import { Injectable, Logger } from '@nestjs/common';
import { PrismaService } from '../../database/prisma.service';

export interface SimulationScenario {
  priceChangePercent: number; // e.g., -10 for 10% discount
  competitorPriceChangePercent: number; // e.g., -5 for competitor drop
  marketTrendPercent: number; // e.g., +5 for seasonal growth
  productId?: string;
}

export interface SimulationResult {
  currentMonthlyRevenue: number;
  projectedMonthlyRevenue: number;
  revenueChangePercent: number;
  currentMonthlyOrders: number;
  projectedMonthlyOrders: number;
  orderChangePercent: number;
  confidenceScore: number;
  insights: string[];
}

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

  constructor(private prisma: PrismaService) {}

  /**
   * Simulates a market scenario and returns projected metrics
   */
  async runSimulation(
    tenantId: string,
    scenario: SimulationScenario,
  ): Promise<SimulationResult> {
    this.logger.log(`Running what-if simulation for tenant ${tenantId}`);

    // 1. Get current baseline (simplified for demo)
    const thirtyDaysAgo = new Date();
    thirtyDaysAgo.setDate(thirtyDaysAgo.getDate() - 30);

    const products = await this.prisma.product.findMany({
      where: {
        tenantId,
        ...(scenario.productId ? { id: scenario.productId } : {}),
      },
      include: {
        orderItems: {
          where: { order: { orderDate: { gte: thirtyDaysAgo } } },
        },
      },
    });

    let currentMonthlyRevenue = 0;
    let currentMonthlyOrders = 0;

    products.forEach((p) => {
      currentMonthlyRevenue +=
        Number(p.price) * p.orderItems.reduce((s, i) => s + i.quantity, 0);
      currentMonthlyOrders += p.orderItems.reduce((s, i) => s + i.quantity, 0);
    });

    // Dummy data for baseline if store is empty
    if (currentMonthlyRevenue === 0) {
      currentMonthlyRevenue = 150000;
      currentMonthlyOrders = 450;
    }

    // 2. Perform Scenario Calculations (Basic Elasticity Model)
    // Price Elasticity: Typically -2.0 for e-commerce (1% price drop = 2% volume increase)
    const elasticity = -2.0;

    // Impact of our price change
    const priceImpactOnVolume =
      (scenario.priceChangePercent / 100) * elasticity;

    // Impact of competitor price change (Cross-price elasticity)
    const competitorImpactOnVolume =
      (scenario.competitorPriceChangePercent / 100) * 1.2;

    // General Market Trend
    const marketImpactOnVolume = scenario.marketTrendPercent / 100;

    // Combined Volume Impact
    const totalVolumeMultiplier =
      1 + priceImpactOnVolume - competitorImpactOnVolume + marketImpactOnVolume;

    // Calculate Projected Results
    const projectedMonthlyOrders = Math.round(
      currentMonthlyOrders * totalVolumeMultiplier,
    );
    const avgPrice = currentMonthlyRevenue / (currentMonthlyOrders || 1);
    const newAvgPrice = avgPrice * (1 + scenario.priceChangePercent / 100);
    const projectedMonthlyRevenue = Math.round(
      projectedMonthlyOrders * newAvgPrice,
    );

    // 3. Generate Insights
    const insights: string[] = [];
    if (projectedMonthlyRevenue > currentMonthlyRevenue) {
      insights.push(
        'Yüksek hacim artışı fiyat indirimini telafi ediyor ve ciroda artış öngörülüyor.',
      );
    } else if (scenario.priceChangePercent < 0) {
      insights.push(
        'İndirim beklenen hacim artışını getirmeyebilir, karlılık riski mevcut.',
      );
    }

    if (scenario.competitorPriceChangePercent < 0) {
      insights.push(
        'Rakip fiyat kırılımı pazar payınızı %' +
          Math.abs(competitorImpactOnVolume * 10).toFixed(1) +
          ' oranında düşürebilir.',
      );
    }

    return {
      currentMonthlyRevenue,
      projectedMonthlyRevenue,
      revenueChangePercent: Number(
        (
          ((projectedMonthlyRevenue - currentMonthlyRevenue) /
            currentMonthlyRevenue) *
          100
        ).toFixed(2),
      ),
      currentMonthlyOrders,
      projectedMonthlyOrders,
      orderChangePercent: Number(
        (
          ((projectedMonthlyOrders - currentMonthlyOrders) /
            currentMonthlyOrders) *
          100
        ).toFixed(2),
      ),
      confidenceScore: 0.85,
      insights,
    };
  }
}