import { Injectable, BadRequestException, Logger } from '@nestjs/common';
import { ConfigService } from '@nestjs/config';
import { RestaurantPaymentMethod } from '../entities/restaurant-payment-method.entity';
import { Order } from '../../orders/entities/order.entity';

export interface PaymentGatewayRedirect {
  redirectUrl: string;
  orderId: string;
}

@Injectable()
export class PaymentGatewayService {
  private readonly logger = new Logger(PaymentGatewayService.name);

  constructor(private readonly configService: ConfigService) {}

  /**
   * Generate payment gateway redirect URL for online payment methods
   */
  generateRedirectUrl(order: Order, restaurantPaymentMethod: RestaurantPaymentMethod): Promise<PaymentGatewayRedirect> {
    const paymentMethod = restaurantPaymentMethod.paymentMethod;

    if (!paymentMethod.isOnline) {
      throw new BadRequestException('Payment method is not online');
    }

    // Get base URL for callback
    const baseUrl = this.configService.get<string>('APP_BASE_URL') || 'http://localhost:4000';
    const callbackUrl = paymentMethod.callbackUrl || `${baseUrl}/public/payments/callback`;

    // Generate payment gateway URL based on payment method keyName
    const redirectUrl = this.generateGatewayUrl(paymentMethod.keyName, {
      orderId: order.id,
      amount: order.total,
      merchantId: restaurantPaymentMethod.merchantId,
      callbackUrl,
      description: `Order #${order.id}`,
    });

    return {
      redirectUrl,
      orderId: order.id,
    };
  }

  /**
   * Generate gateway URL based on payment provider
   * This can be extended to support multiple payment gateways (ZarinPal, Mellat, etc.)
   */
  private generateGatewayUrl(
    paymentMethodKey: string,
    params: {
      orderId: string;
      amount: number;
      merchantId?: string;
      callbackUrl: string;
      description: string;
    },
  ) {
    // Convert amount to smallest currency unit (e.g., Toman to Rials for Iranian gateways)
    const amountInSmallestUnit = Math.round(params.amount * 10); // Assuming Toman to Rials conversion

    switch (paymentMethodKey.toLowerCase()) {
      case 'zarinpal':
        return this.generateZarinPalUrl(params, amountInSmallestUnit);

      case 'mellat':
      case 'bankmellat':
        return this.generateMellatUrl(params, amountInSmallestUnit);

      default:
        // Generic payment gateway URL structure
        // You can customize this based on your payment gateway provider
        this.logger.warn(`Unknown payment method: ${paymentMethodKey}, using generic URL structure`);
        return this.generateGenericGatewayUrl(params, amountInSmallestUnit);
    }
  }

  /**
   * Generate ZarinPal payment gateway URL
   */
  private generateZarinPalUrl(
    params: {
      orderId: string;
      merchantId?: string;
      callbackUrl: string;
      description: string;
    },
    amount: number,
  ): string {
    if (!params.merchantId) {
      throw new BadRequestException('Merchant ID is required for ZarinPal payment gateway');
    }

    // ZarinPal payment gateway URL structure
    // This is a simplified version - you may need to make an API call to get the actual redirect URL
    const zarinPalBaseUrl =
      this.configService.get<string>('ZARINPAL_BASE_URL') || 'https://www.zarinpal.com/pg/StartPay';

    // For ZarinPal, you typically need to:
    // 1. Call their API to create a payment request
    // 2. Get an Authority token
    // 3. Redirect to their payment page with the Authority

    // For now, returning a placeholder URL structure
    // TODO: Implement actual ZarinPal API integration
    return `${zarinPalBaseUrl}/${params.orderId}?Amount=${amount}&MerchantID=${params.merchantId}&CallbackURL=${encodeURIComponent(params.callbackUrl)}&Description=${encodeURIComponent(params.description)}`;
  }

  /**
   * Generate Bank Mellat payment gateway URL
   */
  private generateMellatUrl(
    params: {
      orderId: string;
      merchantId?: string;
      callbackUrl: string;
      description: string;
    },
    amount: number,
  ): string {
    if (!params.merchantId) {
      throw new BadRequestException('Merchant ID is required for Mellat payment gateway');
    }

    const mellatBaseUrl =
      this.configService.get<string>('MELLAT_BASE_URL') || 'https://bpm.shaparak.ir/pgwchannel/startpay.mellat';

    // TODO: Implement actual Mellat API integration
    return `${mellatBaseUrl}?orderId=${params.orderId}&amount=${amount}&merchantId=${params.merchantId}&callbackUrl=${encodeURIComponent(params.callbackUrl)}`;
  }

  /**
   * Generate generic payment gateway URL
   */
  private generateGenericGatewayUrl(
    params: {
      orderId: string;
      merchantId?: string;
      callbackUrl: string;
      description: string;
    },
    amount: number,
  ): string {
    const genericBaseUrl =
      this.configService.get<string>('PAYMENT_GATEWAY_BASE_URL') || 'https://payment.example.com/pay';

    const queryParams = new URLSearchParams({
      orderId: params.orderId,
      amount: amount.toString(),
      callbackUrl: params.callbackUrl,
      description: params.description,
    });

    if (params.merchantId) {
      queryParams.append('merchantId', params.merchantId);
    }

    return `${genericBaseUrl}?${queryParams.toString()}`;
  }
}