# Saleor Async Webhook

Apps are usually connected via webhooks - one App sends a HTTP request to another App, informing about some event or requesting some action to be performed.

To inform your App about events originated from Saleor, you need to expose a webhook handler, which Saleor will call with POST request.

To avoid boilerplate, App SDK provides utility that abstracts connection details, allowing developers to focus on business logic.

Note - this utility works for Saleor Async Webhooks only. Support for Sync webhooks are not yet supported in SDK, but you can write your sync webhook handler
from scratch.

## Creating async webhook with SaleorAsyncWebhook

### Creating webhook handler configuration

To use SaleorAsyncWebhook utility, first create a new instance. It can be created in your API handler file

```typescript
// pages/api/webhooks/order-created.ts

/**
 * To be type safe, define payload from API. This should be imported from generated graphQL code
 */
type OrderPayload = {
  id: string;
};

export const orderCreatedWebhook = new SaleorAsyncWebhook<OrderPayload>({
  /**
   * Name of the webhook, not required
   */
  name: "Order Created",
  /**
   * Relative path to the webhook, required
   */
  webhookPath: "api/webhooks/order-created",
  /**
   * Event type, required
   */
  asyncEvent: "ORDER_CREATED",
  /**
   * Decide if webhook created during app installation should be active or not
   */
  isActive: true,
  /**
   * Provide APL, read more below
   */
  apl: require("../lib/apl"),
  /**
   * Subscription query, telling Saleor what payload app expects
   */
  query: "TODO",
});
```

- Check available events [here](https://docs.saleor.io/docs/3.x/developer/extending/apps/asynchronous-webhooks#available-webhook-events)
- [Read more about APLs](./apl.md)
- [Subscription query documentation](https://docs.saleor.io/docs/3.x/developer/extending/apps/subscription-webhook-payloads)

You can consider created `orderCreatedWebhook` a center point of your webhook configuration. Now, you need to create a handler and add it to manifest.

### Extending app manifest

Webhooks are created in Saleor when the App is installed. Saleor uses [AppManifest](https://docs.saleor.io/docs/3.x/developer/extending/apps/manifest) to get information about webhooks to create.  
`SaleorAsyncWebhook` utility can generate this manifest:

```typescript
// pages/api/manifest

import { createManifestHandler } from "@saleor/app-sdk/handlers/next";

import { orderCreatedWebhook } from "./order-created.ts";

export default createManifestHandler({
  manifestFactory({ appBaseUrl }) {
    return {
      /**
       * Add one or more webhook manifests.
       */
      webhooks: [orderCreatedWebhook.getWebhookManifest(appBaseUrl)],
      // ...rest of your App's manifest
    };
  },
});
```

Now, try to read your manifest, in default Next.js config it will be `GET localhost:3000/api/manifest`. You should see webhook configuration as part of manifest response.

### Creating webhook domain logic

Now, let's create a handler that will process webhook data. Let's back to handler file `pages/api/webhooks/order-created.ts`.

```typescript
type OrderPayload = {
  id: string;
};

export const orderCreatedWebhook = new SaleorAsyncWebhook<OrderPayload>({
  // ... your configuration
});

export default orderCreatedWebhook.createHandler((req, res, context) => {
  const { baseUrl, event, payload, authData } = context;

  console.log(payload.id); // type is inferred

  // Perform some domain logic

  // End with status 200
  return res.status(200).end();
});
```

### query vs subscriptionQueryAst

Subscription query can be specified using plain string or as `ASTNode` object created by `gql` tag.

If your project does not use any code generation for GraphQL operations, use the string. In case you are using [GraphQL Code Generator](https://the-guild.dev/graphql/codegen), which we highly recommend, you should pass a subscription as GraphQL ASTNode:

```typescript
/**
 * Subscription query, you can define it in the `.ts` file. If you write operations in separate `.graphql` files, codegen will also export them in the generated file.
 */
export const ExampleProductUpdatedSubscription = gql`
  ${ProductUpdatedWebhookPayload}
  subscription ExampleProductUpdated {
    event {
      fragment ProductUpdatedWebhookPayload on ProductUpdated {
      product {
        id
        name
      }
    }
    }
  }
`;

export const productUpdatedWebhook = new SaleorAsyncWebhook<ProductUpdatedWebhookPayloadFragment>({
  name: "Example product updated webhook",
  webhookPath: "api/webhooks/saleor/product-updated",
  asyncEvent: "PRODUCT_UPDATED",
  apl: saleorApp.apl,
  subscriptionQueryAst: ExampleProductUpdatedSubscription,
});