OpenIAP Discussion: https://github.com/hyochan/openiap.dev/discussions
• Reference Implementation: feat: implement Open IAP subscription status APIs expo-iap#158

[codecov]

Welcome to Codecov 🎉

Once you merge this PR into your default branch, you're all set! Codecov will compare coverage reports and display results in all future pull requests.

Thanks for integrating Codecov - We've got you covered ☂️