Kordant/packages/shared-billing/src/services/billing.service.ts

import Stripe from 'stripe';
import { loadBillingConfig, SubscriptionTier } from '../config/billing.config';
import type { Subscription, SubscriptionCreateSchema, SubscriptionUpdateSchema } from '../models/subscription.model';

const config = loadBillingConfig();
const stripe = new Stripe(config.stripe.apiKey, { apiVersion: '2023-10-16' });

const processedEvents = new Map<string, number>();
const IDEMPOTENCY_TTL_MS = 24 * 60 * 60 * 1000;

function cleanupOldEvents(): void {
  const now = Date.now();
  for (const [eventId, timestamp] of processedEvents.entries()) {
    if (now - timestamp > IDEMPOTENCY_TTL_MS) {
      processedEvents.delete(eventId);
    }
  }
}

export class BillingService {
  private static instance: BillingService;

  private constructor() {}

  static getInstance(): BillingService {
    if (!BillingService.instance) {
      BillingService.instance = new BillingService();
    }
    return BillingService.instance;
  }

  async createCustomer(email: string, userId: string): Promise<Stripe.Customer> {
    const customer = await stripe.customers.create({
      email,
      metadata: { userId },
    });
    return customer;
  }

  async getCustomer(customerId: string): Promise<Stripe.Customer | null> {
    try {
      const customer = await stripe.customers.retrieve(customerId);
      return customer as Stripe.Customer;
    } catch {
      return null;
    }
  }

  private async verifyCustomerOwnership(
    customerId: string,
    userId: string
  ): Promise<void> {
    const customer = await stripe.customers.retrieve(customerId);
    const customerUserId = (customer as Stripe.Customer).metadata?.userId;

    if (customerUserId !== userId) {
      throw new Error(
        `Customer ${customerId} does not belong to user ${userId}`
      );
    }
  }

  async getUserTier(userId: string): Promise<SubscriptionTier | null> {
    try {
      const customers = await stripe.customers.list({
        limit: 100,
        expand: ['data.subscriptions'],
      });

      const customer = customers.data.find(
        (c: Stripe.Customer) => 
          c.metadata?.userId === userId && c.subscriptions?.data.length && c.subscriptions.data.length > 0
      );

      if (!customer || !customer.subscriptions) {
        return null;
      }

      const activeSubscription = customer.subscriptions.data.find(
        (sub: Stripe.Subscription) => sub.status === 'active'
      );

      if (!activeSubscription) {
        return null;
      }

      const tier = activeSubscription.metadata?.tier as SubscriptionTier;
      return tier || null;
    } catch {
      return null;
    }
  }

  async createSubscription(
    userId: string,
    tier: SubscriptionTier,
    customerId: string
  ): Promise<{ subscription: Stripe.Subscription; customer: Stripe.Customer }> {
    const tierConfig = config.tiers[tier];

    const customer = await this.getCustomer(customerId);
    if (!customer) {
      throw new Error(`Customer ${customerId} not found`);
    }

    await this.verifyCustomerOwnership(customerId, userId);

    const subscription = await stripe.subscriptions.create({
      customer: customerId,
      items: [{ price: tierConfig.priceId }],
      metadata: { userId, tier },
    });

    return { subscription, customer };
  }

  async cancelSubscription(
    subscriptionId: string,
    userId: string,
    cancelAtPeriodEnd: boolean = false
  ): Promise<Stripe.Subscription> {
    const subscription = await stripe.subscriptions.retrieve(subscriptionId);
    const customerUserId = subscription.metadata?.userId;

    if (customerUserId !== userId) {
      throw new Error(
        `Subscription ${subscriptionId} does not belong to user ${userId}`
      );
    }

    if (cancelAtPeriodEnd) {
      return await stripe.subscriptions.update(subscriptionId, {
        cancel_at_period_end: true,
      });
    }
    return await stripe.subscriptions.cancel(subscriptionId);
  }

  async updateSubscription(
    subscriptionId: string,
    userId: string,
    newTier: SubscriptionTier
  ): Promise<Stripe.Subscription> {
    const subscription = await stripe.subscriptions.retrieve(subscriptionId);
    const customerUserId = subscription.metadata?.userId;

    if (customerUserId !== userId) {
      throw new Error(
        `Subscription ${subscriptionId} does not belong to user ${userId}`
      );
    }

    const newTierConfig = config.tiers[newTier];
    
    // Ensure subscription has items before updating
    const firstItem = subscription.items.data[0];
    if (!firstItem?.id) {
      throw new Error(
        `Subscription ${subscriptionId} has no items to update`
      );
    }

    const updated = await stripe.subscriptions.update(subscriptionId, {
      proration_behavior: 'create_prorations',
      items: [
        {
          id: firstItem.id,
          price: newTierConfig.priceId,
        },
      ],
    });

    return updated;
  }

  async createCustomerPortalSession(
    customerId: string,
    returnUrl: string
  ): Promise<Stripe.BillingPortal.Session> {
    return await stripe.billingPortal.sessions.create({
      customer: customerId,
      return_url: returnUrl,
    });
  }

  async getSubscription(subscriptionId: string): Promise<Stripe.Subscription | null> {
    try {
      const subscription = await stripe.subscriptions.retrieve(subscriptionId);
      return subscription;
    } catch {
      return null;
    }
  }

  async getUserSubscription(userId: string): Promise<Stripe.Subscription | null> {
    try {
      const customers = await stripe.customers.list({
        limit: 100,
        expand: ['data.subscriptions'],
      });

      for (const customer of customers.data) {
        if (customer.metadata?.userId === userId && customer.subscriptions) {
          const activeSub = customer.subscriptions.data.find(
            (sub: Stripe.Subscription) => sub.status === 'active'
          );
          if (activeSub) {
            return activeSub;
          }
        }
      }
      return null;
    } catch {
      return null;
    }
  }

  async getTierLimits(tier: SubscriptionTier) {
    return config.tiers[tier];
  }

  async checkUsageAgainstLimit(
    userId: string,
    tier: SubscriptionTier,
    currentUsage: number
  ): Promise<{ withinLimit: boolean; remaining: number; limit: number }> {
    const tierConfig = config.tiers[tier];
    const limit = tierConfig.callMinutesLimit;
    const remaining = Math.max(0, limit - currentUsage);

    return {
      withinLimit: currentUsage <= limit,
      remaining,
      limit,
    };
  }

  async createInvoice(
    customerId: string,
    amount: number,
    description: string,
    metadata?: Record<string, string>
  ): Promise<Stripe.Invoice> {
    const invoice = await stripe.invoices.create({
      customer: customerId,
      metadata: metadata,
    });
    
    await stripe.invoiceItems.create({
      invoice: invoice.id,
      customer: customerId,
      price_data: {
        currency: 'usd',
        unit_amount: amount,
        product: 'default_product',
      },
      description: description,
      quantity: 1,
    });
    
    return await stripe.invoices.retrieve(invoice.id);
  }

  async handleWebhook(
    sig: string,
    body: Buffer
  ): Promise<Stripe.Event | null> {
    const event = stripe.webhooks.constructEvent(body, sig, config.stripe.webhookSecret);
    
    cleanupOldEvents();

    if (processedEvents.has(event.id)) {
      return null;
    }

    processedEvents.set(event.id, Date.now());

    return event;
  }

  async getInvoiceHistory(customerId: string): Promise<Stripe.ApiList<Stripe.Invoice>> {
    return await stripe.invoices.list({
      customer: customerId,
      limit: 100,
    });
  }
}