/**
 * Push Notifications Service
 *
 * Sends push notifications via Expo Push API with:
 * - Notification settings check (push_enabled, alert types, quiet hours)
 * - Batch sending support
 * - Error handling and ticket tracking
 */

const { supabase } = require('../config/supabase');

// Expo Push API endpoint
const EXPO_PUSH_URL = 'https://exp.host/--/api/v2/push/send';

/**
 * Notification types that map to settings
 */
const NotificationType = {
  EMERGENCY: 'emergency',     // Falls, SOS, critical alerts
  ACTIVITY: 'activity',       // Unusual activity patterns
  LOW_BATTERY: 'low_battery', // Device battery warnings
  DAILY_SUMMARY: 'daily',     // Daily wellness report
  WEEKLY_SUMMARY: 'weekly',   // Weekly health digest
  SYSTEM: 'system'            // System messages (always delivered)
};

/**
 * Check if current time is within quiet hours
 *
 * @param {string} quietStart - Start time in HH:MM format
 * @param {string} quietEnd - End time in HH:MM format
 * @param {string} timezone - User timezone (default: UTC)
 * @returns {boolean} True if currently in quiet hours
 */
function isInQuietHours(quietStart, quietEnd, timezone = 'UTC') {
  const now = new Date();

  // Parse quiet hours times
  const [startHour, startMin] = quietStart.split(':').map(Number);
  const [endHour, endMin] = quietEnd.split(':').map(Number);

  // Get current time in user's timezone
  const formatter = new Intl.DateTimeFormat('en-US', {
    hour: '2-digit',
    minute: '2-digit',
    hour12: false,
    timeZone: timezone
  });

  const timeStr = formatter.format(now);
  const [currentHour, currentMin] = timeStr.split(':').map(Number);

  // Convert to minutes since midnight for easier comparison
  const currentMinutes = currentHour * 60 + currentMin;
  const startMinutes = startHour * 60 + startMin;
  const endMinutes = endHour * 60 + endMin;

  // Handle overnight quiet hours (e.g., 22:00 - 07:00)
  if (startMinutes > endMinutes) {
    // Quiet hours span midnight
    return currentMinutes >= startMinutes || currentMinutes < endMinutes;
  } else {
    // Same day quiet hours
    return currentMinutes >= startMinutes && currentMinutes < endMinutes;
  }
}

/**
 * Check if notification should be sent based on user settings
 *
 * @param {Object} settings - User notification settings
 * @param {string} notificationType - Type of notification
 * @returns {Object} { allowed: boolean, reason?: string }
 */
function shouldSendNotification(settings, notificationType) {
  // No settings = use defaults (allow all)
  if (!settings) {
    return { allowed: true };
  }

  // Check if push is enabled globally
  if (!settings.push_enabled) {
    return { allowed: false, reason: 'push_disabled' };
  }

  // System notifications always go through
  if (notificationType === NotificationType.SYSTEM) {
    return { allowed: true };
  }

  // Check specific notification type
  switch (notificationType) {
    case NotificationType.EMERGENCY:
      if (!settings.emergency_alerts) {
        return { allowed: false, reason: 'emergency_alerts_disabled' };
      }
      // Emergency alerts bypass quiet hours
      return { allowed: true };

    case NotificationType.ACTIVITY:
      if (!settings.activity_alerts) {
        return { allowed: false, reason: 'activity_alerts_disabled' };
      }
      break;

    case NotificationType.LOW_BATTERY:
      if (!settings.low_battery) {
        return { allowed: false, reason: 'low_battery_disabled' };
      }
      break;

    case NotificationType.DAILY_SUMMARY:
      if (!settings.daily_summary) {
        return { allowed: false, reason: 'daily_summary_disabled' };
      }
      break;

    case NotificationType.WEEKLY_SUMMARY:
      if (!settings.weekly_summary) {
        return { allowed: false, reason: 'weekly_summary_disabled' };
      }
      break;

    default:
      // Unknown type - allow by default
      break;
  }

  // Check quiet hours (except for emergency which returns early)
  if (settings.quiet_hours_enabled) {
    const quietStart = settings.quiet_hours_start || '22:00';
    const quietEnd = settings.quiet_hours_end || '07:00';

    if (isInQuietHours(quietStart, quietEnd)) {
      return { allowed: false, reason: 'quiet_hours' };
    }
  }

  return { allowed: true };
}

/**
 * Get active push tokens for a user
 *
 * @param {number} userId - User ID
 * @returns {Promise<string[]>} Array of Expo push tokens
 */
async function getUserPushTokens(userId) {
  const { data: tokens, error } = await supabase
    .from('push_tokens')
    .select('token')
    .eq('user_id', userId)
    .eq('is_active', true);

  if (error) {
    console.error(`[Notifications] Error fetching tokens for user ${userId}:`, error);
    return [];
  }

  return tokens?.map(t => t.token) || [];
}

/**
 * Get notification settings for a user
 *
 * @param {number} userId - User ID
 * @returns {Promise<Object|null>} Settings object or null
 */
async function getUserNotificationSettings(userId) {
  const { data: settings, error } = await supabase
    .from('notification_settings')
    .select('*')
    .eq('user_id', userId)
    .single();

  if (error && error.code !== 'PGRST116') {
    console.error(`[Notifications] Error fetching settings for user ${userId}:`, error);
  }

  return settings || null;
}

/**
 * Log notification to history table
 *
 * @param {Object} entry - Notification history entry
 * @returns {Promise<number|null>} Inserted record ID or null on error
 */
async function logNotificationHistory(entry) {
  try {
    const { data, error } = await supabase
      .from('notification_history')
      .insert({
        user_id: entry.userId,
        beneficiary_id: entry.beneficiaryId || null,
        title: entry.title,
        body: entry.body,
        type: entry.type,
        channel: entry.channel || 'push',
        status: entry.status,
        skip_reason: entry.skipReason || null,
        data: entry.data || null,
        expo_ticket_id: entry.expoTicketId || null,
        error_message: entry.errorMessage || null,
        sent_at: entry.status === 'sent' ? new Date().toISOString() : null
      })
      .select('id')
      .single();

    if (error) {
      console.error('[Notifications] Failed to log history:', error);
      return null;
    }

    return data?.id || null;
  } catch (err) {
    console.error('[Notifications] Error logging history:', err);
    return null;
  }
}

/**
 * Update notification history record
 *
 * @param {number} id - History record ID
 * @param {Object} updates - Fields to update
 */
async function updateNotificationHistory(id, updates) {
  if (!id) return;

  try {
    await supabase
      .from('notification_history')
      .update(updates)
      .eq('id', id);
  } catch (err) {
    console.error('[Notifications] Error updating history:', err);
  }
}

/**
 * Send push notifications to Expo API
 *
 * @param {Object[]} messages - Array of Expo push messages
 * @returns {Promise<Object>} Result with tickets
 */
async function sendToExpo(messages) {
  if (!messages || messages.length === 0) {
    return { success: true, tickets: [] };
  }

  try {
    const response = await fetch(EXPO_PUSH_URL, {
      method: 'POST',
      headers: {
        'Accept': 'application/json',
        'Accept-encoding': 'gzip, deflate',
        'Content-Type': 'application/json',
      },
      body: JSON.stringify(messages),
    });

    const result = await response.json();

    if (!response.ok) {
      console.error('[Notifications] Expo API error:', result);
      return { success: false, error: result };
    }

    return { success: true, tickets: result.data || [] };
  } catch (error) {
    console.error('[Notifications] Failed to send to Expo:', error);
    return { success: false, error: error.message };
  }
}

/**
 * Send push notifications to one or more users
 *
 * @param {Object} options
 * @param {number|number[]} options.userIds - User ID(s) to send to
 * @param {string} options.title - Notification title
 * @param {string} options.body - Notification body text
 * @param {string} options.type - Notification type (see NotificationType)
 * @param {Object} [options.data] - Custom data payload
 * @param {string} [options.sound] - Sound name ('default' or custom)
 * @param {string} [options.channelId] - Android channel ID
 * @param {number} [options.badge] - iOS badge count
 * @param {number} [options.ttl] - Time to live in seconds
 * @param {string} [options.priority] - 'default', 'normal', or 'high'
 * @param {number} [options.beneficiaryId] - Related beneficiary ID (for logging)
 * @returns {Promise<Object>} Result with sent count and details
 */
async function sendPushNotifications({
  userIds,
  title,
  body,
  type = NotificationType.SYSTEM,
  data = {},
  sound = 'default',
  channelId = 'default',
  badge,
  ttl = 86400, // 24 hours default
  priority = 'high',
  beneficiaryId = null
}) {
  // Normalize userIds to array
  const userIdList = Array.isArray(userIds) ? userIds : [userIds];

  console.log(`[Notifications] Sending "${type}" notification to ${userIdList.length} user(s)`);

  const results = {
    sent: 0,
    skipped: 0,
    failed: 0,
    details: []
  };

  const messagesToSend = [];
  const historyMap = new Map(); // Maps message index to history entry

  // Process each user
  for (const userId of userIdList) {
    // Get user's notification settings
    const settings = await getUserNotificationSettings(userId);

    // Check if notification should be sent
    const check = shouldSendNotification(settings, type);

    if (!check.allowed) {
      console.log(`[Notifications] Skipped user ${userId}: ${check.reason}`);
      results.skipped++;
      results.details.push({
        userId,
        status: 'skipped',
        reason: check.reason
      });

      // Log skipped notification to history
      await logNotificationHistory({
        userId,
        beneficiaryId,
        title,
        body,
        type,
        channel: 'push',
        status: 'skipped',
        skipReason: check.reason,
        data
      });

      continue;
    }

    // Get user's push tokens
    const tokens = await getUserPushTokens(userId);

    if (tokens.length === 0) {
      console.log(`[Notifications] No active tokens for user ${userId}`);
      results.skipped++;
      results.details.push({
        userId,
        status: 'skipped',
        reason: 'no_tokens'
      });

      // Log skipped notification to history
      await logNotificationHistory({
        userId,
        beneficiaryId,
        title,
        body,
        type,
        channel: 'push',
        status: 'skipped',
        skipReason: 'no_tokens',
        data
      });

      continue;
    }

    // Create message for each token
    for (const token of tokens) {
      // Validate Expo push token format
      if (!token.startsWith('ExponentPushToken[') && !token.startsWith('ExpoPushToken[')) {
        console.warn(`[Notifications] Invalid token format for user ${userId}: ${token.substring(0, 20)}...`);
        continue;
      }

      const messageIndex = messagesToSend.length;
      messagesToSend.push({
        to: token,
        title,
        body,
        sound,
        channelId,
        badge,
        ttl,
        priority,
        data: {
          ...data,
          type,
          userId,
          timestamp: new Date().toISOString()
        }
      });

      // Store history entry info for later update
      historyMap.set(messageIndex, {
        userId,
        beneficiaryId,
        title,
        body,
        type,
        data
      });
    }

    results.details.push({
      userId,
      status: 'queued',
      tokenCount: tokens.length
    });
  }

  // Send all messages in batch
  if (messagesToSend.length > 0) {
    // Expo recommends batches of 100
    const batchSize = 100;
    const batches = [];

    for (let i = 0; i < messagesToSend.length; i += batchSize) {
      batches.push({
        messages: messagesToSend.slice(i, i + batchSize),
        startIndex: i
      });
    }

    for (const batch of batches) {
      const result = await sendToExpo(batch.messages);

      if (result.success) {
        results.sent += batch.messages.length;

        // Log successful notifications and track any failed tickets
        for (let i = 0; i < result.tickets.length; i++) {
          const ticket = result.tickets[i];
          const globalIndex = batch.startIndex + i;
          const historyEntry = historyMap.get(globalIndex);

          if (historyEntry) {
            if (ticket.status === 'error') {
              console.error(`[Notifications] Ticket error:`, ticket);
              results.failed++;
              results.sent--;

              // Log failed notification
              await logNotificationHistory({
                ...historyEntry,
                channel: 'push',
                status: 'failed',
                errorMessage: ticket.message || 'Expo ticket error',
                expoTicketId: ticket.id
              });
            } else {
              // Log successful notification
              await logNotificationHistory({
                ...historyEntry,
                channel: 'push',
                status: 'sent',
                expoTicketId: ticket.id
              });
            }
          }
        }
      } else {
        results.failed += batch.messages.length;
        console.error(`[Notifications] Batch send failed:`, result.error);

        // Log failed notifications for the batch
        for (let i = 0; i < batch.messages.length; i++) {
          const globalIndex = batch.startIndex + i;
          const historyEntry = historyMap.get(globalIndex);

          if (historyEntry) {
            await logNotificationHistory({
              ...historyEntry,
              channel: 'push',
              status: 'failed',
              errorMessage: typeof result.error === 'string' ? result.error : JSON.stringify(result.error)
            });
          }
        }
      }
    }
  }

  console.log(`[Notifications] Complete: ${results.sent} sent, ${results.skipped} skipped, ${results.failed} failed`);

  return results;
}

/**
 * Send notification to all caretakers of a beneficiary
 *
 * @param {number} beneficiaryId - Beneficiary user ID
 * @param {Object} notification - Notification options (title, body, type, data)
 * @returns {Promise<Object>} Result
 */
async function notifyCaretakers(beneficiaryId, notification) {
  // Get all users with access to this beneficiary
  const { data: accessRecords, error } = await supabase
    .from('user_access')
    .select('accessor_id')
    .eq('beneficiary_id', beneficiaryId);

  if (error) {
    console.error(`[Notifications] Error fetching caretakers for beneficiary ${beneficiaryId}:`, error);
    return { error: error.message };
  }

  if (!accessRecords || accessRecords.length === 0) {
    console.log(`[Notifications] No caretakers found for beneficiary ${beneficiaryId}`);
    return { sent: 0, skipped: 0, failed: 0 };
  }

  const caretakerIds = accessRecords.map(r => r.accessor_id);

  return sendPushNotifications({
    userIds: caretakerIds,
    beneficiaryId,
    ...notification
  });
}

/**
 * Get notification history for a user
 *
 * @param {number} userId - User ID
 * @param {Object} options - Query options
 * @param {number} [options.limit=50] - Max records to return
 * @param {number} [options.offset=0] - Pagination offset
 * @param {string} [options.type] - Filter by notification type
 * @param {string} [options.status] - Filter by status
 * @returns {Promise<Object>} { data: [], total: number }
 */
async function getNotificationHistory(userId, options = {}) {
  const {
    limit = 50,
    offset = 0,
    type,
    status
  } = options;

  let query = supabase
    .from('notification_history')
    .select('*', { count: 'exact' })
    .eq('user_id', userId)
    .order('created_at', { ascending: false })
    .range(offset, offset + limit - 1);

  if (type) {
    query = query.eq('type', type);
  }

  if (status) {
    query = query.eq('status', status);
  }

  const { data, error, count } = await query;

  if (error) {
    console.error(`[Notifications] Error fetching history for user ${userId}:`, error);
    return { data: [], total: 0, error: error.message };
  }

  return { data: data || [], total: count || 0 };
}

module.exports = {
  sendPushNotifications,
  notifyCaretakers,
  getNotificationHistory,
  NotificationType,
  // Exported for testing
  shouldSendNotification,
  isInQuietHours,
  logNotificationHistory
};