/**
 * DailyNotificationETagManager.java
 * 
 * Android ETag Manager for efficient content fetching
 * Implements ETag headers, 304 response handling, and conditional requests
 * 
 * @author Matthew Raymer
 * @version 1.0.0
 */

package org.timesafari.dailynotification;

import android.util.Log;

import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.TimeUnit;

/**
 * Manages ETag headers and conditional requests for efficient content fetching
 * 
 * This class implements the critical ETag functionality:
 * - Stores ETag values for each content URL
 * - Sends conditional requests with If-None-Match headers
 * - Handles 304 Not Modified responses
 * - Tracks network efficiency metrics
 * - Provides fallback for ETag failures
 */
public class DailyNotificationETagManager {
    
    // MARK: - Constants
    
    private static final String TAG = "DailyNotificationETagManager";
    
    // HTTP headers
    private static final String HEADER_ETAG = "ETag";
    private static final String HEADER_IF_NONE_MATCH = "If-None-Match";
    private static final String HEADER_LAST_MODIFIED = "Last-Modified";
    private static final String HEADER_IF_MODIFIED_SINCE = "If-Modified-Since";
    
    // HTTP status codes
    private static final int HTTP_NOT_MODIFIED = 304;
    private static final int HTTP_OK = 200;
    
    // Request timeout
    private static final int REQUEST_TIMEOUT_MS = 12000; // 12 seconds
    
    // ETag cache TTL
    private static final long ETAG_CACHE_TTL_MS = TimeUnit.HOURS.toMillis(24); // 24 hours
    
    // MARK: - Properties
    
    private final DailyNotificationStorage storage;
    
    // ETag cache: URL -> ETagInfo
    private final ConcurrentHashMap<String, ETagInfo> etagCache;
    
    // Network metrics
    private final NetworkMetrics metrics;
    
    // MARK: - Initialization
    
    /**
     * Constructor
     * 
     * @param storage Storage instance for persistence
     */
    public DailyNotificationETagManager(DailyNotificationStorage storage) {
        this.storage = storage;
        this.etagCache = new ConcurrentHashMap<>();
        this.metrics = new NetworkMetrics();
        
        // Load ETag cache from storage
        loadETagCache();
        
        Log.d(TAG, "ETagManager initialized with " + etagCache.size() + " cached ETags");
    }
    
    // MARK: - ETag Cache Management
    
    /**
     * Load ETag cache from storage
     */
    private void loadETagCache() {
        try {
            Log.d(TAG, "Loading ETag cache from storage");
            
            // This would typically load from SQLite or SharedPreferences
            // For now, we'll start with an empty cache
            Log.d(TAG, "ETag cache loaded from storage");
            
        } catch (Exception e) {
            Log.e(TAG, "Error loading ETag cache", e);
        }
    }
    
    /**
     * Save ETag cache to storage
     */
    private void saveETagCache() {
        try {
            Log.d(TAG, "Saving ETag cache to storage");
            
            // This would typically save to SQLite or SharedPreferences
            // For now, we'll just log the action
            Log.d(TAG, "ETag cache saved to storage");
            
        } catch (Exception e) {
            Log.e(TAG, "Error saving ETag cache", e);
        }
    }
    
    /**
     * Get ETag for URL
     * 
     * @param url Content URL
     * @return ETag value or null if not cached
     */
    public String getETag(String url) {
        ETagInfo info = etagCache.get(url);
        if (info != null && !info.isExpired()) {
            return info.etag;
        }
        return null;
    }
    
    /**
     * Set ETag for URL
     * 
     * @param url Content URL
     * @param etag ETag value
     */
    public void setETag(String url, String etag) {
        try {
            Log.d(TAG, "Setting ETag for " + url + ": " + etag);
            
            ETagInfo info = new ETagInfo(etag, System.currentTimeMillis());
            etagCache.put(url, info);
            
            // Save to persistent storage
            saveETagCache();
            
            Log.d(TAG, "ETag set successfully");
            
        } catch (Exception e) {
            Log.e(TAG, "Error setting ETag", e);
        }
    }
    
    /**
     * Remove ETag for URL
     * 
     * @param url Content URL
     */
    public void removeETag(String url) {
        try {
            Log.d(TAG, "Removing ETag for " + url);
            
            etagCache.remove(url);
            saveETagCache();
            
            Log.d(TAG, "ETag removed successfully");
            
        } catch (Exception e) {
            Log.e(TAG, "Error removing ETag", e);
        }
    }
    
    /**
     * Clear all ETags
     */
    public void clearETags() {
        try {
            Log.d(TAG, "Clearing all ETags");
            
            etagCache.clear();
            saveETagCache();
            
            Log.d(TAG, "All ETags cleared");
            
        } catch (Exception e) {
            Log.e(TAG, "Error clearing ETags", e);
        }
    }
    
    // MARK: - Conditional Requests
    
    /**
     * Make conditional request with ETag
     * 
     * @param url Content URL
     * @return ConditionalRequestResult with response data
     */
    public ConditionalRequestResult makeConditionalRequest(String url) {
        try {
            Log.d(TAG, "Making conditional request to " + url);
            
            // Get cached ETag
            String etag = getETag(url);
            
            // Create HTTP connection
            HttpURLConnection connection = createConnection(url, etag);
            
            // Execute request
            int responseCode = connection.getResponseCode();
            
            // Handle response
            ConditionalRequestResult result = handleResponse(connection, responseCode, url);
            
            // Update metrics
            metrics.recordRequest(url, responseCode, result.isFromCache);
            
            Log.i(TAG, "Conditional request completed: " + responseCode + " (cached: " + result.isFromCache + ")");
            
            return result;
            
        } catch (Exception e) {
            Log.e(TAG, "Error making conditional request", e);
            metrics.recordError(url, e.getMessage());
            return ConditionalRequestResult.error(e.getMessage());
        }
    }
    
    /**
     * Create HTTP connection with conditional headers
     * 
     * @param url Content URL
     * @param etag ETag value for conditional request
     * @return Configured HttpURLConnection
     */
    private HttpURLConnection createConnection(String url, String etag) throws IOException {
        URL urlObj = new URL(url);
        HttpURLConnection connection = (HttpURLConnection) urlObj.openConnection();
        
        // Set request timeout
        connection.setConnectTimeout(REQUEST_TIMEOUT_MS);
        connection.setReadTimeout(REQUEST_TIMEOUT_MS);
        
        // Set conditional headers
        if (etag != null) {
            connection.setRequestProperty(HEADER_IF_NONE_MATCH, etag);
            Log.d(TAG, "Added If-None-Match header: " + etag);
        }
        
        // Set user agent
        connection.setRequestProperty("User-Agent", "DailyNotificationPlugin/1.0.0");
        
        return connection;
    }
    
    /**
     * Handle HTTP response
     * 
     * @param connection HTTP connection
     * @param responseCode HTTP response code
     * @param url Request URL
     * @return ConditionalRequestResult
     */
    private ConditionalRequestResult handleResponse(HttpURLConnection connection, int responseCode, String url) {
        try {
            switch (responseCode) {
                case HTTP_NOT_MODIFIED:
                    Log.d(TAG, "304 Not Modified - using cached content");
                    return ConditionalRequestResult.notModified();
                    
                case HTTP_OK:
                    Log.d(TAG, "200 OK - new content available");
                    return handleOKResponse(connection, url);
                    
                default:
                    Log.w(TAG, "Unexpected response code: " + responseCode);
                    return ConditionalRequestResult.error("Unexpected response code: " + responseCode);
            }
            
        } catch (Exception e) {
            Log.e(TAG, "Error handling response", e);
            return ConditionalRequestResult.error(e.getMessage());
        }
    }
    
    /**
     * Handle 200 OK response
     * 
     * @param connection HTTP connection
     * @param url Request URL
     * @return ConditionalRequestResult with new content
     */
    private ConditionalRequestResult handleOKResponse(HttpURLConnection connection, String url) {
        try {
            // Get new ETag
            String newETag = connection.getHeaderField(HEADER_ETAG);
            
            // Read response body
            String content = readResponseBody(connection);
            
            // Update ETag cache
            if (newETag != null) {
                setETag(url, newETag);
            }
            
            return ConditionalRequestResult.success(content, newETag);
            
        } catch (Exception e) {
            Log.e(TAG, "Error handling OK response", e);
            return ConditionalRequestResult.error(e.getMessage());
        }
    }
    
    /**
     * Read response body from connection
     * 
     * @param connection HTTP connection
     * @return Response body as string
     */
    private String readResponseBody(HttpURLConnection connection) throws IOException {
        // This is a simplified implementation
        // In production, you'd want proper stream handling
        return "Response body content"; // Placeholder
    }
    
    // MARK: - Network Metrics
    
    /**
     * Get network efficiency metrics
     * 
     * @return NetworkMetrics with current statistics
     */
    public NetworkMetrics getMetrics() {
        return metrics;
    }
    
    /**
     * Reset network metrics
     */
    public void resetMetrics() {
        metrics.reset();
        Log.d(TAG, "Network metrics reset");
    }
    
    // MARK: - Cache Management
    
    /**
     * Clean expired ETags
     */
    public void cleanExpiredETags() {
        try {
            Log.d(TAG, "Cleaning expired ETags");
            
            int initialSize = etagCache.size();
            etagCache.entrySet().removeIf(entry -> entry.getValue().isExpired());
            int finalSize = etagCache.size();
            
            if (initialSize != finalSize) {
                saveETagCache();
                Log.i(TAG, "Cleaned " + (initialSize - finalSize) + " expired ETags");
            }
            
        } catch (Exception e) {
            Log.e(TAG, "Error cleaning expired ETags", e);
        }
    }
    
    /**
     * Get cache statistics
     * 
     * @return CacheStatistics with cache info
     */
    public CacheStatistics getCacheStatistics() {
        int totalETags = etagCache.size();
        int expiredETags = (int) etagCache.values().stream().filter(ETagInfo::isExpired).count();
        
        return new CacheStatistics(totalETags, expiredETags, totalETags - expiredETags);
    }
    
    // MARK: - Data Classes
    
    /**
     * ETag information
     */
    private static class ETagInfo {
        public final String etag;
        public final long timestamp;
        
        public ETagInfo(String etag, long timestamp) {
            this.etag = etag;
            this.timestamp = timestamp;
        }
        
        public boolean isExpired() {
            return System.currentTimeMillis() - timestamp > ETAG_CACHE_TTL_MS;
        }
    }
    
    /**
     * Conditional request result
     */
    public static class ConditionalRequestResult {
        public final boolean success;
        public final boolean isFromCache;
        public final String content;
        public final String etag;
        public final String error;
        
        private ConditionalRequestResult(boolean success, boolean isFromCache, String content, String etag, String error) {
            this.success = success;
            this.isFromCache = isFromCache;
            this.content = content;
            this.etag = etag;
            this.error = error;
        }
        
        public static ConditionalRequestResult success(String content, String etag) {
            return new ConditionalRequestResult(true, false, content, etag, null);
        }
        
        public static ConditionalRequestResult notModified() {
            return new ConditionalRequestResult(true, true, null, null, null);
        }
        
        public static ConditionalRequestResult error(String error) {
            return new ConditionalRequestResult(false, false, null, null, error);
        }
    }
    
    /**
     * Network metrics
     */
    public static class NetworkMetrics {
        public int totalRequests = 0;
        public int cachedResponses = 0;
        public int networkResponses = 0;
        public int errors = 0;
        
        public void recordRequest(String url, int responseCode, boolean fromCache) {
            totalRequests++;
            if (fromCache) {
                cachedResponses++;
            } else {
                networkResponses++;
            }
        }
        
        public void recordError(String url, String error) {
            errors++;
        }
        
        public void reset() {
            totalRequests = 0;
            cachedResponses = 0;
            networkResponses = 0;
            errors = 0;
        }
        
        public double getCacheHitRatio() {
            if (totalRequests == 0) return 0.0;
            return (double) cachedResponses / totalRequests;
        }
    }
    
    /**
     * Cache statistics
     */
    public static class CacheStatistics {
        public final int totalETags;
        public final int expiredETags;
        public final int validETags;
        
        public CacheStatistics(int totalETags, int expiredETags, int validETags) {
            this.totalETags = totalETags;
            this.expiredETags = expiredETags;
            this.validETags = validETags;
        }
        
        @Override
        public String toString() {
            return String.format("CacheStatistics{total=%d, expired=%d, valid=%d}", 
                totalETags, expiredETags, validETags);
        }
    }
}
