Midraの掲示板

```ts
import type { entities as MisskeyEntities } from 'misskey-js'

type WebhookTypes = {
user: 'follow' | 'followed' | 'unfollow'
note: 'note' | 'reply' | 'renote' | 'mention'
}

export type MisskeyWebhook<T = WebhookTypes['user' | 'note']> = {
hookId: string
userId: string
eventId: string
createdAt: string
type: T
body: T extends WebhookTypes['user']
? {
user: MisskeyEntities.User
}
: T extends WebhookTypes['note']
? {
note: MisskeyEntities.Note
}
: null
}

export const WebhookTypeCheck = <T extends WebhookTypes['user' | 'note']>(
type: T,
json: MisskeyWebhook
): json is MisskeyWebhook<T> => json.type === type
```