import { Injectable, Logger } from "@nestjs/common";
import { ConfigService } from "@nestjs/config";
import { Cron, CronExpression } from "@nestjs/schedule";
import { PrismaService } from "../database/prisma.service";
import { EmailService } from "../email/email.service";
import { CarePriority } from "../care-priority/types/care-priority.types";
import { NotificationType, NotificationPriority } from "@prisma/client";
import type { ExpoPushMessage } from "expo-server-sdk";
import {
  CARE_PRIORITY_TEMPLATES,
  BP_ALERT_TEMPLATES,
  SYMPTOM_ALERT_TEMPLATES,
  AUTH_TEMPLATES,
  MONITORING_TEMPLATES,
  TREND_ALERT_TEMPLATES,
} from "./templates/notification.templates";
import { generateEmailHtml } from "./templates/email.template";

/**
 * Notification Service
 *
 * RESPONSIBILITIES:
 * - Send care priority escalation notifications
 * - Send BP alert notifications
 * - Send symptom alert notifications
 * - Log all notifications for audit trail
 * - Persist notifications to database
 * - Send push notifications via Expo
 * - Background monitoring (Inactivity, Daily reminders, Trends, Follow-ups)
 */
@Injectable()
export class NotificationsService {
  private readonly logger = new Logger(NotificationsService.name);
  private expoInstance: any = null;

  constructor(
    private readonly prisma: PrismaService,
    private readonly emailService: EmailService,
    private readonly configService: ConfigService,
  ) {}

  /**
   * Helper to get Expo instance dynamically (fixes ERR_REQUIRE_ESM)
   */
  private async getExpo() {
    if (!this.expoInstance) {
      const { Expo } = await import("expo-server-sdk");
      this.expoInstance = new Expo();
    }
    return this.expoInstance;
  }

  private async getLatestBPDate(userId: string): Promise<Date | null> {
    const latest = await this.prisma.bloodPressureReading.findFirst({
      where: { userId },
      orderBy: { recordedAt: "desc" },
      select: { recordedAt: true },
    });
    return latest?.recordedAt || null;
  }

  private async hasLoggedBPSince(userId: string, cutoff: Date): Promise<boolean> {
    const latest = await this.getLatestBPDate(userId);
    return Boolean(latest && latest >= cutoff);
  }

  /**
   * Helper to get user's email
   */
  private async getUserEmail(userId: string): Promise<string | null> {
    const user = await this.prisma.userAuth.findUnique({
      where: { id: userId },
      select: { email: true },
    });
    return user?.email || null;
  }

  /**
   * Internal helper to send push notifications
   */
  public async sendPushNotification(
    userId: string,
    title: string,
    body: string,
    data?: any,
  ): Promise<void> {
    const user = await this.prisma.userAuth.findUnique({
      where: { id: userId },
      select: { pushToken: true },
    });

    if (!user?.pushToken) {
      this.logger.debug(
        `No push token found for user ${userId}, skipping push.`,
      );
      return;
    }

    const { Expo } = await import("expo-server-sdk");
    if (!Expo.isExpoPushToken(user.pushToken)) {
      this.logger.error(
        `Push token ${user.pushToken} is not a valid Expo push token`,
      );
      return;
    }

    const messages: ExpoPushMessage[] = [
      {
        to: user.pushToken,
        sound: "default",
        title,
        body,
        data,
      },
    ];

    try {
      const expo = await this.getExpo();
      const chunks = expo.chunkPushNotifications(messages);
      for (const chunk of chunks) {
        const tickets = await expo.sendPushNotificationsAsync(chunk);
        this.logger.log(
          `Push notification tickets for user ${userId}: ${JSON.stringify(tickets)}`,
        );
      }
      this.logger.log(`Push notification sent to user ${userId}`);
    } catch (error) {
      this.logger.error(
        `Error sending push notification to user ${userId}:`,
        error,
      );
    }
  }

  /**
   * Daily BP Reminder Monitor
   * Runs every minute to check which users should be reminded
   */
  @Cron(CronExpression.EVERY_MINUTE)
  async checkDailyReminders() {
    const now = new Date();
    const hours = now.getHours().toString().padStart(2, "0");
    const minutes = now.getMinutes().toString().padStart(2, "0");
    const currentHHmm = `${hours}:${minutes}`;

    const today = new Date();
    today.setHours(0, 0, 0, 0);

    // Find users who:
    // 1. Have reminders enabled
    // 2. Their reminderTime matches current time
    // 3. Haven't logged BP today
    const usersToRemind = await this.prisma.userAuth.findMany({
      where: {
        isActive: true,
        profile: {
          notifyReminders: true,
          reminderTime: currentHHmm,
        },
        bloodPressureReadings: {
          none: {
            recordedAt: { gte: today },
          },
        },
      },
      select: { id: true, email: true },
    });

    if (usersToRemind.length > 0) {
      this.logger.log(
        `[REMINDER] Sending daily BP reminders to ${usersToRemind.length} users for time ${currentHHmm}`,
      );
    }

    for (const user of usersToRemind) {
      try {
        if (await this.hasLoggedBPSince(user.id, today)) continue;
        const template = MONITORING_TEMPLATES.DAILY_REMINDER;
        await this.prisma.notification.create({
          data: {
            userId: user.id,
            type: NotificationType.REMINDER,
            title: template.subject,
            message: template.body,
          },
        });

        await this.sendPushNotification(
          user.id,
          template.subject,
          template.body,
          { type: "BP_REMINDER" },
        );
      } catch (error) {
        this.logger.error(
          `Failed to send daily reminder to user ${user.id}:`,
          error,
        );
      }
    }
  }

  /**
   * Inactivity Monitor - Checks for users who haven't logged BP in 3 days or more
   * Runs daily at midnight
   */
  @Cron(CronExpression.EVERY_DAY_AT_MIDNIGHT)
  async checkInactivity() {
    this.logger.log("Running inactivity check...");
    const threeDaysAgo = new Date();
    threeDaysAgo.setDate(threeDaysAgo.getDate() - 3);

    // Find users whose last reading was > 3 days ago or who never logged
    const users = await this.prisma.userAuth.findMany({
      where: {
        isActive: true,
        bloodPressureReadings: {
          none: {
            recordedAt: { gte: threeDaysAgo },
          },
        },
      },
      select: { 
        id: true, 
        email: true, 
        bloodPressureReadings: {
          orderBy: { recordedAt: "desc" },
          take: 1,
          select: { recordedAt: true }
        },
        profile: {
          select: { createdAt: true }
        }
      },
    });

    for (const user of users) {
      try {
        if (await this.hasLoggedBPSince(user.id, threeDaysAgo)) continue;
        
        // Calculate days inactive
        const lastReading = user.bloodPressureReadings[0];
        let daysInactive: number;
        
        if (lastReading) {
          const now = new Date();
          const diffInMs = now.getTime() - lastReading.recordedAt.getTime();
          daysInactive = Math.floor(diffInMs / (1000 * 60 * 60 * 24));
        } else if (user.profile?.createdAt) {
          // Never logged, use days since profile creation
          const now = new Date();
          const diffInMs = now.getTime() - user.profile.createdAt.getTime();
          daysInactive = Math.floor(diffInMs / (1000 * 60 * 60 * 24));
        } else {
          daysInactive = 3; // Fallback
        }

        // Ensure minimum 3 days
        if (daysInactive < 3) continue;

        const template = MONITORING_TEMPLATES.INACTIVITY_REMINDER;
        const body = typeof template.body === 'function' 
          ? template.body(daysInactive) 
          : template.body;

        await this.prisma.notification.create({
          data: {
            userId: user.id,
            type: NotificationType.REMINDER,
            title: template.subject,
            message: body,
          },
        });

        // Send Push
        await this.sendPushNotification(
          user.id,
          template.subject,
          body,
          { type: "INACTIVITY_REMINDER" },
        );

        // Send Email
        if (user.email) {
          const html = generateEmailHtml(
            template.subject,
            body,
            "Log BP Reading",
            `${this.configService.get("FRONTEND_URL")}/bridge?type=inactivity-reminder`,
            "#2DE474",
          );

          await this.emailService.sendEmail(
            user.email,
            template.subject,
            body,
            html,
          );
        }
      } catch (error) {
        this.logger.error(
          `Failed to process inactivity reminder for user ${user.id}:`,
          error,
        );
      }
    }
    this.logger.log(
      `Inactivity check finished. ${users.length} users notified.`,
    );
  }

  /**
   * 4-Hour Follow-Up Monitor
   * Runs every 30 minutes
   */
  @Cron(CronExpression.EVERY_30_MINUTES)
  async checkFollowUps() {
    this.logger.log("Running follow-up recheck monitor...");
    const now = new Date();
    const fourHoursAgo = new Date(now.getTime() - 4 * 60 * 60 * 1000);
    const fiveHoursAgo = new Date(now.getTime() - 5 * 60 * 60 * 1000);

    // Find users who had an elevated reading (130/80 - 159/109) 4-5 hours ago
    // AND haven't logged since then
    const users = await this.prisma.userAuth.findMany({
      where: {
        isActive: true,
        bloodPressureReadings: {
          some: {
            recordedAt: { gte: fiveHoursAgo, lte: fourHoursAgo },
            OR: [{ systolic: { gte: 130 } }, { diastolic: { gte: 80 } }],
          },
          none: {
            recordedAt: { gt: fourHoursAgo },
          },
        },
      },
      select: { id: true, email: true },
    });

    for (const user of users) {
      try {
        if (await this.hasLoggedBPSince(user.id, fourHoursAgo)) continue;
        const template = MONITORING_TEMPLATES.FOLLOW_UP_REMINDER;
        await this.prisma.notification.create({
          data: {
            userId: user.id,
            type: NotificationType.REMINDER,
            title: template.subject,
            message: template.body,
          },
        });

        // Send Push
        await this.sendPushNotification(
          user.id,
          template.subject,
          template.body,
          { type: "FOLLOW_UP" },
        );

        // Send Email
        if (user.email) {
          const html = generateEmailHtml(
            template.subject,
            template.body,
            "Recheck BP Now",
            `${this.configService.get("FRONTEND_URL")}/bridge?type=follow-up-recheck`,
            "#FF9B3E",
          );

          await this.emailService.sendEmail(
            user.email,
            template.subject,
            template.body,
            html,
          );
        }
      } catch (error) {
        this.logger.error(
          `Failed to process follow-up reminder for user ${user.id}:`,
          error,
        );
      }
    }
  }

  /**
   * Trend Analysis Monitor - Analyzes 7 days of readings for patterns
   * Runs every day at 1 AM
   */
  @Cron(CronExpression.EVERY_DAY_AT_1AM)
  async analyzeTrends() {
    this.logger.log("Running trend analysis...");
    const sevenDaysAgo = new Date();
    sevenDaysAgo.setDate(sevenDaysAgo.getDate() - 7);

    const users = await this.prisma.userAuth.findMany({
      where: { isActive: true },
      select: { id: true, email: true },
    });

    for (const user of users) {
      try {
        const readings = await this.prisma.bloodPressureReading.findMany({
          where: {
            userId: user.id,
            recordedAt: { gte: sevenDaysAgo },
          },
          orderBy: { recordedAt: "asc" },
        });

        if (readings.length < 3) continue;

        // 1. Creeping Rise Detection (Consistent rise over 3+ readings)
        let riseCount = 0;
        for (let i = 1; i < readings.length; i++) {
          if (readings[i].systolic > readings[i - 1].systolic) riseCount++;
          else riseCount = 0;
        }
        if (riseCount >= 3) {
          await this.sendTrendAlert(
            user.id,
            TREND_ALERT_TEMPLATES.CREEPING_RISE,
            "CREEPING_RISE",
            user.email,
          );
          continue; // Don't spam multiple trend alerts
        }

        // 2. Repeated High Readings (3+ elevated readings in a week)
        const highReadings = readings.filter(
          (r) => r.systolic >= 135 || r.diastolic >= 85,
        );
        if (highReadings.length >= 3) {
          await this.sendTrendAlert(
            user.id,
            TREND_ALERT_TEMPLATES.REPEATED_HIGH,
            "REPEATED_HIGH",
            user.email,
          );
          continue;
        }

        // 3. Sudden Spike Detection (Latest reading is 20% > personal average)
        const avgSystolic =
          readings.slice(0, -1).reduce((acc, curr) => acc + curr.systolic, 0) /
          (readings.length - 1);
        const latest = readings[readings.length - 1];
        if (latest.systolic > avgSystolic * 1.2) {
          await this.sendTrendAlert(
            user.id,
            TREND_ALERT_TEMPLATES.SUDDEN_SPIKE,
            "SUDDEN_SPIKE",
            user.email,
          );
        }
      } catch (error) {
        this.logger.error(
          `Failed to analyze trends for user ${user.id}:`,
          error,
        );
      }
    }
  }

  private async sendTrendAlert(
    userId: string,
    template: any,
    trendType: string,
    email?: string | null,
  ) {
    await this.prisma.notification.create({
      data: {
        userId,
        type: NotificationType.BP_ALERT,
        title: template.subject,
        message: template.body,
      },
    });

    await this.sendPushNotification(userId, template.subject, template.body, {
      type: "TREND_ALERT",
      trendType,
    });

    if (email) {
      await this.emailService.sendTrendAlert(
        email,
        trendType,
        template.body,
        "Mama" // Default for now
      );
    }
  }

  /**
   * Send care priority escalation notification
   */
  async sendCarePriorityNotification(
    userId: string,
    priority: CarePriority,
  ): Promise<void> {
    const template = CARE_PRIORITY_TEMPLATES[priority];
    const email = await this.getUserEmail(userId);

    // Log notification
    this.logger.log(`[NOTIFICATION] User: ${userId}, Priority: ${priority}`);

    // Persist to database
    await this.prisma.notification.create({
      data: {
        userId,
        type: NotificationType.CARE_PRIORITY,
        title: template.subject,
        message: `${template.body}\n\n${template.callToAction}`,
      },
    });

    // Send email
    if (email) {
      const html = generateEmailHtml(
        template.subject,
        `${template.body}\n\n${template.callToAction}`,
        "View Details",
        `${this.configService.get("FRONTEND_URL")}/bridge?type=tracking`,
        priority === CarePriority.EMERGENCY
          ? "#FF4B4B"
          : priority === CarePriority.URGENT_REVIEW
            ? "#FF9B3E"
            : "#2DE474",
      );

      await this.emailService.sendEmail(
        email,
        template.subject,
        `${template.body}\n\n${template.callToAction}`,
        html,
      );
    }

    // Send Push
    await this.sendPushNotification(userId, template.subject, template.body, {
      type: "ESCALATION_ALERT",
      priority,
    });

    this.logger.log(`✅ Notification handled for user ${userId}`);
  }

  /**
   * Send severe BP alert
   */
  async sendSevereBPAlert(
    userId: string,
    systolic: number,
    diastolic: number,
  ): Promise<void> {
    const template = BP_ALERT_TEMPLATES.SEVERE_HYPERTENSION;
    const email = await this.getUserEmail(userId);

    this.logger.warn(
      `[ALERT] Severe BP for user ${userId}: ${systolic}/${diastolic}`,
    );

    const message = `${template.body}\nReading: ${systolic}/${diastolic}\n\n${template.callToAction}`;

    await this.prisma.notification.create({
      data: {
        userId,
        type: NotificationType.BP_ALERT,
        title: template.subject,
        message,
      },
    });

    // Send email
    if (email) {
      const html = generateEmailHtml(
        template.subject,
        message,
        "Log Now",
        `${this.configService.get("FRONTEND_URL")}/bridge?type=bp-entry`,
        "#FF4B4B",
      );

      await this.emailService.sendEmail(email, template.subject, message, html);
    }

    // Send Push
    await this.sendPushNotification(userId, template.subject, template.body, {
      type: "TREND_ALERT",
      systolic,
      diastolic,
    });

    this.logger.log(`✅ Severe BP alert handled for user ${userId}`);
  }

  /**
   * Send elevated BP notification
   */
  async sendElevatedBPNotification(
    userId: string,
    systolic: number,
    diastolic: number,
  ): Promise<void> {
    const template = BP_ALERT_TEMPLATES.ELEVATED_BP;
    const email = await this.getUserEmail(userId);

    this.logger.log(
      `[NOTIFICATION] Elevated BP for user ${userId}: ${systolic}/${diastolic}`,
    );

    const message = `${template.body}\nReading: ${systolic}/${diastolic}\n\n${template.callToAction}`;

    await this.prisma.notification.create({
      data: {
        userId,
        type: NotificationType.BP_ALERT,
        title: template.subject,
        message,
      },
    });

    // Send email
    if (email) {
      const html = generateEmailHtml(
        template.subject,
        message,
        "Log Now",
        `${this.configService.get("FRONTEND_URL")}/bridge?type=bp-entry`,
        "#FF9B3E",
      );

      await this.emailService.sendEmail(email, template.subject, message, html);
    }

    // Send Push
    await this.sendPushNotification(userId, template.subject, template.body, {
      type: "TREND_ALERT",
      systolic,
      diastolic,
    });

    this.logger.log(`✅ Elevated BP notification handled for user ${userId}`);
  }

  /**
   * Send dangerous symptom combination alert
   */
  async sendDangerousSymptomAlert(
    userId: string,
    symptoms: string[],
  ): Promise<void> {
    const template = SYMPTOM_ALERT_TEMPLATES.DANGEROUS_COMBINATION;
    const email = await this.getUserEmail(userId);

    this.logger.warn(
      `[ALERT] Dangerous symptoms for user ${userId}: ${symptoms.join(", ")}`,
    );

    const message = `${template.body}\nSymptoms reported: ${symptoms.join(", ")}\n\n${template.callToAction}`;

    await this.prisma.notification.create({
      data: {
        userId,
        type: NotificationType.SYMPTOM_ALERT,
        title: template.subject,
        message,
      },
    });

    // Send email
    if (email) {
      const html = generateEmailHtml(
        template.subject,
        message,
        "Open App",
        `${this.configService.get("FRONTEND_URL")}/bridge?type=tracking`,
        "#FF4B4B",
      );

      await this.emailService.sendEmail(email, template.subject, message, html);
    }

    // Send Push
    await this.sendPushNotification(userId, template.subject, template.body, {
      type: "TREND_ALERT",
      symptoms,
    });

    this.logger.log(`✅ Dangerous symptom alert handled for user ${userId}`);
  }

  /**
   * Send warning symptom notification
   */
  async sendWarningSymptomNotification(
    userId: string,
    symptom: string,
  ): Promise<void> {
    const template = SYMPTOM_ALERT_TEMPLATES.SINGLE_WARNING_SYMPTOM;
    const email = await this.getUserEmail(userId);

    this.logger.log(
      `[NOTIFICATION] Warning symptom for user ${userId}: ${symptom}`,
    );

    const message = `${template.body}\nSymptom reported: ${symptom}\n\n${template.callToAction}`;

    await this.prisma.notification.create({
      data: {
        userId,
        type: NotificationType.SYMPTOM_ALERT,
        title: template.subject,
        message,
      },
    });

    // Send email
    if (email) {
      const html = generateEmailHtml(
        template.subject,
        message,
        "Open App",
        `${this.configService.get("FRONTEND_URL")}/bridge?type=tracking`,
        "#FF9B3E",
      );

      await this.emailService.sendEmail(email, template.subject, message, html);
    }

    // Send Push
    await this.sendPushNotification(userId, template.subject, template.body, {
      type: "TREND_ALERT",
      symptom,
    });

    this.logger.log(
      `✅ Warning symptom notification handled for user ${userId}`,
    );
  }

  /**
   * Send reset password notification
   *
   */
  async sendResetPasswordNotification(
  userId: string,
  token: string,
): Promise<void> {
  const email = await this.getUserEmail(userId);

  this.logger.log(
    `[AUTH] Reset password request for user ${userId}. Email: ${email || 'N/A'}`,
  );

  // Store in database
  await this.prisma.notification.create({
    data: {
      userId,
      type: NotificationType.REMINDER,
      title: 'Reset your MaternAlert password',
      message: 'A password reset link has been sent to your email.',
    },
  });

  // Send email if user has one using our new template
  if (email) {
    await this.emailService.sendPasswordReset(email, token);
  }

  // Push notification — tapping it opens the login screen
  await this.sendPushNotification(
    userId,
    'Reset your MaternAlert password',
    'Tap to open MaternAlert and follow the link in your email.',
    { type: 'SESSION_EXPIRY' },
  );

  this.logger.log(
    `✅ Reset password notification handled for user ${userId}`,
  );
}

  /**
   * Register push token for user
   */
  async registerPushToken(userId: string, pushToken: string) {
    this.logger.log(`Registering push token for user ${userId}`);
    return this.prisma.userAuth.update({
      where: { id: userId },
      data: { pushToken },
    });
  }

  /**
   * Get notification history for user
   */
  async getNotificationHistory(userId: string) {
    this.logger.log(`Fetching notification history for user ${userId}`);
    return this.prisma.notification.findMany({
      where: { userId },
      orderBy: { createdAt: "desc" },
    });
  }

  /**
   * Mark notification as read
   */
  async markAsRead(notificationId: string, userId: string) {
    const notification = await this.prisma.notification.findUnique({
      where: { id: notificationId },
    });

    if (!notification || notification.userId !== userId) {
      throw new Error("Notification not found or access denied");
    }

    return this.prisma.notification.update({
      where: { id: notificationId },
      data: { read: true },
    });
  }
}