src/app.module.ts

@@ -1,3 +1,4 @@
+import { CheckoutModule } from './checkout/checkout.module';
 import { CatalogModule } from './catalog/catalog.module';
 import { AddressesModule } from './addresses/addresses.module';
 import { InventoryModule } from './inventory/inventory.module';
@@ -14,6 +15,7 @@ import { HealthModule } from './health/health.module';
     CatalogModule,
     AddressesModule,
     InventoryModule,
+    CheckoutModule,
   ],
 })
 export class AppModule {}

src/catalog/catalog.schemas.ts

@@ -1,4 +1,5 @@
 import { z } from 'zod';
+import { CURRENCIES } from '../common/currency';
 import { text, ids } from '../common/input';
 import { pageSchema } from '../identity/identity.schemas';
 
@@ -38,7 +39,7 @@ export const variantSchema = z
       .string()
       .regex(/^(0|[1-9]\d{0,9})\.\d{2}$/)
       .refine((value) => value !== '0.00'),
-    currency: z.enum(['INR', 'USD', 'EUR', 'GBP']).default('INR'),
+    currency: z.enum(CURRENCIES).default('INR'),
     active: z.boolean().default(true),
     attributes: z
       .record(

src/checkout/cart.controller.ts

@@ -0,0 +1,39 @@
+import {
+  Body,
+  Controller,
+  Delete,
+  Get,
+  Param,
+  ParseUUIDPipe,
+  Put,
+} from '@nestjs/common';
+import { CurrentPrincipal } from '../identity/access.decorator';
+import type { Principal } from '../identity/identity.types';
+import { SchemaPipe } from '../common/validation.pipe';
+import { cartLineSchema, cartVersionSchema } from './checkout.schemas';
+import { CartStore } from './cart.store';
+@Controller('cart')
+export class CartController {
+  constructor(private readonly carts: CartStore) {}
+  @Get()
+  get(@CurrentPrincipal() actor: Principal) {
+    return this.carts.get(actor);
+  }
+  @Put('lines/:variantId')
+  set(
+    @CurrentPrincipal() actor: Principal,
+    @Param('variantId', ParseUUIDPipe) id: string,
+    @Body(new SchemaPipe(cartLineSchema))
+    input: { quantity: number; version: number },
+  ) {
+    return this.carts.set(actor, id, input.version, input.quantity);
+  }
+  @Delete('lines/:variantId')
+  remove(
+    @CurrentPrincipal() actor: Principal,
+    @Param('variantId', ParseUUIDPipe) id: string,
+    @Body(new SchemaPipe(cartVersionSchema)) input: { version: number },
+  ) {
+    return this.carts.set(actor, id, input.version, 0);
+  }
+}

src/checkout/cart.store.ts

@@ -0,0 +1,96 @@
+import { Injectable } from '@nestjs/common';
+import { AccessStore } from '../identity/access.store';
+import type { Principal } from '../identity/identity.types';
+import { AppError } from '../common/errors/app-error';
+
+@Injectable()
+export class CartStore {
+  constructor(private readonly access: AccessStore) {}
+  get(actor: Principal) {
+    return this.access.mutate(actor, null, async (tx) => {
+      const cart = await tx.cart.upsert({
+        where: {
+          userId_organizationId: {
+            userId: actor.userId,
+            organizationId: actor.organizationId,
+          },
+        },
+        create: { userId: actor.userId, organizationId: actor.organizationId },
+        update: {},
+      });
+      const lines = await tx.cartLine.findMany({
+        where: { cartId: cart.id },
+        orderBy: { id: 'asc' },
+        select: {
+          variantId: true,
+          quantity: true,
+          variant: {
+            select: {
+              name: true,
+              sku: true,
+              price: true,
+              currency: true,
+              active: true,
+              product: { select: { name: true, status: true } },
+            },
+          },
+        },
+      });
+      return { version: cart.version, lines };
+    });
+  }
+  set(actor: Principal, variantId: string, version: number, quantity: number) {
+    return this.access.mutate(actor, null, async (tx) => {
+      const cart = await tx.cart.upsert({
+        where: {
+          userId_organizationId: {
+            userId: actor.userId,
+            organizationId: actor.organizationId,
+          },
+        },
+        create: { userId: actor.userId, organizationId: actor.organizationId },
+        update: {},
+      });
+      if (cart.version !== version) throw new AppError('CART_CHANGED');
+      if (quantity === 0) {
+        await tx.cartLine.deleteMany({ where: { cartId: cart.id, variantId } });
+      } else {
+        const variant = await tx.productVariant.findFirst({
+          where: {
+            id: variantId,
+            organizationId: actor.organizationId,
+            active: true,
+            product: { status: 'PUBLISHED' },
+          },
+        });
+        if (!variant) throw new AppError('CART_ITEM_UNAVAILABLE');
+        const lines = await tx.cartLine.findMany({
+          where: { cartId: cart.id },
+          include: { variant: true },
+        });
+        if (lines.some((line) => line.variant.currency !== variant.currency))
+          throw new AppError('CART_CURRENCY');
+        if (
+          lines.length >= 20 &&
+          !lines.some((line) => line.variantId === variantId)
+        )
+          throw new AppError('CART_LIMIT');
+        await tx.cartLine.upsert({
+          where: { cartId_variantId: { cartId: cart.id, variantId } },
+          create: {
+            cartId: cart.id,
+            organizationId: actor.organizationId,
+            variantId,
+            quantity,
+          },
+          update: { quantity },
+        });
+      }
+      await tx.cart.update({
+        where: { id: cart.id },
+        data: { version: { increment: 1 } },
+      });
+      return { version: version + 1 };
+    });
+  }
+}

src/checkout/checkout.module.ts

@@ -0,0 +1,11 @@
+import { Module } from '@nestjs/common';
+import { DatabaseModule } from '../database/database.module';
+import { IdentityModule } from '../identity/identity.module';
+import { CartStore } from './cart.store';
+import { CartController } from './cart.controller';
+@Module({
+  imports: [DatabaseModule, IdentityModule],
+  controllers: [CartController],
+  providers: [CartStore],
+})
+export class CheckoutModule {}

src/checkout/checkout.schemas.ts

@@ -0,0 +1,22 @@
+import { z } from 'zod';
+export const couponCode = z
+  .string()
+  .trim()
+  .toUpperCase()
+  .regex(/^[A-Z0-9][A-Z0-9_-]{0,39}$/);
+export const cartLineSchema = z
+  .object({
+    quantity: z.number().int().min(1).max(100),
+    version: z.number().int().min(0).max(2147483646),
+  })
+  .strict();
+export const cartVersionSchema = cartLineSchema.pick({ version: true });
+export const checkoutSchema = z
+  .object({
+    cartVersion: z.number().int().min(0).max(2147483646),
+    addressId: z.uuid(),
+    couponCode: couponCode.optional(),
+    idempotencyKey: z.uuid(),
+  })
+  .strict();
+export type CheckoutInput = z.infer<typeof checkoutSchema>;

src/common/currency.ts

@@ -0,0 +1 @@
+export const CURRENCIES = ['INR', 'USD', 'EUR', 'GBP'] as const;

src/common/errors/checkout-errors.ts

@@ -0,0 +1,50 @@
+export const CHECKOUT_ERRORS = {
+  CART_EMPTY: [
+    409,
+    'Add items before checkout',
+    'Empty cart checkout rejected',
+  ],
+  CART_CHANGED: [
+    409,
+    'Cart version has changed',
+    'Stale cart command rejected',
+  ],
+  CART_LIMIT: [409, 'Cart line limit reached', 'Cart resource quota exceeded'],
+  CART_ITEM_UNAVAILABLE: [
+    409,
+    'Cart item is no longer available',
+    'Non-sellable cart variant rejected',
+  ],
+  CART_CURRENCY: [
+    409,
+    'Cart items must use one currency',
+    'Mixed currency cart rejected',
+  ],
+  COUPON_NOT_FOUND: [404, 'Coupon not found', 'Scoped coupon lookup failed'],
+  COUPON_INELIGIBLE: [
+    409,
+    'Coupon is not eligible for this checkout',
+    'Coupon eligibility rule rejected checkout',
+  ],
+  ORDER_NOT_FOUND: [404, 'Order not found', 'Scoped order lookup failed'],
+  ORDER_LIMIT: [
+    409,
+    'Too many active orders',
+    'Account active order quota exceeded',
+  ],
+  ORDER_RESERVATION_MANAGED: [
+    409,
+    'Manage this reservation through its order',
+    'Standalone order reservation mutation rejected',
+  ],
+  STOCK_ALLOCATION_LIMIT: [
+    409,
+    'Too many stock locations for one checkout',
+    'Checkout stock allocation bound exceeded',
+  ],
+  MONEY_RANGE: [
+    409,
+    'Order amount exceeds the supported limit',
+    'Checkout arithmetic bound exceeded',
+  ],
+} as const;

src/common/errors/error-catalog.ts

@@ -1,4 +1,9 @@
+import { CHECKOUT_ERRORS } from './checkout-errors';
 import { PLATFORM_ERRORS } from './platform-errors';
 import { COMMERCE_ERRORS } from './commerce-errors';
-export const ERRORS = { ...PLATFORM_ERRORS, ...COMMERCE_ERRORS } as const;
+export const ERRORS = {
+  ...PLATFORM_ERRORS,
+  ...COMMERCE_ERRORS,
+  ...CHECKOUT_ERRORS,
+} as const;
 export type ErrorCode = keyof typeof ERRORS;

test/cart.spec.ts

@@ -0,0 +1,93 @@
+import { identityApp, type IdentityApp } from './helpers/identity-app';
+import { checkoutFixture } from './helpers/checkout';
+import { secondActor, seedProduct } from './helpers/commerce';
+
+describe('private versioned carts', () => {
+  let ctx: IdentityApp;
+  beforeAll(async () => {
+    ctx = await identityApp();
+  });
+  afterAll(async () => {
+    await ctx.close();
+  });
+  beforeEach(async () => {
+    await ctx.clearLimits();
+  });
+  it('isolates carts, rejects stale edits and removes lines', async () => {
+    const f = await checkoutFixture(ctx);
+    const other = await secondActor(ctx);
+    const own = await ctx
+      .api()
+      .get('/api/v1/cart')
+      .auth(f.actor.token, { type: 'bearer' })
+      .expect(200);
+    expect(own.body.lines).toHaveLength(1);
+    const empty = await ctx
+      .api()
+      .get('/api/v1/cart')
+      .auth(other.token, { type: 'bearer' })
+      .expect(200);
+    expect(empty.body).toEqual({ version: 0, lines: [] });
+    const stale = await ctx
+      .api()
+      .put('/api/v1/cart/lines/' + f.variant.id)
+      .auth(f.actor.token, { type: 'bearer' })
+      .send({ quantity: 3, version: 0 })
+      .expect(409);
+    expect(stale.body.code).toBe('CART_CHANGED');
+    await ctx
+      .api()
+      .put('/api/v1/cart/lines/' + f.variant.id)
+      .auth(f.actor.token, { type: 'bearer' })
+      .send({ quantity: 3, version: 1 })
+      .expect(200);
+    await ctx
+      .api()
+      .delete('/api/v1/cart/lines/' + f.variant.id)
+      .auth(f.actor.token, { type: 'bearer' })
+      .send({ version: 2 })
+      .expect(200);
+    const result = await ctx
+      .api()
+      .get('/api/v1/cart')
+      .auth(f.actor.token, { type: 'bearer' })
+      .expect(200);
+    expect(result.body).toEqual({ version: 3, lines: [] });
+    await ctx.api().get('/api/v1/cart').expect(401);
+  });
+  it('rejects draft, foreign and mixed-currency items and mass assignment', async () => {
+    const f = await checkoutFixture(ctx);
+    const draft = await seedProduct(ctx);
+    await ctx
+      .api()
+      .put('/api/v1/cart/lines/' + draft.variant.id)
+      .auth(f.actor.token, { type: 'bearer' })
+      .send({ quantity: 1, version: 1 })
+      .expect(409);
+    const foreign = await secondActor(ctx, false);
+    await ctx
+      .api()
+      .put('/api/v1/cart/lines/' + f.variant.id)
+      .auth(foreign.token, { type: 'bearer' })
+      .send({ quantity: 1, version: 0 })
+      .expect(409);
+    const usd = await seedProduct(ctx, true);
+    await ctx.db.productVariant.update({
+      where: { id: usd.variant.id },
+      data: { currency: 'USD' },
+    });
+    const response = await ctx
+      .api()
+      .put('/api/v1/cart/lines/' + usd.variant.id)
+      .auth(f.actor.token, { type: 'bearer' })
+      .send({ quantity: 1, version: 1 })
+      .expect(409);
+    expect(response.body.code).toBe('CART_CURRENCY');
+    await ctx
+      .api()
+      .put('/api/v1/cart/lines/' + f.variant.id)
+      .auth(f.actor.token, { type: 'bearer' })
+      .send({ quantity: 1, version: 1, price: '0.01' })
+      .expect(400);
+  });
+});

test/helpers/checkout.ts

@@ -0,0 +1,43 @@
+import { randomUUID } from 'node:crypto';
+import type { IdentityApp } from './identity-app';
+import { addressInput, secondActor, seedStock } from './commerce';
+
+export async function checkoutFixture(ctx: IdentityApp, stock = 10) {
+  const item = await seedStock(ctx, stock);
+  const actor = await secondActor(ctx);
+  const address = await ctx
+    .api()
+    .post('/api/v1/addresses')
+    .auth(actor.token, { type: 'bearer' })
+    .send(addressInput)
+    .expect(201);
+  await ctx
+    .api()
+    .put('/api/v1/cart/lines/' + item.variant.id)
+    .auth(actor.token, { type: 'bearer' })
+    .send({ quantity: 2, version: 0 })
+    .expect(200);
+  return {
+    ...item,
+    actor,
+    address: address.body,
+    input: {
+      cartVersion: 1,
+      addressId: address.body.id,
+      idempotencyKey: randomUUID(),
+    },
+  };
+}
+export function couponInput() {
+  return {
+    code: 'SAVE-' + randomUUID().slice(0, 8),
+    kind: 'PERCENT',
+    percentBps: 1000,
+    currency: 'INR',
+    minimumSubtotal: '100.00',
+    maxUses: 10,
+    perUserLimit: 1,
+    startsAt: new Date(Date.now() - 60000).toISOString(),
+    endsAt: new Date(Date.now() + 3600000).toISOString(),
+  };
+}