/**
 * Offline Manager
 * Handle offline queue, sync, and storage
 */

import AsyncStorage from '@react-native-async-storage/async-storage';
import NetInfo from '@react-native-community/netinfo';

const QUEUE_KEY = '@quixzoom:observationQueue';
const SYNC_INTERVAL = 30000; // 30 seconds

/**
 * Add observation to offline queue
 */
export async function queueObservation(observation) {
  try {
    const queue = await getQueue();
    const queuedObservation = {
      ...observation,
      id: `queued_${Date.now()}_${Math.random().toString(36).substr(2, 9)}`,
      queuedAt: new Date().toISOString(),
      retryCount: 0,
    };
    
    queue.push(queuedObservation);
    await AsyncStorage.setItem(QUEUE_KEY, JSON.stringify(queue));
    
    return queuedObservation.id;
  } catch (error) {
    console.error('Failed to queue observation:', error);
    throw error;
  }
}

/**
 * Get offline queue
 */
export async function getQueue() {
  try {
    const queueJson = await AsyncStorage.getItem(QUEUE_KEY);
    return queueJson ? JSON.parse(queueJson) : [];
  } catch (error) {
    console.error('Failed to get queue:', error);
    return [];
  }
}

/**
 * Remove observation from queue
 */
export async function removeFromQueue(observationId) {
  try {
    const queue = await getQueue();
    const filtered = queue.filter(obs => obs.id !== observationId);
    await AsyncStorage.setItem(QUEUE_KEY, JSON.stringify(filtered));
    return filtered.length;
  } catch (error) {
    console.error('Failed to remove from queue:', error);
    throw error;
  }
}

/**
 * Update observation in queue
 */
export async function updateInQueue(observationId, updates) {
  try {
    const queue = await getQueue();
    const index = queue.findIndex(obs => obs.id === observationId);
    if (index !== -1) {
      queue[index] = { ...queue[index], ...updates };
      await AsyncStorage.setItem(QUEUE_KEY, JSON.stringify(queue));
    }
  } catch (error) {
    console.error('Failed to update queue:', error);
  }
}

/**
 * Clear queue
 */
export async function clearQueue() {
  try {
    await AsyncStorage.removeItem(QUEUE_KEY);
  } catch (error) {
    console.error('Failed to clear queue:', error);
  }
}

/**
 * Get queue count
 */
export async function getQueueCount() {
  const queue = await getQueue();
  return queue.length;
}

/**
 * Check if device is online
 */
export async function isOnline() {
  const netInfo = await NetInfo.fetch();
  return netInfo.isConnected && netInfo.isInternetReachable;
}

/**
 * Sync queue with server
 */
export async function syncQueue(apiClient) {
  try {
    const online = await isOnline();
    if (!online) {
      console.log('Device is offline, skipping sync');
      return { synced: 0, failed: 0 };
    }

    const queue = await getQueue();
    if (queue.length === 0) {
      return { synced: 0, failed: 0 };
    }

    console.log(`Syncing ${queue.length} observations...`);
    let synced = 0;
    let failed = 0;

    for (const observation of queue) {
      try {
        // Attempt to upload
        await apiClient.observations.create(observation);
        await removeFromQueue(observation.id);
        synced++;
      } catch (error) {
        console.error(`Failed to sync observation ${observation.id}:`, error);
        
        // Increment retry count
        const newRetryCount = (observation.retryCount || 0) + 1;
        if (newRetryCount >= 5) {
          // Max retries reached, remove from queue
          await removeFromQueue(observation.id);
          console.log(`Observation ${observation.id} removed after max retries`);
        } else {
          await updateInQueue(observation.id, { retryCount: newRetryCount });
        }
        failed++;
      }
    }

    console.log(`Sync complete: ${synced} synced, ${failed} failed`);
    return { synced, failed };
  } catch (error) {
    console.error('Sync failed:', error);
    return { synced: 0, failed: 0, error: error.message };
  }
}

/**
 * Start automatic sync
 */
export function startAutoSync(apiClient, interval = SYNC_INTERVAL) {
  console.log('Starting auto sync...');
  
  // Initial sync
  syncQueue(apiClient);
  
  // Periodic sync
  const syncInterval = setInterval(() => {
    syncQueue(apiClient);
  }, interval);
  
  // Listen for network changes
  const unsubscribe = NetInfo.addEventListener(state => {
    if (state.isConnected && state.isInternetReachable) {
      console.log('Network restored, triggering sync...');
      syncQueue(apiClient);
    }
  });
  
  // Return cleanup function
  return () => {
    clearInterval(syncInterval);
    unsubscribe();
  };
}

/**
 * Get queue status
 */
export async function getQueueStatus() {
  const queue = await getQueue();
  const total = queue.length;
  const pending = queue.filter(obs => (obs.retryCount || 0) === 0).length;
  const retrying = queue.filter(obs => (obs.retryCount || 0) > 0).length;
  
  return {
    total,
    pending,
    retrying,
    oldestObservation: total > 0 ? queue[0].queuedAt : null,
  };
}