feat: Create payment sessions (#6549)

~~Opening a draft PR to discuss a couple of implementation details that we should align on~~

**What**

Add workflow and API endpoint for creating payment sessions for a payment collection. Endpoint is currently `POST /store/payment-collection/:id/payment-sessions`. I suggested an alternative in a comment below.

Please note, we intentionally do not want to support creating payment sessions in bulk, as this would become a mess when having to manage multiple calls to third-party providers.

integration-tests/modules/__tests__/payment/payment-session.workflows.spec.ts

@@ -0,0 +1,142 @@
+import {
+  createPaymentSessionsWorkflow,
+  createPaymentSessionsWorkflowId,
+} from "@medusajs/core-flows"
+import { ModuleRegistrationName } from "@medusajs/modules-sdk"
+import { IPaymentModuleService, IRegionModuleService } from "@medusajs/types"
+import path from "path"
+import { startBootstrapApp } from "../../../environment-helpers/bootstrap-app"
+import { getContainer } from "../../../environment-helpers/use-container"
+import { initDb, useDb } from "../../../environment-helpers/use-db"
+
+jest.setTimeout(50000)
+
+const env = { MEDUSA_FF_MEDUSA_V2: true }
+
+describe("Carts workflows", () => {
+  let dbConnection
+  let appContainer
+  let shutdownServer
+  let paymentModule: IPaymentModuleService
+  let regionModule: IRegionModuleService
+  let remoteLink
+
+  beforeAll(async () => {
+    const cwd = path.resolve(path.join(__dirname, "..", ".."))
+    dbConnection = await initDb({ cwd, env } as any)
+    shutdownServer = await startBootstrapApp({ cwd, env })
+    appContainer = getContainer()
+    paymentModule = appContainer.resolve(ModuleRegistrationName.PAYMENT)
+    regionModule = appContainer.resolve(ModuleRegistrationName.REGION)
+    remoteLink = appContainer.resolve("remoteLink")
+  })
+
+  afterAll(async () => {
+    const db = useDb()
+    await db.shutdown()
+    await shutdownServer()
+  })
+
+  afterEach(async () => {
+    const db = useDb()
+    await db.teardown()
+  })
+
+  describe("createPaymentSessionWorkflow", () => {
+    it("should create payment sessions", async () => {
+      const region = await regionModule.create({
+        currency_code: "usd",
+        name: "US",
+      })
+
+      let paymentCollection = await paymentModule.createPaymentCollections({
+        currency_code: "usd",
+        amount: 1000,
+        region_id: region.id,
+      })
+
+      await createPaymentSessionsWorkflow(appContainer).run({
+        input: {
+          payment_collection_id: paymentCollection.id,
+          provider_id: "pp_system_default",
+          context: {},
+          data: {},
+        },
+      })
+
+      paymentCollection = await paymentModule.retrievePaymentCollection(
+        paymentCollection.id,
+        {
+          relations: ["payment_sessions"],
+        }
+      )
+
+      expect(paymentCollection).toEqual(
+        expect.objectContaining({
+          id: paymentCollection.id,
+          currency_code: "usd",
+          amount: 1000,
+          region_id: region.id,
+          payment_sessions: expect.arrayContaining([
+            expect.objectContaining({
+              amount: 1000,
+              currency_code: "usd",
+              provider_id: "pp_system_default",
+            }),
+          ]),
+        })
+      )
+    })
+
+    describe("compensation", () => {
+      it("should delete created payment collection if a subsequent step fails", async () => {
+        const workflow = createPaymentSessionsWorkflow(appContainer)
+
+        workflow.appendAction("throw", createPaymentSessionsWorkflowId, {
+          invoke: async function failStep() {
+            throw new Error(
+              `Failed to do something after creating payment sessions`
+            )
+          },
+        })
+
+        const region = await regionModule.create({
+          currency_code: "usd",
+          name: "US",
+        })
+
+        let paymentCollection = await paymentModule.createPaymentCollections({
+          currency_code: "usd",
+          amount: 1000,
+          region_id: region.id,
+        })
+
+        const { errors } = await workflow.run({
+          input: {
+            payment_collection_id: paymentCollection.id,
+            provider_id: "pp_system_default",
+            context: {},
+            data: {},
+          },
+          throwOnError: false,
+        })
+
+        expect(errors).toEqual([
+          {
+            action: "throw",
+            handlerType: "invoke",
+            error: new Error(
+              `Failed to do something after creating payment sessions`
+            ),
+          },
+        ])
+
+        const sessions = await paymentModule.listPaymentSessions({
+          payment_collection_id: paymentCollection.id,
+        })
+
+        expect(sessions).toHaveLength(0)
+      })
+    })
+  })
+})