import { Platform } from 'react-native';
import { 
  HKQuantityTypeIdentifier,
  HKQuantitySample,
  getMostRecentQuantitySample,
  isAvailable,
  authorize,
} from 'react-native-health';

interface HealthData {
  oxygenSaturation: number | null;
  heartRate: number | null;
  lastUpdated: Date | null;
}

class HealthDataService {
  private static instance: HealthDataService;
  private isAuthorized = false;

  private constructor() {}

  public static getInstance(): HealthDataService {
    if (!HealthDataService.instance) {
      HealthDataService.instance = new HealthDataService();
    }
    return HealthDataService.instance;
  }

  async requestAuthorization(): Promise<boolean> {
    if (Platform.OS !== 'ios') {
      return false;
    }

    try {
      const available = await isAvailable();
      if (!available) {
        return false;
      }

      const permissions = [
        { 
          type: HKQuantityTypeIdentifier.OxygenSaturation,
          access: 'read' as const 
        },
        { 
          type: HKQuantityTypeIdentifier.HeartRate,
          access: 'read' as const 
        }
      ];

      const authorized = await authorize(permissions);
      this.isAuthorized = authorized;
      return authorized;
    } catch (error) {
      console.error('Health data authorization error:', error);
      return false;
    }
  }

  async getOxygenSaturation(): Promise<number | null> {
    if (!this.isAuthorized) {
      return null;
    }

    try {
      const sample: HKQuantitySample | null = await getMostRecentQuantitySample(
        HKQuantityTypeIdentifier.OxygenSaturation
      );

      if (sample) {
        return Number(sample.value.toFixed(1));
      }
      return null;
    } catch (error) {
      console.error('Error reading oxygen saturation:', error);
      return null;
    }
  }

  async getHeartRate(): Promise<number | null> {
    if (!this.isAuthorized) {
      return null;
    }

    try {
      const sample: HKQuantitySample | null = await getMostRecentQuantitySample(
        HKQuantityTypeIdentifier.HeartRate
      );

      if (sample) {
        return Math.round(sample.value);
      }
      return null;
    } catch (error) {
      console.error('Error reading heart rate:', error);
      return null;
    }
  }

  async getHealthData(): Promise<HealthData> {
    const [oxygenSaturation, heartRate] = await Promise.all([
      this.getOxygenSaturation(),
      this.getHeartRate()
    ]);

    return {
      oxygenSaturation,
      heartRate,
      lastUpdated: new Date()
    };
  }
}

export default HealthDataService.getInstance();