// Alert Service
// Sends alerts for critical events and risk violations

import { logger } from '@/infrastructure/monitoring/logger';
import { metricsService } from './metrics.service';

export enum AlertSeverity {
  LOW = 'low',
  MEDIUM = 'medium',
  HIGH = 'high',
  CRITICAL = 'critical',
}

export interface Alert {
  severity: AlertSeverity;
  message: string;
  dealId?: string;
  violationType?: string;
  metadata?: Record<string, any>;
  timestamp: Date;
}

export class AlertService {
  private alertChannels: AlertChannel[] = [];

  constructor() {
    // Initialize alert channels based on environment
    if (process.env.SLACK_WEBHOOK_URL) {
      this.alertChannels.push(new SlackAlertChannel(process.env.SLACK_WEBHOOK_URL));
    }
    
    if (process.env.PAGERDUTY_INTEGRATION_KEY) {
      this.alertChannels.push(new PagerDutyAlertChannel(process.env.PAGERDUTY_INTEGRATION_KEY));
    }
    
    if (process.env.EMAIL_ALERT_RECIPIENTS) {
      this.alertChannels.push(new EmailAlertChannel(process.env.EMAIL_ALERT_RECIPIENTS.split(',')));
    }
  }

  /**
   * Send alert
   */
  async sendAlert(alert: Alert): Promise<void> {
    logger.error('Alert triggered', {
      severity: alert.severity,
      message: alert.message,
      dealId: alert.dealId,
      violationType: alert.violationType,
    });

    // Record in metrics
    if (alert.violationType) {
      metricsService.recordRiskViolation(alert.violationType, alert.severity);
    }

    // Send to all channels
    const promises = this.alertChannels.map(channel => 
      channel.send(alert).catch(err => {
        logger.error('Failed to send alert via channel', {
          channel: channel.constructor.name,
          error: err instanceof Error ? err.message : 'Unknown error',
        });
      })
    );

    await Promise.allSettled(promises);
  }

  /**
   * Alert on risk violation
   */
  async alertRiskViolation(
    violationType: string,
    message: string,
    dealId?: string,
    severity: AlertSeverity = AlertSeverity.HIGH
  ): Promise<void> {
    await this.sendAlert({
      severity,
      message: `Risk Violation: ${message}`,
      dealId,
      violationType,
      timestamp: new Date(),
    });
  }

  /**
   * Alert on LTV threshold
   */
  async alertLtvThreshold(dealId: string, currentLtv: number, maxLtv: number): Promise<void> {
    const percentage = (currentLtv / maxLtv) * 100;
    let severity = AlertSeverity.MEDIUM;
    
    if (percentage >= 95) {
      severity = AlertSeverity.CRITICAL;
    } else if (percentage >= 85) {
      severity = AlertSeverity.HIGH;
    }

    await this.alertRiskViolation(
      'ltv_threshold',
      `LTV at ${(currentLtv * 100).toFixed(2)}% (${percentage.toFixed(1)}% of max ${(maxLtv * 100).toFixed(2)}%)`,
      dealId,
      severity
    );
  }

  /**
   * Alert on USDTz exposure
   */
  async alertUsdtzExposure(dealId: string, exposure: number, maxExposure: number): Promise<void> {
    const percentage = (exposure / maxExposure) * 100;
    let severity = AlertSeverity.MEDIUM;
    
    if (percentage >= 95) {
      severity = AlertSeverity.CRITICAL;
    } else if (percentage >= 85) {
      severity = AlertSeverity.HIGH;
    }

    await this.alertRiskViolation(
      'usdtz_exposure',
      `USDTz exposure at $${exposure.toFixed(2)} (${percentage.toFixed(1)}% of max $${maxExposure.toFixed(2)})`,
      dealId,
      severity
    );
  }

  /**
   * Alert on deal failure
   */
  async alertDealFailure(dealId: string, error: string, step?: string): Promise<void> {
    await this.sendAlert({
      severity: AlertSeverity.HIGH,
      message: `Deal execution failed: ${error}`,
      dealId,
      metadata: { step },
      timestamp: new Date(),
    });
  }

  /**
   * Alert on system error
   */
  async alertSystemError(error: string, metadata?: Record<string, any>): Promise<void> {
    await this.sendAlert({
      severity: AlertSeverity.CRITICAL,
      message: `System error: ${error}`,
      metadata,
      timestamp: new Date(),
    });
  }
}

// Alert Channel Interfaces
interface AlertChannel {
  send(alert: Alert): Promise<void>;
}

class SlackAlertChannel implements AlertChannel {
  constructor(private webhookUrl: string) {}

  async send(alert: Alert): Promise<void> {
    const color = {
      [AlertSeverity.LOW]: '#36a64f',
      [AlertSeverity.MEDIUM]: '#ffa500',
      [AlertSeverity.HIGH]: '#ff6600',
      [AlertSeverity.CRITICAL]: '#ff0000',
    }[alert.severity];

    const fields: Array<{ title: string; value: string; short: boolean }> = [
      ...(alert.dealId ? [{ title: 'Deal ID', value: alert.dealId, short: true }] : []),
      ...(alert.violationType ? [{ title: 'Violation Type', value: alert.violationType, short: true }] : []),
      { title: 'Timestamp', value: alert.timestamp.toISOString(), short: true },
      ...(alert.metadata ? Object.entries(alert.metadata).map(([k, v]) => ({ title: k, value: String(v), short: true })) : []),
    ];

    const payload = {
      attachments: [{ color, title: `Arbitrage Alert: ${alert.severity.toUpperCase()}`, text: alert.message, fields }],
    };

    try {
      const res = await fetch(this.webhookUrl, {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify(payload),
      });
      if (!res.ok) throw new Error(`Slack webhook failed: ${res.status}`);
    } catch (err) {
      logger.error('Slack alert delivery failed', { error: err instanceof Error ? err.message : err });
    }
  }
}

class PagerDutyAlertChannel implements AlertChannel {
  constructor(private integrationKey: string) {}

  async send(alert: Alert): Promise<void> {
    const severity = {
      [AlertSeverity.LOW]: 'info',
      [AlertSeverity.MEDIUM]: 'warning',
      [AlertSeverity.HIGH]: 'error',
      [AlertSeverity.CRITICAL]: 'critical',
    }[alert.severity];

    const payload = {
      routing_key: this.integrationKey,
      event_action: 'trigger',
      payload: {
        summary: alert.message,
        severity,
        source: 'arbitrage-service',
        custom_details: {
          dealId: alert.dealId,
          violationType: alert.violationType,
          ...alert.metadata,
        },
      },
    };

    try {
      const res = await fetch('https://events.pagerduty.com/v2/enqueue', {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify(payload),
      });
      if (!res.ok) {
        const text = await res.text();
        throw new Error(`PagerDuty API ${res.status}: ${text}`);
      }
    } catch (err) {
      logger.error('PagerDuty alert delivery failed', {
        error: err instanceof Error ? err.message : String(err),
      });
    }
  }
}

class EmailAlertChannel implements AlertChannel {
  constructor(private recipients: string[]) {}

  async send(alert: Alert): Promise<void> {
    if (alert.severity !== AlertSeverity.CRITICAL && alert.severity !== AlertSeverity.HIGH) {
      return;
    }

    const emailApiUrl = process.env.EMAIL_ALERT_API_URL;
    if (!emailApiUrl) {
      logger.warn('Email alert skipped: Set EMAIL_ALERT_API_URL (e.g. SendGrid) to enable');
      return;
    }

    try {
      const res = await fetch(emailApiUrl, {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({
          to: this.recipients,
          subject: `[${alert.severity.toUpperCase()}] Arbitrage Alert`,
          text: alert.message,
          html: `<p>${alert.message}</p><p>Deal ID: ${alert.dealId || 'N/A'}</p>`,
        }),
      });
      if (!res.ok) throw new Error(`Email API failed: ${res.status}`);
    } catch (err) {
      logger.error('Email alert delivery failed', { error: err instanceof Error ? err.message : err });
    }
  }
}

export const alertService = new AlertService();