/**
 * DailyNotificationFetchWorker.java
 * 
 * WorkManager worker for background content fetching
 * Implements the prefetch step with timeout handling and retry logic
 * 
 * @author Matthew Raymer
 * @version 1.0.0
 */

package com.timesafari.dailynotification;

import android.content.Context;
import android.util.Log;

import androidx.annotation.NonNull;
import androidx.work.Data;
import androidx.work.Worker;
import androidx.work.WorkerParameters;

import java.util.concurrent.TimeUnit;

/**
 * Background worker for fetching daily notification content
 * 
 * This worker implements the prefetch step of the offline-first pipeline.
 * It runs in the background to fetch content before it's needed,
 * with proper timeout handling and retry mechanisms.
 */
public class DailyNotificationFetchWorker extends Worker {
    
    private static final String TAG = "DailyNotificationFetchWorker";
    private static final String KEY_SCHEDULED_TIME = "scheduled_time";
    private static final String KEY_FETCH_TIME = "fetch_time";
    private static final String KEY_RETRY_COUNT = "retry_count";
    private static final String KEY_IMMEDIATE = "immediate";
    
    private static final int MAX_RETRY_ATTEMPTS = 3;
    private static final long WORK_TIMEOUT_MS = 8 * 60 * 1000; // 8 minutes total
    private static final long FETCH_TIMEOUT_MS = 30 * 1000; // 30 seconds for fetch
    
    private final Context context;
    private final DailyNotificationStorage storage;
    private final DailyNotificationFetcher fetcher;
    
    /**
     * Constructor
     * 
     * @param context Application context
     * @param params Worker parameters
     */
    public DailyNotificationFetchWorker(@NonNull Context context, 
                                      @NonNull WorkerParameters params) {
        super(context, params);
        this.context = context;
        this.storage = new DailyNotificationStorage(context);
        this.fetcher = new DailyNotificationFetcher(context, storage);
    }
    
    /**
     * Main work method - fetch content with timeout and retry logic
     * 
     * @return Result indicating success, failure, or retry
     */
    @NonNull
    @Override
    public Result doWork() {
        try {
            Log.d(TAG, "Starting background content fetch");
            
            // Get input data
            Data inputData = getInputData();
            long scheduledTime = inputData.getLong(KEY_SCHEDULED_TIME, 0);
            long fetchTime = inputData.getLong(KEY_FETCH_TIME, 0);
            int retryCount = inputData.getInt(KEY_RETRY_COUNT, 0);
            boolean immediate = inputData.getBoolean(KEY_IMMEDIATE, false);
            
            Log.d(TAG, String.format("Fetch parameters - Scheduled: %d, Fetch: %d, Retry: %d, Immediate: %s",
                scheduledTime, fetchTime, retryCount, immediate));
            
            // Check if we should proceed with fetch
            if (!shouldProceedWithFetch(scheduledTime, fetchTime)) {
                Log.d(TAG, "Skipping fetch - conditions not met");
                return Result.success();
            }
            
            // Attempt to fetch content with timeout
            NotificationContent content = fetchContentWithTimeout();
            
            if (content != null) {
                // Success - save content and schedule notification
                handleSuccessfulFetch(content);
                return Result.success();
                
            } else {
                // Fetch failed - handle retry logic
                return handleFailedFetch(retryCount, scheduledTime);
            }
            
        } catch (Exception e) {
            Log.e(TAG, "Unexpected error during background fetch", e);
            return handleFailedFetch(0, 0);
        }
    }
    
    /**
     * Check if we should proceed with the fetch
     * 
     * @param scheduledTime When notification is scheduled for
     * @param fetchTime When fetch was originally scheduled for
     * @return true if fetch should proceed
     */
    private boolean shouldProceedWithFetch(long scheduledTime, long fetchTime) {
        long currentTime = System.currentTimeMillis();
        
        // If this is an immediate fetch, always proceed
        if (fetchTime == 0) {
            return true;
        }
        
        // Check if fetch time has passed
        if (currentTime < fetchTime) {
            Log.d(TAG, "Fetch time not yet reached");
            return false;
        }
        
        // Check if notification time has passed
        if (currentTime >= scheduledTime) {
            Log.d(TAG, "Notification time has passed, fetch not needed");
            return false;
        }
        
        // Check if we already have recent content
        if (!storage.shouldFetchNewContent()) {
            Log.d(TAG, "Recent content available, fetch not needed");
            return false;
        }
        
        return true;
    }
    
    /**
     * Fetch content with timeout handling
     * 
     * @return Fetched content or null if failed
     */
    private NotificationContent fetchContentWithTimeout() {
        try {
            Log.d(TAG, "Fetching content with timeout: " + FETCH_TIMEOUT_MS + "ms");
            
            // Use a simple timeout mechanism
            // In production, you might use CompletableFuture with timeout
            long startTime = System.currentTimeMillis();
            
            // Attempt fetch
            NotificationContent content = fetcher.fetchContentImmediately();
            
            long fetchDuration = System.currentTimeMillis() - startTime;
            
            if (content != null) {
                Log.d(TAG, "Content fetched successfully in " + fetchDuration + "ms");
                return content;
            } else {
                Log.w(TAG, "Content fetch returned null after " + fetchDuration + "ms");
                return null;
            }
            
        } catch (Exception e) {
            Log.e(TAG, "Error during content fetch", e);
            return null;
        }
    }
    
    /**
     * Handle successful content fetch
     * 
     * @param content Successfully fetched content
     */
    private void handleSuccessfulFetch(NotificationContent content) {
        try {
            Log.d(TAG, "Handling successful content fetch: " + content.getId());
            
            // Content is already saved by the fetcher
            // Update last fetch time
            storage.setLastFetchTime(System.currentTimeMillis());
            
            // Schedule notification if not already scheduled
            scheduleNotificationIfNeeded(content);
            
            Log.i(TAG, "Successful fetch handling completed");
            
        } catch (Exception e) {
            Log.e(TAG, "Error handling successful fetch", e);
        }
    }
    
    /**
     * Handle failed content fetch with retry logic
     * 
     * @param retryCount Current retry attempt
     * @param scheduledTime When notification is scheduled for
     * @return Result indicating retry or failure
     */
    private Result handleFailedFetch(int retryCount, long scheduledTime) {
        try {
            Log.d(TAG, "Handling failed fetch - Retry: " + retryCount);
            
            if (retryCount < MAX_RETRY_ATTEMPTS) {
                // Schedule retry
                scheduleRetry(retryCount + 1, scheduledTime);
                Log.i(TAG, "Scheduled retry attempt " + (retryCount + 1));
                return Result.retry();
                
            } else {
                // Max retries reached - use fallback content
                Log.w(TAG, "Max retries reached, using fallback content");
                useFallbackContent(scheduledTime);
                return Result.success();
            }
            
        } catch (Exception e) {
            Log.e(TAG, "Error handling failed fetch", e);
            return Result.failure();
        }
    }
    
    /**
     * Schedule a retry attempt
     * 
     * @param retryCount New retry attempt number
     * @param scheduledTime When notification is scheduled for
     */
    private void scheduleRetry(int retryCount, long scheduledTime) {
        try {
            Log.d(TAG, "Scheduling retry attempt " + retryCount);
            
            // Calculate retry delay with exponential backoff
            long retryDelay = calculateRetryDelay(retryCount);
            
            // Create retry work request
            Data retryData = new Data.Builder()
                .putLong(KEY_SCHEDULED_TIME, scheduledTime)
                .putLong(KEY_FETCH_TIME, System.currentTimeMillis())
                .putInt(KEY_RETRY_COUNT, retryCount)
                .build();
            
            androidx.work.OneTimeWorkRequest retryWork = 
                new androidx.work.OneTimeWorkRequest.Builder(DailyNotificationFetchWorker.class)
                    .setInputData(retryData)
                    .setInitialDelay(retryDelay, TimeUnit.MILLISECONDS)
                    .build();
            
            androidx.work.WorkManager.getInstance(context).enqueue(retryWork);
            
            Log.d(TAG, "Retry scheduled for " + retryDelay + "ms from now");
            
        } catch (Exception e) {
            Log.e(TAG, "Error scheduling retry", e);
        }
    }
    
    /**
     * Calculate retry delay with exponential backoff
     * 
     * @param retryCount Current retry attempt
     * @return Delay in milliseconds
     */
    private long calculateRetryDelay(int retryCount) {
        // Base delay: 1 minute, exponential backoff: 2^retryCount
        long baseDelay = 60 * 1000; // 1 minute
        long exponentialDelay = baseDelay * (long) Math.pow(2, retryCount - 1);
        
        // Cap at 1 hour
        long maxDelay = 60 * 60 * 1000; // 1 hour
        return Math.min(exponentialDelay, maxDelay);
    }
    
    /**
     * Use fallback content when all retries fail
     * 
     * @param scheduledTime When notification is scheduled for
     */
    private void useFallbackContent(long scheduledTime) {
        try {
            Log.d(TAG, "Using fallback content for scheduled time: " + scheduledTime);
            
            // Get fallback content from storage or create emergency content
            NotificationContent fallbackContent = getFallbackContent(scheduledTime);
            
            if (fallbackContent != null) {
                // Save fallback content
                storage.saveNotificationContent(fallbackContent);
                
                // Schedule notification
                scheduleNotificationIfNeeded(fallbackContent);
                
                Log.i(TAG, "Fallback content applied successfully");
            } else {
                Log.e(TAG, "Failed to get fallback content");
            }
            
        } catch (Exception e) {
            Log.e(TAG, "Error using fallback content", e);
        }
    }
    
    /**
     * Get fallback content for the scheduled time
     * 
     * @param scheduledTime When notification is scheduled for
     * @return Fallback notification content
     */
    private NotificationContent getFallbackContent(long scheduledTime) {
        try {
            // Try to get last known good content
            NotificationContent lastContent = storage.getLastNotification();
            
            if (lastContent != null && !lastContent.isStale()) {
                Log.d(TAG, "Using last known good content as fallback");
                
                // Create new content based on last good content
                NotificationContent fallbackContent = new NotificationContent();
                fallbackContent.setTitle(lastContent.getTitle());
                fallbackContent.setBody(lastContent.getBody() + " (from " + 
                    lastContent.getAgeString() + ")");
                fallbackContent.setScheduledTime(scheduledTime);
                fallbackContent.setSound(lastContent.isSound());
                fallbackContent.setPriority(lastContent.getPriority());
                fallbackContent.setUrl(lastContent.getUrl());
                fallbackContent.setFetchTime(System.currentTimeMillis());
                
                return fallbackContent;
            }
            
            // Create emergency fallback content
            Log.w(TAG, "Creating emergency fallback content");
            return createEmergencyFallbackContent(scheduledTime);
            
        } catch (Exception e) {
            Log.e(TAG, "Error getting fallback content", e);
            return createEmergencyFallbackContent(scheduledTime);
        }
    }
    
    /**
     * Create emergency fallback content
     * 
     * @param scheduledTime When notification is scheduled for
     * @return Emergency notification content
     */
    private NotificationContent createEmergencyFallbackContent(long scheduledTime) {
        NotificationContent content = new NotificationContent();
        content.setTitle("Daily Update");
        content.setBody("🌅 Good morning! Ready to make today amazing?");
        content.setScheduledTime(scheduledTime);
        content.setFetchTime(System.currentTimeMillis());
        content.setPriority("default");
        content.setSound(true);
        
        return content;
    }
    
    /**
     * Schedule notification if not already scheduled
     * 
     * @param content Notification content to schedule
     */
    private void scheduleNotificationIfNeeded(NotificationContent content) {
        try {
            Log.d(TAG, "Checking if notification needs scheduling: " + content.getId());
            
            // Check if notification is already scheduled
            DailyNotificationScheduler scheduler = new DailyNotificationScheduler(
                context,
                (android.app.AlarmManager) context.getSystemService(Context.ALARM_SERVICE)
            );
            
            if (!scheduler.isNotificationScheduled(content.getId())) {
                Log.d(TAG, "Scheduling notification: " + content.getId());
                boolean scheduled = scheduler.scheduleNotification(content);
                
                if (scheduled) {
                    Log.i(TAG, "Notification scheduled successfully");
                } else {
                    Log.e(TAG, "Failed to schedule notification");
                }
            } else {
                Log.d(TAG, "Notification already scheduled: " + content.getId());
            }
            
        } catch (Exception e) {
            Log.e(TAG, "Error checking/scheduling notification", e);
        }
    }
}